R
RichD
Who do MOSFET sound better than bipolar, as an audio amp output
driver?
driver?
Who do MOSFET sound better than bipolar, as an audio amp output
driver?
RichD said:Who do MOSFET sound better than bipolar, as an audio amp output
driver?
Damon Hill said:They do? Seems like it's possible to design good amplifiers either
way.
--Damon
RichD said: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,
exhibit VASTLY more THD than BJTs.
Trevor Wilson said:**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.
RichD said:Who do MOSFET sound better than bipolar, as an audio amp output
driver?
Kevin said:Exactly - zero difference in quality capabilities. It's usually a
matter of impedance matching. Silicon transistors have a fixed loss
around 0.5 volts. MOSFETs have a resistive loss inversely proportional
to their voltage rating. That usually makes MOSFETs less expensive for
low impedances and transistors less expensive for high impedances.
Trevor said:**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.
Kevin McMurtrie said:That's nonsense.
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.
even incapacitate every radio within two blocks of your home then
violently explode. The circuits to drive MOSFETs and bipolars are a
little different.
Phil said:"Trevor Wilson"
"RichD"
** Same old red-herring BOLLOCKS from know nothing Wilson.
It is totally irrelevant how DEVICES behave on their own.
Only when they are properly configured and suitably biased in a
complimentary output stage can performances be compared.
operating at typical bias currents (say) 10-50mA, MOSFETs
** UTTER BOLLOCKS !!!
When configured in typical amplifier topologies, THD is vanishingly small at
all power levels and with minimal bias current.
This is true for LATERAL mosfets as made by Hitachi and Semelab ( ie 2SK176,
BUZ905 etc ).
Switching mosfets ( ie IRFPxxx etc) are not the same.
Kevin said:That's nonsense. MOSFETs have a lower voltage gain
Randy said:That may be true, but only because of the negative feedback that Trevor
referred to. The basic device IS more nonlinear.
Jorden said:The device properties of BJTs are superior to those of MOSFETs in all
respects,
except for offset - there MOSFETs have the advantage. Whether you
will actually hear this depends on many more factors.
Gareth said:Well this is probably an urban myth/load of bollocks, but years ago lots of
people were talking about power Mosfets exhibiting different distortion
characteristics than BJT's in the same way thermionic valves distort with
differening harmonics and sound nicer.
Fact or crapology?
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.
"Phil Allison"
No it's not.
That may be true, but only because of the negative feedback that Trevor
referred to.
The basic device IS more nonlinear.
Well this is probably an urban myth/load of bollocks, but years ago lots
of people were talking about power Mosfets exhibiting different distortion
characteristics than BJT's in the same way thermionic valves distort with
differening harmonics and sound nicer.
Fact or crapology?
Well in that case the OP's question is thus answered, as far as I can
tell.