5 Homebrew Electret & Condenser Microphones

I got a bit obsessed with modding and building microphones. Here are five Frankenstein mic builds I've put together from various microphone donor bodies and capsules.
A particular thanks to Jules Ryckebusch (@SoundSleuth) for his excellent Instructables guides which inspired these builds.
Mic #1: Schoeps 4 mini electret
Body: Maplin "Prosound" dynamic mic
Capsules: RS PRO Omni-directional 6mm through-hole electrets (uk.rs-online.c...)
Circuit: Schoeps on matrix board
Mic #2: Pimped Alice dual large electret
Body: BM900 (longer version of BM800 cheap Chinese mic www.aliexpress...)
Capsules: Generic 25mm large capsule electrets (www.aliexpress..., or if you want better quality and are in USA or don't mind high shipping fees TSB2555B (www.jlielectro...)
Circuit: Pimped Alice on matrix board (see guide www.instructab...)
Mic #3: 8-capsule electret BM900 mod
Body: BM900 (longer version of BM800 cheap Chinese mic www.aliexpress...)
Capsules:
---- 4 x Generic 25mm large capsule electrets (www.aliexpress...) x 4
---- 4 x Generic 16mm electrets (www.aliexpress...)
Circuit: Native BM900 with lower noise 5.1V Zener + low pass RC filter on DC rail
Grille: Isopon Aluminium Mesh (www.amazon.co....)
[You're nuts if you want to build this mic.]
Mic #4: LDC Alice full condenser
Body: BM900 (longer version of BM800 cheap Chinese mic www.aliexpress...)
Capsule: 34mm large diaphragm true condenser (www.aliexpress...)
Circuit: LDC Alice on matrix board with inductor-based DC bias generator
Mic #5:
Body: BM800 (www.aliexpress...)
Capsule: 77JC 34mm large diaphragm true condenser (www.aliexpress...)
Circuit: OPA Alice + hex inverter DC-DC (see: www.instructab...)
---- PCB #1: Dual OPA Alice in blue (www.pcbway.com...)
---- PCB #2: DC-DC Hex Inverter Multiplier in red (www.pcbway.com...)
----- Operational amplifier: OPA1642 (www.aliexpress...)
I have since built a microphone using a clone U87 body (www.aliexpress..., the Mic #4 34mm true condenser (not the 77JC one), and the two PCBs from Mic #5. The results are outstanding. Very low self noise and excellent sensitivity.

[@MichaelBrooksDr]

Somebody asked about what audio path I used for the black background shots. This was: - Microphone connected to Millenium PP2B Phantom Power Supply (www.thomann.de/gb/millenium_pp2b.htm) - Millenium PP2B Phantom Power unit connected to Behringer DX2000USB mixer - Output from mixer connected to ESI Maya 44 USB+ soundcard interface The video of those shots was from a 1080p webcam! My advice to anyone who wants to easily record video with decent audio, cheaply, is to actually keep it simple: - Use a smartphone for its rear-facing camera because they have excellent cameras on them - Get a USB "on the go" cable (www.amazon.co.uk/Keple-OTG-Converter-Connector-15/dp/B071W6LT5W/) - Buy a reasonable USB powered condenser mic like the AT2020 USB (www.thomann.de/gb/audio_technica_at2020_usb.htm) or Rosde NT-USB (www.thomann.de/gb/rode_nt_usb.htm) - Connect the mic to your smartphone via the USB on-the-go cable.

[@SoundSleuth]

Yes, My Pimped Alice circuit at 12:48! Go man Go!

[@MusicalRiolu]

There's something incredibly funny about the super duper cardiod mid , between the grill and the fact you can see right through it, revealing 8 freaking capsules Next time you gotta make the ultimate omni mic by having 20 or so capsules in a disco ball pattern

[@matijatatomirovic3351]

By lowering the zener you lowered the headroom and increased the thd. The capsules don't use the voltage regulated by the zener, the zener sets maximum signal swing voltage fet can use to provide output signal. Also arranging capsules like that doesn't do anything for it's directivity. Take a look at some microphone array papers, and what you need to do to achieve more directivity. Capsules would need to be stacked behind each other, which is also why shotgun mics are long. You would need a chamber to test and measure the effect, otherwise you are just picking up random surface reflections. Fun video though.

[@Chinhnguyen0497]

is it possible to increase the output signal of usb mic ? im using fifine k669b but it's pretty bad, it works like a compressor, small sounds it's very loud, but when i speaking my voice is very low . like when I scream the sound doesn't cut but it becomes lower.which is great but it reduces the sound even when I speak normally, ambient sound and noise even louder than my voice

[@MichaelBrooksDr]

Not exactly. Zeners above 6V conduct by avalanche breakdown which is much more noisy. Zeners below 6V conduct by the tunnelling effect which is lower noise. The whole point of dropping the Zener to 5.1V is to get out of the avalanche zone and lower the self-noise of the circuit. A side by side set of microphones is essentially a broadside array. Broadside arrays are more directional than single cardioid capsule. Capsules stacked behind each other as you describe makes an endfire array. *Both* are methods of attaining directionality.

[@matijatatomirovic3351]

@@MichaelBrooksDr then use several low voltage zeners in series. There's a filter after the zener, so the inherent noise of the zener shouldn't matter. By lowering zener voltage you definitely worsen the THD, just measure it.

[@pavelcollee-foley7997]

Hey I wonder what the circuit for the inductor based high voltage generator was. It's not on the instructables guides and I'm trying to fit two alice circuits into a Nw800 style chassis, so the hex inverter board won't fit. I also ordered a bunch of normal alice pcbs so I won't be getting the dual channel pcb.

[@migalito1955]

Nice. I am not sure, but it looks like your building essentially a pre-amp into many of your Electret Mic bodies. I'll have to look up the Schoeps circuit your using. I am a retired mathematician that took up stringed instrument building in my retirement & a consequent has become researching with the aim of building transducers and pre-amps to amplify my acoustic instruments. I am likely going to use Electrets with an op-amp serving as a pre-amp because under saddle pickups tend to dampen the instrument when played strictly in acoustic mode thus your experimentation has been appreciated & I can see why you like the concept of op-amps after a quick Google look at the Schoeps circuit.

[@MichaelBrooksDr]

That is correct, the pre-amp is built into the mic body. This is the case with pretty much all condenser (whether electret or "true condenser") mics because the capsules have a very high impedance thus are unable to drive a long signal line to a mixer or amplifier. The power to drive the circuit comes from phantom power, which puts a 14mA limit on the total current you can draw. That's what makes the "OPA Alice" op-amp OPA1642 chip very special: high impedance inputs and low current consumption. Electrets are without a doubt the most compact condensers you'll be able to get your hands on. For audio fidelity, Primo and JLI make some excellent 20Hz-20kHz electrets with good dynamic range.

[@migalito1955]

@@MichaelBrooksDr Yes, for a stage Mic or Studio Mic the lead could be pretty darn long thus pose a big voltage loss issue without the pre-amp built in to the Mic's body. I'll be having the preamp tucked in the body of the instrument so at least that saves me the difficulty of making a geometry work with respect to transducer and body. I've assembled a few pre-amps out of lm741 and lm386 chips just because they were in a pile of odds and ends. I must say at first the Dual Power Supply common to the 741 threw me until I realized that it was not a single power supply scheme, but while the 741 is likely not best for my intent with the instruments I find it and op-amps in general interesting because they were and still are used to create math operations in analog computers and to keep busy this winter I'd like to build a simple analog computer. Thanks for the additional information....

[@david_31]

great video! gave me inspiration to go down this rabbit hole as well, some question though, are all the mics you showed designed to use phantom power and if so can i get away with the cheapo $13 ones from aliexpress (or can i stick with my usb soundcard and or modify it in some way to make it work)

[@MichaelBrooksDr]

Yes these are all phantom powered. You'll want a sound card capable of taking a balanced mic input, or an external mixer which can take a mic input and output line level. You will then need to buy a phantom power supply if your USB card or mixer do not output phantom power. The one I use is the Millenium PP2B Phantom Power Supply: www.thomann.de/gb/millenium_pp2b.htm

[@david_31]

@@MichaelBrooksDr thank you so much!

[@AnalogDude_]

So you put power on the XLR, direct that to PNP transistor and use the Base of them of extract power? Would that work on a Akai MPC X and it does have 48 volt phantom. I do have half a XLR cable, a shop around the corner that sells them. Was looking at the J113 a couple of days ago, but i got a few of BF256. I have the get of a phone, but it contains normal 10 mm electric cells.

[@MichaelBrooksDr]

The "Pimped Alice" circuit (modified Schoeps used in Mic 2 and Mic 4) gets its power from phantom power on pin 2 and 3 on the XLR. So the XLR hot and cold lines (pins 2 and 3) each have a 48V DC bias on them. You will need a mixer capable of supplying phantom power to get this to work, which the Akai MPC X does indeed have on its two XLR ports. See: content.instructables.com/FSE/84ZJ/IJHFDPU2/FSE84ZJIJHFDPU2.png To extract power from the phantom power, the circuit bridges the two collectors of the PNP transistors together, which will sit at 48V, then via the 4k7 resistor drops this down to 12V using the 1N5242B Zener. The best circuit of the lot however is the OPA Alice with the DC-DC Hex inverter to produce the bias voltage. (Mic 5). This has much less self noise.

[@AnalogDude_]

@@MichaelBrooksDr Thnx, i was looking if LM4040-12 existed, but it doesn't, would a TL341 shunt do the job without causing noise? for the OPA circuit? Could this also be applied to use "electret" microphones on the Akai MPC X 48 phantom power? witch is what i got at home sourced from a old home phone.

[@MichaelBrooksDr]

​@@AnalogDude_ I wouldn't worry about the noise of the zeners until you've optimised your capsule. An old home phone microphone capsule won't be very good quality because home phones are narrow bandwidth, so the mics used in them are lacking in bass and treble pickup. Cheap capsules are usually also relatively noisy. If you're looking for a quality electret, JLI electronics electrets are generally very good (e.g. 2555B). Also Primo makes some high performance electrets with a full 20Hz-20kHz response (e.g. EM23). You will need an electret that does NOT have a built-in FET transistor in the package if you want to use the OPA Alice or Pimped Alice circuits with them. Electret mics don't need a separate backplate bias voltage, so you won't need to use a DC-DC Hex inverter supply at all for an electret. You just need to tap the phantom power to supply the microphone's signal processing circuit. As for getting 12V from phantom power in a low noise fashion: a 12V zener followed by an RC filter (as is the case in the OPA Alice and Pimped Alice circuits) works well. An adjustable shunt regulator is just overkill and won't be lower noise. You could improve on a 12V zener theoretically by replacing it with three 4V Zeners in series because zeners below 6V use tunnelling instead of the noisier avalanche method of higher voltage zeners.

[@AnalogDude_]

@@MichaelBrooksDr Thank you, i saved your explanation to a text file for the time when I'm going to build on. if you don't mind. : )

[@joedoe3446]

Is there a way to turn a "cardioid mic capsule" into a super cardioid polar pick up pattern?? thank you (:

[@MichaelBrooksDr]

You can do this in a couple of ways: 1) For side-address mics, mount a second lower-sensitivity cardioid capsule facing backwards, attenuate its signal slightly, then mix it out of phase with the main capsule's signal. 2) Enclose the capsule in a directional horn. This will make the response to higher frequencies more directional than the response to lower frequencies though. 3) Drill some more holes in the backplate. This is very hard to get right and for capsules with a rear membrane would require dismantling the capsule.

[@andrestp]

Thanks Michael... What would happen if LDC Alice full condenser board paired with 25mm large capsule electrets? I mean true condenser board paired with electret capsule?

[@MichaelBrooksDr]

The LDC Alice circuit is essentially two PCBs. One is the 60-100V generator for biasing the capsule, the other board is the impedance converter and pre-amplifier to turn the signal from the capsule into something that can be sent down XLR cable. An electret capsule doesn't need the bias voltage part. So you can absolutely use the FET Alice / OPA Alice circuit with the electret capsules.

[@andrestp]

@@MichaelBrooksDr Thanks Michael...

[@theoriginalKland]

Why in series? I would think that would kill the signal.

[@NBryanBlack]

I'm confused. You mention that the true condenser mic element needs around 50 volts for the charge, but 48 volts is right at 50 volts, so why the voltage-doubling circuitry? Charging the plate is the whole purpose that phantom power is set at 48 volts. It would seem to me that you'd require more current to convert down to 12v and back up than you would use if you just used the 48 volts that you already have. Is there a reason that I am missing? Thanks!

[@MichaelBrooksDr]

It is all to do with the current limitations of phantom power. 48V would be capable of causing painful shocks if it wasn't current limited. So phantom power supplies deliver 48V through 6.8kOhm resistors. This current-limits the 48V. What this means is that phantom power is 48V when floating and nothing is connected to the end of it, but the moment you start to draw current from it, the actual voltage starts to fall (those 6.8 kOhm resistors and the load you connect to it act as a potential divider). It would be fine if all we were doing is charging a backplate which has a very high effective resistance, but we also need to draw some current from it to power the pre-amp circuitry in the microphone. This causes the 48V to fall downwards (typically to around 20V when drawing just 10mA), so we no longer have a high enough voltage to charge the backplate of the true condenser. In order to get a reliable voltage for the backplate, the OPA Alice circuit picks a voltage below what the phantom power gets dragged down to, and uses a Zener diode to derive a reliable voltage (12V) even when the amplifier circuitry is drawing slightly different amounts of current as it amplifies the varying sound input signal. The 12V is split two ways: one to power the operational amplifier and the other to charge the backplate To get back to a high enough voltage to charge the backplate, we need to use a voltage multiplier circuitry, bringing the 12V back up to about 84V. Since that 84V has been derived from our rock-solid 12V, it'll be a nice reliable 84V.

[@NBryanBlack]

@@MichaelBrooksDr Thank you for the kind reply. I knew about the current limiting(and even the 6.8K resistors), but I didn't think about the resulting voltage sag. The voltage doubler circuitry makes more sense to me now. Thanks again.

[@carlosfernandes8919]

CLASSE A, Muito bom mesmo...Voce é muito inteligente... Eu comprei uma Capsula dessas, pra colocar no meu NEWMANN U-67, e usei um /circuito pcd, da marca MARCHAL, e ficou com um som muito bom , parecido com o original u-87 ou tlm-107. Eu gostei muito de ver seu Vídeo, Eu sou do Brasil , que Voceis conhecem com , BRAZIL...Parabéns...Very good. Na China vende Circuitos , cópias de u-87, no ALI-EXPRESS.

[@MichaelBrooksDr]

Muito obrigado! I've bought a couple of those clone U87 bodies off AliExpress and put the OPA Alice circuit in them along with one of the large capsule condensers and a DC-DC Hex Inverter bias voltage circuit. The results have been so good that it has become my everyday studio microphone.

[@carlosfernandes8919]

@@MichaelBrooksDr I'm an amateur, I don't know much about electronics. But I did the basics. your invention, it's much better and more professional I learned things from you...thanks GOD BLESS YOU. Sorry, I don't speak English.. kkk

[@ClassicalRomance]

Is it fine to parallel a 25mm capsule to a BM800 with 16mm without any electrical piece addition? Or maybe in Series? We have the same circuit board

[@MichaelBrooksDr]

It's not exactly kosher! I got away with it because the impedances of the two types of electret were similar. In the 8 capsule mic, the configuration is a series chain of 4 x 25mm, in parallel with a series chain of 4 x 16mm. I'd not recommend mixing capsules like that for any serious microphone though!

[@vaporizer1000]

about last one mic I guess you have too big pop protection on mic and in this case you can`t hear hi-end quality of sound from this mic.

[@MichaelBrooksDr]

It's probably the KZbin audio compression affecting it. Though the centre-terminated capsule is definitely less "bright" than the middle terminated ones, so you may be noticing the difference between that and Mic 4.

[@shel1282]

Sir vi need to make a microphone for church preaching please advice

[@MichaelBrooksDr]

You're describing an indoor live PA scenario here, where the microphone will be used in the same indoor space as the speakers which are relaying the microphone. Your main problem, especially in a church, will be feedback from the speakers into the microphone. So you should avoid anything with too high sensitivity. You should also aim for a directional (cardoid or supercardoid mic) so you can keep the speaker sound from being picked up. Lapel electret mics would be a bad choice because they are too sensitive and not very directional Other factors to consider are: Handling: do you intend to hold the microphone by hand, or in a microphone stand, or do you want a worn headset mic? Cables: will this mic just be used on stage or do you intend to roam around the entire audience with it? Ruggedness: will it just be you using this, or are you looking for something that will last years with occasionally being dropped and knocked about? Mixer and amplifier: what other equipment do you have? If you already have a mixer, can it provide phantom power on microphone channels or not? If we assume a typical setup: your church has a simple 4 channel mixer with no phantom power, feeding into a few active speakers at the sides pointing towards the audience, and you'll be using this on stage at the front, then I recommend the Sennheiser e835 vocal dynamic mic, or the Shure SM58 which is more expensive but even more durable. If you're on a really tight budget, go for the Behringer XM8500 Ultravoice, but be aware that Behringer gear has a habit of developing faults after a few years.

[@AbdoZaInsert]

33:30

[@steveflynn8311]

One might assume that people who found their way here don’t need a for dummies explaination at the start..2 mins in and i’m leaving