[sdiy] removing dc offset

[harrybissell]

I did not suggest this but I'll answer anyway.

If the thump is caused by turn on of power... you put a cap in series with the
output and a resistor to ground.  This will cause a AC spike what will settle
out
to ground. Add a relay in series with the FAR side of the capacitor...and do not

close it until you are sure the spike has had time to die down.  Maybe use a 555

timer that starts on power up.

I got the impression that this is not your case... it seems like the thump is
there
everytime you make the sound. This can be really hard to get rid of unless you
know
exactly when the sound will occur.

This can happen with some cheap circuits where the power is OFF whenever a
sound is not being produced...then the unit 'one shots' when triggered. So the
voltage might go from zero to 1/2 the supply with an AC wave riding it...and
back to zero.

If you can predict when the sound starts, you can generate an opposite DC offset

(dynamic) that will largely cancel the one from your circuit.

It will NOT be a simple toy anymore...

I had a similar problem with my guitar synth design. When there are no strings
playing, the waveforms do not go to zero, but to the peak value. This make a
huge thump in the VCF. Because I know when this will happen, I force the waves
to
zero (they are still at the peak but I am clamping them to ground).  You could
do similar...

H^) harry

gregory zifcak wrote:

> how would this work? can you explain it a little more?
> thanks,
> greg
>
> >
> >Ah, so you are worried about the thump, i.e. the sudden step in dc voltage,
> >not the dc itself.
> >
> >Perhaps a relay in series with the output would help, which is turned on
> >delayed?
> >
> >Ingo
> >