[sdiy] Clipping summing opamp issue..

[Derek Holzer]

Agreed. In any system you need headroom. Just because you have +/- 15V 
doesn't mean you have to get as close as you can to it constantly! I use 
a DC mixer to combine four waveforms often, with the attenuators set at 
about 12 o'clock (50% with linear pots). The levels are still plenty 
strong when they get to my audio mixer (remember that synth level is +4 
dB from line level usually).

Any "autovariable" gain that would react fast enough to deal with these 
transient peaks wouldn't be a compressor, it would be a waveshaper--in 
other words a kind of distortion that would leave audible artifacts in 
your waveforms.

Best!
Derek

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?


-- 
::: derek holzer ::: http://macumbista.net :::
---Oblique Strategy # 134:
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