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"additional complexity"

Posted by Allen Wright (M) on January 30, 2007 at 07:27:53

In Reply to: Some of a PP amp's circuitry is balanced--the driver and output stages. posted by jeffreybehr on January 29, 2007 at 10:35:00:

Why should there be a need for any added complexity to provide balanced AND unbalanced inputs?

As one needs a balanced signal to drive the output tubes anyway, why not just supply enough gain and drive power in a single stage differential amp to do all the gaining and driving? This also gives balanced and unbalanced inputs with NO extra circuitry except a switch or soldered link!

Even if you want far more gain to allow for 30dB of NFB (not me!), then you just need one more double triode, also wired as a diff stage. This is still no more tubes than the classic Williamson amp but still retains the balanced and unbalanced input possibilities.

And if you don't want the speed and clarity of the cascode driver - then you would still have enough gain using two stages to run both stages as normal differential "non-cascodes" and avoid using the dreaded cascode. This then becomes the classic circuit recommended by H.L. Eisenson in his landmark book "tu-be or not tu-be" to be used in ALL modifications of P-P tube amps. But it won't, by actual test, sound anywhere as good as the single cascode stage.

I say KISS rules!

Regards, Allen

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