MOSFET output stage
In article ,
"Trevor Wilson" wrote:
"RichD" wrote in message
...
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.
That's nonsense. MOSFETs have a lower voltage gain, more capacitive
load, and infinite DC current gain. If you swap your bipolar
transistors for MOSFETs and crank up the bias voltage, yeah, it will run
like crap because the local feedback gain is totally wrong. It might
even incapacitate every radio within two blocks of your home then
violently explode. The circuits to drive MOSFETs and bipolars are a
little different.
MOSFETs do not sound better than BJTs. At best, they can sound as good. All
things being equal.
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