[sdiy] Clipping summing opamp issue..

[Tom Wiltshire]

Alternatively, you could have a rotary switch to select different op- 
amp feedback resistors for different numbers of inputs.
Then you could just select "3 inputs" or "5 inputs" or whatever, and  
have the right amount of headroom in the mixer.

T.

On 27 Jan 2010, at 23:39, David G. Dixon wrote:

> 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?
>
> _______________________________________________
> Synth-diy mailing list
> Synth-diy at dropmix.xs4all.nl
> http://dropmix.xs4all.nl/mailman/listinfo/synth-diy