[sdiy] Clipping summing opamp issue..

cheater cheater cheater00 at gmail.com
Thu Jan 28 14:56:39 CET 2010

Seconded. If you hear trouble, just attenuate more.

Either way it's a very good idea to select an input that will
overdrive in a nice, soft way, rather than going all zippy.

Another comment is that a waveshaper ain't that bad, it doesn't have
to sound ugly you know.


On Thu, Jan 28, 2010 at 13:22, Tom Wiltshire <tom at electricdruid.net> wrote:
> 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?
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