Thursday, March 28, 2013
20 Watt Class A Power Amplifier Circuit
A single-ended Class-A amplifier is essentially one where there is only one active driven output device. The passive "load" may be a resistor, an inductor
(or transformer) or - as in this amplifier - a current sink. Of the
three basic options, the current sink offers the highest linearity for
the lowest cost, so is the ideal choice.
Some esoteric (some might say idiosyncratic) designs use inductors
or 1:1 transformers, but these are bulky and very expensive. Unless
made to the utmost standards of construction, they will invariably have a
negative effect on the sound quality, since the losses are frequency dependent and non-linear.
This amp uses the basic circuitry of the 60W power amp (see Index), but modified for true Class-A
operation - it should be pretty nice! This amp has been built by
several readers, and the reports I have received have been very
positive.
With simulations, everything appears to be as expected,
but although I have yet to actually build it and test it out
thoroughly, no-one has had any problems so far. Using /-20 Volt supplies - either conventional, regulated or using a capacitance
multiplier, it should actually be capable of about 22 W before
clipping, but expect to use a big heatsink - this amp will run hot.
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