The View Up Here

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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!

Tom

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88 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 (http://www.epanorama.net/circuits/electret_xlr1.gif) 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: https://groups.yahoo.com/neo/groups/micbuilders/files/EM172/

      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: http://micbooster.com/primo-microphone-capsules/9-em173.html)

      I hope this helps!

      Tom

      • 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:
    https://rearwndw.wordpress.com/2012/08/28/branchement-dun-micro-electret-sur-une-xlr/

    • 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?

    Thanks

    Maggie

  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 micbooster.com. 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

        Thanks,
        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:

      http://www.zachpoff.com/diy-resources/low-noise-binaural-mics-primo-em172/
      http://www.wildmountainechoes.com/equipment/diy-stereo-electret-mics-primo-em-172-capsules/

      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 http://micbooster.com/ (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.

      Cheers,

      Tom

    • 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 => https://clyp.it/5xbxgudq
    Image => https://s15.postimg.org/4b7yv00nf/IMG_8679.jpg

    Thanks!

    • 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:

      https://www.directap.com/Microphones

      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.
        Ian

      • 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 micbooster.com (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.
        -Akira
        Pleasanton, CA, USA

      • Tom Benedict said

        Excellent!

        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

      • 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: http://caperteebirder.com/index.php?p=1_17_recording-gear-1
      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

    Tom,

    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.

    Thanks,

    A

    • 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!

    Best!

  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?

    http://microphone-data.com/media/filestore/articles/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.

      Cheers!

      Tom

  31. Dreyfus said

    Hey,

    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 (http://tascam.com/content/downloads/products/799/e_dr-60d_om_va.pdf), 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! 🙂

    Regards,
    Drefus

  32. Dreyfus said

    Edit:
    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:
    https://imgur.com/a/XgrIA

    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,
    Dreyfus

  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…?

    Thanks,

    Mark.

    • 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.

      Cheers!

      Tom

      • 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.

        Cheers,

        Tom

  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!

      Tom

  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!
    Pierre

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