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DIY impedance adapters?
MUFF WIGGLER Forum Index -> Music Tech DIY  
Author DIY impedance adapters?
I'm looking to connect some contact mics to a field recorder and need a pair of impedance adapters so they sound decent. The only problem is the high to low adapters I can find I really don't like, such as the Hosa ones. They stick out way too far when plugged in which then once the mics are also plugged in will be putting quite a bit of stress on the recorder's connectors over time, as well as make the thing almost twice as long as it already is. So I want to try instead building a stereo impedance adapter box which I could then velcro onto the back of my recorder or onto a tripod.

Do I need anything more than just a transformer? I'm guessing a few resistors? Impedance is still one of these things which I get muddled about very quickly, but from what I understand these adapters are just a small transformer wedged into a connector casing. Any tips on what transformer to use (for values or particular models)? I'm guessing the adapters probably use compact custom winds- something small would be good but if I can fit a pair in a small project box thats small enough for me.
I'm assuming contact mics means piezos as it usually does. In that case google eg "piezo buffer" for solutions - the usual way of buffering very high impedance sources is to go active, and cheap & simple solution seems to be to use one or a couple of FETs (or a FET input opamp if you're prepared to hack together bipolar power) together with either a 9V battery or phantom power.

Eg. runs on phantom power if your recorder provides it.

It's worth noting that the cable will become a part of the equation, so ideally you'll want to buffer the piezo signal as close to the source as possible. So depending on how far from the recorder you're planning to mount the contact mics, it might make more sense to actually have the buffer box close to the mics and not close to the recorder.
How about a Radial PZ-DI or SB4?
I've looked at the Alex Rice preamp and thought about it. the nice thing with a passive solution is it won't drain my recorder's batteries so quick. I know there are 9v similar circuits too and if I go the active direction I figure I would just spring for something like a Fishman active endpin. I'm also curious if going the passive route makes any difference with the cable length and noise.

The Radial for a stereo pair would sound nice I am sure, but two of them costs more than my field recorder and is more than twice the size I would hope to have my passive box be.
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