I have been an audio guy for a long time and an avid DIY'er. Which means my favorite kinds of projects relate to Audio. I am also a firm believer that for a DIY project to be cool there has to be one of two outcomes to make the project worth doing. It either has to be something you can't get commercially, or something you can build your self that is way cheaper than buying what is available commercially. This project is of the second kind. Build a cheap but good LDC microphone. LDC stands for “Large Diaphragm Condenser”. This project can be built for about $50 in parts and rivals microphones costing way more. It is quiet, sounds very neutral, and will handle large SPL (Sound Pressure Levels).

First a little history of microphones.
There are three basic types in use for studio and live sound use; dynamic microphones, ribbon microphones, and condenser microphones. A dynamic microphone is like a speaker but in reverse. A small diaphragm is coupled to a coil of wire that moves when sound hits diaphragm. The coil is in a magnetic field. When it moves a small electrical signal is generated that you can then amplify or record that represents the sound. A ribbon microphone is similar except the ribbon, a thin strip of foil, usually aluminum, is placed in a magnetic field. Sound waves cause the ribbon to move in the field and an electrical signal is generated. Read more here: Microphones

A condenser microphone starts with a very thin membrane that has metal sputtered onto it so it conducts electricity. The membrane is stretched and placed very close to a backplate to form a capacitor. Grandpa Ryckebusch used to call capacitors condensers and now you know that we should really call them capacitor microphones... When sound waves hit the diaphragm and it moves, the capacitance changes. If there is a charge on the capacitor, there will be a change in voltage that corresponds to the sound. Like the other two microphone designs above, if you amplify or record the voltage, you get the sound. There are two styles of condenser microphones. Some use a high voltage (50-70 volts) to charge the condenser capsule and others use what is called an Electret Capsule. The Electret (Electrostatic) has a permanent charge associated with it read here: Electret.

What this means for us is that if we use an Electret capsule there is no need to apply 50-60 volts to it, which means simpler circuitry.

one of the benefits of a condenser microphone is that the diaphragm can be very light and it is easier to get a smoother frequency response with one. The downside is that you have be very careful when getting the signal off of the diaphragm without adding noise which brings us to the electronics.

To pull the signal off of the capsule you need a very high impedance device. Tubes have this one covered and were the main way this was accomplished 40 years ago. Not to get into a debate on sonic quality of tubes vs anything else, you have to admit; using a tube inside a microphone body does not lend itself to simplicity. Or normal DIY skills! After the tube the Field Effect Transistor or FET was invented. This is how most condenser microphones work today. Even the really inexpensive mic capsules have one internally mounted. A German company Schoeps. arguably one of the top microphone manufacturers in the world, designed a circuit for condensers microphones that defined how this was done a long time ago. See the Schoeps Circuit for details. (If you google “Schoeps circuit” this is what you find!) The circuit runs off of phantom power from the mic pre-amp. Part of this circuit is used to generate a stable high voltage to charge the capsule. In our case we wont need that. The DIY community simplified this circuit down to its basic form for electret capsules that is almost identical to the original Schoeps Circuit. Scott Helmke designed a version of this circuit for his “Alice” microphone. I am using the same circuit with slightly different values and a different FET transistor. I chose the J305 which is used by several of the high end manufactures. I located it here. You can certainly use the parts list from Scott. His latest list is from 2013 and the parts are available from both Mouser and Digikey. I built the circuit on a small perfboard which is perfect for fitting inside the microphone body.

Here is how the circuit works; let's look at the signal path then the power:

The 1Gig (Yes one gigohm...) resistor develops the signal coming off of the capsule. The FET and the two 2.43K resistors form a phase splitter and impedance converter. The two .47uF capacitors couple the signals to the two bipolar transistors. These are PNP transistors setup as emitter followers. The two 100K resistors bias the transistors. Uber simple. If you are wondering about the 1gig resistor, it is key to a condenser microphone. It is also the most expensive component, coming in at around $2 each from Digikey. On the powering side, we connect the microphone to phantom power form a mixer or preamp. That brings 48 volts into pins 2 and 3 of the XLR connector and the two transistors. UPDATE October 2015: I added two 22nF capacitors at the XLR jacks and two 49Ohm 1% resistors on the inputs to the transistors for RF noise suppression. I didn't realize this until I used a different mic preamp when in a "noisy" environment. Schematic Updated! The 6.8K resistor and the zener diode take that and drop it to 12 volts. The 10uF and 68uf capacitors along with the 330Ohm resistor filter this and provide a stable voltage to the FET circuitry. Once again, very simple and elegant. The critical component and one we haven't talked about yet is the capsule itself. I am using the TSB2555B from JLI electronics. it is a Transound capsule and is what makes this project what it is. It costs $12.95 and uses nickel instead of gold on the diaphragm. It is also used commercially in at least one microphone I know of, the CAD e100s.

Now that we have the capsule and electronics all set, you could actually build one of these into whatever housing you want. I have tried this and learned a couple things. Because of the high impedance of the capsule and the FET electronics, the wire between the two acts like an antenna and unless the whole thing is fully shielded by metal or metal screen, you will have all sorts of noise.Both 60hz hum and white noise from all the RF leaking into it. In essence you need to put the capsule and electronics inside a Faraday cage.

I found an easier way than building my own. It turns out that there are several Chinese manufactured really cheap mics that actually have great metal cases somewhat decent electronics (very similar circuit...) and a small capsule. And the cost about $20 bucks. They make a great donor body, which is what we are using it for. Search for them on eBay by searching for “BM700” and “BM800” microphones. I got mine for about $22. Interestingly as you can see form the pictures it doesn't say BM800 on it. It also came in a paper mailer with the foam casing but no box. OK, now that we have covered the background, lets build one!

Edit: 9 October: Here is some audio with these recording my kids high school orchestra: Guyer HS Intermezzo Orchestra

Step 1: Step One: the Electronics

The electronics section is easily built on some perf board. I cut mine to 1” by about 1.5” then populated it from the PNP transistors working towards the FET end. The critical part here is the junction of the FET Gate and the 1gig resistor. Notice I am “floating” the leads. This is where the FET gate to capsule wire connects. We don't want that touching anything or using the circuit board that my have flux residue or attract moisture in a high humidity environment. Also look at the positioning of the FET. See the data sheet in the article. I had my pin 1 of the FET backwards until I realized the position mentioned in the data sheet was the top view of the transistor, not the bottom. If you use Scotts recommended FET, download the data sheet and read it! I left a spot to one side that lat me drill a hole large enough for the mounting screw to hold it to the chassis. I actually lucked out here... I built this before I thought through how I was going to mount it.

The type of zener should not matter. You need one rated for 1/2W or better but they get larger as power rating goes up.<br><br>Jules
<p>Hi Jules, I'd like to re-draw the circuit and PCB in KiCad. Should I use the circuit in the ZIP file with the two zener diodes on the output or use the PDF version with the two 22p capacitors? Also, is there any need to suspend the 1G Resistor/FET Gate connection or can I route it through a connector on the PCB?</p>
I have not used the two Zeners and there is much discussion on their need for protection of the PNP transistors. My thoughts on this are that the original Schoeps circuit used them. If you want to be bullet proof then please do. WIth the original circuit they did not use the 47-49 ohm input resistors that I am using, they used ferrites and no resistor. I have not abused my mics by hot plugging them multiple times either, but I have once twice with no ill effect. Also many variants of the circuit (Original Alice etc. do not use them)<br><br>My prototypes suspended or floated the 1gig resistor and the gate lead of the FET. I have not had a problem with the circuit board version. I use water soluble flux based solder and then clean well with soapy water and a toothbrush. FInal clean with isopropyl and let air dry before installation. No issues. Good luck and please share the KiCad drawing! <br><br>Jules
<p>Another quick question; Having trouble finding the Zeners in the UK at a reasonable price. Can I use BZX types as substitutes?</p>
<p>Hi Jules, Many thanks for the info. I'll definitely share the KiCad files once I've built and tested it.</p>
<p>Hey Jules, or any other helpful posters. I recently built the Pimped Alice circuit and am having an issue. I can't seem to adjust the POT as stated in the instructions. If I'm adjusting 12VDC for example I can only achieve 12VDC over A and 0 over B up to 6VDC over A and 6VDC over B. I cant adjust beyond that to make up the 3VDC over A and 9VDC over B. I soldered a mic on and that part works. In trying to figure this out I built another board and it has the same issue. Any ideas?</p>
It sounds like it is adjustable and the mic works, which is good! The goal of adjustment here is to split the voltages so that the FET has the ability to handle the largest theoretical signal it can. If you can go 0 to 6 volts on the lower leg and 6-12 on the upper you are able to adjust this. I may be misunderstanding your description here. Please read this and see if it helps:<br><br>https://www.dropbox.com/s/kqqx2fc2z3i46eo/FETbias.doc?dl=0<br><br>Jules<br>
<p>awesome, thanks Jules. I will for sure go over this. It is adjusting for sure. the issue is that the instruction on splitting the VDC says to put a 1/4 of the VDC(3 in the example) across TP A and 3/4 of the VDC(9 in the example) across TP B. my boards are maxing out at 1/2 the VDC accross TP B and I cant increase it to the instructions 3/4 of the VDC. The Pot is turned the max and wont go more. when I turn the POT down(off i guess) I have the full VDC acroos TP A and none across TP B.</p>
Can you post some pictures. It sounds like the pot maybe open or something. the 12VDC and 0VDC indicates that there is no adjustment going on at all. One other possibility its the FET is not connected correctly. I did that a few times (rather embarrassingly...) but the pin outs do change between manufacturers also.<br><br>Jules
Yeah, the pot does adjust but not as far as it should. It will go from 12vdc on point A and 0 on B to 6vdc on A and 6vdc on B turned to the maximum. I'm almost certain I have the Fet correct as well, as I checked it to the digikey data sheet and the mic works when hooked up.
<p>Jules, Thank you so much for the work on your instructables (both this one and the MS Alice one) -- I'm so grateful for the detail you provided of your build and that you're so responsive on these threads! I'm going to attempt a Pimped-Alice BM-800 first, and then hopefully go for the Pimped-MS-Alice next (VERY excited by the idea of using one mic to achieve the MS sound!!). </p><p>After reading both of your Alice instructables (along with the Homero page and Tom Benedict's links), I'm wondering: Would it be possible/advisable to do this single Pimped Alice mod with a TSB-165 like those used in the MS version (as opposed to the TSB-2555B)? Thanks in advance for any info, and thank you again for so graciously sharing your work here! (You should get on Peterson Goodwyn's DIYRE website/podcast and see if TapeOp would be interested in featuring your work!)</p><p>All the best,</p><p>-Steve</p>
You are welcome! Yes a single TSB-165 works in place of the TSB2555B. I have four of these I built into BM-700 bodies. They are very nice small diaphragm condensers. If you build the MS Alice, order one of the 3D printed capsule holders that another reader designed. I bought three of them and they are going in BM-800 bodies shortly.<br><br>All the best,<br>Jules
<p>Thanks, Jules -- Will do!</p><p>Out of curiosity, what would be involved with making a different capsule work with this circuit? I found <a href="https://www.amazon.com/Jbbtop1-Microphone-Double-sided-Professional-Replacement/dp/B019VZ9OOC/ref=pd_sbs_267_2?_encoding=UTF8&pd_rd_i=B019VZ9OOC&pd_rd_r=7P34XYKJPP544948YP46&pd_rd_w=NXd6t&pd_rd_wg=BOLXA&psc=1&refRID=7P34XYKJPP544948YP46" rel="nofollow">this LDC one</a> today, and it got me wondering what the results might be like if it were to be incoroporated into the Alice circuit...</p><p>This also got me wondering if an omni capsule could be leveraged in the MS Alice build, orienting a single omni capsule below a TSB-165.</p>
Not to hijack the discussion, but I have a related question maybe for Jules about a capsule swap in the MS Alice design. Would it mess with the mid-side concept to maybe use a single-sided large diaphragm capsule (perhaps a TSB-2555B?) for mid while for space reasons staying with two TSB-165s for side? Or do the cartridges all have to acoustically match?
Heh. I just ordered two BM800's for donor bodies (total 30 euros delivered with shockmounts and wind shields). Now I'm thinking of actually ordering the PCB from China as well, I mean they do proto PCB's for nearly nothing. What's your take on this approach? I mean if the PCN maker is not a scam company it should work great?
Yea that will work. They usually have a minumum order, not to large. Go for it!<br><br>Jules
<p>Hi,<br>I'm about to order 10 boards, just in case I happen not to fail and want to build a second one.. and a third one.. and fourth..</p><p>I am going to report back to you with pictures as soon as I actually get my hands on the stuff. It might take a few weeks since I took the cheapest (snail mail - free) delivery option for the mics and PCB's.<br><br>Thanks for your super-duper-awesome instructions. Who knows, I might actually build a working microphone without causing a deadly accident.</p>
<p>Hi, do you possibly have to of the boards left I might buy from you? I'd be interested. I also need to collect the needed resistors &amp; caps. I'm years away from having soldered a circuit but this project really appeals to me and I've already ordered two mic bodies and 6 capsules (for two MS Alices).</p>
<p>Actually need 4 boards if each board is a single pimped Alice circuit.</p>
Hi AtteM, about the 4 pimped Alice boards I had asked you about, if not too inconvenient, would you mind measuring one of the boards? Not sure they'll fit in a BM800 mic body. Jules' original perfboard was 1&quot; x 1.5&quot;. If too large, how hard for me (a newby) to modify the Gerber file(s)?
<p>Wow, I had completely forgotten about this project. I ordered the PCB's from Seeedstudio and also got the capsules but I never actually got around to getting the resistors and caps and soldering them which is a bit embarassing. Anyway the PCB's look just fine and flawless but I do not know if they would actually work (something may have theoretically gone wrong when I made the Gerber files for the PCB house).<br><br>I have 10 boards, 2 of which I might use some day so I could definitely send you 4. I could also send you the Gerber files if you'd like to order a whole bunch yourself (I used Seeedstudio which was quite cheap and I really enjoyed their service). Up to you which would you prefer?</p>
<p>AtteM, would you by any chance have any more you'd like to sell? I'm only looking for 1 to 3.</p>
<p>I would actually like to thank you for reminding me about this. I just ordered components for two mics from mouser.com. Fantastic!</p>
Let me know how the Boards work out!
<p>If i make this, should I worry about about matching the transistors, capacitors, etc.? I know with some amplifier circuits call for matched pairs of transistors in order to maintain symmetrical output.</p>
No need to match components. I used 1% resistors and 5% capacitors. Usually the actual values are much closer than their tolerance level would suggest. <br><br>Jules
<p>Hi, Jules,</p><p>Great tutorial! I built this and your M-S Alice microphone, and added the HF EQ modification in Ricardo Lee's document to both since I'm using these for field recording rather than for voice or instrument. They're both solid performers.</p><p>My BM-800 came with a 10mm capsule and a saddle that would've been tough to modify for the TSB-2555B capsule, so I made a saddle and post out of aluminum for my mic. A convenient solution for me, but not for others who might run into an unsuitable donor saddle.</p><p>Since not every DIYer has machine tools, I also designed one that can be 3D printed. It's up on Thingiverse for folks who have a 3D printer, and on Shapeways for those who don't.</p><p><a href="http://www.thingiverse.com/thing:2036552" rel="nofollow">http://www.thingiverse.com/thing:2036552</a></p><p><a href="https://www.shapeways.com/product/PEWRFKNHA/alice-tsb-2555b-capsule-saddle?optionId=61697185&key=677364a04326bc04389a3c0944522563&li=shop-inventory" rel="nofollow">https://www.shapeways.com/product/PEWRFKNHA/alice-...</a></p><p>I attached the capsule to the saddle with E6000 adhesive.</p><p>Cheers!</p>
Thank you for this! Great Saddle.<br><br>Jules
<p>Hi Jules! Thanks so much for this great tutorial! I have a BM-700, as we are not awesome solder jedis could I ask how much improvement does one get from merely replacing the capusle? We were going to use a TSB-2555B from microphoneparts.com their LCD capsules are great. And how much difference over that does it make changing out the capacitors for higher quality ones? Thanks sir and have a great day!</p>
<p>The capsule will make a huge improvement. MicParts is great. There will be a bit of residual noise with the existing electronics but not horrific.</p><p>Jules</p>
<p>I solved the noise problem by building a second mic with much higher quality capacitors. The picture shows the new board and capsule mounted in the Behringer frame with the original parts on the side...</p>
<p>I built this project into an old Behringer C-1 body that I had and it worked right from the start. It's very sensitive and has a great tone BUT there is a constant snap crackle electrical sounding interference that probably makes up at least 20% of the sound. I've changed a few components (mostly the 470pf caps for higher quality, tried other values) and when the noise is reduce so is the sensitivity and the noise never goes away completely. Could the diode be the culprit here? I can't find any shorts or cold solder joints. Any suggestions would be appreciated!</p>
Unfortunately USB supplies 5VDC so this won't work without additional electronics. It will work with a USB audio interface that supplies phantom power. <br><br>Jules
Thank you for an awesome instructable! I've been trying to look for good tutorials and sources for DIY mics and you linked to several good sources for reading up on that. How difficult is this on a scale from beginner to pro? I've done a few piezo electric disc contact mics but that's it and I wonder if this over my head.
What I did here is probably the easiest way to go. You can go in steps. Buy a &quot;Chinese&quot; mic and start with just swapping the capsule with this one, keeping the original electronics. Or, but out the soldering iron and go full in. Read through the stuff in the Yahoo Groups too. <br><br>Best of Luck,<br><br>Jules
<p>I just tried this out, I used that capsule and the original electronics, I had my headphones on im not sure, but I could of sworn the capsule made like a speaker for a brief moment. I plan to finish this product, so I think my approach from here, is to pick up the electronics, then try it, and I hope my capsule is still good</p>
<p>so anyways, I soldered the original capsule on, and the mic still works (lol) I noticed on the original capsule, there is a tiny circuitboard, and there is a diode on there, </p>
<p>if there is a circuit board on the back of the capsule, that means there is a FET on the board. Which means there isn't one on the main PSB. So, you can't just swap the capsule. You will need to build the board in the instructable.</p><p>Jules</p>
<p>First, thanks so much for this tutorial. So if the capsule in my mic doesn't have a circuit board on the back, it means the FET is on the board, and i can try swapping out just the capsule? </p>
<p>Correct. If there is no circuit board on the capsule you can swap the capsule with the one in the instructable.</p><p>Good Luck</p><p>Jules</p>
<p>I did just that and it sounds great! The only thing is it doesn't seem to handle even moderatley high SPL without getting fuzzy. Is that a product of the capsule, or do the elctronics have something to do with that too? Have you tried any of the other available capsules? Thanks</p>
<p>Are you still using the orignal electronics? I can't help with that one, they vary so much. Go full blown with whats in the instructable and you will get great results.</p>
<p>Yep, that's why I was asking. I didn't know what part of the chain was most responsible for what sound pressure levels it can take. I plan on building the board, actually have half the pieces so far, but I just didn't know if it would effect that. As of right now it can't really handle a loud guitar amp like my other condensers. Thanks! </p>
<p>DJJules!!! what a Great Instructable.......Thank you,,,got mine up and Running.....I used the bare bones schematic, and it sounds 15X better than any mic I Have Merry Christmas dude!! :)</p>
<p>Thank you Clint! Glad you got yours up and running. Merry Christmas to you too!</p>
<p>Thanks!! DJJules! :)</p>
<p>if anybody has got a couple pointers for me that would be awesome, I got the BM700 body</p>
Nice project! I, too, had the PNPs the wrong way round. After correcting that, there is good clear sound but the bass is very attenuated. Is there something obvious I could try to correct this?
<p>I put another cap in parallel with the 0.1mF one, having read Henry Spragens's detailed analysis and it is improved, though still less low end than I thought there would be - easily fixed with EQ, and a very nice quality sound. </p>

About This Instructable




Bio: I started taking things apart when I was 6 started putting them back together at 8 and they actually worked again when I was 10 ... More »
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