On Thu, 18 Nov 2004 10:09:19 GMT, "Kevin Aylward"
wrote:


It's actually not a bad idea to have an opamp per output transistor,
if you do it right, which this guy clearly hasn't. I make a power amp
that uses 32 300-watt fets in the output (16 p-ch, 16 n-ch, +-200 volt
rails) and do just that.

Bloody hell. That's some amp, probably about 20KW out. This will
certainly kick the **** out of you at 50 Hz.

How did you get the opamp voltage rating, or was it a discrete one?


It's a transconductance amp, so the fet sources are at the rails
(through current-sense resistors) and the drains are the output. So
the gate-drive fets work on the +-200 power supply rails (with small
floating local supplies) and only need to swing enough to drive the
gates.

Nice thing here is that all 32 fet drains are common, so they are
bolted (actually clamped) to copper heat spreaders on the main
heatsink, without insulators.

So long as the loop is stable its ok.

Well, sure!

John