I must have tried an infinity of permutations of
accordion mics by now
I think that one of the simplest and most effective
is to simply to clip a condenser mic (like the Audio
Technica ATM 35) onto your bellows-lock strap.
It is easy to change from one accordion to another and
requires no modification to the instrument and it will
"follow" you if you move around on stage.
(It also could be plugged into a transmitter for
wireless operation.)
A 57 on a stand is a good idea too ..
if you don't move around much, like when one is
seated while playing.
Agree with what the Big Man says. To add to the option of using a mic on a stand, the times I've had to do that, I've found it very challenging. Especially when I'm singing, in that now I've got to keep track of two mics simultaneously. Although that said, I've talked to one very good player who does it that way, and likes it because he can manipulate his sound and volume, based on the relationship of the accordion to its' microphone. But, that's what he grew up doing so he's used to it.
For my taste, a mic attached to the instrument is the only way to go.
The cheapest, easiest, and most authentic solution is to use the mic element from an old rotary dial phone. It sounds remarkable and with a simple piece of wood, a 1/4" jack, and two stainless steel snaps, you've got instant big sound and Cajun envy. All of these goosenecks and vocal mics make accordions sound like Stephen Hawking at a physics conference. Nobody wants to sit through that. There's a ton of rotary phone parts available on ebay for cheap.
I remember hearing that the old zydeco guys used carbon mics. But this is a good point Big - hard to imagine them also having the required carbon "phantom" supply required to make it work.
I use a large dynamic capsule inside my one row and three row. Sounds great - and it gives me the zydeco sound required for the music I play. Quite different from the cajun sound most people playing cajun music prefer.
I was reading in this discussion to see if I could find any information on those U shaped mounts some guys use on the front of their accordions. The fist I saw was Bois Sec Ardoin, but more recently I have been seeing Andre from lost Bayou ramblers using the same thing. I emailed Andre and he told me that it's the element from a Dynamic mic in there but I still don't get what those mounts are. Also in response to folks talking about using a Telephone element, you can take the earpiece and use that as microphone or you make a simple circuit with a 9volt battery. I was actually considering that myself having seen that done for Harmonica mics.