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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

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Hi everyone. I'm currently in the process of building an OPA Alice based microphone using a NW-700 body and TSB2555B capsule. Jules instructable is an amazing guide that makes it trivial for anyone to build an OPA Alice using the linked supplies. But one thing I find lacking is more information regarding the component selection. As someone who's new to mic building and analog circuitry in general, I wonder how exactly the passive components got selected. For this reason I've kept most components I plan to use for my mic the same as the provided BOM on PCBWay. I did substitute some as I think they may perform better or because I already have them in stock. If anyone could give me some feedback on these choices I would be more confident in my ability to finish this project. For the 47, 2.2k and 47K resistors I went with 0.1% 25ppm/C 0603 resistors from the YAGEO RT series. As I understand it matching the resistors on the XLR3 and XLR2 lines is important for good performance. The 200 Ohm resistor is just a basic 1% thick film resistor as it doesn't really affect anything important in the circuit AFAIK. I also plan on replacing the output capacitors with non-polar Panasonic ECE-A1HN4R7U caps. This is based on the data from Henry at Audio Improv who showed that non-polar caps on the output reduced distortion. Finally I replaced the 22nF EMI/RF suppression caps with TDK FG14C0G2A223JRT06 as these have a C0G dielectric making them non microphonic. (BTW these are shown as 0.22nF on the instructables schematic which was super confusing) I hope my modifications and my reasoning behind them make sense and thanks in advance for taking a look.

Picking back up with the Primo capsules. I managed to lose one of the EM172 in a gap in the loft floor, so bought some EM272s. Today I wired them up but there was a weird discrepancy of about 5dB between the two of them (They were both plugged into XLR ports on a MixPre6ii with pan L and R and both set to 50dB of gain). So I stopped and went back and checked everything was as it should be. The capsules were a matched pair, both resistors are reading 149.9K and they are wired as in the image below. As I've learned from the previous responses, the FET forms part of the circuit, so to ascertain that both capsules were getting the same voltage I probed them with the DMM, This is where it becomes more weird. Now I am seeing 0.19v on both no way near the expected 5V. Even accounting for the low voltage it doesn't explain how there is a 5dB difference between the two of them. My question is two-fold; 1. How using 4u7F Al caps correctly polarised, and 150k 1% resistors am I getting 0.19v across the +/- terminals on the capsules? 2. What could explain the 5dB difference between the two capsules? The capsules came from Micbooster, who I trust implicitly. Apologies for my lack of knowledge...

Hello Everyone, With the information I learned from this forum and elsewhere, I also tried a PuiAudio AOM5024 + SimpleP48 circuit. The recording noise is extremely low and the sound quality is very good, but I have some "hum" noise to deal with... These are what I did: 1. A Heat Shrink Tubing was covered the capsule (AOM5024) and the copper tape wrapped on shrink tubing, copper tape soldered to shield pair on the cable and directly goes to XLR connector. The pressed and shaped as mic capsule metal grill mesh insulation piece was also put on the head of the capsule and it does not touch the capsule but connected to copper tape and cable shield. On the outside, a shrink tube was used to wrap it all. I used multi-turn potentiometer in XLR connection part for first time testing the best voltage for capsule. 2. West Penn Wire 25291B was used as the cable (actually I also had Mogami W2697, but I didn't use Mogami for the first test, because I thought there was not too much difference between them, maybe I'm wrong :) ) 3. I also used the Neutrik NC3MXX-EMC Cable Connector as a XLR connector, but then the supply voltage of the microphone dropped to 3.1 volts, so I gave up using it... As an Audio interface-mixer, I used Allen & Heath Qu-16C, Audient EVO 4, M-Audio AIR 192. I would like to thank everyone who shares knowledge-info-experience with us in the group, Knowledge is nice when it is shared :) I look forward to your comments... Best,

Hello everyone, Are you aware of this website? I have been following it for a while and I would like to make this microphone WM-61A Probe-T . What are your opinions about this microphone? Mr. Shin used SMD ED8 5P 600¦¸£º600¦¸ Audio isolation transformer and Mic capsule Panasonic WM-61A. I ordered 15 of them and I want to experiment with them. Since I can't find a topic about this DIY microphone in this group, I wanted to start a topic and ask for your opinion. Many thanks, and I am waiting for your opinion.

When cell phones became common, Shure lavalier microphones were picking up GSM noise. Shure changed their FET circuit, added a dot on the lavs so you'd know they're the new type and marketed them as having "CommShield Technology for RF Filtering". I was curious about the circuit so I opened up a Shure WL185. The family of lavs (WL185, WL184, WL185) have interchangeable 10mm-ish capsules (cardioid, supercardioid, omnidirectional) and are very popular for sound reinforcement applications. Here is the circuit I traced: a few caps (not 100% sure of values, but they should be close to what is below), a SMD ferrite bead, no real surprises in the schematic apart from the 100 ohm resistor which actually increases the output impedance of the mic. I believe R1 is to allow the caps to kick in from a lower frequency, any other ideas? The real surprise, however, is the PCB layout. The source terminal of the JFET is routed as a ring trace all around the gate terminal capsule connector, on both sides of the board! Is this FET circuit using PCB losses to bias Vgs instead of a large value resistor (or, as would be expected for a small electret, back-to-back diodes)? Or is it RF magic? To me it seems that the first one is more likely: the trace is a full ring around the capsule terminal, routed with minimal clearance. Any other explanation? Identifying the FET would help, but it has no marking.

Everybody seems to complain how JFETs are hard to bias and therefore a pain to build circuits around, especially cheap, mass produced ones, which can¡¯t afford matched components or manual adjustment. I think there may be a reasonable way out, and I¡¯m not talking about using an op amp bias servo, which is akin to killing a fly with a sledgehammer. The circuit below, which is a derivative of the input stage and phase splitter from Pimped Alice, uses a single NPN transistor and a few passives to automate what the 1Meg potentiometer does manually in the classic Schoeps design (and Pimped Alice): set the gate voltage for the target drain current, but using a Miller Integrator. Here's a simplified version of what's going on at DC, which somewhat resembles a two transistor NPN current source: R3 sets ID (approx. 0.6V/0.47K = 1.27mA), R2 sees practically the same current (the BJT base current is a couple hundred nA), so (R2+R3)*ID sets the voltage at the JFET source. So these two resistors set the Q-point of the JFET, and most importantly their values are independent of the JFET parameters! To bias correctly in this configuration, the JFET only has to have: IDSS higher than the bias point (target IDS for this circuit is about 1.3mA, so any JFET having datasheet ¡°min. IDSS¡± above 2mA is good) |VGSoff| lower than the target voltage at the source of the JFET (3.1V for the schematic below) minus the BJT¡¯s VCEsat, so let¡¯s say any JFET with datasheet ¡°max. |VGSoff|¡± less than 2.8V. These requirements are not strict at all, and certainly do not require measuring, sorting and matching individual parts. The DC circuit is simple enough to build an intuitive understanding of what¡¯s going on. Qualitatively, there is a tug-of-war between the JFET and the BJT, which settles at a ¡°happy medium¡±. If the BJT were to conduct more than this ¡°happy medium¡±, we¡¯d have a high collector current and a high VBE (and equivalently a high current across R3). The high collector current would produce a high voltage drop across R1 and pull the JFET gate low, while the high current across R3 would push the source of the JFET to a high voltage. VGS would go more negative, reducing the JFET IDS, and therefore the current through R3 and consequently VBE, moving back to the ¡°happy medium¡±. Conversely, if the BJT were to conduct less, VGS would be more positive, causing the JFET to conduct more, raising VBE and moving back to the ¡°happy medium¡±. The bias point is as reliable as any other circuit relying on a VBE as a reference (which is a large proportion of BJT circuits). As far as I can tell, thermal stability is the main drawback of the circuit: a variation of about +/- 20% in drain current over -25C to 85C, vs +/- 5% for a potentiometer-biased gate. Over a more realistic usage range of -10C to 50C, the NPN-based bias produces a variation of +/-10% in drain current. I think this is perfectly acceptable for the condenser (or electret) head amp application. It gets slightly more complicated when we want an AC circuit for a head amp (without turning the thing into an oscillator). The answer is using the BJT as a Miller Integrator, which ¡°amplifies¡± the time constant R6*C4, effectively limiting the gate voltage adjustment to very low frequencies. Based on simulations with varying JFETs, BJTs, capacitances, temperatures, input signal amplitude (including dynamically switching from 0V to 2V), this seems reliable enough to build. I know the devil¡¯s in the details, but is there a significant drawback that I¡¯m missing here? I plan to breadboard it when I have some time.

An electronic Albuterol inhaler had me puzzled. Somehow it senses air motion, drawn by the user's lungs, to vaporize and deliver medication; there is no power switch but an LED indicates air motion. I ripped one open - unfortunately destructively - and found an apparent 6-lead 6mm mic element with an interesting rubber structure on it. Inhaled air appears to pass through the structure which looks like a tiny whistle. Hmmm. An ultrasonic whistle? Can a digital mic be dormant in silence, yet active when in sound? Tom