if you mean http://www.pcpaudio.com/pcpfiles/proyectos_amplificadores/Vag/etapa.pdf
Than I think it has a fatal mistake at feedback network.
Too high order of high-pass filters in loop create a potential sub-audio oscillation.
One should use either a DC-opamp-servo or a DC stopper capacitor, but not both.
Than I think it has a fatal mistake at feedback network.
Too high order of high-pass filters in loop create a potential sub-audio oscillation.
One should use either a DC-opamp-servo or a DC stopper capacitor, but not both.
The potentiometers to adjust the zener diode currents are a bit strange. If this is an attempt to null the output offset voltage, I’d question its efficacy. The input long tail pairs are running a decent tail current (about 4.3mA) which is good, but the emitter degeneration is unnecessarily large – 47 ohms would be better than 470. Making them larger than that would do virtually nothing for linearity, but just unnecessarily sacrifices open loop gain. The VAS transistors are cascoded with a rather low Vce. With the large emitter degeneration resistors, this might excessively constrain the amount of current drive the VAS stages can deliver to the driver/output stage when the beta of the output pair drops off at high peak currents.
The time constant of the DC servo is rather small, the method of frequency compensation looks inadequate and the Vbe multiplier wiring is a definite no-no. If the wiper goes open circuit, so does the output stage. With these niggles addressed though, it should work all right.
Cheers,
Glen
The time constant of the DC servo is rather small, the method of frequency compensation looks inadequate and the Vbe multiplier wiring is a definite no-no. If the wiper goes open circuit, so does the output stage. With these niggles addressed though, it should work all right.
Cheers,
Glen
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