On 01/05/2014 03:29 AM, N_Cook wrote:
On 05/01/2014 07:53, Jeff Urban wrote:
I wanted to reply to this when you first posted it but I couldn't for
whatever reason. ****ing thing. As you can see I am not posting from
google, which I no longer capitalize !!!! LOL

Anyway, what characterizes ANY part for the transmission of audio is
linearity. Even though the gate of a MOSFET is driven wildly different
than the base of a BPT, linearity of gain fro the very small signal to
the very large signal is the prime. We used to look at the hfe and HFE
gain curves of bipolars in the old days, not it is different.

Any kinds of spurious **** like oscillations would be no good in
switcxhers as well. the thing is, switchers somethimes have a gain curve
that is like, made to be on or off.

An audio transistor must operate in the analog range, that means the
gain curve should be as flat as possible through the operating current
range.

The same is true of a MOSFET.


or on rereading . If an audio application can tolerate a certain amount
of cross-over distortion and general harmonic distortion then there is
no difference in powerfet useage type , up to some power level where
these distortions become too apparent.

I learned what I needed to know to rebuild a fried Ampeg SVT3Pro. 4 [ea]
irfp9240s 4 [ea] irfp240s. Will oscillate itself to death. Must use a
scope and a light bulb current limiter to detect sudden current surging
due to rf feeding back. I think Vishay has some linear application notes
for these MOSFETs. They can be biased for very tiny crossover notch, but
the spec is bias for 800ma at the AC mains with no signal. Not terribly
efficient. But it's a bass guitar amp.