preamp for piezo transducer

I'm thinking about building a little preamp for an upright bass that has a piezo transducer built into the bridge. I'd like it to mount right on to the tailpiece so as to keep the transducer's signal as short as possible. I've got some Mellenia Media MM-990 opamps lying around so I think I'd like to use one and just make a fixed gain preamp running off 2? 9V batteries. Just thought I'd lay this on you guys to see if anyone could give me advice on if you think this is a good idea or not...
Best Regards,
Freddy :sam:

the 990'es will draw an awful lot of current from your batteries. For a piezo, you really need little or no voltage gain, but a rather high input impedance.

I'd use TL061/062's - they're low-current versions of TL071/072. Runs forever on a 9V-battery. Yes, they don't have the low dist and high GBP of the 990, but you can have all the gain in the feedback loop (x1 amplification), so it should behave just fine.

Use two 100K resistors to make a "virtual ground" between 0 and +9V. Connect this to the non-inv input through a signal load resistor, say 2.2MOhms. Connect your input signal to the the non-inv input as well, through a 100nF polyester capacitor. Connect out to inv.input. take output signal through a 10uF or so electrolytic capacitor (+ to the opamp output, you have +4.5V DC here now)...

Jakob E.

I would make a SF fet circuit. Use a >=10meg or greater gate R. Simple and low current if done right.

A source follower FET is a fine idea. The output from a piezo can be pretty hot, though, especially from an acoustic bass. You'll probabaly need to pad it down a bit with a series resistor between the piezo and the FET gate, say a 4,7 meg series resistor with a 4.7 meg bias resistor to start.

Maybe check out this schematic for DI type FET circuits:
http://www.jensen-transformers.com/as/as004.pdf

You could even run it off phantom if you wanted. (or had it avaliable.)

http://www.till.com/articles/GuitarPreamp/
I use this for my upright and have been very pleased with the results
I now can be heard in a live situation I use K and K piezo's and
was never to pleased with the dropout of some frequencies but this
quick little circuit does the trick. My next project for my bass though is to add
a three band eq and volume control using the circuit