Re: Single-supply piezo-preamp circuit for e-guitar

From: Tony (tony_roe_at_tpg.com.au)
Date: 11/28/04


Date: Sun, 28 Nov 2004 20:53:58 +1000

On 27 Nov 2004 01:41:48 GMT, rolavine@aol.com (Rolavine) wrote:

>>From: seimens@gmx.ch (Simon Schneiter)
>
>>I've designed a circuit using single-rail supply, since the
>>A/D-converter requires the signal to be between 1V and 4V. I assumed
>>the peak output voltages of the piezo to be at +10V respectively -10V.
>
>I think your way too high there on your assumption, I've fed Piezo guitar
>pickups, both buffered and unbuffered into a mixer board, my guess is between 1
>volt and 100 mv max rms output.

Most would be in that range. To a large extent, the mechanics
determine the output from a piezo, but open circuit piezos can
occasionally reach as much as 10Vp-p. As a result, many designers opt
for 18V or even 36V batteries. But all that's really needed is a
regular hi-Z buffer with low voltage supply; because the piezo is a
capacitive source, one simply shunts it with a larger capacitor to get
the voltage swings under control (and at the same time, make it much
more tolerant of lower input impedances). This is generally a far
better solution all 'round than trying to handle very high voltages at
very high impedances. My new piezo buffer runs fine on 3 AA cells for
decent battery life (along with a DSP to do the "Variax" thing).

Tony
Tony (remove the "_" to reply by email)



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