5 May, 2010 – 6 January, 2017
Rest in peace, my friend
Posted by Tom Benedict on 07/01/2017
Posted by Tom Benedict on 19/12/2016
Since writing my last post Homero Leal pointed out that I could mitigate some of the harshness of the Alice microphone (for field recording, mind you) by adding a capacitor across the 2.2k drain resistor. I didn’t have the size I needed (6.8nF), but I had everything to make a similar modification by adding an 8.2nF capacitor in series with a 750 ohm resistor, both across the 2.2k drain resistor. All of this is spelled out in Ricardo Lee’s ChinaMod+U87.doc file on the micbuilder forum.
I walked out into the park behind my work, recorded for about five minutes, and headed back inside to modify the microphone. After adding the HF EQ mod I walked back out into the park and recorded again.
Prior to the mod my recording had a background hiss that sounded like microphone self-noise. I knew from testing the mic inside my car that it’s not, and is actually a sound from the environment. While testing the mic with a 22″ parabolic dish a couple of weeks ago I panned around to try to identify the source. I’m almost certain the hiss comes from the sounds of tree leaves rattling against each other in the wind. It only takes a breath of wind to make the leaves rattle, so the sound is almost always there. After the mod, that background hiss was reduced quite a bit. Enough so that I wanted to try it more rigorously out in the field.
Last night conditions were almost perfect. We had a storm system rolling in, the air was still, and the sky was overcast. Perfect conditions for people to stay home, get off the road, and let people like me lurk in the shadows with headphones on. I packed both my Alice microphones along with my SASS and Olson Wing, and headed out to an old cane haul road to record coqui frogs and insects. I was rained out in the end, but even that worked to my favor.
Alice with HF EQ vs. Stock Alice
This is an A-B test between the Alice with Ricardo Lee’s HF EQ mod (thanks for the pointer, Homero!) and an unmodified Alice. The mics alternate every ten seconds, with a two-second cross-fade. That’s probably excessive on the cross-fade, but c’est la vie. Keep in mind there was very little wind during the test, so the difference is subtle. But it’s there.
SASS vs Olson Wing
While I was there I also tested the SASS against the Olson Wing. In this case both were populated with Primo EM-172 capsules. After I got home I realized I had wind protection on the SASS, but none on the Olson Wing. So this isn’t a fair test of frequency response, but it should be a fair test of the depth of stereo imaging, and to some degree, sound localization. (The frogs really don’t move around that much.)
I was content to let this setup run for a while, but it started to rain. Without any rain protection on either array, I knew the rain would eventually soak the mics. So I packed it all in and pulled out my rain gear.
I’m still trying to get a good, clean recording of rain. A while back I took a tip from Gordon Hempton and built a microphone rain shelter. It’s a hard aluminum plate covered with two inches of non-woven air filter material. The aluminum plate keeps the mics dry, and the filter material diffuses the rain drops to a soft “fuff” sound. I also added a layer of carpet foam underneath to cut down on the residual “fuff” sound. It’s set up to take my DIY shock isolator, a small ball head, and my ORTF bar. (Sorry, no pictures of the whole setup just yet.) With the whole mess set up on a tripod or c-stand, it protects the mics from rain while minimizing the sound of the drops hitting the rig.
Finally finally I had a chance to use it in the field. And it worked! It worked great!
Only problem is that I managed to damage one of my EM-184 cardioids while testing the Alice mics. It barely responded at all, and produced a deep wumping noise in the recording instead. So the stereo recording is rubbish, unfortunately. I thought the wump sound was the mic picking up rain drops hitting the tripod legs, so I switched to a c-stand, re-arranged, tied up cables, did all sorts of things. None of it helped. After about half an hour I finally admitted to myself that the mic wasn’t working, and packed it all in.
But the rain gear worked! It worked great!
And once I dried the EM-184 mics out they worked great again, too. (Lesson learned:Don’t let it rain on your mics. DOH!)
All in all it was a good night of testing. I have one other test I’d like to do with the two Alice mics (ocean waves!), and I’d like to do one more side-by-side of the SASS and the Olson Wing to see if I can shorten the length of the Olson Wing and still get a good boundary effect out of it. But I’m pleased as punch with the rain gear.
P.S. I also learned that I need to finish this project before watching another season of Stranger Things. There’s something about driving way the hell out on some abandoned road to some spot in the woods in the middle of nowhere with fog and rain and nothing but the buzz of the insects and the calls of the frogs to… WHAT THE HELL WAS THAT?!
Posted by Tom Benedict on 12/12/2016
“See any whales?”
I’d been recording at Kiholo Bay for several hours before the man spoke to me, but the first hour had been plagued by technical issues. For some reason my DR-70D kept reporting a write timeout error – something usually attributed to using a slow memory card – but I knew the card was good. Helicopters and airplanes had ruined the rest of the first hour.
At that point I was almost done with my first completely clean hour of waves on my SASS and Mid-Side setup. My other recorder, a DR-05, was positioned at a small beach to the south of me, recording waves receding off of loose pebbles.
I turned around to see who’d spoken to me. He was an older man who’d been hiking along the coast and had stopped to talk. I knew his words would show up on the recording, so I figured if I’m editing I’m editing. I might as well be civil about it.
“No, not from here.”
He nodded and walked on. I turned back to my gear, but out of the corner of my eye I saw him turn and head down to the little pebble beach.
People here are, on the whole, really nice about other people’s stuff. At one point years ago I left some kites at Hapuna Beach, one of the busiest beaches on the Big Island. It wasn’t until I was unloading my car at home that I realized my kite bag was missing. I jumped back into my car, headed back to the beach, and found that someone had brought my kites up off of the sand and left them for me at the showers. People here really are great.
But still… Strange guy hiking down to a beach where I’d left gear… I didn’t want him knocking my gear over inadvertently or anything. So I kept an eye on him as he made his way down to the beach and… proceeded to relieve himself not four feet from where I’d left my gear. Recording sound. All sound. Beach sound. And now his sound. His very personal sound. He kept glancing up at me like I was being rude. I did turn away while he was occupied with his… task. But eventually I knew he’d finish and realize I’d been recording him. Which he eventually did.
One of my more awkward sessions.
(But I got a lot of really good winter wave on rock sounds!)
Anyway, I think I’ve finally answered some open-ended questions about microphones. The Alice microphones I’ve been building are beautiful, crisp, and punchy, but not all that great for recording outdoor sounds. They’re very bright, which works great for a number of subjects. Waves, streams, and wind in the trees just don’t happen to be any of those subjects. Unfortunately those are the subjects I’m interested in.
I also don’t think I’m a huge fan of mid-side recording for creating big spacious soundscapes. No matter how much I play with the balance of mid to side, I just can’t get as much of a sense of space as I do with the SASS. I find myself firmly in the camp of the partially baffled microphone array. So for now I’ll save the mid-side and LDC Alice mics for indoor recording and go back to my Primo-based mics for nature. (Though I still intend to convert my Behringer C-2 mics to surface-mount Alice electronics. They’ll make good instrument mics, if nothing else.)
There’s one last test I want to repeat, though. Early on I built an Olson Wing – a baffled double-boundary array invented by Curt Olson. This pre-dated my SASS. I remember I liked the sound, but that I liked the sound of my SASS better. Now that I’ve had a chance to try a number of other stereo recording techniques (X-Y, A-B, ORTF, M-S, and SASS), I’d like to resurrect my Olson Wing and try it and the SASS side-by-side. I’ve still got all the bits, so it’s just a matter of rigging everything back up and getting out with the gear.
It’s something of a pressing question because of something else that happened. Earlier today my wife bought me an early present: a pair of ammo boxes.
I joked with the kids that they’re for the Zombie Apocalypse. They just rolled their eyes. They know me too well. She got me the ammo boxes for a recording project.
One of the problems with unattended recording is that conditions change, weather turns, and gear gets rained on. My first unattended overnight session wound up that way. I set up to record the dawn chorus in the Upper Waiakea Forest Reserve on International Dawn Chorus Day, but during the night the clouds came in and rained on my gear. The evening chorus was spectacular, but with the rain on the leaf mast making a staccato drumming sound, the dawn chorus part of the recording was practically useless.
My gear survived, but the weather proofing was tentative at best. I’ve been looking for a good way to build a completely watertight, rain proof recording setup. Enter the ammo box.
Ammo boxes are made out of steel. They’re tough. And they have a rubber weather seal that’ll keep out a hurricane. Perfect for cramming recording gear into! My plan is to use the larger of the two boxes to house my gear, and either build an Olson Wing or an SASS around the box, depending on which one I like better. The microphones would be the only thing poking out. Everything else goes inside the box, which can then be latched shut. The whole unit can then be left overnight without any chance of rain getting inside and killing my gear.
Or pee, for that matter.
Posted by Tom Benedict on 23/11/2016
This is the second half of a two-part article describing my build of the mid-side Alice microphone, following the Instructable written by Jules Ryckenbusch: Build the MS Alice Stereo Microphone. In Part 1 of this article I ran through how I was planning to build it (mostly following the same steps I used in another two-part series I wrote about another of Jules’s Instructables, Modify a Cheap LDC Condenser Microphone, namely: BM-800 Microphone Conversion Part 1 and Part 2.) I also covered my design for the saddle and post that holds the three capsules in the particular orientations required for Jules’s MS microphone build. (Jules used a different method, using PVC pipe, which you’ll see in his Instructable if you decide to build one of your own.)
Since writing Part 1 all the bits and pieces came in. I was eager to see how the 3D printed saddle and post turned out, and how well the TSB-165A capsules fit.
I designed the cavities for the capsules at-size, meaning I didn’t leave any slop for fit. The plastic Shapeways uses to make their least expensive printed parts is described as “strong and flexible”. I took them up on that, figuring the part would flex enough to allow the capsules to snap into place. It worked like a charm.
The fit is snug, but not snug enough to hold the capsules in use. As with my first Alice, I glued the capsules into the saddle with E-6000 adhesive.
I’m a little disappointed with the handling noise on my first Alice mic. I chalk some of that up to the metal saddle and post, but some of it I chalk up to the relatively stiff wire I used to connect the capsule to the PCB. It was stiff enough that manipulating the wire wound up breaking off one of the ground tabs from the TSB-2555B capsule I used on that mic. Rather than repeat that experience, and in an effort to reduce conduction paths for handling noise, I gutted some of the Mogami cable I use for all my microphone projects and used the wires to connect the capsules. (NOTE: It didn’t actually affect handling noise that much. After thumping various bits of the mic, I’ve come to the conclusion the dominant frequency of the handling noise is driven by the resonant frequency of the mesh in the headbasket.)
I already had two Pimped Alice PCBs built, tuned, and ready to go for this project. The remaining steps were to screw one board onto each side of the mic frame, solder the capsule wires to the boards, solder the four 0.022uF capacitors between the ground pin (pin 1) and the remaining pins of the XLR connector (2, 3, 4, and 5), and to solder wires between the XLR and the PCBs.
Since I oriented the two capsules of the figure-eight mic side-by-side, they won’t fit inside the headbasket with the foam liner in place. So I stripped the foam out before closing up the mic.
The very last step was to build the 5-pin XLR to dual 3-pin XLR splitter cable. There are a number of ways I could’ve done this, but I followed (mostly) Jules’s build on the cable as well, using separate Mogami lavalier cables for each channel. This is a wonderfully floppy wire, and does an excellent job of reducing handling noise transmitted through the cable.
The one change I made to Jules’s design was to jacket the central eight feet of cable in a woven sleeve to keep it from tangling.
I left the last foot and a half at each end loose, though, to take advantage of the wire’s floppiness. (Hey, that’s actually a word spellcheck recognizes!)
And at long long last I’m able to play with mid-side recording and compare it against my EM-172 based SASS.
Big big thanks to the following for making this all possible:
For my own contribution, here’s the link to the MS Alice capsule saddle and post on Shapeways. I’ve listed these at-cost, with no mark up (meaning I don’t see a dime of the 5.35 USD price tag at the time of this writing – labor of love).
Have fun recording!
Posted by Tom Benedict on 11/11/2016
This is a short pair of articles that glosses over most of the details of how I’m building a self-contained mid-side (MS) Alice microphone into a Neewer NW-800 microphone body. Part 1 covers most of the design and preparation, and Part 2 will cover the build.
The reason why this pair of articles is so brief is that most of the nitty-gritty was already covered in another pair of articles: BM-800 Microphone Conversion Part 1 and Part 2. The major differences between that microphone and this one are a change in capsules (Transsound TSB-165A instead of a Transsound TSB-2555B), the number of capsules (three instead of one), the number of Pimped Alice boards (two instead of one), and a change tof XLR connector (5-pin rather than 3-pin).
With the exception of how I’m planning to mount the capsules, all of this follows the Instructable written by Jules Ryckenbusch: Build the MS Alice Stereo Microphone. That’s the real reference for this build, so if you decide to build one of these yourself be sure to follow Jules’s notes.
The easy stuff first:
When I built my first Alice microphone I built three PCBs rather than just the one I needed, so I already have two Pimped Alice boards ready and waiting in the wings. I was on the fence whether to build a second mic around a TSB-2555B capsule or go straight to the MS Alice. After some recent field tests, I decided to commit the two boards to an MS Alice.
Jules pulled a neat trick for getting two signals out of a single XLR connector: use a different XLR connector! In his build he replaced the 3-pin XLR that came with his BM-800 microphone with a 5-pin. The two outputs share a common ground, but have independent signal pins. I’m following this part of his plan to the letter. (As a side note, this also gives me a spare 3-pin XLR connector to use when I finally build out my parabolic mic. New project in the works!)
The only things left to do were to order three TSB-165A capsules (done) and to figure out how to mount them.
Jules has a nice tutorial on how to build a 3-capsule saddle out of PVC pipe, but I had so much fun machining a custom saddle for my TSB-2555B capsule, I couldn’t pass up the opportunity to massively over-complicate life by designing a custom saddle for the MS Alice as well. Here’s what I came up with:
Which looks neat and all, but would be stupidly difficult to machine. It’s possible, provided you got rid of, or at least filleted the inside corner between the two side capsules, but it wouldn’t be fun. And since this is all about fun, I cheated. I sent it off to be 3D printed out of nylon. (If this pans out and there’s any interest, I’m happy to make the 3D model available for other people to print.)
So now I’m back to playing the waiting game. I’ve got parts coming in from Redco Audio (5-pin XLR to dual 3-pin XLR splitter cable), Mouser (smaller capacitors for the Alice boards to address the space constraint issue I ran into), Amazon (Switchcraft 5-pin XLR connector, NW-800 body, and associated doodads), JLI Electronics (three TSB-165A capsules), and finally Shapeways (the 3D printed mic saddle).
I’ll write the second half of this series once all the goodies show up.
Posted by Tom Benedict on 10/11/2016
When I built the Alice / TSB-2555B microphone, my intention was to get out with my normal recording gear, bring the Alice along, and get some side-by-side nature recordings to demonstrate how good or how bad the self-noise on the Alice is.
I have yet to pull this off. But in the process I became utterly paranoid about my gear, and feared I’d somehow broken it. In the process I made a number of completely useless recordings in the Upper Waiakea Forest Reserve and out on the Cane Haul Road north of Honokaa. I got some really interesting bird calls and some halfway decent coqui frogs, but most of all what I recorded was what sounded for all the world like… noise… (I’m pretty sure it was wind, but I’m giving away the punch line.)
This finally led me to do a series of recordings in the back seat of my car, parked in the relative un-quiet of my yard, under what is finally a wind-free clear night. In the process I think I demonstrated the excellent noise characteristics of the Alice microphone, and I’m pretty sure I recorded my own heartbeat from the seat next to my gear. (Yes, I had the gain cranked up that high.)
I found that the Alice edges out the Primo EM-172 capsules for noise, potentially by more than -3dB. I also found that even at ten o’clock at night there are very few windows of time when cars aren’t going by on the nearby highway. (I also found there’s a limit to how long I can sit still, not tic, and breathe shallow.)
With my faith in my gear restored and an expectation of the performance of the Alice microphone, I’m planning to head out Friday to record inside a lava tube. It’s not the rain recording I’ve been trying to nail for the past several months, but if I manage to get water dripping from the roof into underground pools, I’ll count that as something pretty cool.
This also gave me the confidence to order all the parts to build Jules Ryckenbusch’s MS Alice microphone. I still have mixed feelings about how mid-side is likely to fit into how I record in the field, but I know I’ll have a good mic to try it with.
Posted by Tom Benedict on 03/11/2016
The field tests on my BM-800 Alice conversion will have to wait. Late last week I handed it over to a friend for tests I’m not equipped to make, including several mic comparisons. I’m eager to see (and hear!) his results.
Meanwhile my Behringer C-2 mics showed up. These are the ones I placed a bid on over at Ebay before I realized they were coming from Haifa, Israel. Despite the distance the shipping was actually less than FedEx charges to ship a letter-shaped package from the mainland US to Hawaii. (Go figure.) It still ramped the price of the mics up almost to market value, which on Amazon with its super saver free shipping basically means I could’ve ordered them new and had them weeks ago.
But they’re here. And they’re mine. And… to be honest they’re in pretty ratty shape. One of them had something loose in the capsule. If you pointed the mic up and shook it, it made a hellish noise and clipped constantly. Turn it upside down and shake, and you hear something rattling around. The other mic has something massively wrong with its circuit board. It sounds for all the world like a Huey is hovering overhead. Bup bup bup bup bup bup bup… It never ends.
So long story short, I don’t mind gutting these things and building something new. In the short term I put the good capsule on the good mic body so I have one working mic to play with. The other one I started taking apart.
These have interchangeable capsules, though I don’t know if Behringer (or anyone else) makes any other capsules for it. The one that came with my mics is a hypercardioid. (At least that’s what the icon on the side of the capsule looks like.) Given the size of the vents at the back, I can believe it.
Underneath the capsule is a white plastic plug with a pogo pin centered in it. Not much to look at. And no real clue how to open things up past there.
To gain access to the innards of the mic, peel back the the “Behringer Condenser Microphone” name tape at the base. This reveals a small set screw that should be familiar to anyone with Switchcraft XLR connectors. Screw the set screw all the way in. This releases the XLR connector from the body. Next, center the pad/high-pass filter switch and pull the switch button out with needle nose pliers. Finally, push on the white plastic plug to expose the circuit board.
Here’s what’s inside:
Since one of my mics has a damaged board, rather than figure out how to tweak what’s already here, I went ahead and tried to figure out how to pack a Pimped Alice into the same board space. I started by taking measurements.
The board is 15.5mm wide x 52.35 mm long, and is 1mm thick. The thickness is important because the board slots into the white plastic insert. One nice thing about this method of mounting the board is that there are no screw holes, and except for the humongous XLR pins and the 2mm area that slots into the plastic insert the rest of the real estate on the board is free. The board is mounted just below the centerline of the mic, so there’s vertical room as well. Up to a point, anyway. Those capacitors are 6.5mm diameter x 8mm tall. Nothing bigger than that will fit, even centered on the board.
There’s really not enough room to use through-hole components everywhere, so I converted most of the Pimped Alice circuit to 0805 SMT components. The exceptions are the filter capacitors, the 1Gohm resistor, and the FET.
There seems to be some resistance to using surface mount technology for DIY mics, but SMT has been used for over a decade for DIY robotics and electronics. I’ve built AVR processor boards using SMT components, and figured this wouldn’t be much different. With the exception of the big filter caps and the FET, that’s how Behringer built the original board for the C-2, so I figured it was a safe way to go. As soon as I have a new PCB layout, I’ll send it out for fab.
Meanwhile I started taking apart the capsule. Just looking through the grille, it seems like the C-2 uses a Transsound capsule similar to the TSB-165A Scott Helmke used in the original Alice.
I started by removing the back plate. This is just pressed into place, but it’s a bear to get out. I eventually removed it by gripping it by an inside edge with needle nose pliers (pushing outward), and spinning it out. It took a couple of attempts, but it came apart.
The rear side of the capsule has an open cell foam washer in it, presumably to provide wind protection and to act as a delay plate to shape the hypercardioid pickup pattern. With the washer removed, the back side of the capsule is visible, held in place by a brass retaining ring
The holes in the ring are really tiny. My existing pin wrench didn’t work, so I used an old divider with dull points as a pin wrench. There’s a bit of red enamel to prevent the ring from backing out, which took a little force to crack. Once that was done, though, the ring backed out easily. (I’ll need to be sure to apply a fresh bit of enamel when I get the new capsule installed.)
I was hoping the capsule was a Transsound TSB-165A, the same one Scott Helmke used in his original Alice microphone. Unfortunately it’s not. The capsule in the C-2 is 16mm in diameter x 6mm thick. The TSB-165A is 16.5mm x 8mm. But after some poking around on the JLI Electronics web site I think I found a match: the TSB-160A. The specs are almost identical to the TSB-165A, so it should play nicely with the Alice circuit (yay!), but the form factor matches what’s in the C-2. I’ll order a pair of these when I place the order for the 165A capsules for my MS Alice.
Another concern with the C-2 capsule holder is how the capsule is recessed, and how close the edges of the holder come to the input ports on the capsule. From my experiences with my first rev of mic bodies, I know that can color the sound enough to hear it. I’d like to open this up, if possible. It’s a simple enough job on a lathe as long as I can get the grill out.
The grill looks like it’s a two-layer mesh that’s either glued or soldered into the capsule holder. That should be easy enough to remove with heat, one way or the other. I might even be able to re-use it if I’m not too rough getting it out.
The grill serves two purposes. First and foremost, it’s an RF shield to keep stray electromagnetic radiation from getting into the signal path. Second, it helps to keep the capsule free of debris. Third, some manufacturers will stick enough mesh in front of the capsule to act as a rudimentary pop filter, and at least reduce the effect of wind. The problem with that third purpose is that you need a lot of tight mesh to pull that off. Enough so that it colors the sound of the mic. Not surprisingly, one of the more obvious mic mods is to remove a layer of mesh from the capsule housing.
But given how open the outer mesh is, I’m afraid it will make the mic prone to RF interference. For now I’ll leave it alone.
The next steps are to finalize the design of the new board, send it out for fab, and source all the components and capsules. But before I can finalize the board design I want to see if I can add in one of the features of the C-2: The switch on the side of the mic lets you select a high pass filter or a -10dB pad. If I can find the real estate on the board to accommodate the switch and the components necessary to add these into the Alice circuit, I will.
Posted in Audio, Electronics, Engineering | Tagged: Alice, Audio, Behringer, C-2, C2, Disassembly, Hack, Microphone, Mod, Modification, Recording, Sound, Transsound, TSB-160A, TSB-165A | Leave a Comment »
Posted by Tom Benedict on 22/10/2016
This is the second half of a two-part article describing my conversion of a BM-800 microphone to an Alice microphone using a Transsound TSB-2555B cardioid capsule. All of this is based off of a pair of Instructables written by Jules Ryckebusch: Modify a cheap LDC Condenser microphone and Build the MS Alice Stereo Microphone.
Part 1 of this article showed pretty pictures of the donor mic (a Neewer NW-800 with an excess of bling), a description of the cable that came with the mic (which I don’t intend to use), photos of the mic in various stages of disassembly, and a CAD drawing of the salient features inside the microphone to help others lay out circuit boards for their own conversions.
Since writing part 1, all of the bits and pieces I ordered to do the conversion arrived: enough electronics to build three Alice boards, and a TSB-2555B capsule to put in the first one.
Before populating the boards I did a test fit to make sure they would actually fit. I was pleased to see how well the screw holes lined up, and I came pretty close with the taper.
The next step was to populate the boards. Opinions differ on how to wire the high-impedance (high-Z) end of the board, so I started with all of the low-Z components.
The circuit used in Jules’s first article had zener diodes on the output stage to protect it against over-voltage on the XLR pins. The circuit as-built in his second article omits the zeners since the 2N5087 transistors are rated for more than the 48V likely to be seen on an XLR connector. I ordered the zeners, but left them out for now.
After I’d already wired all the boards I installed one in the mic and ran into my first problem: With the board installed right-side-up, the 47uF capacitor pokes up high enough that it interferes with the body tube. For my first mic I’m planning to install the board up-side-down to give the capacitor more room. But if I wind up building the MS mic from Jules’s second Instructable, I’ll need to install new capacitors that lay flat against the circuit board.
The reason for the difference of opinions on the high-Z end of the circuit is that it’s sensitive to contamination: leftover solder flux, dirt, dirt combined with humidity, oxidization, etc. on the high-Z end can all cause unwanted noise in the mic. Jules soldered his components to the board without issue. Others have used Teflon standoffs to float that part of the circuit above the PCB. Homero Leal built his Charis mic by point-to-point soldering the high-Z components, letting them float above the board without standoffs. Scott Helmke, the original designer of the Alice circuit, solders the high-Z components directly to the back of the mic capsule. For my first pass at this I soldered the low-Z legs of the FET to the board, but floated the high-Z circuit without stand-offs, similar to Homero’s Charis mic. I can always change my mind later and re-wire them.
With the board built, the next step was to add 22nF capacitors between pins 1 and 3 and pins 1 and 2 on the XLR connector to provide additional RF noise filtering. After that I installed the modified connector and the board in the mic body.
The rest of the action takes place inside the headbasket.
It’s possible to cut away the original mic capsule to leave a saddle for mounting the TSB-2555B, but I wanted to make an entirely new saddle. Chalk some of this up to not wanting to make a modification I can’t back out. Chalk some of it up to my wanting a machining project to go along with the electronics project. Either way it needlessly complicates an otherwise pretty simple project.
Space inside the headbasket is tight, so rather than run into more interference issues I fleshed out the 2D CAD drawing and turned it into a 3D model. The space constraints almost entirely dictated the shape of the new saddle and post. The mic frame is drilled and tapped for M2.5 screws on a 10mmx15mm rectangular pattern, only two of which are used on the original saddle. I chose to use all four. The mic wires pass through holes spaced 20mm apart, centered on the long axis of the bolt pattern. In the CAD model I indicated these with 3.13mm holes, but in the final part I cut them as slots to make installing and removing the capsule easier.
I attached the TSB-2555B capsule to the saddle with E-6000 silicone adhesive. A better method for the saddle shape I used would’ve been a polyurethane adhesive like Gorilla Glue, but I wanted to be able to remove the capsule in case I decide to add shock isolation inside the mic to cut down on handling noise. As-built the capsule can be removed by passing a fine wire between the capsule and the saddle, cutting the silicone bond.
EDIT: The first time through, I missed an important step: One of the charms of the Pimped Alice circuit is the potentiometer next to the 1Gohm resistor. It allows you to bias the FET properly, regardless of which FET you use. The catch is that by definition, if you don’t do anything with the potentiometer it will not be properly biased! In all ignorance I soldered everything up, closed up the mic, and went testing. Even with an improperly biased FET it still performed beautifully. I did go back and do a proper job of it, though.
In Jules’s first Instructable, toward the end, there’s a nice write-up for how to bias the FET. The catch is that this step must be done before the capsule is soldered to the board.
With the FET properly biased and the capsule attached to the saddle and post, all that was left was to put it all together and close it up.
I did a quick side-by-side against one of my Primo-EM184 cardioid mics. The Alice runs a little hotter, but not by too much. I’m reserving further judgement on the new mic until I have a chance to get it out in the field and try it on some quiet sources.
Posted by Tom Benedict on 09/10/2016
Several posts ago I mentioned a plan to build an MS mic by following an Instructable written by Jules Ryckebusch. Jules used a BM-800 microphone as a donor mic and replaced its guts with two Pimped Alice circuits and three cardioid capsules. After several Ebay vendors whose listings indicated they would ship to Hawaii later changed their story and said they wouldn’t, I finally picked up a BM-800 microphone off of Amazon. The one I got is a Neewer NW-800. (I liked its shock mount better than the other one I found.) It arrived, and I started poking and prodding at it.
Along the way I discovered another reason to use a windscreen on a microphone. This thing is bling central. To be fair some of the other BM-800 mics I found on Ebay didn’t have nearly as much… presence… but this is the one I could get.
Unless I’m recording birds that are drawn to shiny objects the windscreen will probably become a permanent fixture on this mic, just to keep me from going blind.
Before tearing into the thing I decided to try it as-is. On the face of it it’s a phantom powered cardioid condenser mic. This means plugging it into a device that doesn’t provide some kind of power (aka my laptop, my phone, even my kids’ desktop computer) won’t work.
The mic has a male XLR jack at the back, and came with an XLR-to-3.5mm cable. 3.5mm inputs that provide power typically provide plug-in-power (2.3V to 5V, depending on the device). XLR inputs provide phantom power (typically 12V, 24V, or 48V). That discrepancy made me a little leery of just plugging this into whatever and cranking volts through it. I started by ringing out the cable to see what it was actually doing.
Up to this point all the XLR plugs I’ve dealt with have been for balanced signals. That is to say that one pin of the 3-pin XLR is ground (pin 1), another is the positive signal (pin 2), and the third is the inverse or negative signal (pin 3).
3.5mm inputs typically use a TRS connector and unbalanced signals. In the case of the 3.5mm stereo input on my recorders the tip is the left positive channel, the ring is the right positive channel, and the sleeve is ground.
The cable supplied with the BM-800 ties XLR pins 1 and 3 together and routes them to the sleeve of the 3.5mm plug, and routes XLR pin 2 to both the tip and ring of the 3.5mm plug. This effectively turns the balanced output of the mic into two channel mono unbalanced output on the 3.5mm plug, meaning it should be able to be plugged into any 3.5mm stereo input and drive both left and right channels with the same signal. Neat!
What this also means is that as long as the mic can run on a wide range of voltages, the plug-in-power on any recorder should be able to drive this thing. So should the battery box I got from Church Audio. Or by removing the XLR-to-3.5mm cable and plugging in an XLR-to-XLR cable, I should be able to power it with phantom power (12V or 48v – the only two options on my recorder) and use it as a single channel balanced input.
Still leery of running such a wide range of voltages through it, I tried all three configurations anyway. I’m planning to gut this mic, after all, so if I burned it out the loss would be minimal. To my surprise all three worked! The plug-in-power on my DR-70D puts out a little under 3V, and my battery box from Church Audio puts out a little over 9V with a fresh battery. The 48V phantom power on the XLR inputs on the DR-70D put out right around 48V. I noticed a gain difference between the PiP and battery box, but because of the different gains on the XLR vs. 3.5mm inputs on the DR-70D I wasn’t able to tell if the additional voltage was doing anything to the mic itself. (My guess is it doesn’t. To survive that wide a range of voltages I’m guessing the mic has a voltage regulator on board. Past a certain point it’s just dissipating as heat.)
So how does it sound?
How to put this…
I’ve seen the shock mount it came with listed for more than what I paid for the mic. I don’t think this is too far out of line with how it sounds. It’s not bad, mind you. It’s just not anything I’d write home about. A little creative EQing would probably make it a decent podcast microphone. But as for making ambient nature recordings? Mmmm… no.
So without further ado I tore into it to see what I was going to have to deal with.
The first step in disassembling the microphone is to unscrew the butt cap. This also releases the shell, which simply slips off to expose the circuit board. The shell is keyed to a tab just under the headbasket which fixes the orientation of the logo on the mic. This is important since the mic is a side-entry rather than end-entry, meaning sound must enter from the side and not the end. Added to that, it’s a directional microphone so it’s only sensitive on one side. Can you guess which side? (Answer: The one with the logo.)
Some nice features on the inside of the thing: First, there’s a ton of room. Second, there’s a nice frame with mounting holes tapped for M2.5 screws. (More about those in a sec.) The only weird part is the taper on the frame and the circuit board. I like the look of the tapered board, so I decided to taper the boards for my Alice conversion, too, and put mounting holes in the boards to make use of the holes in the NW-800 frame.
Two M2.5 flat head Phillips screws hold the headbasket in place. They’re located just under the headbasket, above the circuit board. Once the screws are removed the headbasket lifts off, exposing the capsule.
Despite the appearance, the capsule in this mic is the same size as the EM-172 and the EM-184 capsules from Primo: 10mm diameter. At this point I was sorely tempted to gut the mic, drop an EM-184 capsule in the mic saddle, and call it quits. But the whole purpose of this exercise is to move beyond Primo all-in-one capsules and try my hand at building more complicated (and better performing!) microphones.
All of this starts with the circuit board.
Simple stuff first: The screws are M2.5, spaced 30mm apart. They’re biased a couple of millimeters above the centerline of the cavity. If you’re planning to make a rectangular circuit board to fit inside this mic, that’s probably all you’ll need. (The tube with the logo has vertical walls, so a rectangular board will fit fine.)
Since I wanted to make a tapered board I measured the whole cavity and threw it into CAD. At some point I’ll draw it in 3D, but for now a 2D representation is plenty for me to design the new board outlines. I’m building the Alice boards using through-hole components, so I needed a little more real estate than the original board provided. The 2D drawing of the cavity and the new board outline looks like this:
I sent the boards out for fab and ordered enough components from Mouser to build out three of them. One is destined to receive the TSB-2555B capsule I ordered from JLI. The other two will eventually be used to build a copy of Jules’s MS mic using three TSB-165A capsules, but that’s a project for another time. Once all the bits arrive I’ll write the second half of this article, which will cover the construction of the TSB-2555B mic.
Posted by Tom Benedict on 20/09/2016
One of the questions I’ve asked myself over the years is whether I would be proud to tell my kids what I do for a living.
Much of the time the answer has been yes. When I worked for Academic Computing at the University of Texas I spent close to a year working in the Student Health Center. We took care of the servers that maintained medical records, handled customer satisfaction surveys, and made sure the desktop and handheld computers of the doctors, nurses, and administrators all worked. We helped them help the student body of UT stay healthy. Feel good about it? You bet!
Some of the time the answer has been a resounding no. The last year I was with IBM my job was to spy on my co-workers. I was the weenie who read all the logs from all of our servers and flagged “security risks”. During that time we never had an actual outside attack, and I think we had fewer than ten internal “ethical hacks”, all of which we caught. But I lost count of how many times my co-workers had a typo or tried to do something as root out of innocent ignorance. I had to report them all. Not one was a malicious act, and yet my job was to ding them for it anyway. Feel good about it? You gotta be kidding me…
Working at CFHT is solidly in the yes category. I’ve had downer days. Heck, I’ve had downer months, if not years. But at the root of it all we’re in the business of exploring the universe to better understand how the whole thing works. When people ask what I do for a living I tell them that my job description basically amounts to doing whatever is required so we can collect science-grade photons at night. Sometimes this means designing and building new instruments; sometimes it means sweeping the floors. When things get floor-sweepy it’s easy to lose sight of the fact that all of the things we do here contribute to our understanding of the universe.
Yesterday I brought in my camera bag and lighting gear so I could photograph a set of filters for customs paperwork. We’re shipping the filters to France to be scanned on a better spectrophotometer than the one we have here. Customs had a set of requirements for the photographs, so I was taking my time to make sure I got everything right. Toward the tail end one of our resident astronomers came in to see what I was doing. I explained about customs, about their need for documentation and serial numbers, etc. Not exactly sweeping floors, but documentation photography is pretty mundane stuff.
He listened patiently, then said, “You understand the importance of what you’re doing?”
“What do you mean?” I asked as I moved the last of the filters from the lighting scoop, back to its packing crate.
“Right now the tightest constraint on the cosmological constant is the SNLS survey, made with these filters. The scans they’re planning to do will further refine our understanding of the cosmological constant.” He pointed to the filter I was holding, the r’ filter. “That filter is key.”
Yeah. Even the act of photographing these filters so the customs agents can identify them and their serial numbers was helping to contribute to our understanding of the universe. No “Eureka!” moment. No lone genius. Just a lot of people doing a lot of seemingly mundane tasks, all of which is further refining our knowledge of how the universe works.
Today I’m processing the pictures, putting together documentation packets for customs, and packing the filters lovingly in their cases for shipment to France. Am I proud to tell my kids what I’m doing for a living?
You bet your ass.