Kevin Aylward wrote...
It worked out very well, Tony. Remember the schematic I sent you?
Personally, I think this type of method is a truly dreadful way to
design an amp. There are so many issues with it. The output devices
bias is completely undefined, unless it set to essentially zero.
With the crummy circuit in the gif, perhaps, but not with a sensible
circuit. In fact it's remarkably easy to define the class A current.
And control the crossovers, because one is using current-source mode
to drive the output, with drive circuitry pegged to the rails, rather
than an awkard floating bias circuit.
The transfer function is not well controlled or modelled, in addition
to poor hf response.
It has a well behaved transfer function, although the load figures in.
Which in the end may limit bandwidth, but allows good output linearity
and is especially well suited for current drive amplifiers.
In the case of Mark Alexander's current-feedback design (Analog Devices
AN-211), a much wider bandwidth was achieved than with common circuits.
Its really grungy, like finger nails down a blackboard sort of thing.
Those that use this type of circuit should be shot on sight, and have
their entrails thrown to the vultures.
Why don't you tell us how you really feel?
In general, putting an op amp in the feedback loop is bad news. It
justs gets you extra poles that you could avoid with a discrete
design.
Actually, not here, because with the opamp acts as a voltage-current
converter, via the opamp power-rail cascode transistors. The current
transfer function is determined by resistor ratios: the high-voltage
rail resistor, the opamp's output load resistor (and capacitor!), and
the Darlington output-transistor's emitter-degeneration resistor.
Right, Tony, it looked very bad.
Right, a beautiful addition suggested by Tony, nicely enhancing the
transfer function.