Buffer - problem with low headroom and nasty distortion

[Sacorus]

I built a simple dual buffer for a guitar with magnetic pickups and an active piezo system (graphtech) wired up to ring & tip.

Aim of buffer was to cut noise from y cables and connectors.


at 3/4 volume on the guitar, everything works, but once the signal gets hotter it clips the TL072 in an unpleasant way.  As the IC is socketed, i tried a 4558.  same problem 

Is my BIAS wrong? why no headroom on the buffers?

[slacker]

Yes your bias is wrong, you have the inputs biased to ground so you are clipping most of the negative part of the wave form. You need the inputs to be biased to half the supply voltage, which is 4.5 volts in this case. The easiest way to fix this on your existing layout would be to add 3M3 resistors from pins 3 and 5 to V+. This will put the + inputs of the opamp at 4.5 volts and it should work properly.

For more information have a look at the opamp examples here http://www.muzique.com/lab/buffers.htm

[Sacorus]

Will do.

I was trying to save on parts (those 2 resistors valued at $0.01c, what was i thinking )