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Old 10th February 2002, 12:25 AM   #1
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Default Hagerman's Vbe Multiplier

Anyone use or have comments, subjective or objective, on Hagerman's Vbe multiplier.


Its at the bottom of the page as a postscript file called 'Improved Vbe Doubler'
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Old 10th February 2002, 03:07 AM   #2
AKSA is offline AKSA  Australia
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Default Vbe Multiplier Circuit


I have seen this circuit and studied the explanation.

It is based on the industrial need for a consistent collector/emitter voltage across a range of currents, a situation which does not normally prevail in the biasing chain of a PP SS amplifier since the current through the voltage amplifier is close to constant, or at least, plus and minus about 10% (yea verily, even with a bootstrap!!).

In audio amps the Vbe multiplier contends with only minor current variation, but must compensate with considerable accuracy for temperature variation in the output stage. Base/emitter voltages in output and driver devices change widely over the temperature operating range, and this has profound effect on bias stability unless the Vbe multiplier is thermally coupled to and thus tracks this temperature. Bias stability is important in Class AB amps because it strongly influences the sonics and keeps the amp operating safely.

Thus the lengths Hagerman goes to are not strictly required in audio, but I suspect in industrial instrumentation this feature might be very useful.



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Old 10th February 2002, 10:47 PM   #3
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The Values for each part in his text are not readable.
can someone give them to me?
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Old 11th February 2002, 12:32 AM   #4
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I'd be happy with the values in circuit 2d.
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