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Old 1st April 2007, 06:49 PM   #1
tadiam is offline tadiam  Argentina
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Default class a amplifier opinion

see link

http://www.pcpaudio.com/pcpfiles/pr...s/Vag/etapa.pdf
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Old 1st April 2007, 07:08 PM   #2
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Default Re: class a amplifier opinion

Quote:
Originally posted by tadiam
see link

http://www.pcpaudio.com/pcpfiles/pr...s/Vag/etapa.pdf
see error 404
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Old 1st April 2007, 07:24 PM   #3
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if you mean http://www.pcpaudio.com/pcpfiles/pro.../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.
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Old 2nd April 2007, 07:07 AM   #4
GK is offline GK  Australia
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The potentiometers to adjust the zener diode currents are a bit strange. If this is an attempt to null the output offset voltage, Id 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
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Old 2nd April 2007, 12:04 PM   #5
tadiam is offline tadiam  Argentina
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thanks i search other best schema...i have an intuition of this....
rare values 0m5...no clear dates....
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