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In Reply to: The Electro Voice A20C posted by Ralph on March 11, 2025 at 08:37:09:
That schematic is from EV. See link.
"It has no bias controls because at idle, it doesn't need them."
Class B devices idle at "off". The question is how "off" are they? If they are so off that it takes 1 volt positive to turn them on, that will be a major problem.
"You might want to read Bruno Putzeys' paper about feedback"
I've read it. You missed my point. You can have an output stage that has crossover distortion but with feedback it can look like it doesn't.
A Class B amplifier without feedback will (or other tricks), by definition, have discernible crossover distortion. Unless you use output devices that are perfectly linear all the way to cutoff....but they don't exist. Real world amplifying devices are very non-linear in the cutoff region.
Non-linearity can be masked by feedback but that doesn't mean that it doesn't exist.
It is much better to design a circuit that has the lowest distortion possible before applying feedback. What would mean only allowing the amplifying devices to operate in their "most linear part of the dynamic curve" and that brings us back to real Class A. Where the amplifying devices are biased to idle right in the middle of the "most linear part of the dynamic curve". Never allowed to operate in the non-linear cutoff or saturation regions. You might remember that we have had this conversation before.
Tre'
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- RE: The Electro Voice A20C - Tre' 10:21:29 03/11/25 (0)
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