[sdiy] JX8P aftertouch circuit..

[Bob Weigel]

What am I missing here?.... I was getting some baseline modulation.  (IE 
you turn up the control for senetivity and begin hearing vibrato or 
whatever before you press.

Looking at the diagram and measuring...

pin 3 (non inv) of opamp varies from zero to 2.9V  as you move the 
slider.  That looks right since the slider is hooked to a voltage on one 
end, ground on the other and the sweep goes to pin 3

Pin 2 is connected to the 470 ohm resistor that goes tot he AT strip and 
all that is ok and the strip measures 8M to 9Kohm when you press hard.

Sounds....good.  A bit stiff though I think

Ok so pin 1 the output has of course... 2.9V when you turn it all the 
way up also since the circuit is just a inv amp with that 8M from the 
inv in to ground and some relatively negligable 15K feedback resistor 
:-).  So..yea I'd expect to see the 2.9V there and that we do!  CHeck!

And the problem is of course... there is only a diode between pin 1 
forward biased...and the ADC/MUX input.!

So yeah is the thing designed to give you a pre-pressure modulation?  
Has anyone else dealt with this?

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