Using 2 chips to boost voltage handling
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 Chip Amps Amplifiers based on integrated circuits

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 2nd February 2005, 04:57 AM #31 simon5   diyAudio Member   Join Date: Nov 2004 Location: Québec, Québec You couldn't bias each OPamp with some DC offset of like 1,5 V ? Like in a class AB? __________________ DIYaudio for President !
 2nd February 2005, 05:47 AM #32 Stocker   diyAudio Member   Join Date: Dec 2003 Location: Austin 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?! __________________ Jesus loves you.
HDTVman
diyAudio Member

Join Date: Aug 2001
Location: Chicago area
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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