[Eeyore]

Kevin Aylward wrote:

Trevor Wilson wrote:
"RichD" wrote

Who do MOSFET sound better than bipolar, as an audio amp output
driver?

**Non-sequitur. If you're saying that MOSFET outputs sound better,
they don't.

As a device, operating at typical bias currents (say) 10-50mA, MOSFETs
exhibit VASTLY more THD than BJTs. Only when bias currents are
elevated (around 0.5A - 1A) do MOSFETs exhibit THD characteristics
which are almost as good as BJTs.

MOSFETs are very tough, have an exceptional ability to deliver high
power, high frequency audio (and RF), but distortion is very high.
They require lots of Global NFB in order to operate linearly.

MOSFETs do not sound better than BJTs. At best, they can sound as
good. All things being equal.

Ahmm.... welll....here we go...

Well, I like mosfet outputs because they are easier to design with, imo.
Bipolars, often need an equivelent of 3 stage darlingtons. This makes it a
tad harder to stabilse the feedback loop because of each stage pole.

Basically, you only need about 6 low current transistors, or so, to achieve
silly distortion and bandwidth figures, with mosfets.

As far as "sounds better", that's all moot. Any competently designed amp
should have thd, imd below audibility.

Seems to be a few that miss that though. Esp those Chinese copies of copies.


Anyone that claims that a general purpose PA amp, sounds bad or not good, if
it has thd and imd 0.005% and slew rates of 100V/us, is pretty much
delusional. Roll on the £200 oxygen free mains cable I say....

Why stop at £200 ? Oh !
http://www.asa.org.uk/asa/adjudicati..._ADJ_44177.htm

Kevin, you'd be just the guy to do a harmonic analysis of the distortion
spectrum of a properly biased bipolar vs lateral mosfet amp wouldn't you ? Any
chance ?

Graham