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I am designing a "mic activator" with some design goals that are not satisfied by the simpler ones (e.g. FetHead, CloudLifter), but are possibly already done by the more complex ones like SE Electronics DM1 / DM2 (but I don't know the schematic of that one, if anyone knows, please share). In short, I want decent CMRR, PSRR and low output impedance. I have a schematic I could build, but the part count to satisfy these requirements is pretty high. So I don't think I can fit it into the regular XLR male-female "tube" adapter, e.g. this one on AliExpress, which is similar to what FetHead uses. The PCB that can fit inside that one is 13mm wide by 15mm long, but 5.5mm of that length are used by the XLR connector. I could have a second PCB ride on the first, but I'd lose some area for the header connectors between the two. Ideally, I would like a longer tube, e.g. like Audio-Technica AT8202, which is ~36mm longer than the FetHead. Even 10mm longer would probably be enough for this circuit. Is there any way to source such a body?

I wanted to use a t.bone EM700 (which I believe uses a 797 AUDIO CY011C 16mm electret capsule) as a boom mic into a XLR transmitter, but it’s sensitivity of about 8 mV/Pa was a bit low for my needs (and the XLR transmitter doesn’t have massive gain I can play with). I wanted to get at least 20 mV/Pa out of it. So I wanted to replace its preamp with one where it's easy to add gain, which usually is a charge amp, but without the complications of a transformer. Here is the topology I arrived at, which I’d like to call chOPA (pronounced cho-pah, of course). Because of the battery powered XLR transmitter, I used one OPA1641 and one ADA4084 to save 1.15 mA of the P48 current budget vs. using one OPA1642. OPA1692 doesn’t come in singles, I would’ve liked that instead of the ADA4084. The mic sounds fine and has the sensitivity I wanted, with no perceivable SNR degradation vs. the original circuit (although that’s something I need to characterize more rigorously). Of course it will have a lower max. SPL, especially when considering the input impedance of the XLR transmitter. The original mic had pad and low-cut switches, I covered the holes with conductive tape (there's a layer of proper copper tape under the aluminium). Feedback and criticism are welcome.

Hello everyone, I've build very few microphones and they've all been Electret with two pads and pretty easy. But i'm looking to try and build a microphone with this capsule: https://www.jlielectronics.com/microphone-capsules/jli-160a11uc680/ I see on the diagram though, that an external resistor and compactor to make it able to work. Also, is there anything additionally that I need to do to make it compatible with phantom power? Sorry for all the probably obvious answers, but I'm super new to this whole realm of audio. Thank you all!

Good day all, I am new to the group but learning much from digging through old posts and files. Microphones, specifically, is a relatively new area of interest. I have tinkered with electronic and electro mechanical devices for many years, mostly related to RF communications. What brought me here is an interest in what is often referred to as "natural radio" - listening to and recording the sferics, tweaks, whistlers and chorus of extremely low frequency (ELF) radio waves emitted by charged particles in the Earth's atmosphere and magnetosphere in the range of 10kHz to 25kHz ( plus and minus ). It occurred to me that the likes of electret and condenser microphones and their circuits are not that much different to something suitable for monitoring "natural radio" - the need to interface a very high impedance transducer, the electret or condenser capsule in the case of the microphone and the electrically very short antenna in the case of the receiver, to the much lower impedance electronic amplifier circuits which follow. As is often the case, my interest in a specific application area developed into a much broader interest in the very interesting and much broader subject area of microphones. In my tinkering with various types of microphones I have a need to boost the output of a dynamic microphone. Easy enough to do - just plug in one of those generic inline phantom powered microphone preamp/boosters - job done. However, plug and play just does not cut it with respect to learning and understanding. Opening up a couple of these inline preamps plus many hours of searching and reading online has helped in the learning and understanding but has also left many more questions. What brings me to my post today was prompted by my recent comparison of a Klark Technique CM-1 inline preamp and the Rodyweil AC-1 inline preamp. Certainly not high end devices but suitable for my current needs. On comparing the PCB's from these two devices it quickly became apparent that the designs of these two devices were exactly the same - same components ( 2x PNP BJT, 2x NPN BJT, same number of capacitors and resistors of same value) and similar PCB layout, almost as if these two devices used the same "common" or "reference design" circuit. I have yet to fully sketch out the circuit diagrams of these two devices but that will come with time. That was a long way around to the crux of my posting - Is there somewhere ( that I've not yet stumbled upon) a circuit diagram of these or similar devices ( i.e. phantom powered 4x BJT inline microphone booster/preamp). Is it or are they in fact some "common" or "reference design" of some older origin and now often copied and duplicated in these low cost Asian sourced implementations? cheers, Graham

My experiments with the JFET-PNP topology (used in non-CORE DPA lavs, as discussed in this thread, and this Audio-Technica patent) prompted me to make a replacement PCB (10mm diameter circle) for Shure WL185/184/183 using this topology. My design goals were: must fit in the original WL185 lavalier body, must have similar or better tolerance to RF interference, must minimize self noise. The original PCB is a 10mm diameter circle with an outer ring as the ground contact, and a “leaf spring” contact for the capsule. The leaf spring has a large footprint and is mounted thru hole. This is the design I settled on. Using a SMD pogo pin (Mill-Max 0900-2-15-20-75-14-11-0) instead of the leaf spring frees up a lot of board space, which means I was able to cram everything onto the tiny board. For the JFET I used OnSemi 2SK3557 (almost identical to 2SK2394), and for the PNP I chose OnSemi MMBT5087L. The ferrite beads are both TDK MAF1005GAD352AT000. I ordered the boards both on Elecrow and PCBWay (PCBWay has better quality, but Elecrow has way faster shipping to where I live). The way Elecrow routed out the boards, there is a nub remaining, which I filed down: After filing, the board fits the chassis nicely and you can see I was conservative with the size of the outer ring: R2 and R3 must be matched for the JFET, so step one is measuring the JFET that will populate the board in order to select R2 and R3. Alligator clips are the wrong tool for the job, they make intermittent contact and may deform the SMD leads. I should’ve used test hook clips, but since I don’t have any (yet), this got the job done. I measured the voltage between drain and ground with two different value resistors between these two nodes: 10K and 20K. Based on this, I calculated R2=18K for 50uA and R1=16K for 1.7V at the source. Measuring Idss (multimeter in amp mode and no resistor) and VGSoff (multimeter in voltage mode and no resistor, so the resistor is the ~10Meg impedance of the multimeter) and then applying the JFET equation is not as reliable because the exponent in the JFET equation is not really ? (at least not for 2SK3557 anyway). I got better results by actually using values around the expected range, extracting VGSoff and IDSs based on these (they won’t match the directly measured ones) and using these to calculate the resistor. Once this is done, the top side of the board can be assembled. I used a hot plate (cheap USB Power Delivery one from AliExpress) for reflow, with no solder paste stencil, just using a toothpick to place solder paste on each pad. (Yes, the amount I ended up applying is excessive on some pads.) On the back side, I assembled the components one by one with solder paste and a soldering iron. I place a dab of paste on a pad, hold the component with tweezers, solder the pad with the iron. Then I can apply paste to the other pad (or pads, in the case of the two transistors), and finally revisit the first pad if necessary. After cleaning with isopropanol, this is what the board looks like. 1 Eurocent Coin for scale: Adding the wire and wrapping it up again: I need to apologize in advance for the quality of my measurements, I don’t really have a good setup for this. Really the best setup would be using wired preamps into an XLR interface, I don’t have either of those. I mostly use Sony UWP-D transmitters, but measuring noise through a compander is unreliable. I also have a Rode Filmmaker Kit (2.4GHz) in which I’ve rewired the connector to match Sony UWP (because it’s a back-up for those). It’s a digital line with a 24-bit ADC and DAC. Connecting the Rode RX to a Sony A7s III (again, far from ideal), I got: 5-6 dB higher signal from the new PCB (likely because of the <100 Ohm output impedance vs. ~1800 Ohm of the original) same noise floor after adjusting for the gain difference better RF suppression (there is a slight RF demodulation noise at 3.2 kHz with the Rode and the original PCB, it’s absent with the new PCB). A vanishingly small fraction of the signal gain could also be because the JFET-PNP topology bootstraps both Cgs and Cgd, wh

Apologies the PNG had alpha background so rendered wrong.