[RichD]

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


--
Rich

[Damon Hill[_2_]]

RichD wrote in news:b78fc9c2-fe9c-444c-8ac5-
:

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

They do? Seems like it's possible to design good amplifiers either
way.

--Damon

[Kevin McMurtrie[_2_]]

In article ,
Damon Hill wrote:

RichD wrote in news:b78fc9c2-fe9c-444c-8ac5-
:

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

They do? Seems like it's possible to design good amplifiers either
way.

--Damon

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.

--
Google is a pro-spamming service. I will not see your reply if you use Google.

[Eeyore]

Kevin McMurtrie wrote:

In article ,
Damon Hill wrote:

RichD wrote in news:b78fc9c2-fe9c-444c-8ac5-
:

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

They do? Seems like it's possible to design good amplifiers either
way.

--Damon

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.

TOTAL AND COMPLETE GARBAGE.

[Arny Krueger]

"Eeyore" wrote in
message
Kevin McMurtrie wrote:

In article ,
Damon Hill wrote:

RichD wrote in
news:b78fc9c2-fe9c-444c-8ac5-
:

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

They do? Seems like it's possible to design good
amplifiers either way.

--Damon

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.

TOTAL AND COMPLETE GARBAGE.

Agreed. Actually, what Kevin said is the exact reverse of generally accepted
practical knowledge. Bipolar is generally more efficient when the impedances
get really low. MOSFETs were trendy for a while, but most new power amp
designs seem to have bipolar outputs.

[Kevin McMurtrie[_2_]]

In article ,
"Arny Krueger" wrote:

"Eeyore" wrote in
message
Kevin McMurtrie wrote:

In article ,
Damon Hill wrote:

RichD wrote in
news:b78fc9c2-fe9c-444c-8ac5-
:

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

They do? Seems like it's possible to design good
amplifiers either way.

--Damon

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.

TOTAL AND COMPLETE GARBAGE.

Agreed. Actually, what Kevin said is the exact reverse of generally accepted
practical knowledge. Bipolar is generally more efficient when the impedances
get really low. MOSFETs were trendy for a while, but most new power amp
designs seem to have bipolar outputs.

Time to check the specs for this decade. Visit IRF. You can get a
surface mount MOSFET in package similar to TO-220 that has 0.0008 Ohms
on resistance, 300W dissipation, 24V rating, and a 1600A surge rating.

Now I remember why I left this newsgroup.

--
Google is a pro-spamming service. I will not see your reply if you use Google.

[Tony[_11_]]

Exactly. I believe that even the very worst designers were generally able to get a
half-decent result with MOSFETs, whereas bipolars require a little more skill. So it may
well be that MOSFETs DO sound better in car audio, consumer-grade home theatre and cheap
"pro" sound systems, where the standards of the products and the designers are low.
Tony

On Wed, 17 Sep 2008 20:52:28 -0500, Damon Hill wrote:

RichD wrote in news:b78fc9c2-fe9c-444c-8ac5-
:

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

They do? Seems like it's possible to design good amplifiers either
way.

--Damon

[[email protected]]

On Sep 17, 6:12*pm, RichD wrote:
Who do MOSFET sound better than bipolar, as an audio amp output
driver?

--
Rich

MOSFETS HAVE WIDER BANDWIDTH ,less phase shift , lower odd harmonic
distortin. on and on.

[Arny Krueger]

wrote in message

On Sep 17, 6:12 pm, RichD wrote:
Who do MOSFET sound better than bipolar, as an audio amp
output driver?

MOSFETS HAVE WIDER BANDWIDTH ,less phase shift , lower
odd harmonic distortin. on and on.

Not in any relevant way for audio power amps.

[Eeyore]

Arny Krueger wrote:

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

MOSFETS HAVE WIDER BANDWIDTH ,less phase shift , lower
odd harmonic distortin. on and on.

Not in any relevant way for audio power amps.

The first two are highly relevevant in ANY circuit using NFB. Basic
stability criteria.

For Christ's sake has everyone except Phil's and my brain turned to jelly
overnight ?

Graham

[Chronic Philharmonic]

"Eeyore" wrote in message
...


Arny Krueger wrote:

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

MOSFETS HAVE WIDER BANDWIDTH ,less phase shift , lower
odd harmonic distortin. on and on.

Not in any relevant way for audio power amps.

The first two are highly relevevant in ANY circuit using NFB. Basic
stability criteria.

Only if the bandwidth and the phase margins are small relative to the target
audio bandwidth, which is unlikely.

[Eeyore]

Chronic Philharmonic wrote:

"Eeyore" wrote in message
Arny Krueger wrote:
wrote
RichD wrote:
Who do MOSFET sound better than bipolar, as an audio amp
output driver?

MOSFETS HAVE WIDER BANDWIDTH ,less phase shift , lower
odd harmonic distortin. on and on.

Not in any relevant way for audio power amps.

The first two are highly relevevant in ANY circuit using NFB. Basic
stability criteria.

Only if the bandwidth and the phase margins are small relative to the target
audio bandwidth, which is unlikely.

Modern audio amplifiers are expected to have a bandwidth far greater than 20kHz.
If not, you may experience slew limiting problems and associated THD and IMD
IIRC.

Yet another one totally out of date with modern practice.

Graham

[Kevin Aylward[_3_]]

Chronic Philharmonic wrote:
"Eeyore" wrote in message
...


Arny Krueger wrote:

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

MOSFETS HAVE WIDER BANDWIDTH ,less phase shift , lower
odd harmonic distortin. on and on.

Not in any relevant way for audio power amps.

The first two are highly relevevant in ANY circuit using NFB. Basic
stability criteria.

Only if the bandwidth and the phase margins are small relative to the
target audio bandwidth, which is unlikely.

Ahmmmm....

Lets say we are after a 50khz closed loop BW, i.e. so that there is
negligible loss at 20khz. Now suppose we are after silly distortion levels,
say , 0.005% at 20Khz. Typically this means large amounts of feedback, say a
minimum of 40db at 20khz, maybe up to 60db even. This means that we need
say, a loop unity gain bandwidth of say 5Mhz min. Now, if the Ft of a big,
high voltage high current, bipolar was say 50Mhz, which is a tad on the fast
side, its current gain would have dropped to 10, which aint so great.
Furthermore, it would be really pushing a 50Mhz ft transistor to get an
overall stable loop at 5Mhz., not forgetting that there will already be, by
design, a dominant pole rolloff, prior to the output stage.

Lets do some sums:

Cin of a bipolar ~= gm/2.pi.ft X re/RL, in emiter follower mode, i.e. Cin =
1/(2.pi.ft.RL)

For a 50Mhz bipolor this would be 800pf. at 4 ohms.

A mosfet, would be Cin ~= Cgs/(gm.RL), which at typically 1A/V and 600p,
would be Cin=125pf.

So, despite the much larger gm of a bipolar to back off its inherent large
Cbe in source follower mode, they still typically need much more high
frequency drive than mosfets. Furthermore, without additional buffering,
this larger capacitance kills the h.f gain of the class a main gain stage,
as already mentioned by Graham. Indeed, in the early 80s, such 50Mhz devices
were made from unobtainium.

There are a lot of other details, but I really don't have the time to go
into any more detailed technical design at the moment.

So... try putting full on voltage on a mosfet without a heatsink for a
while, then try that with a bipolar!.

And hopefully I haven't made any errors in my calcs;-)

Kevin Aylward
http://www.kevinaylward.co.uk/ee/index.html

[MooseFET]

On Sep 18, 7:40*am, Eeyore
wrote:
Arny Krueger wrote:
wrote
RichD wrote:
Who do MOSFET sound better than bipolar, as an audio amp
output driver?

MOSFETS HAVE WIDER BANDWIDTH ,less phase shift , lower
odd harmonic distortin. on and on.

Not in any relevant way for audio power amps.

The first two are highly relevevant in ANY circuit using NFB. Basic
stability criteria.

For Christ's sake has everyone except Phil's and my brain turned to jelly
overnight ?

Checking brain ..... Mashed potatoes detected

Mine hasn't.



Graham

[Arny Krueger]

"Eeyore" wrote in
message
Arny Krueger wrote:

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

MOSFETS HAVE WIDER BANDWIDTH ,less phase shift , lower
odd harmonic distortin. on and on.

Not in any relevant way for audio power amps.

The first two are highly relevevant in ANY circuit using
NFB. Basic stability criteria.

Yes, but we're talking about modern devices, not legacy devices. A ton of
very acceptable power amps were built with power devices with FT on the
order of a MHz. Every modern bipolar device designed for power amps that I
see has FT above 10 MHz.

I'm not saying that 100 KHz devices are optimal for audio, I'm saying that
in 2008, higher bandwidth than commonly available devices for audio power
amps is irrelevant.

[Eeyore]

Arny Krueger wrote:

"Eeyore" wrote
Arny Krueger wrote:
wrote
RichD wrote:
Who do MOSFET sound better than bipolar, as an audio
amp output driver?

MOSFETS HAVE WIDER BANDWIDTH ,less phase shift , lower
odd harmonic distortin. on and on.

Not in any relevant way for audio power amps.

The first two are highly relevevant in ANY circuit using
NFB. Basic stability criteria.

Yes, but we're talking about modern devices, not legacy devices.

It's relevant regardless ALWAYS. "Basic stability criteria" as I said above.

Those Hitachi style lateral mosfets are STILL faster than any audio specific
bipolar. Plus no SOA issues.

Show me an audio bipolar that'll switch off in 60ns.

Graham

[Eeyore]

Arny Krueger wrote:

I'm not saying that 100 KHz devices are optimal for audio

Even early 2N3055s were 8x better than that.


I'm saying that in 2008, higher bandwidth than commonly available devices
for audio power
amps is irrelevant.

Plenty still have an fT of only 4MHz (published).

Graham

[MooseFET]

On Sep 18, 5:05*am, "Arny Krueger" wrote:
wrote in message



On Sep 17, 6:12 pm, RichD wrote:
Who do MOSFET sound better than bipolar, as an audio amp
output driver?
MOSFETS HAVE WIDER BANDWIDTH ,less phase shift , lower
odd harmonic distortin. on and on.

Not in any relevant way for audio power amps.

This is not true.

The phase shift in the output section of a power amplifier is a
significant issue. If you want to have much of a gain sacrifice
factor in the audio band, the gain cross over point will be well above
the audio band.

NFB can't make a silk purse out of a sows ear. It can only lower the
distortion by about the gain sacrifice factor. This makes if better
to start with a low distortion topology.

Rumors aside MOSFETs are not really easier to operate in parallel.
You still need emitter / source resistors.

[Phil Allison]

"MooseFET"

Rumors aside MOSFETs are not really easier to operate in parallel.
You still need emitter / source resistors.


** Which MOSFETS ????

Amazing how so many MOOSE like idiots have no idea there are TWO kinds
!!!!!!!!!!!!!!

The kind known as " lateral " share current just fine when in parallel in
LINEAR applications with no source ballast resistors.

Septic Tank Imbecile.





...... Phil

[Eeyore]

Phil Allison wrote:

"MooseFET"

Rumors aside MOSFETs are not really easier to operate in parallel.
You still need emitter / source resistors.

** Which MOSFETS ????

Amazing how so many MOOSE like idiots have no idea there are TWO kinds
!!!!!!!!!!!!!!

The kind known as " lateral " share current just fine when in parallel in
LINEAR applications with no source ballast resistors.

Septic Tank Imbecile.

It's quite clear that there are just TWO people in this thread who really
understand the use of lateral audio mosfets.

Graham

[Eeyore]

MooseFET wrote:

Rumors aside MOSFETs are not really easier to operate in parallel.
You still need emitter / source resistors.

Not needed for lateral mosfets ! It's a whole different ball game.

Graham

[Eeyore]

RichD wrote:

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

As a driver ?

Now if you said as an output stage it might make sense.

Graham

[RichD]

On Sep 17, Eeyore wrote:
Who do MOSFET sound better than bipolar, as an audio amp output
driver?

As a driver ?

Now if you said as an output stage it might make sense.

There's a difference?

--
Rich

[Eeyore]

RichD wrote:

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

As a driver ?

Now if you said as an output stage it might make sense.

There's a difference?

Damn right there is.

Graham

[RichD]

On Sep 18, Eeyore wrote:
Who do MOSFET sound better than bipolar, as an audio
amp output driver?

As a driver ?
Now if you said as an output stage it might make sense.

There's a difference?

Damn right there is.

I'm thinking of the bits that attach to the
copper thingy which loops around the
magnets which make the air move.

-
Rich

[Eeyore]

RichD wrote:

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

As a driver ?
Now if you said as an output stage it might make sense.

There's a difference?

Damn right there is.

I'm thinking of the bits that attach to the
copper thingy which loops around the
magnets which make the air move.

An unusual design but the copper thingy is very likely a heatsink, in
which case you're referring to the actual output devices. They in turn
usually have devices called 'drivers' which precede them, although it's
less necessary with mosfets, only for ultimate performance..

Graham

[Trevor Wilson[_2_]]

"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.

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


--
Trevor Wilson
www.rageaudio.com.au

[Phil Allison]

"Trevor Wilson"
"RichD"

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,


** Same old red-herring ******** 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
exhibit VASTLY more THD than BJTs.


** UTTER ******** !!!

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.



...... Phil

[Randy Yates]

"Phil Allison" writes:

"Trevor Wilson"
"RichD"

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,


** Same old red-herring ******** 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
exhibit VASTLY more THD than BJTs.


** UTTER ******** !!!

No it's not.

When configured in typical amplifier topologies, THD is vanishingly small at
all power levels and with minimal bias current.

That may be true, but only because of the negative feedback that Trevor
referred to. The basic device IS more nonlinear.

It comes down to device physics. MOSFETs, when operating in the
saturation region, have a square law relationship between Vgs and
Ids. It is only through either a) the application of negative feedback,
or b) the reduction of input level (the smaller the operating range, the
more approximating linear the Ids/Vgs relationship becomes) that the
device distortion is mitigated.
--
% Randy Yates % "Maybe one day I'll feel her cold embrace,
%% Fuquay-Varina, NC % and kiss her interface,
%%% 919-577-9882 % til then, I'll leave her alone."
%%%% % 'Yours Truly, 2095', *Time*, ELO
http://www.digitalsignallabs.com

[Randy Yates]

Randy Yates writes:

"Phil Allison" writes:

"Trevor Wilson"
"RichD"

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,


** Same old red-herring ******** 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
exhibit VASTLY more THD than BJTs.


** UTTER ******** !!!

No it's not.

When configured in typical amplifier topologies, THD is vanishingly small at
all power levels and with minimal bias current.

That may be true, but only because of the negative feedback that Trevor
referred to. The basic device IS more nonlinear.

It comes down to device physics. MOSFETs, when operating in the
saturation region, have a square law relationship between Vgs and
Ids. It is only through either a) the application of negative feedback,
or b) the reduction of input level (the smaller the operating range, the
more approximating linear the Ids/Vgs relationship becomes) that the
device distortion is mitigated.

PS: See, e.g., [gray] and [razavi].

--Randy


@book{gray,
title = "Analysis and Design of Analog Integrated Circuits",
author = "Paul R. Gray and Paul J. Hurst and Stephen H. Lewis and Robert G. Meyer",
publisher = "Wiley",
edition = "fourth",
year = "2001"}
@book{razavi,
title = "Design of Analog CMOS Integrated Circuits",
author = "Behzad Razavi",
publisher = "McGraw-Hill",
year = "2001"}

--
% Randy Yates % "So now it's getting late,
%% Fuquay-Varina, NC % and those who hesitate
%%% 919-577-9882 % got no one..."
%%%% % 'Waterfall', *Face The Music*, ELO
http://www.digitalsignallabs.com

[Eeyore]

Randy Yates wrote:

"Phil Allison" writes:

When configured in typical amplifier topologies, THD is vanishingly small at
all power levels and with minimal bias current.

That may be true, but only because of the negative feedback that Trevor
referred to. The basic device IS more nonlinear.

But when given suitable NFB, the transfer characteristic IS 'cleaner'. Very little
odd harmonic distortion (the nasty stuff) and very very low crossover distortion
(which makes a big difference).

I know, I've designed audio amps with both types. As in designed from the ground
up for commercial pro-audio sale.

Graham

[Phil Allison]

"Randy Yates"
"Phil Allison"

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

As a device,


** Same old red-herring ******** 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
exhibit VASTLY more THD than BJTs.


** UTTER ******** !!!

No it's not.


** Yes it is you pathetic, know nothing MORON,



When configured in typical amplifier topologies, THD is vanishingly small
at
all power levels and with minimal bias current.

That may be true, but only because of the negative feedback that Trevor
referred to.

** Bull.

The basic device IS more nonlinear.


** Irrelevant.

Can't you read - dickhead.



..... Phil

[Eeyore]

Phil Allison wrote:

"Trevor Wilson"
"RichD"

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,

** Same old red-herring ******** 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
exhibit VASTLY more THD than BJTs.

** UTTER ******** !!!

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.

Yes.

Just for fun once I configured a lateral mosfet output stage with zero feedback.
Its THD at almost all power levels was ~ 1%. From that you can get a good idea
of the negative feedback required to obtain any THD you like.

Lateral mosfets, correctly biased also exhibit virtually NO crossover
distortion. This is all but impossible with bipolars due to their inherent
transfer characteristics unless operated in pure Class A.

Graham

[Kevin McMurtrie[_2_]]

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.

--
Google is a pro-spamming service. I will not see your reply if you use Google.

[Trevor Wilson[_2_]]

"Kevin McMurtrie" wrote in message
...
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.

**Er, nope. Here are the specs for a modern high power BJT:

http://www.toshiba.com/taec/componen...c//66/7890.pdf

Note the hFE vs. Ic. Particularly at elevated temps. It is almost a straight
line, from less than 10mA to several Amps. I call that spectacular
linearity.

Now, I draw your attention to a high power MOSFET:

http://www.magnatec-uk.com/pdf/magnatec/BUZ900.pdf

Note the characteristics of this device. They're pretty good, but as good as
a modern BJT.

Here is another, older, worse example:

http://www.datasheetarchive.com/pdf-...SA-158541.html

Quite ordinary lineariy.

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.

**I never suggested anything of the sort. I mentioned ONLY the intrinsic
linearity of the devices. MOSFETs are inferior to BJTs. For now. When
installed in an appropriate topology, it is likely that there will be little
audible, nor measurable difference between a MOSFET amp and a BJT amp.
Device linearity is another story.

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.

**Again, not in dispute. The intrinsic linearity, is what I refer to.


--
Trevor Wilson
www.rageaudio.com.au

[Eeyore]

Kevin McMurtrie wrote:

That's nonsense. MOSFETs have a lower voltage gain

Mosfets are used as source followers in an audio output stage you inane idiot.

Voltage gain is NOT AN ISSUE, regardless of whether or not your statement is true.

Graham

[Eeyore]

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.

GRaham

[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.

[Eeyore]

Fred Bartoli wrote:

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.

If you're such an expert, built one and see for yourself. And use LATERAL mosfets
designed for audio.

TWIT.

Graham

[Fred Bartoli[_2_]]

Eeyore a écrit :

Fred Bartoli wrote:

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.

If you're such an expert, built one and see for yourself. And use LATERAL mosfets
designed for audio.

TWIT.


You don't need to build one. It's just basic maths that you don't seem
to grasp...

Oh, and vertical or lateral mosfets has nothing to do with that.


--
Thanks,
Fred.