[sdiy] simple class A bipolar power amps?

[Harry Bissell Jr]

Hi Anthony

--- anthony <aankrom at bluemarble.net> wrote:

> I suppose I could be overstating it a little bit,
> but I have never seen a 
> datasheet for a MOSFET claiming its intended use to
> be for high-end audio as 
> do the datasheets for both the 2SC3182 & 2SA1264.

I can't see what parameter would make them more
suitable for "high-end" audio than another transistor.

Essentially the ability to deliver power to a reactive
load would be desired.  Either MOSFET or Bipolar
could do that...

 
> I suppose I haven't sat down and compared several
> bipolar and MOSFET amps, 
> but the Alpine amp I had was better than both of the
> MOSFET amps that I've 
> had. I always understood that the main reason amp
> designers go for MOSFETs 
> is that they don't have the thermal runaway problems
> that bipolar 
> transistors do.

MOSFETS would have the advantage of ability to be
paralleled and have inherent current sharing without
emitter resistors (necessary waste of power...).
Beside
thermal runaway, they would deliver less current as
they get gotter so sharing is enhanced.

Often overlooked is that although they do not need
static current to drive the gates (as bipolar need for
the base)... but they need really high peak currents
for the gate capacitance...

> 
> I seem to recal readign somewhere that a true class
> A amp would have less 
> problems with thermal runaway than a typical class B
> design, but that could 
> be nonsense.

A real class A is just a heater for my house in
Michigan... I will not play music in the summer   ;^P

H^) harry