On Thu, May 26, 2022 at 07:20 PM, Jesse Hudson wrote:
Very low self noise is very important. I can find a bunch of mics that have much higher self noise, but I want ultra quiet....?
One option you might like to consider if this really is important to you?
?If you are building a? 'True Condenser OPA mic' using the circuit in the Instructable, you can gain an extra 2 or 3dB in lowering to absolute noise floor by taking the negative of the 47uF output capacitor from the second op amp (pin 7) directly to ground instead of from the opamp output.
Although that will make the audio single sided? - rather than differential? - it won't affect the impedance balance of the output.
In reality, these noise figures are - to quote Jules - 'way down in the weeds' anyway, and it will be the capsule noise that dominates, but in the interests of squeezing a couple of extra dB in lower noise floor, you might like to try the grounding option?
Here's? an audio clip showing the difference:?? ?
? A 'single sided' output signal, followed by the associated noise floor present.
? Then a second? 'differential' audio signal - adjusted? to the same amplitude - followed by the associated noise floor.
About 2 or 3dB worse...
Some folk do prefer a fully differential audio signal, and the 'real world' difference in noise floor is minimal -- but you did say you wanted 'ultra quiet'!? :)
