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Old 2nd February 2005, 04:57 AM   #31
simon5 is offline simon5  Canada
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You couldn't bias each OPamp with some DC offset of like 1,5 V ?
Like in a class AB?
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Old 2nd February 2005, 05:47 AM   #32
Stocker is offline Stocker  United States
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HDTVman, I am not saying you are wrong, as I suspect you are right. I recall however one webpage explaining opamp use fundamentals; there was a class-B output stage on the opamp the fellow was using... the output went from horrible crossover distortion to <0.1% with a wire (follower) for feedback.

If you could avoid clipping, or exploding chips, it could work eh?!
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Old 2nd February 2005, 12:55 PM   #33
HDTVman is offline HDTVman  United States
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Quote:
Originally posted by Stocker
HDTVman, I am not saying you are wrong, as I suspect you are right. I recall however one webpage explaining opamp use fundamentals; there was a class-B output stage on the opamp the fellow was using... the output went from horrible crossover distortion to <0.1% with a wire (follower) for feedback.

If you could avoid clipping, or exploding chips, it could work eh?!
The problem is you are clipping as part of the design here. This is not at all like a discrete output stage. The design is being forced to be nonlinear at the 0 crossing because the + chip output can't go below some voltage greater than 0 volts, 1.5 v for example and the - chip can't go more + than -1.5 v. A 3 volt notch you can't avoid and the output can never be 0 volts.

With a class B amp stage at the 0 crossing no current flows and output voltage is 0 but as you start to turn on one of the transistors the voltage starts to increase. Yes you can help the nonlinearity of this type of output with feedback.

I would guess the page you refer to in the quote was using a single opamp in a more normal mode, and yes feedback could help a " Class B " output stage. The basic problem with the described circuit is that in reality it is not " Class B " but a push/pull "Class C " amp near "Class B".

BZ
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