Looking for high-fi condenser capsule

The usual reason the cheap electrets sound bad is that their internal preamp is run on too low a voltage. I got some capsules intended for hearing aid use (I needed very small), which cost about 50 cents each because I bought 20 of them (I think I still have one or two left). They were ruler flat, could have been used as calibration mics, but distorted early in their original circuit because it ran on a 1.2 volt mercury cell. Their specification said they could accept more voltage, and with 12 volts derived from 48 volt phantom they could accept 113dB levels before distortion became disturbing.

But the inside of an accordion doesn't sound very nice at all; all clicky bits, and nasty sharp harmonics and bellows noise and wind. I find a bit of HF rolloff, rather than accurate reproduction, to be easier to work with (accordions were never made to be listened to from inside).
 
I bought a Shure KSM27 to do piano from about 4' away. You see them a lot where they are recording several members of a string band with one mike, for example on KET Jubilee at the W C Handy festival, or Woodsongs. I think getting that far away would reduce the noise of your body breathing key clicking etc, and focus on the music. In the diy realm, though, I did build the anti-vibration mount out of rubber industrial belting, and mount it on an old camara tripod instead of an official mike stand. Look around, I got mine for $80 used, sounds fine.
 
Thank you for the links, adason. Yes, high threshold is going to be important because it must get pretty damned loud inside of an accordion.

Chris, I'd been wondering about those cheap ones. So indeed I'll try a cheap one first, give it 12 V DC, and see how it works. An accordion has rich formants with a really wide spectral range.

Fortunately, I don't need to worry about the preamp because I play into a pro audio console that also has 48V phantom power, and equalization if needed.

As far as clicks and clacks, us acordeonestas think that sounds cool.

It seems like there might be a nasty near/far issue among the reeds, and that several mics might be needed. Some people solve that problem by mounting the mic outside on a gooseneck, but it looks like a real hassle. A friend of mine has an accordion with a pickup inside and it sounds great.

Great advice. I'm going to try the simplest thing first and go from there.
 
The usual reason the cheap electrets sound bad is that their internal preamp is run on too low a voltage. I got some capsules intended for hearing aid use (I needed very small), which cost about 50 cents each because I bought 20 of them (I think I still have one or two left). They were ruler flat, could have been used as calibration mics, but distorted early in their original circuit because it ran on a 1.2 volt mercury cell. Their specification said they could accept more voltage, and with 12 volts derived from 48 volt phantom they could accept 113dB levels before distortion became disturbing.

But the inside of an accordion doesn't sound very nice at all; all clicky bits, and nasty sharp harmonics and bellows noise and wind. I find a bit of HF rolloff, rather than accurate reproduction, to be easier to work with (accordions were never made to be listened to from inside).

Agree and add: I have built many accordion Mic and preamp systems.

Electret mics are way too good for that, sound must be dulled a lot to be bearable.

Cut highs sharply to damp buzzyness/clicks/whistling, cut lows to avoid thumpiness, specially because there's a lot of "atmospheric pressure" variation inside, and modify them to kill gain.

The basic idea is well explained in
Recording and Measurement Microphones
Just so you know what we are talking about, this is the basic mod
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but read it all at Rodd Elliott's page.

*After* you modify the capsule, build a basic preamp, an unity gain buffer may do because signal level will be high and then add lowpass and highpass filters to limit range.
Use Op Amps, no reason to go discrete, and it speeds up design.
And remember here "Lo Fi" is best.

One trick I used to get good EQ was to set up around a player a couple SM57 microphones on booms, as an acoustic reference system, and my internal electrets, then switch back and forth , tweaking the latter until sound was roughly comparable.
You'll need "cup" type headphones (or in-ear) so you actually hear what microphones pick and not the "air" sound.

Result was *very* good.
I used 4 electrets, 2 on each half, one on the high side, one on the low one.

So it can be done, but it takes a lot of tweaking.

In my case it was worth it, because our Tango players rely heavily on the "Bandoneon"
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so I sold a lot.