[Fred Bartoli[_2_]]

Eeyore a écrit :

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.

With the required amount of feedback (which isn't rocket science - just good
design) they have no trouble meeting VERY low THDs such as one I designed with
0.0008% THD @ 1 kHz.

They sound better because of the predominance of 2nd harmonic distortion and
almost complete absence of 3rd and ditto up the range AIUI with even and odd
harmonics.


Uhhh.

Please explain how you obtain even distortion products from a
symmetrical (suppose paired mosfets) push-pull.

Any symmetrical function produces odd (and no even) harmonics.

:-) ...unless you used single ended output stages.


--
Thanks,
Fred.