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Inverted vs. non-inverted OPAMP gain stages.

Started by armstrom, June 20, 2008, 01:15:06 PM

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armstrom

This may seem like a dumb question, but here goes... Is there any obvious difference (with regard to the quality/tone of the audio) between an inverted and non-inverted opamp gain stage?

I understand the technical differences such as the fact that non-inverted stages can't have a gain of less than unity and the fact that the output of an inverted opamp stage is out of phase with the input. But other than these technical differences, why would you choose one configuration over another? To me, it seems that setting a high input impedance on a non-inverted stage is easier since the impedance is set by the pull-down resistor rather than the series resistor before the inverted input.

Any thoughts?
-Matt

J M Fahey

There has been some discussion rolling about that very same subject, and, in theory, the inverting one was *Very* slightly better (in distortion but more importantly in noise figure) because you "kill" one of the input differential transistors, or, more precisely, ground its base (or gate, if a FET). Anyway, the consense was that the difference is practically inaudible, so, the choice becomes based more in architecture, such as: multi-input or channel mixers become easier with inverting stages (which provide a virtual-ground input) ;    and high impedance stages become easier to build with inverting op-amps, as you correctly suggested.