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DIY Microphone: EM172 Capsule and XLR Plug

Posted by Tom Benedict on 05/03/2016

This is the last in a four part series about powering the Primo EM172 microphone capsule. Part 1 outlined the problem of how to provide 5-10v to the capsule and predicted some results. Part 2 shared some results and pointed out that the gain differences between inputs on my recorder invalidated my predictions. Part 3 discussed my reasons for going with XLR connectors on all my microphones, and some of the details of that. This last part puts it all together into a step-by-step DIY for building microphones with Primo EM172 capsules, powered by 48v phantom power on an XLR plug.

If you need to build a microphone based around the EM172 capsule that plugs into the 1/8″ mic jack on your recorder, or a laptop, tablet, whatever, there are already several excellent tutorials out there. Rather than adapt this one to your needs, refer to one of the existing tutorials. The two I used when I first started building EM172 microphones were the ones on Zach Poff’s page and the one on Wild Mountain Echoes.

In this DIY I’m going to assume you already have a plan for making a mic body. I made mine out of Delrin bar stock on a lathe. Others have used Sharpie pen caps, which also provide a nice clip for clipping the mic to things (see the tutorial on Wild Mountain Echoes), PVC pipe, brass tubing, etc. When mounting the mic in the mic body, make sure the front of the capsule is flush with or slightly proud of the mic body. Don’t recess it. I made that mistake with my first set of mics and wound up with mics that sounded like they were inside a sewer pipe. If in doubt experiment by wiring up the mic completely, plugging it in, and listening to it as you slide it in and out of the mic body you plan to use. After all, this is DIY. Experimentation is part of the deal.

Primo BT-EM172 to P48 XLR Wiring

Credit for the circuit goes entirely to David McGriffy, and credit for the component choice goes entirely to David McGriffy and Ricardo Lee. Ricardo Lee’s writeup, SimpleP48wm61, goes into the theory of the circuit and the reasons for the component choices in depth. It’s the real reference for this. (In order to use that link to download Ricardo’s file, you may need to be a member of the micbuilders group on Yahoo!. If you’re doing this DIY you’re a mic builder, so it’s not a stretch.)

EDIT: A couple of weeks ago Akira So brought to my attention that I had the capacitor poloarity reversed from how David McGriffy and Ricardo Lee have it in SimpleP48. I’ve since corrected the schematic here. Credit where credit’s due.

EDIT: Akira also pointed out that my value for R (120k) resulted in something like 1.3-1.5V at the capsule. I experimented with a number of resistors to see what value of R would produce 7.5V at the capsule on my recorder, and for a Tascam DR-70D, R=40k produces just over 7.5V. When you do this build, you will have to find what works best for your equipment.

EDIT: I also swapped the supplier for the EM172 from Frogloggers to Micbooster (FEL Communications). I haven’t heard from Gene at Frogloggers in a while. Hoping he’s doing ok.

For my build I used the following:

I also used some metal tape (copper in my case, from the local gardening center), heat shrink of various sizes, and the solder I found on the bench in the lab. (My Alphametals solder I’ve been using for the past 20 years isn’t ROHS certified, so I can’t say “use this stuff, it’s great!”)

Not including the tools necessary to fabricate the mic bodies, you’ll also need:

  • Soldering iron (temperature regulated if possible)
  • Source of heat for heat shrink (heat gun, lighter, etc.)
  • Assortment of wire cutters, strippers, fine tip pliers, etc.

Since most of the bodies people use for these require the mic to slide in  from the front end of the housing, we’ll start with the mic capsule.

EM172 Back End

The first step is to strip one end of the cable, trim back the red and white wires to a workable length, and still leave plenty of shield exposed. The red and white wires are then soldered onto the appropriate pads on the capsule.

Warning: The EM172 capsule is sensitive to heat. These two photos were made with a capsule I’d killed using an unregulated soldering iron, which is why the capsule looks a little ugly. If you have access to a regulated iron set your iron no higher than 735C and don’t hold the iron on a pad for more than a few seconds. If you don’t have access to a regulated soldering iron, be sure to get EM172 capsules with stub leads already soldered in place. The tutorial on Wild Mountain Echoes uses capsules with stub leads, so you can see how she did it. Do all your work on the stub leads. Don’t fry your microphones!

EM172 With Wires

Now we build the shielding around the capsule itself. Insulate the sides and back of the capsule with some heat shrink.

Capsule Isolated

Be sure to account for every strand in the shield as you bring it up and over the heat shrink. Wrap with foil tape and trim back the shield so no wires protrude. Be sure no wires cross over the heat shrink and touch the front of the capsule.

Making a Shield

Apply a second layer of heat shrink over the foil tape. I like to apply a short length of colored heat shrink to help me identify which mic is which when I’m running wires and plugging things in out in the field.

Heat Shrunk Ready To Go

At this point go ahead and run the mic cable through your mic body, but don’t mount the capsule just yet. Once you’ve soldered the connector end of the cable, it’s a good idea to test everything to make sure you didn’t make any soldering mistakes, and to make sure the capsule didn’t get damaged during soldering. Strip the other end of the cable, leaving a little more wire to work with than on the capsule end. Thread the wire through the end cap for the XLR connector and set it aside. Since the XLR connector provides its own shield you don’t have to do any metal tape trickery on this end. Gather the wires from the cable’s shield, twist into a bundle, and cover with heat shrink tubing. This is also a good time to apply a length of colored heat shrink to match the capsule end of the cable.

Cable Prepped With Shell

Grab the XLR connector body in a vise or some other holding fixture. If you don’t have a vise, a set of vise-grip pliers with tape over the serrated part of the jaw works well. Just don’t grab it so hard that the connector body is damaged or distorted. Another way to hold these connectors that works great is to have the mating connector screwed into a board. Plug the connector you’re working on into its counterpart and solder to your heart’s content. (I used a vise.)

Trim back the leads on the capacitor and resistor to something reasonable that’ll fit inside the XLR connector. Save the snipped off bits of the leads. One of these works well to bridge from pin 1 to the ground tab.

Resistor and Capacitor

Solder a leftover component lead from pin 1 to the ground tab. Next, solder one end of the resistor to the ground tab as well. Next, solder the (+) end of the capacitor to pin 2. Finally, tie the two free ends of the capacitor and resistor together.

XLR Plug with McGriffy Components

All that’s left is to solder the cable onto the plug. Red goes to pin 3, white goes to the (+) lead of the capacitor as well as the free end of the resistor, and the cable’s shield is soldered to the ground tab. (In this photo the connector is rotated 180 degrees from how it’s drawn in the schematic, but that’s how the solder cups are oriented. Flip it around in your mind and it’ll make sense.)

XLR Plug with Cable

At this point your microphone’s electronics are finished. Put the connector together and screw things tight.

This is a good time to test the mic to make sure nothing went wrong. Plug it into your recorder, turn on phantom 48v power, and dial up the gain. If all went well you should have a low noise microphone ready to be installed in its mic body. If not, go back and check each step to find out what went wrong.

Finished Mic

Have fun recording!



158 Responses to “DIY Microphone: EM172 Capsule and XLR Plug”

  1. Javi said

    Thanks Tom. I adapted my EM172 to XLR following this post. Fantastic!

  2. Dom Turchi said

    Hey Tom, thank you so incredibly much for this write up! I was researching this stuff about a year ago and now realize I was certainly taking the hard route with this project. I’m no electrical engineer, so I was always confused to see more complex circuits like this ( when I thought all that is necessary is the cold line have an electrolytic capacitor with the whole circuit having enough resistance. Glad to see that I wasn’t wrong! I did have a couple questions I’m hoping you can answer though:

    1) Do the resistors and capacitors have to be matched in any way if using a stereo pair?
    2) As the specs for the EM172 say operating voltage is 5V, are there any negative impacts on using a near 10V?
    3) One things I was trying to research was using the EM173 which has higher sensitivity and thus a larger dynamic range and higher Max SPL. Would you suggest a different resistor or capacitor in the circuit if I went this route? I’m assuming the circuit design itself would remain the same and I’d just solder the ground to the third terminal instead of creating a Faraday Cage?

    • Tom Benedict said

      To answer #1, I don’t really know. I got 1% resistors so the ones I used are all pretty close. I could probably get closer by matching, but they’re close. I didn’t measure the caps before installing them. If in doubt, matching wouldn’t be a bad idea. (The resistors and caps are relatively cheap, so it wouldn’t add a lot of cost to the project.)

      To answer #2, the EM172 seems to do better if it’s biased a little higher. The datasheet says it’ll operate between 3-10V with a nominal Vcc of 5V. There’s a file on the Yahoo! micbuilder’s group that gives more details on how the EM172 performs at different bias voltages, feeding into different impedance preamps. It can be found here:

      The file in question is “Primo EM172 Sens Noise vs RL VL.pdf” There’s another file in there, “EM173 Sens & Noise vs RL.VL.pdf” that has similar information on the EM173 capsule.

      I really don’t know what changes you’d want to make to use this to drive an EM173. As far as I know the EM172 and EM173 are almost identical. The big difference is that there’s an internal resistor going from source to ground in the EM172, and on the EM173 the source pin of the FET is brought out so you can wire in the resistor of your choice. (I’m getting all this off the micbooster page for the EM173:

      I hope this helps!


      • Dom Turchi said

        Thank you for the response! After thinking about it, I think I can just do your exact circuit on the EM173, not using the third terminal. The whole purpose of the circuit is to supply the 9.6V and use the ground as both ground and the inverted signal, so the mic would be efficiently powered and I’d have all the advantages of the the EM173 (with maybe even better impedance matching?). I’ll try it out and let you know what I find!

      • Tom Benedict said

        Cool! Looking forward to hearing how it goes.

      • Hey Dom! I’m looking to do what you did! Would you mind sharing how your turned out??

  3. Carlos said

    Thanks a lot for sharing such a neat way to encapsulate these mics and connect them to XLR!!

  4. Kenny said

    Hello, Tom! Thank you so much for the post! And I’d like to learn what’s not right about this method:

    • Tom Benedict said

      I don’t think there’s anything wrong with it. At first glance it looks like it’s designed to work with a bare electret element. The BT-EM172 has a FET and resistor built into it. The SimpleP48wm61 circuit is designed to work with that built-in FET.

      One difference I do see is that the author says it’s inherently unbalanced. The SimpleP48wm61 document I drew this design from says that up to about 10m of cable it’s “balanced” because it floats the capsule across XLR pins 2 and 3. I haven’t built both circuits, so I can’t compare the two directly, but I can say from testing that the one here does provide a balanced input.

  5. Maggie Pretorius said

    Hi Tom, we are going to sell Copper foil tape on Amazon and was wondering if i can use of the photos in this blog?



  6. GeorgeD said

    Hi, This is great, I plan to build some. However, what if I want to use the em184 cardoid capsule? Would the wiring be the same? Would you recomend a different casing?

    • Tom Benedict said

      Funny you should ask! Just yesterday I built a pair around some EM184 caps I picked up from Everything worked fine. If you grab the datasheet for the EM184 and the datasheet for the EM172, you can see the hot and ground pads on each of the mics. The red wire goes on the hot, and the white (black in the diagram) goes on the ground pad. Do the same on the EM184 and you should be good to go.

      For what it’s worth I picked up a pair of Clippy mic bodies, foam wind screens, and lapel clips at the same time I got the EM184 capsules. Everything went together well, and the vents at the back of the Clippy mic bodies play nicely with the cardioid capsules.

      • GeorgeD said

        With those clippy mic bodies, they’re aluminum… did you insulate the capsules from them then connect them to ground, like how you use the copper foil in the directions on this page?

      • Tom Benedict said

        I didn’t, and I have mixed feelings about that.

        The mic bodies are anodized, so there’s no real conduction path to the capsule.

        But I wish I had tied the cable shield to the mic body, and the mic body to the grill. That would make for a really nice Faraday cage around the capsule – even better than my copper tape. (Basically what you mentioned.)

        For now they’re not all that sensitive to EMR, but at some point I might go back and make that change. The nice thing with the Clippy mic bodies is that you can open them up any time. The Delrin bodies I made for my mics are a lot more permanent.

      • GeorgeD said

        Hi again,
        So I got my parts from mic booster. Assembly looks straight forward, but i thought i’d ask for some advice anyway because you’re obviously a creative problem solver. The capsules rattle in the clippy bodies because they’re 0.5mm smaller than the body’s inner diameter. How did you solve this? Also, what did you do for strain relieve where the cable enters the back of the body? thanks!

      • Tom Benedict said

        To strain relieve the cables I applied umpteen zillion layers of heat shrink tubing to the cable to bring it up to the right diameter. By using different lengths it made a tapered strain relief sleeve.

        It’s not my favorite solution. In 20/20 hindsight I wish I could’ve found some real strain relief that was a better fit in the back of the mic body. I’m curious what they use with their pre-built Clippy mics.

        This sort of solved the rattling capsule issue as well. I left a bit of length on the wires where they solder onto the back of the capsule. Once the cable was pulled down into the mic body, I still had to compress the wires to get the capsule into the body. When the front cap was screwed on, the mic was under some spring pressure from the back because of the wires. That pushed it up against the cap enough to keep it from rattling.

        I’m not 100% happy with how I built them out, but they work. The cords are under enough compression that they don’t pull out, and the capsules are under enough spring force they don’t rattle. There has to be a better way to do this, though.

      • Tom Benedict said

        Hey, I was cruising the micbooster site again yesterday, and I saw they have strain relief boots for the Clippy mic bodies. They look WAY better than the built up heat shrink I used on my mics. I’ve got some on order, and will retrofit my Clippy cardioids with them when they show up. I’ll let you know how that goes, and take pictures so you can see what the finished mic looks like.

        I’m also going to take more care putting the mics together in the Clippy bodies this time, so I might have a better solution to the whole rattly fit problem. I’ll keep you posted.

  7. […] same circuit I used to make my EM172 omni mics can be used with other FET-enabled Primo capsules, including the EM184 cardioid capsule. FEL […]

  8. […] same circuit I used to make my EM172 omni mics can be used with other FET-enabled Primo capsules, including the EM184 cardioid capsule. FEL […]

  9. Mike Wall said

    Excellent write up, Tom. Thank you.

  10. […] Benedict made a thorough description of the simplest method on his blog The View Up Here. (It’s only 2 […]

  11. […] lavalier mic I built back when I started building external mics for my DR-05. It’s since been converted to XLR and received the full shielded treatment the rest of my EM-172 mics got when I did that […]

  12. Bill said

    Hi Tom,
    I’m planning on making a couple of these mics. One set would be for stereo and use phantom power, but I’m not sure how to wire them for stereo? I just see the diagram for mono.

    Thanks for all your help, and all the great info.

    • Tom Benedict said

      3-pin XLR inputs are inherently mono. The only stereo XLR arrangement I’ve seen used a 5-pin connector, sharing a common ground between the two mics. But even that one came with a splitter cable to split the 5-pin stereo output from the mic into two 3-pin XLR plugs so they can plug into the recorder.

      Take a look at your recorder. If it’s got 3-pin inputs you should be able to make two independent mono mics and plug them into the left and right channels of your recorder.

      If your recorder takes a 3.5mm input and provides plug-in-power rather than phantom power, those typically are wired for stereo. There are some really good references out there for building stereo pairs of EM172 mics with 3.5mm inputs. These are the two I based my original pair off of:

      To be honest the 3.5mm build is easier since you don’t need the additional circuitry. The two reasons I wound up converting all my mics to XLR were flexibility (I’ve got four XLR inputs on my recorder, so this let me plug any mic into any channel) and gain (for some reason the Tascam recorder I use doesn’t provide as much gain on the 3.5mm input as it does on the XLR inputs).

      • Bill said

        Thanks for your quick response.
        I’m using the Zoom h5. It does have two xlr inputs, so yes I could just plug one in to each input. Sorry for the newbe questions, but I just started in sound about two months ago. Your site has been very helpful. Thanks again, Bill

      • Tom Benedict said

        No problem with the questions. I just started recently, too, and the learning curve still looks like a vertical cliff at times. I’m currently stumbling my way through my first Alice mic, and have been peppering the Yahoo! micbuilders forum with questions. Some of them probably have obvious answers, but people have been really helpful. If I can help at all, please don’t hesitate to ask.

        I don’t have any experience with the H5, but I built some mics for a friend’s H4. Zoom seems to use the same amps for the XLR and the 3.5mm inputs, so it doesn’t have that weird gain difference the Tascams have. You should be able to build them either way, and they should work well.

        Have fun!

  13. This is so great… thanks a million! i’m working a an omni mic so i’ll post when done!

  14. Bill said

    Hey Tom,
    I’m getting close to building my mics. I ordered the mics from Frogloggers almost three weeks ago. I know they are a small operation so I suspect it would take a while. I did try to contact them to get an estimated shipping date about a week ago. I didn’t get a response from phone or email? I thought maybe you would know if they are still doing business. Thanks Bill

    • Tom Benedict said

      I’m not sure if they are. I haven’t heard from Gene in months. I know he’s had health issues in the past, and has had to stop his business occasionally, but this is the longest I haven’t heard from him. I’m a little worried.

  15. steph sandberg said

    I want to ask that on the micbuilders group, but I am not able yet, so I figured you might know the answer: the electronic shop I am used to buy from, gave me all the wrong components, gave me 5% resistor which I immediately returned but unfortunately (I do feel really stupid) I didn’t catch that the capacitors where 47uF and not 4.7uF… I build the first mic of my stereo set, tested it, works fine and figured it out before soldering the second capacitor. I didn’t notice anything strange when testing, self noise seems pretty good just maybe a bit unusual in it tone (?) I WILL rebuild the first mic but wanted to know what was the “role” of the capacitance in this circuit. The capacitor’s voltage and resistor are correct so it seems I sent the right voltage to the capsule, but did I tamper with my capsule in anyway? In which case I would rather order a new stereo set…

    Anyway thanks a ton for the write up, it’s very nice and detailed and I wouldn’t have found an XLR solution without it.

    • Tom Benedict said

      Re-reading Ricardo’s SimpleP48wm61.PDF off the micbuilders group, the biggest concern is the resistor since it determines how much of the 48V makes it to the microphone element.

      The first time I read through that part of Ricardo’s article, I didn’t appreciate a key point: most of these circuits rely on the resistors in the P48 output on the recorder. The 6.8k resistors in the recorder and the resistor in the SimpleP48 circuit (the one you built) act as a voltage divider. I finally figured this out when scratching my head over the Alice circuit, and reading an article on AudioImprov where he outright says that the circuit only makes sense if you mentally include two more resistors that live inside the recorder. GAH!

      But getting back to your question about the capacitor: As far as I know the idea is to have the mic electrically float between pins 2 and 3 of the XLR. The capacitor is what makes that happen.

      The cable between the mic and the recorder serves two purposes: It’s bringing a DC 48V to the mic, and it’s bringing an AC ~1V signal back to the recorder. The capacitor decouples these, allowing some DC voltage (reduced by the resistor) to reach the microphone, but then letting the AC signal get back through to the recorder.

      The catch is you have to pick a number and say “stuff below this frequency is DC, and should be filtered out, and stuff above it should make it through to the recorder”. Most mics aren’t sensitive below 20Hz, so if the capacitor is tuned to treat anything below 20Hz as DC, it doesn’t really hurt the response of the mic. If it’s tuned so it starts creeping up into the audible part of the spectrum, the low frequency stuff will get lost.

      The 4.7uF capacitor, combined with the 120kohm resistor should have an RC time constant of about half a second, or 2Hz. Bumping that to 47uF would bring that up to 20Hz, so it should still work fine. There might be a little low frequency roll-off, but that’s about it.

      In any case nothing you did should’ve tampered with the capsule in anyway. I’ve lost count of how many times I’ve re-soldered stuff on my mics. The only way to really ding the capsule is to overheat it the way I did, and essentially un-solder stuff inside. As long as you’re working at the XLR end, you should be fine swapping capacitors and resistors to your heart’s content. But if the 47uF cap is working for you, I’d run with it.

      Actually, that raises a neat possibility: High end recorders tend to have their low frequency cut-off in the analog part of their circuit, but lower end recorders (like mine!) handle that in the digital end. The problem, of course, being that once low frequency wind noise has saturated your preamps, getting rid of the low frequency stuff digitally really doesn’t buy you anything. The signal is already clipped and distorted at that point.

      But by tuning the capacitor, you should be able to build in a low frequency roll-off into the EM-172 / XLR circuit. I’m not sure I’d want to make it a permanent thing, but having a couple of capacitors on a multi-position switch where you could set the low frequency cut-off to 2Hz (4.7uF), 20Hz(47uF), 80Hz(~200uF) would be pretty darned cool.

      • steph sandberg said

        Wow, thanks a lot, I am now able to understand that circuit (I had pretty much given up…). Thanks especially for pointing me out to the famous 6.8k resistors.

        I was indeed very proud of the successful soldering of the capsules, so I was really a bit scared of those capacitors… Well the soldering wasn’t thanks to me… my cousin is doing magic with an iron. We also used a desktop computer heatsink that I brought to prevent overheating. That how they do it (using a heatsink) at (shoutout to those guys, they helped a lot and they’re awesome).

        Now I wasn’t aware of the digital vs analog HPF in recorders. The point you’re making is quite fascinating to me. I want to start nature recording (I just saw you recently did to and I will now most likely come back to you about this as well…) with a Fostex FR2-LE (I also have a Rode NT1 A stereo pair). I have no idea if the HPF in those are analog or digital, but I will be sure to look into this and building a specialized filtered version of those mics if fluffy deadcats don’t cut it (I was only doing indoor recording until now. so never had wind problems 🙂 Or building some with a switch, that would be even cooler.

      • Tom Benedict said

        Glad I could help you with the circuit, and thank you for sharing the idea of using a heat sink. That’s cool! I managed to fry one of my EM-172 capsules. Never again! Do you have any pictures of your setup with the heat sink?

        It’s funny, I’ve been doing photography since the mid-90’s. It’s amazing how much the conditions have to be juuust right to pull off a good photo. But none of that prepared me for how much the conditions have to be juuust right to pull off a good nature recording. I can stand next to a highway with a camera and still get a good photo of a flower if the light’s right. But I’ve lost count of how many times I’ve walked for miles, stopped, listened, and thought, “Nope. Still too close to the highway.” It’s humbling.

        Have fun!

  16. Bill said

    Hey Tom,

    Received my em172s and finished my build tonight. Everything went good as per the diagram. These mics sound great, and a lot more sensitive then my H5. I can’t wait to get them out in the field. I had to get the mics from Micbousters. I never heard back from Frogloggers? I hope the guy is ok. Well thanks for an awesome blog! I know they’re not your plans, but without you posting them on your blog I might not have found out. I’ll keep you posted on the field tests. Thanks again, Bill

    • Tom Benedict said

      Excellent! Looking forward to hearing your results.



    • Bill said

      Sorry it’s taken me so long to do some testing on the 172s. Today I recorded some really low ambient nature sounds, first with my Zoom H5 internal mics, then with the em172s (two separate xlr 172s going to xlr inputs on Zoom H5 48volts). The difference is like Night and Day. Not that the H5 doesn’t sound good it’s just the 172s have no noise to speak of and way more sensitive. The 172s are awesome!
      I would have probably spent hundreds of dollars for this setup If I wouldn’t have not seen your blog . I don’t have a SoundCloud account yet so I can’t upload any samples. Thanks again for the great blog!

  17. srburni said

    Hi guys! Thanks for the great info you’ve posted here! Helps a lot!

    Probably this is not the right place to ask this question but I’m having trouble with the EM173 mic, which is the same as EM172 except the fact that the EM173 has no internal resistor and it has 3 pins instead of just two.
    I used the same schematic to build the EM173 as the one published here (with minor differences ofcourse) but I seem to have a problem.

    The microphone works great on both my Saffire Pro 40 (with 48V phantom) and the MOTU UltraLite that I have at home.
    However, the same mic has a weird problem when connected to my video camera (BM URSA mini 4.6K). The camera provides 48V Phantom power as well but what I’m getting is mostly noise. I’ve tested other condenser mics on the camera and they work just fine.

    I’ve tried adding a 120 Ohm resistor between the Source and the Ground on the mic capsule, which in theory should give me exactly what EM172 but that didn’t help as well. The whole signal just drops a little bit.

    I’m posting links to an audio clip with both recordings (the first part is the noisy camera and the second is the Saffire Pro 40).
    Also, I’m attaching a picture of EM173’s schematic and what I’ve built so far.

    Can anybody tell me what am I doing wrong?

    Audio =>
    Image =>


    • Tom Benedict said

      I should probably start my reply with a rendition of what I’ve been doing since reading this: scratching my head and going, “Huh… Aha! Wait… Huh…”

      I haven’t used the EM173 capsule before, so I haven’t run into this yet. But I’ve been playing around with another Primo capsule that’s wired similarly to the EM173 (no internal resistor). When I read its datasheet that’s what I did: I scratched my head and went “Huh…” I wound up shelving the project until I had some clue how to proceed.

      The Aha! came from trying to find an answer to your question. So thanks for posing it! This helps!

      The short answer is that the SimpleP48 circuit David McGriffy came up with wasn’t designed to work with a three-terminal capsule.

      One circuit that you may or may not be interested in is this one:

      It’s for a Linkwitz modified Panasonic WM61. The Linkwitz mod turns the WM61 – a two-terminal capsule similar to the EM172 – into a three-terminal capsule similar to the EM173.

      From what I can tell, that last schematic on that page should work. It’s a very stripped-down version of the Schoeps CMC5 circuit with a voltage divider instead of a Zener diode to drop the 48V phantom power to something the capsule can use. It’s a way to marry the Alice circuit I’ve used on two other microphones to capsules with a built-in FET.

      That being said, I’m still curious how the SimpleP48 can be made to work. There aren’t any active components in the circuit, so it’s about as low-noise as you can get. And that you got it to work with the Saffire Pro and the MOTU UltraLite makes me think it should be possible. So I kept poking.

      I ran across a thread on the micbuilders Yahoo! group that should give you an answer. (And as it turns out I actually participated in that thread. Just not on the bits about the EM173!)

      Jerry Lee Marcel came up with a modification to the SimpleP48 circuit for three-terminal capsules. Basically, you add the resistor back into the circuit and wire it up like a two-terminal.

      Jerry Lee’s mod puts a 2.2k resistor between Source and Ground at the capsule. (Ricardo Lee made the point that this resistor has to be at the capsule and not at the XLR.)

      At that point the SimpleP48 circuit can be wired into the XLR shell: Pin 3 goes to Drain on the capsule, and the wire coming off of the resistor and capacitor goes to the ground side of the 2.2k resistor at the back of the capsule.

      Let me know if that makes sense. I probably won’t get a chance to try it on my own capsules for a couple of weeks, so you’ll know if this works before I do.

      Thanks again for asking!

      • srburni said

        Thank you!

        I managed to make them both work properly in-camera and on the audio interfaces! I believe the audio interfaces worked with the previous setup that I did because the inputs are multi-purpose. The ones where you can insert XLR and stereo/mono 1/4″ audio jack. The camera had only the three pin XLR inputs and obviously the schematic I created was connected incorrectly.

        If anyone is interested I can post a demo of the EM173 mics as a matched stereo pair.

        Thanks again!

      • Tom Benedict said

        I’d be interested in the stereo sample. Please feel free to post a link here.

        Glad everything worked out!

  18. Ian said

    Thank you Tom, I adapted my 172 to XLR following your post but I have some problems. The inner noise is really low but the mics are super-silent (I used them with Tascam HD-P2). Instead of 4.7uF 25v aluminum electrolytic capacitor I used 4.7uF 50v, so I have no idea if there is the problem or I just burn them during soldering (I used unregulated iron). Can you tell me what I am doing wrong? Thx a lot!

    • Tom Benedict said

      Not sure. One thing you can do is check the voltage at the capsule to see what kind if bias voltage it’s getting. With the resistor quoted in the article it should be something around 8.5-9.5v. If you’re getting significantly lower than that, you might check what’s coming out of your XLR plugs.

      Kind of the default phantom power is 48V, but on some recorders it’s possible to set 24V or 12V phantom power. The circuit is basically a voltage divider, so if your recorder is supplying a lower voltage you can change out the resistor for one that’ll work with the lower voltage.

      Let me know how it goes.

      • Ian said

        Hi Tom, at first thank you for your quick response. I am still kinda lost. The recorder is sending out 48V. When I put in the recorder just the XLR with soldered capacitor, resistor and the joint (without microphone cable and microphone) is sending something around 8,5-9V. But when I solder the microphone cable and microphone it is something around 0,3-0,5V. I have no idea what is wrong.
        Thank you for your help.

      • Tom Benedict said

        Eeks! That sounds like something is shorting out.

        One question about your microphone capsule: Did you solder directly to the capsule? Or did you solder to leads that were already attached to the capsule?

        Early on I managed to fry one of my EM-172 capsules by using an unregulated iron. It ran too hot, and damaged the capsule’s internal circuitry.

        The symptoms you’re describing sound a lot like how it behaved.

      • Ian said

        I am afraid we found the problem. I solder directly to the capsule with an unregulated gun. I tried to be fast, but maybe not enough. Or maybe I burned it during heatshrink tube application, don’t know.

      • Tom Benedict said

        Dang. That sucks. I wish I had a way to bring one back from the dead.

  19. Akira So said

    Hi Tom, Thanks for putting together a very helpful web page on this. I was studying it as I was getting ready to wire up my own EM172’s, but noticed that you have the polarity of the capacitor in reverse of what’s shown in Ricardo’s SimpleP48.pdf file in Yahoo micbuilders forum. I was just wondering why you wired it that way. Best, -Akira

    • Tom Benedict said

      Thanks for pointing this out!

      The simple answer is that I used a photo of a wired microphone from page 4 of Ricardo’s SimpleP48.pdf, which also shows the capacitor backward, rather than David and Ricardo’s schematic. DOH!

      I’m not going to have a chance to look at this until tomorrow, but I think it would be better to follow David and Ricardo’s schematic rather than mine.

      Thanks again for pointing this out.

      • Akira So said

        Hi Tom, Thanks for your quick reply – glad I could help. 🙂 Your clear instructions were very helpful to me, so this would be the least I could do in return.

        I went ahead and temporarily wired up the matched pair of EM172’s that I just purchased from (UK) to take some preliminary voltage measurements. And Ricardo’s schematic was indeed correct. (i.e., the positive lead of capacitor should go to pin 2 of XLR connector.)

        Another interesting discovery for me was that the R value of 120k ohm suggested for EM172 in naturerecordists/micbuilders Yahoo forums was clearly too high, at least for my samples of EM172 capsules and Fostex FR2LE. (48.8V phantom voltage, measured.)

        My measurements of voltage at EM172 capsule terminals for different R values were:
        100k ohm -> ~1.7V
        68k ohm -> ~4.2V
        47k ohm -> ~7.5V

        So I am planning on using 47k ohm to provide 7.5V to the mic capsule, a bit higher than the standard 5V for extra sensitivity. (While I didn’t take careful notes about mic sensitivities, I had music playing in my room, and just looking at the recorder’s meters as I was doing the above experiments, I could see higher voltages offered higher mic sensitivities.)

        Of course final test will be in field recording – which will have to wait until next weekend. But I have high hopes for these little microphones!

        Thanks again.
        Pleasanton, CA, USA

      • Tom Benedict said


        I need to run those measurements, too. I remember running them for the 120k resistors and got close to 9.7v, but I don’t know if I had the capsules attached at that point. (I was paranoid about the voltage being too high and blowing the EM-172 mics before I’d had a chance to use them.) It’d be good to repeat the measurements with the caps attached to see if our results agree. If not, I need to replace my resistors AND swap the capacitors around.

        Thanks again for bringing all this up!


      • Tom Benedict said

        So I just measured the bias voltage on my EM-172 mics and came up with 1.43v, really similar to what you were seeing. Unloaded they’re closer to 9V, but with the capsule attached that’s what it draws down to.

        Your 7.5V is really close to the ~8V the graphs on the micbuilder forum indicate is ideal for these capsules. Let me know how the 47k resistors work for you, and I’ll make that change on my mics.

        As for the capacitor, I think you’re right. I’ve got mine in backwards. That’s another change I need to make in the schematic. Thanks again for pointing that out.

      • steph sandberg said

        Oups! Just checked mines and it seems I followed your guide a bit too religiously Tom!

        So now my limited understanding is going to show but how come our mics didn’t explode (don’t see any damage on the caps)? Do you need a certain current intensity to explode polarized capacitors? And the other obvious question I never asked myself: since the goal of the capacitor is to block DC and allow AC, why are we using polarized caps in the first place?

        Anyhow, thanks Akira, I am actually rather happy with that mistake because of your second discovery, which I might not have read without this cap issue. Will definitively change those resistors as well!

        Please let us know about your findings!

  20. bugman13 said

    Is it possible to connect multiple em 172’s in parallel ?

    • Tom Benedict said

      Vicki Powys did exactly this for her SASS:
      Scroll down to where she has the schematic for wiring parallel EM-172 caps into a 3.5mm plug.

      The same should hold true for wiring them into an XLR, but I haven’t tested it. I have a bunch of EM-172 caps on order, though, so I can build two quad-capsule SASS arrays similar to Vicki’s. I was planning to write an article covering the build, so if I run into any problems I’ll go into the details there.

  21. Mo said


    I must be really stupid but I don’t get this:

    Red (+ on the capsule) goes to pin 3 ( cold) on the XLR….. while white (- on the capsule) goes to the capacitor/resistor which is coming from the pin2 (hot) on the XLR.

    Shoulden’t this be the other way around…. ?

    Meaning that the plus cable from the capsule is going to the capacitor/res, and through theses, reach the signal from pin 2 (hot). Why is the plus connected to pin 3?

    I’ve seen a simple “drawing” somewhere which put it that the other way around.



    • Tom Benedict said

      Sorry for the delay in responding. I came down with the flu earlier this week, and I’m just now coming up for air.

      I had to break out a meter to make sure I wasn’t spouting BS. The upshot is that the way the XLR plug is wired, pin 3 has a higher potential than the junction between the resistor and capacitor. Since it’s those two points that are applying the bias voltage to the capsule, that dictates the polarity of the wiring.

      But it’s not obvious at first glance! I kept going between my diagram and the one in Ricardo Lee’s document (the one drawn by David McGriffy) to make sure I wasn’t screwing that part up. In the end I needed the meter to convince me.

  22. Mo said

    Hey Tom…. thanks for clearing this out and doing so when you’re sick. Much appreciated here.

    I hold no deep knowledge at all, but pulling together my own quasi binuaral little set ups since a year or so. No SASS’s but earmounted on myself, Jecklins and will have a go with some kind of lightweight Olson. They say the Olson needs to be massive and heavy to work best.

    Short brasstubes for the 172’s and that route… 😉 I’ve added the mini-XLR chassiecontacts in the other end of the tube. The Rean Tiny’s have a version with rubber hoods pulled over the cable connectors. All-in-all it creates a cool mini-mic with the option to switch cables easily. Which is nice to be able to use the same capsules for different setups an concepts

    So far, the M10 has been enough for me with the pluginpower. Probably getting the F4 (Zoom) in the very near future. The 4-6 channels would make it easy to testdrive different set ups and mics side by side in a total sync. The preamps seem very nice despite the reputation that brand has in the past regarding preamps and plastic feeling.

    The P48 > 9 volt for the power came up because of the F4 and I’ve been lurking around to find out how to best deal with it. Your information earlier on your site about this and the reply now really helped. Thanks for sharing in such a depth!

    Let me ask you a follow up question, I plan to run the 172’s in a double artillery set up. Parellell wired alligned vertically on top of each other. I will try and see if the full HF’s (on axis) could be expanded sidewise by turning one of the capsules slightly to the side.

    Let say, the first capsule at 20 degrees and the other one about 45 degrees. Higher sensitivety and less preamp is the main goal, but if the slight diff in angle could add a broader field with maxed out HF’s…. then that would be a very appreciated bonus. Phaseproblems or not, I don’t know how much crazy two sharp on axis would create to a human ear. Only a testdrive could show us. My question is more about the p48>9 conversion. Do you have any idea what value I would need for the resistor to get the same voltage to the two capsules on the same channel, as with the basic concept (1 capsule only on the channel). I could order a set of different resistors and measure me blue, but if you already been there…. 😉


    Tom, let me tell you that I just read about your loss of your dear cat a month ago. It really hurts here too. Been looking at the pictures of your beautiful cat and I understand your pain. I’ve been there, believe me. We went through the diabetes, insulin and bloodcurves at the age of 15. Complete recovery after 2-3 months. Never came back. We had two wonderful years after that and ended at almost 18. Been through many griefs, but loosing my cat was the worst I ever experinced of them all. Grief and Healing from it went according to the phases in the beginning, I had the tools from all my experince.

    But then it turned into another direction where I’ve never been. I don’t need to say more than it was very close to take me down for good. Period.

    I found a new friend at a the shelter. I waded through hundreds of different cats on that website, no one did pull the trigger for me. Not at all. I just didn’t care. Then, one late night at work he just sat there on the monitor. 9 months old at that time. Those pictures…..and those eyes……it all just snapped into place in a nano-second. I can see that your lost friend had the same depth in the eyes as mine. Hard to put the finger on what that depth is coming from. Been together here now for 9 years, each day is a gift of pure love. And full speed 😉 The best choice I’ve ever made in my life. I didn’t think it would be possible to find again. So, when the time is right for you…. please do the same.

    Thanks again for hooking up your meter for me while sick. No rush with the follow up wonderings here.

    Take care!

    • Tom Benedict said

      Ooooh! Let me know what you think of the F4 when you get it. I’m looking at eventually upgrading my DR-70D. Initially I was looking at the 680, but Robin Parmar pointed me toward the F4. If everything Robin says about the preamps is true, that’s one nice machine!

      Having four channels makes comparisons a lot easier, so I think you’re on the right track there, too. That’s the only way I was able to do the side-by-side tests I’ve done so far. It makes it really straightforward to compare two mic setups.

      Unfortunately I don’t have an answer on the resistors you’d need for doubled-up 172s. I should soon, but I don’t yet.

      Like you, I’m planning on building some vertically stacked dual capsule mics with a bunch of EM-172s I just ordered from Micbooster. They’re destined to go in a pair of SASS units I’m building. One will have XLR plugs, the other will have a 3.5mm plug for a handheld. I’ve got a 9V battery box I was going to use to power the 3.5mm SASS, and as much as possible I’d like to feed the two the same bias voltage.

      Akira So did some testing with other values for the resistor on single capsule mics, and found the 120K I’m using is way way high, providing a very low bias voltage to the capsule. He had better luck with a 48k resistor, which provided 7.5V to the capsule. I don’t know how that’ll translate into dual capsule arrangements, but I hope to find out soon.

      Meanwhile I started playing with different resistors today, hoping to duplicate what Akira saw. But I managed to blow up one of my EM172 mics. I think I’m still mentally addled from recovering from having the flu, and should’ve waited. Rather than blow anything else up I’m going to wait a little more before experimenting again.

      Thanks for your words on cats. They resonated with me a lot.

      We still have three cats, one of which is Ember’s mother and another of which is his brother. The third cat is unrelated, and at various times acted as Ember’s nemesis, his playmate, and his aunt. They drove each other up the wall, but of all the cats still in the house I think she misses him the most and needed the most comforting after he died. Cats are complicated individuals.

      At some point I know another cat will enter my life, but for now our house has reached… not exactly harmony, but stability. That works for now.

      Thanks, and take care.

  23. Mo said

    Hi again Tom,

    just a quick reply on the go here;

    Very happy to hear that you still have cats in the family, as you say – they’re very much individuals. And no doubt….high in rank mentaly…. I’m the “one-cat-only-and-closer-relation” type myself. That concept hit’s back hard on us when loosing them. The emptyness is total in many ways. Very good to hear that everything is at least ok for you. Time heals the worst of it.

    As for the electronic stuff, yes I did realize that there was information in the comments here about what I’m asking. Read to fast in the first place. I measured my M10 last night. A couple (one per channel) of 172’s loaded gave a PIP of left: 1.14 – right: 1.39 volt from the recorders PIP output. Unloaded it pumped out the equal 2.99 volt on each channel. Matched pair and sound really good and equal. Why the diff, I don’t know. One is probably more hungry. Like cars you know, same speed – different need of energy 😉

    That means a drop of more than half in volt when under the load from the 172’s when using the original feed from the M10 recorder.

    So, my thinking is; what is the specs for 172’s actually saying…. operatingvoltage: 5 volt (specs date: july 2015). 5 volt unloaded or loaded? Nowhere that is mentioned. Not in the specs, not on the web from any DIY freak.

    In other specs for the 172 (unkonown dates) it can be read something like 5 volt, span 2-10 volt.

    But the key is…. unloaded or loaded. I can see that this was a surprise for us all here to see the drop. But an insight is that it also happens with the M10’s original PIP……

    A few weeks ago Nick at MB told me to measure across the capsule and adjust the whole thing to 5 volt. That is loaded…. ( I was asking about parallell capsule and adjustment of the resistor like I asked you). Then, the unloaded must be much higher.

    Now, they (MB) do have there own new P48 solution for the clippys and I think it was nice of him to to give an answer for the simpleP48 arrangements anyway. Even though this was untested, it was what he thought about it. There own solution seems to handle any different phantom from 12v > 48 and be regulated to 8volt. It would be nice if they sold the XLR plug separately with cables only sticking out or a 3.5 mm plug /mini XLR mounted in the cableintake. As it is now it is only connected to the clippy mic and sold as a kit. They have added that the signal is balanced all the way from the recorder to the capsule! Also something I’ve been wondering – now they put it out there in the text like they were mindreaders. I really like them, Nick is very serviceminded.

    The local electronic shop guy here said that it (simpleP48) was an odd arrangement since it all depends on how much current each capsule consume. But that’s also what the intention is – keep it simple and as cheap as possible.

    I’ve got the components for the simpleP48 with the 120k res, but I’m not sure if I rather would ask Nick for a custom build of the regulated one to use, either for single capsules per channel – or in parallell. Or it might take care of that part itself as is, since it is regulated. That would solve things on the fly.

    There are also a lot of these adapters on e-bay, but those are targeting 5 volt. I’ve asked one of the resellers in France. I think it could be a nice market for MB – selling adapters separately. They know what we’re asking for. But it has to be without the clippy adding up to the costs. I think it would be very easy to mount a chassie 3.5 or chassie Tiny-XLR in the rubber bendprotection of the Neutrikplug. This way they could keep it sealed/glued and protect their solution as far as it’s possible. The e-bay versions are all metaltubes and sealed.

    I’m not sure exacly when I order the F4 but it will be soon, if nothing comes inbetween. I’m kind of hesitating playing around with the P48 and unsafe builds of adapters on that unit. Could testdrive the simpleP48 with a cheapo i-Rig PRE, but anyway…. you know what I mean…. you capsule blower there 😉

    Let’s keep this subject alive and keep writing about your experinces (and guide and inspire us). It works as triggers to learn more. Don’t stop becuase of the turbulens of new insights regarding the P48 voltage in the end.

    Good luck with the testing today!


  24. Mo said

    Just want to add this;

    When measurering the PIP of the M10 unloaded to 2.99 volt, it was based on batterys in the M10 that was half-full.

    The batterys measured unloaded to around 2.6 volt in serial. So, the PIP got about 0.3 volt more from elsewhere for the unloaded output to the mics.

    That was kind of uplifting…..

  25. Jon said

    i have been having a hard time gaining access to the yahoo group. So I can’t see the PDF that everyone is referring to. I was wondering if you let me know how to determine the resistor value to use if supplying the capsule with 48v phantom power. I used a circuit app and if I laid out the circuit correctly, and am supplying it correctly I’m getting a 20k ohm resistor. This seems off as most articles are suggesting 120k ohm. It’s a little closer to you number. Thoughts?

    Hopefully I will get access to the group soon but for. Ow I’m in the dark.

    • Tom Benedict said

      I don’t know the right way to calculate the value of R, but I can tell you what I did to come up with the ~40k value I wound up re-wiring all mine with last weekend.

      I gutted one of my mics, wired in a 100k potentiometer, dialed it up to 95k, plugged it in, and measured the voltage across the capsule. Then I tuned it until I got 7.5v. It wound up being right around 40k.

      I think the value depends on the actual P48 voltage supplied by the recorder and the amount of current it can source. One thing I learned about my Tascam DR-70D is that both of those dip if the battery level is low. First time I did the potentiometer trick I wound up with something closer to 30k. Then I realized my batteries were almost dead. I plugged in an external battery pack, powered everything back in, and just about fried one of my mics. (I thought I had, but even though I put over 10V through it it somehow survived.) Lesson learned: Use fresh batteries when doing that test, and test on the recorder you intend to use. Even so, the value I came up with was a far cry from the 120k I started with.

      I hope you get access to the group soon. Ricardo Lee updated it last October. At this point it’s geared more toward the EM-172 and EM-184 capsules than it is the WM61 capsule, which hasn’t been available for some time.

  26. Randy Tanimal said

    Thank you for posting this thorough document. I used your instructions to construct a binaural dummy head. Something I’ve always wanted to try but never wanted to pay the money for the Neumann.

    I am an audio engineer and educator and will share this valuable resource with my learners.

    • Tom Benedict said

      Hey cool! Glad I could help.

      As much as I’d like to take credit for this, that really does lie with David McGriffy and Ricardo Lee. Ricardo’s SimpleP48.pdf is the real reference for this, and would probably be a really good handout for your students.

  27. […] thru its XLR connection, which powers the EM 172 via a simple additional circuit as detailed by Tom Benedict (also the Micbuilders group on Yahoo). Zach Poff also has a great blog entry about building out the […]

  28. […] thru its XLR connection, and can power the EM 172 via a simple additional circuit as detailed by Tom Benedict (also the Micbuilders private group on Yahoo). The comments in Tom Benedict’s blog post […]

  29. […] was turned on to the mini-XLR connectors by Mo, who shared them in a comment on my EM-172 and XLR Plug article. I have to say these things are the cat’s pajamas. They’re small, […]

  30. Dreyfus said

    Hey Tom,

    thank you very much for that wonderful article!

    I am just planning to build a new stereo setup with some EM172s but am not quite sure about connecting them to my Tascam DR 60D (non-MKII).

    The capsules are specified with approximately 2.4 kΩ (may even further increase with the XLR circuitry) whilst the XLR inputs of my recorder provide 2 kΩ and the 3.5mm input 10 kΩ. Wouldn’t it be better using the 3.5mm jack in this case to avoid a loss of level, clarity and SNR?

    Click to access Mic%20impedance-10.pdf

    Another aspect I thought about – in case of going with XLR – was to utilize 24V instead of 48V with a appropriate resistor to increase the battery life of the recorder. Any thoughts or possibly even experiences on this subject?

    Would be very happy hearing from you.

    Best wishes from Germany,
    – Dreyfus

    • Tom Benedict said

      On your 24V vs. 48V question, you’re absolutely right. Ricardo Lee pointed out that same thing in the SimpleP48 document I based that build off of. The one warning he gave is that you should label any P24 microphones very clearly so you don’t put 48 volts through them. When I built mine I went with simplicity over efficiency, making all of mine P48 so I couldn’t over-drive them. But in terms of battery life, sizing the resistor for 24 volts would give you a much longer recording time.

      On the other question, I honestly don’t know. Part of what drove my decision to go with XLR plugs instead of 3.5mm plugs was that my recorder, the DR-70D, has different gain ranges for the XLR inputs and the 3.5mm inputs. I forget the specifics, but the XLR inputs provide something like 12dB more gain than the 3.5mm input on the DR-70D. I don’t know about the DR-60D.

      The nice thing is, it’s not that expensive to give yourself both options. A while back I decided to try using an Android phone as a field recorder, so I converted one of my existing EM-172 mics to use a 3.5mm plug. It only took a couple of minutes, and the 3.5mm plug wasn’t that expensive. You can always try it both ways, and decide which one works best for you.



  31. Dreyfus said


    thanks for your rapid response! 🙂

    The danger of driving a 24V with 48V by accicent is of course a danger. Might indeed label the connectors to ensure I don’t forget about that.

    Regarding the impedance I’m not quite sure if the listed value in the spec sheet actually represents the load impedance which – as far as I have read so far – should be about four times higher than the mic impedance to ensure the best performance.
    Since I don’t want to solder and trial and error that much (to protect the capsule), it would have been nice to know whether the phantom or plugin power inputs work better. On paper (, the mini jacks have +10 dBV max. input whilst the xlr jacks offer only 0 dBV max. input.

    However, thanks so far for your great documentation and kind response! 🙂


  32. Dreyfus said

    you are absolutely right, the actual input gain is higher on the XLR input. Both on the DR-60D as well as on the DR-70D.

    I guess I will do some further digging on the impedance subject to determine which option might work better in theory.

    • Dreyfus said

      Hey there,
      me again 😛

      I’m still not entirely sure which option to go for. In theory, the plugin-powered input would be a better choice in reference to the ohm-ratio, whilst the phantom-powered input would have the advantage of the higher voltage supply.

      Since both factors could theoretically interfere with the signal quality in some way I ordered some mini jacks as well as some XLR connectors.
      My plan was to (more or less directly) fix the capsules to a 3.5mm socket each so I can plug in various extensions just when I need them. The first option would be a XLR P48 cable for my interface, the second a XLR P24 cable for the recorder (due to battery life) and maybe a third one with a simple 3.5mm TRS connection for testing the 5V plugin-power of the recorder.

      Do you have any recommendations for a P24 resistor?
      Any idea which current the mic will draw with 7.5V so I could calculate R?

      Thanks for any help!

      • Tom Benedict said

        Unfortunately I don’t really have answers to either of your questions. When I first built mine I built them exactly as Ricardo Lee described in SimpleP48 (despite the fact he said you have to tune the resistor to your capsule. DOH!) After someone asked me to measure the voltage across the capsule, I realized I was supplying only something like 1.5V.

        What I did was to wire a 100K potentiometer in place of the fixed resistor, and dial it until I got the voltage I wanted (right around 9V, if I remember right). Then I took it out, measured the resistance I’d dialed in, and replaced it with a fixed resistor.

        What made that possible was that Homero Leal pointed out that precision resistor assortments show up on Ebay all the time at reasonable prices. I think I got mine for under $20, and it has tons of sizes to choose from. If I use up too many of on size, I tack that onto the next order from Mouser or Digikey.

        Sorry for not having a more satisfactory answer for you.

  33. Dreyfus said

    Hey Benedict,

    thanks for your response anyway!

    I have finished my build in the meantime.
    Here is a series of photos of my modular setup in case you are interested:

    As for the technical aspects, my DR-60D recorder works with about 45.5V on the 48V rail, with 23.5V on the 24V rail.
    First of all I tried the P48 XLR build with a 41.2K resistor and hit a voltage peak of 9.0V just at the first attempt 🙂

    On the next step I soldered a TRS cable for the plugin-powered version and found out, that the recorder emmits only 2.5V per channel which – as expected – result in a higher noise floor.

    After deciding to work with XLR I tried to solder another pair of XLR cables for 24V phantom power. Finding the right value for R was quite easy as well since I ordered a large variety of different resistors between 10k and 50k. I ended up with a 25.5kOhm resistor resulting in just about 9.9V at the loaded capsule. You can see a chart with a few reistor values I have tried out in the imgur gallery linked above.

    So finally I ended up with a pair of P24 and P48 cables, both giving me about 10V of power at the capsules. To keep the system fully modular I used some 3.5mm TRS male and female jacks with threaded couplings by Hicon connecting the XLR cables with the capsule cables.

    I haven’t done that much testing so far. But as far as I can tell the EM172s sound pretty amazing for the price.

    I’m planning to integrate the capsules to a binaural setup for field recording soon. Hope they work well for that purpose. I am just figuring out how linear both capsules operate on a free field / open space. Guess I have to do a lot of homework regarding the equalization, especially when using the capsules for a binaural system with silicon ear models.

    However, thank you so much for your inspiration! I would’nt have found that great and even extremely cheap solution without your blog!

    By the way:
    here are some audio samples regarding the plugin power vs phantom power noise floor:

    P24 and P48 perform basically the same in this case.

    And finally a list of the components I used for my build:
    – Cable: Cordial CPK 220 BK (0.2mm² cross section , 4.7mm total diameter)
    – XLR jacks: Amphenol AX3M
    – TRS jacks: Hicon HI-J35S-Srew-F, Hicon HI-J35S-Screw-M
    – Electrolytic Capacitors: Panasonic FR-A, 50V, low ESR, 5000-10.000h lifetime, 2mm spacing, 5mm diameter
    – some regular metal film resistors with 1% tolerance
    – Felder Sn62 Pb36 Ag2 soldering wire (low melting point to make sure the capsules don’t fry)

    Best wishes,

  34. Mark said

    Hi Tom, just stumbled across your article. Thanks for doing this. One question I have however is with the polarity of the capacitor. On the circuit diagram you have the +ve side connected to pin 2 but on the photos of the build it looks like the black-stripe side (the -ve) is connected to pin 2…?



    • Tom Benedict said

      Good eye!

      Thanks for reminding me of that. When I first wrote the article I had the polarity backward. Another observant reader, Akira, saw that and wrote to me about it. I fixed the schematic and re-wired all of my mics, but I didn’t have my camera gear with me so I never made new photos.

      I need to make new photos!

      I’ll grab my camera bag and some mics and see if I can knock them out today. Thanks again for the reminder.



      • Mark said

        Aha! Thanks, Tom. No rush, just glad I wasn’t going mad. 🙂

      • Alex said

        Also, in the text, you have “Next, solder the (-) end of the capacitor to pin 2” and “Red goes to pin 3, white goes to the (+) lead of the capacitor” where, unless I’m very much confused, the (-) and (+) should be swapped. (Sorry if you’re already aware of this!)

        I’m thinking of trying this with an EM258 because I want to record ultrasonics. I haven’t been able to find much about using that capsule at all, let alone with XLR P48 — one blog (in French) where they use an external 3V. Nothing in micbuilders although I’ve only just requested to join, so I can’t see the files yet.

      • Tom Benedict said

        Again, good catch! I’ve corrected the text in that section. Thanks!

        WHOA! I’d never even seen the datasheet on the EM258. That’s cool! And it’s great that Nick at Micboosters carries it. The list of Primo capsules available to the general public is so small, it’s discouraging at times.

        Yeah, the datasheet for the EM258 specifies 3V operating voltage. Primo’s pretty good about indicating if there’s a range of operating voltages, so my guess is they’re not kidding about the 3V. You should still be able to use the P48 circuit by changing the value of R until you get 3V at the capsule. (A multi-turn pot is handy for finding what this should be, just start at the ~0V end!) But with a 3V operating voltage it’d be an ideal candidate for running off of PiP on a 3.5mm plug. For those you can likely use the wiring diagrams on Vicki Powys’s site, or on Zach Poff’s or Christine Hass’s sites. It’s about as simple as it gets.

        Kind of a bummer. I used to live in Austin where there are huge Mexican freetail bat populations, so the ultrasonic soundscape would’ve been seriously interesting. But that pre-dated my getting interested in field recording. There are bats out here in Hawaii, but they’re endangered and quite rare. I still wouldn’t mind playing with an EM258, but I don’t know what I’d find.

        Thanks again, and let me know how your experiments with the EM258 go.



  35. Pierre said

    Dear Tom,
    just found your article. Thanks so much! I’m quite a noob on electric circuits so hopefully you can help me out. I want to be able to use my DIY binaural microphone with a Zoom H6N and also with Interfaces (for example a Focusrite Saffire Pro Interface). Both provide Phantom power. The Zoom has either +12, +24, or +48 volts, the Focusrite +48. In my case which would be the correct resistor? Thanks so much! Best, Pierre

    • Tom Benedict said

      That’s the one drawback with this design. It really only works with one voltage. Something using a voltage regulator or a Zener diode would be able to work with any of the ones your Zoom can use, but wind up being a more complicated (and potentially noisy) circuit.

      For +48v, the resistor I wound up using on mine was around 40k ohms. If I remember right this resulted in about 7.5v across the capsule.

      But rather than taking that number on faith, a safer route would be to wire in a variable resistor (I used a 100k ohm trim pot), set it at the high end, measure the voltage across the capsule and slowly lower the resistance until you hit your target voltage. 7.5v to 9v is ideal. Once you hit that, measure the resistance across the variable resistor and use that value.

      When I first wrote this article I used a much higher resistance than I should’ve because I just pulled the numbers from Ricardo Lee’s article. In the article, though, he points out that the values he quotes won’t necessarily be ideal, and that you really do need to do the measurements yourself. Oops! Once I did the measurements I came up with a much lower value for that resistor (and a higher bias voltage for the capsule). At some point I need to go back and re-do all the photographs for this article to reflect the new values.

      Best of luck, and have fun recording!


  36. Pierre said

    Hey Tom,m
    thanks for your fast reply. +48 is the most common standard so I will give it a try with the 40k ohms you recommend. I just reordered a couple of EM172’s capsules. I’m very surprised how good they sound and will do some more DIY projects.

    Thanks again!

  37. Andrzej Sochon said


    I plan to connect the EM172 Capsule with XLR plug. Stupid question: measurements of voltage at EM172 capsule terminals for different R values : do you mean voltage between 1 and 2 capsule terminals ?

    Best Regards,

    • Tom Benedict said

      Not a stupid question at all. I didn’t understand that, either, when I built my first one. Yes, it’s the DC voltage between the two capsule terminals.

      Good luck on your project!


  38. Andrzej Sochon said

    Sensational microphones! I installed in metal housings of an old flashlights, the housings are heavy and the internal cables are very thin – thanks to this, the level of unwanted vibrations from external wires is small. I used a typical PC-housing audio shielded dual cables, 3.5mm jack , 2x47uF, 2x2k2 and 9V battery. I must fill up the microphone housing with something because I feel there is a small acoustic signature of empty space inside.
    Wishing you The Merry Christmass and a Happy New Year 2018,

    • Andrzej Sochon said

      Small modifications: 2x10uF/50V, 2x1k5.
      Now with the 9V battery I got 8.15 and 8.24V between the two capsule terminals.
      I do not know if the difference of 0.1V brings an acoustic result, I bought matched capsules.

      Big improvement: I placed the Jecklin disk (DIY) between mics: very good channel separation, very good acoustic results on headphones.
      I choosed a larger version of Jecklin concept, i.e 35 cm disk diameter and distance 36 cm between capsules.

      Some words about my recording equipment:

      Samsung Galaxy Tab A (2016) with the USB Audio Recorder Pro application (
      DIY pre-amplifier (uPC4572 op amp)
      Creative Sound Blaster X-Fi HD (SB1240)

      Cooperation between Creative module and application is not perfect because of fixed recording level, there is no possibility to controll; this is why I use an additional pre-amp. Application producer informed me that Creative does not give an access to all of the SB1240 internal registers. But finally I am very satisfied: I am able to record with Hi-res quality (24 bit 96 kHz, stereo).

      Best Regards,

      • Tom Benedict said

        Excellent! And thanks for telling me your experiences with your Jecklin disc. I wanted to try one a while back, but never got around to it. A few weeks ago someone told me the SASS sounds very close to a Jecklin disc, so that combined with what you said makes me REALLY want to try one. I love my SASS, but it’s bulky to carry and travel with. I hope the disc works out. It’d be a lot more convenient in the field.

        That’s a shame you can’t get at the internal registers of the Sound Blaster, but I like your fix.

        Congratulations! And have fun recording!

      • Andrzej Sochon said

        SASS – thank you very much for an information, this is something new for me… Looks nice and is smaller than Jecklin. My Jecklin is large, bulky: occupies a space measuring approximately 35 x 36 cm (disk is 35 cm diameter, and there are two perpendicular arms, protruding from the middle of the disk, approx 18 cm each). I plan to modiffy my Jecklin to make it a little bit more compact / flat, for transport / travel. I would like to attach small hinges between Jecklin Disk and microphones arms.

      • Tom Benedict said

        That’s similar to what I was thinking: hinged arms or arms that could come off so the disc could lie flat when not in use.

  39. Andrzej Sochon said

    Jecklin disk is large and draws attention very much. Especially my, because I use damping material, which accidentaly is intense blue in colour. Yesterday I was recording airplanes, stood next to the fence, there was a runway behind the fence, for the aircraft passing boiling to take off. There were several spotters photographers next to me, I looked bizarre with a strange large blue disk on a tripod so the airport security guard was interested asking me what is this: dron, laser, radio remote controller or what…

    • Tom Benedict said

      Yikes! Yeah, I tend to leave my gear out overnight so most of my stuff is either black or camouflaged. Bright blue will get you noticed!

      I hope they didn’t make you stop recording, though. A couple of years ago I heard a really cool recording of a jet coming in for a landing under heavy clouds. The reverberation was amazing. I was hoping to hike out to the end of the runway near my house to see if I could make a similar recording. I just don’t want to get in trouble!

  40. Andrzej Sochon said

    The security was very polite, I prooved that simply demonstrated what is going on on tablet screen while knocking to the microphnones.
    Thanks microphones experiences I pay more attention what I am hearing everywhere: on street, at large halls, underground station.
    I am unpatiently waiting for the spring to record ambient in the country, at forests.
    About 10 years ago I made some such forrest/country recordings using professional mics attached XLR to the E-MU module connected to laptop via special PCMCIA card. This is my reference. Strange is that I much more like ambient with distant voices of birds, barking dogs, clatter of storks, screams of cranes, echoes, than close bird voices.

    • Andrzej Sochon said

      Hi Tom,

      Another stupid question: presented XLR connection creates balanced interface?
      I plan to use Scarlett 2 i 2 2 gen.

  41. Andrzej Sochon said

    Patiently reading this page I think I found the answer: the design presented at the top of this page is ballanced if the cable length is below 10m.

    Best Regards,

    • Andrzej Sochon said

      I have recently been a member of Micbuilders. I struggle to move around this forum looking for fully balanced signal from EM172. Digging through the diagrams, asking many questions, I think I started to slowly understand what’s going on. So I decided just to check does the fully ballanced electronics work or not with the EM172 and try to compare with the presented here the ‘Simple P48’ design (I mean the circuit at top of this page).

      I choosed the ‘Best So Far’ solution from ‘Direct Approach’ web pages to build one chanel only.
      (See the last schematic diagram at dedicated to the Panasonic WM61-A Linkwitz Moded capsule).

      My construction looks like a spiderweb. And works!!!

      Necessary parts I paired, as much as I was able to do.

      My EM172 capsule is attached to the ‘Direct Approach’ circuit this way: Hot to 1, GND to point 2. Names Hot and GND – according to soldering tips of the EM172 capsule.

      I got the following voltages at one of my capsules: 8.2V (7.7V at the second one, I bought ‘paired’ capsules), what is almost perfect.

      While both capsules are attached to my Scarlett 2i2gen (one via ‘Direct Approach’, another one via ‘Simple P48’ design), I can hear stronger signal from the ‘Direct Approach’. I do not have possibility to measure signal and noise levels, my audio software shows that the diffference between both chanels is +6dB approx. Noise level is higher too, maybe because of not shielded spiderweb and the very simplified slimmed circuit.

      Best Regards,

      • Tom Benedict said

        The “Best So Far” circuit is very similar to one Henry Spragens has on his site:

        It’s the second schematic in the first figure. It’s basically a stripped-down Schoeps with the FET stage removed (since the EM-172 has an internal FET).

        The SimpleP48 is handy for short cable lengths because it doesn’t have any active components in it. The only source of noise is the Johnson noise from the resistor. The benefits are low noise, low cost, and simplicity. According to Ricardo Lee, the SimpleP48 presents a balanced signal to the preamp, provided cable lengths stay short (<10m)

        For longer cable runs the Schoeps approach (the "Best So Far" approach) is better because it is a true balanced circuit and will provide a balanced signal, even with longer cable lengths.

        One difference between Henry's schematic and the "Best So Far" is that in Henry's the voltage to the capsule is set by a Zener, while in the "Best So Far" it's set via a voltage divider. Henry's can be powered by P12, P24, or P48. Voltage divider circuits like the "Best So Far" and the SimpleP48 will only work with one phantom power voltage.

        The advantage of a voltage divider approach, though, is that they're inherently lower noise than a zener, so they require less filtering.

        In any case, adding shielding to your spider web should certainly improve the noise floor. (If for any reason it doesn't, let me know!) It might not bring it down all the way to the noise floor of the P48, but I bet you can get really close. With the +6dB higher signal, you may still come out ahead on signal-to-noise.

      • Andrzej Sochon said


        I am slowly beginning to understand, the image of the true ballanced low noise preamplifier slowly shaping in my head
        Thank you very much for the tips.


      • Andrzej Sochon said

        At the MICBUILDERS Forum I created the ‘EM172 capsule and XLR’ FILE and uploaded my file showing EM172 and fully balanced XLR connection; this is my modification of Homero scheme ZenerLessAliceV40.png. Now is the time to in-filed recordings…

  42. Matias said

    Hi Tom

    Just one quick question. I’m pretty sure I have everything like in the schematics, but the DC voltage still measures 43.2V if measured from the other end of the cable. The same voltage as straight from my mixers mic input. I have made two identical cables and both of them measure the same.
    Is this the right way to measure or should I measure with the EM172 capsules attached?
    I have now 4.7uF/50V capacitor and 2k2 resistor in both of the circuits/cables.

    • Tom Benedict said

      That’s how I started out building these things, but I found adding the capsule tended to drop the voltage. (Makes sense.) Still, I’d be leery of wiring a capsule into something that’s showing 43.2V open circuit!

      If you have a variable resistor that you can use (0-100k or so), temporarily wire that in place of the 2k2 and dial it to max. Measure the voltage at the end of the cable to make sure it’s lower than 5V. Unplug, wire in the capsule, and plug back in. Measure the voltage at the rear of the capsule as you dial down the resistance. Once you hit 5V, write down the resistance. You can keep going, but I wouldn’t go over 9V at the capsule. Once you know what the values are, replace the variable resistor with a fixed resistor of that value.

      • Matias said

        Hi again and thanks for the swift answer, Andrzej and Tom.

        Update: I tried with a 100K variable resistor and put it in the place of fixed resistor.. still nothing. The voltage remained over 40V. I had now built the circuit 5 times from the scratch.
        However, yesterday I saw this one:
        It had the capacitor the other way round (than on this page’s instructions) so the capacitor minus is connected to XLR pin 2. I tried that and now the voltage is floating nicely between 8.5-9V. The resistor is now fixed 33K.
        I really don’t understand why this works as everyone are clearly doing the opposite and the circuit in the above flickr link should be wrong, but I’m testing the capsules next week.

      • Tom Benedict said

        Thanks for bringing this to my attention, Matias. If I remember right, Ramon built his off of my original diagram, in which the capacitor was oriented the way it’s shown in his photo. (The way it’s still oriented in the photos in this article, since I never went back to re-shoot the whole process.)

        To be fair, when I first wrote this, I was more or less guessing about the orientation of the capacitor. As bad as that sounds, here’s why:

        The diagram in the original SimpleP48.pdf document written by Ricardo Lee (and the basis of this whole build) shows the capacitor with the + side going to XLR pin 2 and the – side going to the negative pad on the capsule. But then further down in the document, in the photos of Casey Connor’s build, the capacitor has its – terminal going to XLR pin 2 and the + lead going to the capsule.

        Since the photos indicated a working mic (I assumed), that’s the orientation I originally followed for my build. Since then I had a couple of people point out I’d wired it in backward, so I went back and rebuilt all my mics, re-tuned the resistors, and updated the schematic. As I said, though, I never went back to re-photograph the process.

        So now both Ricardo’s document and the article I wrote here have the same flaw: a schematic that shows things one way and photos that show things the opposite way. I managed to get both ways to work, but that doesn’t mean that both ways are right.

        Your experience seems to indicate that Casey Connor had the right of it from the beginning. Clearly, I need to go back and build one of these each way and measure voltage drop at each point in the circuit to try to figure out what’s going on. I leave on a trip in a couple of weeks, and won’t have a chance to do this until I get back, but if you or anyone else is interested in pursuing this in the mean time, I’m curious to learn what you find.

        Thanks again, Matias.

    • Andrzej Sochon said

      R = 2k2 is approximately fine for 9V power, but at 48V, this resistance is dramatically low. Phantom’s source output current is very low, so it is hoped that your capsules are not damaged.

      I use a very old E-MU 1616m; phantom voltage is 46V.
      I purchased EM172 capsules from (UK).
      Today I made EM172 capsule voltage measurements with different R values:

      150k = 0.7V
      43k = 7.5V
      39k = 8.0V
      36k = 8.3V
      33k = 8.7V

      Results may be different for other devices generating 48V.

      Best Regards,

      • Andrzej Sochon said


        My EM172 capsules are ‘paired’ and both R resistors are paired too and are 43k.
        But I observe small differences between capsules voltages. I do not observe acoustic tone / volume differences, maybe my ears are to old, I am 68 (-:

        Question: Do these differences matter or not? See the notes below:

        E-MU 1616m; phantom voltage 46V
        Capsule voltages:
        first chanel: 7.54V
        second chanel: 7.90V

        Focusrite Scarlett 2i2gen, phantom voltage (open connector) is 46.7 – 46.8 V
        Capsule voltages:
        first chanel: 7.60V
        second chanel: 8.00V

        I will appreciate any suggestion.

        Best Regards,

    • Andrzej Sochon said


      … the capacitor minus is connected to XLR pin 2…
      Maybe it makes no sense, my sugestion: check voltages at pins 2 and 3 (between 2 and 1, between 3 and 1, open circuit).
      Maybe your preamp does not deliver phantom supply to pin 2.


  43. Mo said

    Have a look at the simulation at this link.

    A zenerdiod is added to the koncept to finetune/dump/regulate the voltage after the resistor.
    It’s a classic concept to “regulate” overflow in the most simple way. The zener is a safety gate…..

    The 14 k resistor simulates the load (mic capsules currentdraw). The capsule draws around 600uA according to the specs, that 14K resistor just simulates that, nothing else. Hold the mouse pointe above the resistor or the groundpoint and get around 585 uA.

    As you can see…. the voltage is simulated to 8.2 V if using a resistor around the value 7.5K to zero in the voltage from 48 down to 8.2V, so that the zener doesn’t have to dump off to much = generate to much heat. As little as possible through the zener is the goal with the main resistor at 7.5K here.

    You can double click any of the components and change your values. But the specific capsules need of current – 600uA – is the referens. The zener regulates the voltage. This zener is in this case a BZX55C8V2 DO-35 8.2V 500mW.

    Just got this tip from a good guy, how to regulate with a zener and use this online simulator. You can build whatever and simulate. As you can see…. there is a menu row at the top of the window. Have a nice weekend and don’t get stuck with this now 😉

    Have not tried this in real world yet but bought the zener a few months ago – at almost no cost. We’ll see when I get time and lust for it. Just wanted to share the simulator with you.



    • Hey Mo, quite interesting what you did there, thanks for sharing.
      I’m interested in building the mics as well but what are the advantages of regulating the voltage with that semiconductor?
      Or the other way around: What could happen to the capsule if I build it without the Zener?
      Sadly I have little to no experience in this and would like to build it as safe and reliable as it gets.



      • Tom Benedict said

        My concern with zeners is that they’re inherently noisy devices. You have to filter them. The real beauty of McGriffy’s circuit is that except for the Johnson noise of the resistor, there’s nothing in there that adds noise to the signal. Adding a zener would break that mold.

        Not saying it’s not a good idea to tinker and think outside the box, just pointing out one of the things that makes the Simple48 circuit what it is.

        Along similar lines, though, if you’re looking for a more flexible design (regulated capsule voltage, the option to use longer cable runs, etc.) another approach would be to go with something closer to a Schoeps circuit, minus the circuitry to supply the bias voltage (EM-172 are electrets, and don’t require it) and minus the FET stage (the FET is internal to the EM-172). This page from Henry Spragens’s “Audio Improv” site goes into a really good discussion of this:

  44. Mo said

    Hi Jorne and Tom,

    from the impression I’ve got it depends a lot on the quality of the zener when it comes to noise. But I’m sure that Tom is right on this based on the research and insights from this phantom road trip. And as you mean, the beauty of the simplicity has a very good reason from the beginning.

    It’s an interesting subject, how to do it and in the best way. Somewhere a point is reached when it’s just to much to wrap the mind around. A part from sound quality, noiselevels and the good feeling of done it ourselves….. there are sturdy solutions readymade at a decent cost now since a while back. They do deliver regulated 8 volts to the capsule regardless of Phantom source. At least they say so.

    Both the LOM and Micbooster sites do offer them. What kind of circuit they use are to me unknown. It’s regulated and you can hook up to any recorder without worries about differences in voltage to the capsule. (Jorne, that’s the advantage the zener tries to mimic in the minimalistic way started here of doing things. Just to avoid blowing the capsule if connected to a recorders phantom output the basic resistor value doesn’t match or is calibrated for….).

    LOM is quite transparant in showing the circuitcard on picture which they solder into a XLR plug. The question in my little noughty mind is if this is a readymade card availble or if it is custom made. I suppose Micbooster uses the same stuff or similar.

    The costs are so low readymade, it would also be very flexible using the finished plugs as is. I doubt that any of these two sources would sell them if they degraded the sound. These are both up at 8 volt rather than 5 which is common with the unknown ebaystuff that can be found. So…. 40€ for two plugs in a set usable for any phantom source 24-48 volt. Or in the case of Micoooster adapter – from 12 volt up to 48. Fluctuations in the phantomsource o different currentdraw from the capsules would be equaled out, I guess?

    2x fullsize XLR including 2 mini Rean XLR’s in the other end of the cable:

    Micbooster can offer the plugs/adapters with a open cable without these clippys attached:



    • Tom Benedict said

      I’m pretty sure both LOM and Micboosters build their PCBs in-house. At a guess they’re both Schoeps variants. It’s about the simplest, cleanest way to get balanced output. And no, neither should degrade the sound. Both Jonáš and Nicholas are very good with their design work.

  45. tobygifford said

    Hi, thanks for this blog, it is really informative. I’m about to order some Primo capsules for a DIY binaural rig. I’m wondering if anyone who has gone down the EM173 route can comment on whether it was worth the trouble compared with EM172s? I guess it depends on what one wants to record. I’m interested in wildlife soundscape recording – do the EM172s with P48 mods have a favourable sensitivity for this kind of thing?

    • Tom Benedict said

      Glad the blog helped!

      I haven’t done a build with the 173s, so I can’t address that question. But the EM-172 based mics do quite well with wildlife soundscape recording. Not sure what kind of binaural rig you’re planning, but the motivation for my SASS was Vicki Powys’s SASS, both of which use the EM-172 capsules. Many of the recordings on her site were made with that mic. Christine Hass also uses EM-172 mics for wildlife recording. Here are their sites:

      Vicki Powys:
      Christine Hass:

      And here’s one of mine:

      • Andrzej Sochon said

        I made some nature soundscape recordings using EM172 capsules connected to my mixing device via simple P48 XLR and I am very satisfied. Sensitivity is very good. If I set my input potentiometers to the max – there is to much sensitivity even for a small birds located at approx 7-10 meters. The biggest difficulties create wind and noisy environment – microphones are catching every sounds, the presence of which we are not aware.
        Regarding EM173 – this mike is 9 dB less sensitive then EM172. But if somebody would like to record extremal sounds like a storm – in my opinion better is EM173 (13 dB bigger max input SPL (Sound Pressure Level))

    • Andrzej Sochon said

      I made DIY binaural rig to my camcorder, I use the same EM172 capsules with 9V battery and 1k5 resistors. Sensitivity od capsules is so high, I set the internal camera recording level to -6dB or even lower. Results are drastically beteer in comparison of integrated camera mics. The only negative thing: mics catch my every breath.

      Andrzej Sochon

  46. tobygifford said

    Thanks everyone, EM-172s ordered!

  47. Andrzej Sochon said – this is my very first Youtube upload, result of bat voices recordings made with my system based on the EM172 capsules, DIY Jecklin disk and Focusrite Scarlett 2i2 gen.

    Best Regards,
    Andrzej Sochon

    • Tom Benedict said

      That is too cool! The fly-by in the second sequence (downsampled to 22.05kHz) is fantastic.

      • Andrzej Sochon said – my second ‘bat’ Youtube upload – more bat voices including social voices, a movie shows the environment of bats, more comments.
        As suggested by my son, I used words “slowed down 16 times” instead of “downsampled to xxx kHz”.

        Best Regards,

  48. Vhrwerk said

    Hello Tom!
    I write you because i need a small help from you: i built my primo EM172s and they’re made like this

    they have RCA connectors as you can see and i want to power them with phantom (48v).
    The question is: can i make the cables exactly as described on your blog but without the copper foil and a terminal RCA connector?
    Then why is the red (hot for 172) connected to pin3?
    Thank you very much!

    • Tom Benedict said

      It’d be tough to make that work with the RCA because you’re going from a 3-pin XLR to, essentially, a 2-pin at the mic. You have to lose something along the way. You can choose to lose one leg of the XLR and go unbalanced, but at that point you’re back to a PiP setup (or a TS setup if you have 1/4″ inputs). Or you can lose your ground, which would invite all manner of noise.

      Another possibility: Can you replace the RCA with something else? Some options would be a 1/4″ TRS jack (fairly large, would change the size of your mic heads) or something like a mini-XLR (TA3 / TB3) like these:

      That would let you run all three wires (GND / Sig+ / Sig-), would let you shield it the whole way, etc. The TA3 is about the same size as an RCA. It might fit in the existing hole in your mic body.

      As for why the red wire’s hooked up to pin 3, I’ve been around that one a couple of times, but for positive polarity (positive pressure change results in an up-swing of the signal), that’s just how it worked out. At some point I need to sit down with an oscilloscope and find out why it is the way it is, but as far as I’ve been able to see, that’s it.



      • Vhrwerk said

        To be more precise i’d do this:
        Exactly as described by your project but with no copper foil in the end, i’ll let the shield of the microphone dead ended.
        I’m not an expert as i mentioned but i think it should work. The only difference i see is in the very last centimeters of the mic body which are unshielded but the connections to the capsule are the same (hot and ground soldered to the two poles of the RCA).
        Am i wrong?
        Thank you a lot for your patience, much appreciated! 🙂

      • Vhrwerk said

        Sorry if i bother again but: i built the XLR with capacitor and resistor exactly as described by you (i can attach pics if needed), but before soldering the RCA as previously described i measured the volts beetween the white and the red: it still have almost 48V (47.8 or something like that) instead of 7.5 as expected. I checked again and again for errors in the circuit path but there are none. The only difference is the capacitor, it’s 50v instead of 25v but that shouldn’t be a issue, it’s still 4,7 uF and the resistor is a 47k. I’m really afraid i’d blow my mics if i connect them now.
        I know it’s a bit hard to ask but… is there anything wrong? What? I’m loosing my mind.
        Thank you!

      • Andrzej Sochon said

        If I understand you measured voltages without the mic capsule? Try to simulate capsule: instead capsule use resitor approx 3 koHm to to force the current flow, and measure now.

      • Vhrwerk said

        Yes! It’s what i did! I use a Zoom H5 and it provides 2.39V to the PlugInPower, this is measured in same conditions (with no mic plugged in).
        I don’t have a 3K resistor now but i tried with another 47k between the two connectors and the voltage goes something near to 22V. Isn’t it strange?

      • Andrzej Sochon said

        The ‘new’ 47k between the two connectors and the voltage goes something near to 22V – it is OKAY: this ‘new’ 47k is in serial with the 47k (resistor in pair with capacitor) – you measure approx the half of your phantom voltage (48V) on the ‘new’ 47k. Now you can put mic capsule instead of the ‘new’ 47k resistor, measure, should be 5 – 7V.

      • Vhrwerk said

        Oh! So everything’s correct, no mistakes in my work, right?
        But, forgive my ignorance, why does the pluginpower of the recorder provides a much different voltage with same measure?
        Thank you a lot sir!

      • Andrzej Sochon said

        I am sorry, I am not familiar to the H5, but I will try to answer.
        I downloaded the User Manual and I see H5 has the MIC/LINE Input jack, which, in my opinion, plays the same role like MIC jack at the typical photo camera or/and camcorder: you can attach an external mic. Such jack delivers power (taken from internal H5 battery) to supply an external mic. Voltage measured here is low, about 2 – 5V. This is an amateur solution, which, if you use hi quality external mics, can produce much better sound than is available by integrated mics.
        XLR is a professional solution, supporting more posibilities an the best results.
        You are on a good way to go pro…

    • Abc said

      Nice enclosure, but that wide and fat front surface around the capsule will create a very sharp and nasal character of the sound compared to a more narrow tube. A smaller en enclosure will give much more balanced sound with more bottom and smooth register.

      Depends on what you will use them for, but just put your hand or fingers around a more narrow tube mounted 172’s and listen to the big difference. Or put a rubber ring in that size behind the front. The airy feel of the omni 172 is lost.

      • Tom Benedict said

        You’re absolutely right. I didn’t add a link to it in this article, but a little over a year after I wrote it I got rid of the chunky body and put these capsules into Clippy lav bodies from The Clippy bodies come with a screw-in mesh face that I left out (been down that road, too, and didn’t like what it did to the sound). Instead, I flush-mounted the capsules in the Clippy bodies, more or less hanging the capsules out in space with nothing around them. MUCH better sound.

        The one place I still have EM-172 capsules in the chunky bodies is the pair I have installed in my SASS. Since that uses them in a boundary configuration, it doesn’t really matter. The capsules are flush-mounted with the boundary surface.

        Thanks for pointing this out for future readers, though.



      • Vhrwerk said

        I didn’t build other 172 but to me it doesn’t sound nasal or something like that. The body is not left hollow, the back of the capsule is filled with glue so it doesn’t create any resonant chamber.

  49. Heloise said

    Hi Tom, Thanks for the info. Would this set up work for Primo EM258s?



    • Tom Benedict said

      It should work for the EM258 capsules, too, but I don’t know what their max supply voltage is for that capsule. If I remember right they may max out at +5V. Be sure to check the Primo datasheet before picking a supply voltage.

  50. Andrzej Sochon said


    I plan to replace my EM172 with EM173 capsules.
    The main idea: EM173 better feds to my schematic (I mean ballance) than EM172.
    I will appreciate very much for any sugestion, I mean insulation, shielding, connections, cables, and schematic diagram.
    First think: I will need 3-wire shielded cable.

    Best Regards,

    • Andrzej Sochon said

      Slowly I begin to understand…
      Months ago, by experimenting with EM172, I accepted the information and scheme available on this site, for obvious reasons, without thinking. But now, when I started to wonder how to connect EM173 – I understood why the EM172 capsule must be isolated. There is a voltage on her metal housing ! The EM173 has no voltage on the housing so it does not have to be isolated from the ground and therefore I do not need to use a 3-wire cable, I will use a 2-wire cable, shielded of course.


      • Tom Benedict said

        Aaaah! Cool! Let me know how that works out. Like I said, I’ve never used the EM-173 capsules before. If the isolation requirements are a little easier with the 173, that would make a lot of things simpler.

    • Tom Benedict said

      I haven’t used the EM-173 capsules yet. Just looking at the differences in the schematic on the two datasheets, I think you’re on the right path: 3-wire shielded cable and otherwise treat it like an EM-172 from the standpoint of insulation and shielding.

      • Andrzej Sochon said


        I just replaced EM172 with EM173. I use 2-wire shileded cable, 3-wire not necessary. One wire is for SOURCE, second one is for DRAIN, case=GND is for cable shield. As you said, isolation requirements are simple..

        I did not checked the SimpleP48 supply version, I am sorry. If SOURCE is connected to GND through 100 oHm then EM173 is electrically identical to EM172, so all rules described at your page can be applied. I plan to check this later with XLR, and with 9V battery and camera.

        Now EM173 is attached, like EM172, to my version of the ZenerlessAlice/Sziklai – schematics is available at micbuilders FILES, you can find the following file:


        Files > EM172, EM173 capsule and XLR > EM173 balanced output

        EM173 SOURCE is connected via 10kohm to the GND rail , DRAIN to the supply rail via 10kohm. I know such connection is not perfectly ballanced but gives better fit for EM173 than EM172.
        I checked capsules voltages, almost are the same like at EM172. I only slightly tunned R9 to get 8V,

        Capsules are fine, but there is a noticeable difference in sensitivity compared to EM172, according to specifications.
        I hope that I still have enough amplification reserve to record birds and bats. And now I have a much better max SPL – I will try to do some recordings of the canonade of fireworks on New Year’s night.

        Best Regards,

      • Tom Benedict said

        Excellent! Yeah, I’m familiar with that schematic. (Though I’ve never paired a Primo capsule to it.)

        It sounds like having a higher SPL set of Primo omnis in your bag would be a good thing. I’ve run out of room on my EM-172 omnis before and wished I had something that could stand more sound pressure. (Drums and pounding ocean waves are biggies for me.) This sounds like it would be a good way to do that.

        Thanks for posting the details of your build!


      • Andrzej Sochon said

        Hello Tom,

        I just uploaded 4 fragments of my very first birds recordings using EM173. The quality of the recordings pleases me very much and I get the impression that I prefer this lower sensitivity of the EM173 in comparison with the EM172 – I simply can forget about one of the parameters: the amplifier sensitivity I set to max; when I listen recordings via headphones I have a feeling that sound of birds is more natural, I mean volume level. The breeze of wind a little disturbed…

        Files EM172, EM173 capsule and XLR EM173 recordings Spring 2019


      • Andrzej Sochon said

        Hello Tom, long time no signs from me…

        During 2019 I made only a few recordings of bats using the EM173 instead of EM172. Unexpectedly problem appeared: after ‘slowing down’ procedure I discovered distortions at the background – like clock ticking. Tried to locate the source by switching off all electronic devices around, swapping EM173 capsules, changing location – without success. Ticking sometimes disappears and reappears immediately, I do not detect any regularities. There must be something in combination of EM173 mic capsules and attached electronics, maybe Scarlett 2i2 gen internal clock has influence. Strange is fact that such phenomena (I mean ‘clock’) does not appear with EM172 capsules. So for now for me EM172 capsules are better for bats voices recordings than EM173 capsules.


      • Andrzej Sochon said

        I just bought used Galaxy S9 and made some experiments with my mics. Mentioned above phenomena does not appeared in combination with S9 – so ‘ticking’ effect must be result of cooperation between Samsung Galaxy Tab A (SM-T580) and Focusrite Scarlett 2i2 gen. Of course immediately I maked test with tablet also, ticking exist but level is very low, almost not noticeable. The only change is updated Samsung software, maybe producer made some improvement.


      • Andrzej Sochon said

        EM173 capsules – bat recording – ticking problem solved: tablet screen generates such ticking. Ticking disappears when screen is switched off. (Samsung Galaxy Tab A (SM-T580))
        Andrzej Sochon

  51. John said

    Hi, this is exactly what I want to build, and can copy your diagrams but how do I determine what resister to use? I have absolutely no experience of any of this!

    • Tom Benedict said

      A good starting point is the 100k ohms called out in Ricardo Lee’s SimpleP48.PDF document on the Yahoo! micbuilders forum. This will get you in the right ballpark and will result in a good mic that’ll work well with practically any recorder that can supply 48V phantom power.

      • stav26 said

        hi Tom! Tell me please, have you ever seen an EM-272 on sale anywhere? I am from russia, and i haven’t seen this model anywhere here .. judging by the datasheet, it is a little better than that mic in your post of noise levels, so i’m want to looking for it to record nature .. what did you think about this? thanks!:)

      • Tom Benedict said

        I haven’t found the 272 anywhere, unfortunately. Primo capsules can be hard to find, except for specific ones from a handful of vendors. is my go-to for Primo capsules, and they don’t currently list them.

        At one point someone (Jonáš Gruska?) said that Primo has minimum orders of hundreds to thousands of capsules, so they only really deal with large-scale vendors. Jonáš said he buys his in bulk, then builds mics around them until he runs out and places another order.

        But it’s always worth asking Primo if they know of a vendor who buys the 272 capsule:

  52. reg dade said

    I have been trying to get primo usa to talk to me for a while now. I need to call them or perhaps turn up on their doorstep once day, they do list a street address. It is sad that a business with good products seems to unwilling to sell them. Has anybody else managed to get any kind of a reply out of them?

    • Tom Benedict said

      Yeah, no one has ever had any luck getting Primo to sell to them directly. Used to be Gene at Frogloggers sold them one at a time here in the US, but no one has heard from Gene in a while. Right now your best bet is to order from in the UK. Despite being overseas, his shipping is pretty reasonable. Even better, he’s now stocking a range of Primo capsules. Nic is a good guy and is really helpful with any questions you might have.

  53. barrypwan said

    Hello! may I ask if I have this mic: which resister is appropiate please?

  54. Tom Benedict said

    When I first started building Simple P48 mics with Primo capsules I was pretty careful to measure the voltage across the capsule and dial in the ideal resistor value. I hate to say that in recent years I’ve just been sticking with 100k resistors. I haven’t fried a capsule with one and they work great.

  55. […] Oczywiście osoby, które posiadają zaplecze oraz zdolności elektroniczne, mogą same zbudować swój własny zestaw bazujący na kapsułkach EM272. Tutaj znajdziesz przykładowy sposób wykonania mikrofonów. […]

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