[sdiy] Clipping summing opamp issue..

[David G. Dixon]

I deal with it by not doing it!  I would (and do) plug the VCOs into a
mixer, which again is just an inverting summer, but with attenuating pots on
each input.  If you use 100k pots and have a 100k resistor in the opamp
feedback loop, then you will get unity gain at full pot rotation.  I often
find that I have to turn the pots way down when I'm summing a pile of
inputs.

> Suppose the following setup:
> 6 VCO's wave outputs wired to summing amp inputs.
> Each VCO has +/-5vpeak waveforms. (10vpp)
> At some points all VCO's will allign their
> peak levels all together.
> That means 6 X 5vpeak = 30vpeak (instantaneous)
> positive or negative.. doesn't matter here.
> This means clipping to me for normal summing
> opamps supplied to +/- 15vdc.. ??
> How do you guys manage this overvoltage situation?
> By reducing the summing gain of the receiving opamp?
> If so let's reduce the summing opamp to 50%.
> Then if sometime we receive only one wave form
> to this opamp it's gonna be attenuated at 50%...
> bad thing to me.
> Conclusion, to me a autovariable gain (compressor)
> summing amp would be neat here keeping a strong level
> but never clipping..
> What do you do in your projects to overcome this?