Balanced piezo contact mic?

[Consul]

I'd like to build some piezo disc contact mics for sample collection in the wild, but the catch is I want to be able to plug them into a standard mic pre with +48v phantom power. I'm thinking the easiest solution would be an impedance matching circuit (I'll definitely need one of those anyway) that can be powered from phantom, but I'm not doing so well finding one at the moment. Any pointers to anything that might help? Thanks!

 

[Consul]

You know, I can't help but think that something as simple as a 10K/600 transformer would do the trick.

 

[Bryson]

http://www.alexrice.co.uk/content/projects/piezo_preamp.php

 

[Consul]

That's close to what I was thinking, but I need to go from unbalanced to balanced. I have an Edcor WSM10k/600 transformer handy, so I'll see if I can make it work.

 

[PRR]

Piezos don't drive transformers well.

The alexrice circuit WILL work. If you have a naked 2-wire piezo, run each wire to an input. This will reject buzz. Optionally add a grounded shield. If you only have a pre-made piezo configured unbalanced, drive one input relative to ground, and ground the unused input.

 

[Consul]

Well, I was really, really hoping I could avoid having to sort through a pile of FETs to match two of them, but if there's no other way...

Thanks, Bryson and PRR for the hand.

 

[chrlilje]

Hey

Came across this thread, and thought I would contribute another solution.

- Using two piezo elements sandwiched together, you get perfect balanced output.
I Have been using this for a while now, and it performs very very well.

I have written up a little guide to the wiring here:
http://christian.liljedahl.dk/guides/noise-free-piezo-microphone

Hope it will help others

Kind regards
Christian Liljedahl