[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]

"Kevin McMurtrie" wrote in message

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.

Been there done that.

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.

The low voltage rating takes this device out of consideration for serious
audio amps for home or professional use. It may or may not be up to snuff
for automotive use.

Try coming up with a relevant example - something that can take at least 100
volts.

Now I remember why I left this newsgroup.

I lack the time or bad judgment required to feel any remorse at all over
that. If you can't stand the heat - get out of the kitchen!

[MooseFET]

On Sep 18, 2:25*am, "Jorden Verwer" wrote:
RichD wrote:
Who do MOSFET sound better than bipolar, as an audio amp output
driver?

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.


Radiation hardness
Safe operating area
Bandwidth

[Arny Krueger]

"Phil Allison" wrote in message

"Kevin McMurtrie"


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.


** So you can use it to replace the engine starter relay
in a car.
Yawnnnnnnn ....

Actually, it is marginal even for that. Most automotive guys like devices
that are safe at higher voltages. However, the solar panel inverter guys
might love it to death.

[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

[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.

[MooseFET]

On Sep 18, 9:55*am, "Jorden Verwer" wrote:
Eeyore wrote:
Jorden Verwer wrote:
RichD wrote:
Who do MOSFET sound better than bipolar, as an audio amp output
driver?

The device properties of BJTs are superior to those of MOSFETs in all
respects,

How about SOA for one you UTTER MORON ?

Fine, fine, but that doesn't have any direct influence on what you'll hear,
because it's a boundary condition.

When I hear BLAM-FIZZZT-POP-KAPOW from an SOA problem, I gain and
understanding of how the SOA of a BJT is not better than that of a
MOSFET.


Do you even know what SOA is ?

Like I said, it's a boundary condition. It can influence the performance of
the circuit, but only indirectly, through other design decisions.

You can design around a problem with a device but that doesn't make
the device not have that problem.


except for offset - there MOSFETs have the advantage. Whether you
will actually hear this depends on many more factors.

YET MORE INSANE ********

Now you're being the moron (not that I admit to being a moron before). It
seems that either you don't know what you're talking about, or personal
attacks are a hobby of yours. Because, frankly, everything I said was
true...

Fact - MOSFETs have lower offset than BJTs.

How are you defining offset?


Fact - The fidelity of the sound depends on much more than just device
properties.

Yes a Class-C audio output sounds quite bad regardless of the type of
device used. It sure gets rid of that annoying hiss.

[Eeyore]

Spehro Pefhany wrote:

the renowned John Larkin wrote:
Kevin McMurtrie wrote:
"Arny Krueger" wrote:
"Eeyore" wrote in
Kevin McMurtrie wrote:
Damon Hill wrote:
RichD wrote in

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.

IR is famous for creating incredible specs, with tiny footnotes
retracting the wilder numbers. No TO-220 is going to last long at 300
watts; not many milliseconds.

John

Anything approaching 1600A would blow the leadwires off a TO-220. The
fusing current of a long wire of that cross-section area is only in
the 30-50A range. 100A-rated wire is around 6mm (1/4") in diameter.

Hence those ceramic power puks and the like.

Graham

[Arny Krueger]

"Eeyore" wrote in
message
Arny Krueger wrote:

"RichD" wrote

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

Who do? That's voodoo!

Only to be expected from Arny "Any amp with less than
0.1% THD at full power sounds the same as all other amps."

As usual, you're misrepresenting me.

Nonlinearity corresponding to 0.1% THD can be audible given choice of
musical program material. So, that number is way too high. Measurements
made at just one power level, like full power, are obviously bogus.

Obviously, the amp has to be able to perform within spec while driving a
real-world tough (but not badly designed) speaker load.

That all said, the world is full of good power amps. There are some bad
ones, too.

[MooseFET]

On Sep 18, 10:39*am, "Jorden Verwer" wrote:

[... BJTs are better ....]
As for offset, here's one explanation (in the context of opamps):http://en.wikipedia.org/wiki/Operati..._imperfections

Note that I never claimed that this is relevant in audio applications - but
it's there.

You may not have claimed it mattered but you sure implied it. That
aside since we are talking about the output section of an amplifier,
this sort of offset has no effect at all on the quality of the op-amp.

If you look for an op-amp with an extremely low offset voltage, you
will find that it uses MOSFETs to obtain that extreme low offset.



As for your personal attacks towards me, I should mention that I'm under the
impression that your experience with electronics outside audio applications
is fairly limited, given that you've apparently never heard of the term
offset.

[Eeyore]

Arny Krueger wrote:

"Eeyore" wrote
Arny Krueger wrote:

This whole "amp sounds better" stuff was fully debunked
30 years ago. Good power amps sound the same and they
sound like a piece of wire with gain.

There are tons of power amps that can't be distinguished
from a piece of wire with gain, while driving
well-designed speakers.

There are quite a few amps that meet the same criteria
while driving even the weirdest speaker load.

A really good power amp will destroy a poorly-designed
speaker before it starts sounding bad, and really good
power amps aren't all that unique.

The speaker is a large part of it. Highly reactive ( i.e.
lots of inductance or capacitance ) speakers can
prematurely trigger device protection.

Agreed. Speakers that require heroic amplifiers (heroic amps definitely
exist and are easy enough to obtain) are IMO not well designed.

We discovered that
EV's SX500 was particularly bad in this respect in PA for
example. Now that is certainly audible.

Agreed. However we have only part of the equation - the name of the
speaker. What was the amp?

With our own D Series amps. It was the only speaker we had trouble with. The VI
limiting was quite generous for a 4 ohm rated amp but not enough for an SX500. I
slackened off the VI protection and in the later AX series took a totally
different approach to protection.


The SX 500i EDS suggests that it might be a handful for weak-kneed amps. Its
impedance curve does go down to 4 ohms at several points below 1 KHz.

It's the phase angle that's insane more than the modulus of impedance. A D
series amp would drive 3 typical 8 ohm speakers in parallel quite happily.


http://www.electrovoice.com/documents/ev/sx500-eds.pdf

Using pairs paralleled can be a short road to amp problems.

In contrast, the sequel ZX-5 stays above 8 ohms over the same range:

http://www.electrovoice.com/document...X560PI_EDS.pdf

Needless to say, I have 4 ZX-5s. ;-)

A better choice I imagine. I didn't even like the sound of the SX500s, very
harsh and boxy.

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]

Arny Krueger wrote:

"Kevin McMurtrie" wrote in message

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.

The low voltage rating takes this device out of consideration for serious
audio amps for home or professional use. It may or may not be up to snuff
for automotive use.

Try coming up with a relevant example - something that can take at least 100
volts.

More like 230-250V !

Graham

[Arny Krueger]

"Eeyore" wrote in
message
Arny Krueger wrote:

"Kevin McMurtrie" wrote in message

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.

The low voltage rating takes this device out of
consideration for serious audio amps for home or
professional use. It may or may not be up to snuff for
automotive use.

Try coming up with a relevant example - something that
can take at least 100 volts.

More like 230-250V !

Well, yes, now that they are so easy to obtain.

I was trying to make things easy for him.

In fact we built a lot of pretty good power amps with 60-90 volt parts, back
in the day.

[Eeyore]

MooseFET wrote:

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

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.

Radiation hardness
Safe operating area
Bandwidth

Not too worried about the first of those but gimme loads of the next two !

Hmmm - turn-off time 60ns @ 4A. That's why it pays to drive them from a
complementary emitter follower stage. Just like SMPSs.

Graham

[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

[John Larkin]

On Fri, 19 Sep 2008 11:41:15 +0100, Eeyore
wrote:



Kevin McMurtrie wrote:

"Arny Krueger" wrote:
"Eeyore" wrote
Kevin McMurtrie wrote:
Damon Hill wrote:
RichD wrote in

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.

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.

These are NOT used in audio amps.

Learn something about LATERAL mosfets that were designed for audio. I've already
given part number and links to data sheets.

Graham


That doesn't really matter. The transfer function only needs to be
continuous so that you can close a loop around it, and the fet needs
to be able to stand the peak power dissipation. That can easily be
done with vertical "switching" type fets. A modern FLOOD architecture
[1] works great with most any kind of fet. Lots of things have changed
in the last few decades.

John

[1] Of course you've never heard the term before. I just invented it.

[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

[Don Pearce]

Eeyore wrote:

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



High gain bandwidth products are important for a good reason. If you can
keep device phase shifts well up in frequency, the dominant pole (I know
you didn't implement one specifically, but I'm sure it was still there)
can also move up in frequency. That means that global feedback will
carry on working instead of disappearing towards the top of the audio
band, at which point it has usually changed to local feedback in the
voltage amp, leaving output stage non-linearities uncorrected.

d

[MooseFET]

On Sep 18, 7:06*am, Vladimir Vassilevsky
wrote:
RichD wrote:
Who do MOSFET sound better than bipolar, as an audio amp output
driver?

In most cases, this is fallacy, and the result is just the opposite.
Reason: FETs have lower transconductance compared to BJTs. It is
impossible to build a half bridge stage with an ideal transfer curve.

However there are few special cases when a FET output stage has an
advantage:

1) With FETs, it is simpler to control bias current, because of the
negative dependency from the temperature. That simplifies the life.

Bewa Mosfets like the STW55NM60 have a decreasing threshold
voltage for increasing temperature. This means that biasing them to a
low idle current isn't so easy.

[Eeyore]

Arny Krueger wrote:

"Eeyore" wrote
Arny Krueger wrote:
"RichD" wrote

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

Who do? That's voodoo!

Only to be expected from Arny "Any amp with less than
0.1% THD at full power sounds the same as all other amps."

As usual, you're misrepresenting me.

It's not 'as usual' at all. I can clearly recall you making that claim.


Nonlinearity corresponding to 0.1% THD can be audible given choice of
musical program material.

I'm sure I've mentioned before I did a test when I thought the 0.1% spec was
pretty good against another amp with 0.01% (both bipolars). It was chalk and
cheese. The differences were NOT subtle. Nor were they 'level matching'
issues or whatever. It stood out like a sore thumb. One sounded 'gratey' the
other sounded 'clean'.

Since then a 0.01% spec is my minimum target. I like to get into the 0.00X%
area though.


So, that number is way too high. Measurements
made at just one power level, like full power, are obviously bogus.

I agree. As Chris Hornbeck has noted, low-level linearity is crucial.
Full-power specs are almost verging on the irrelevant but make good
advertising copy.


Obviously, the amp has to be able to perform within spec while driving a
real-world tough (but not badly designed) speaker load.

That all said, the world is full of good power amps. There are some bad
ones, too.

I'm not quite sure at the moment whether the overall trend is positive or
negative. It's certainly debatable.

Graham

[Eeyore]

Arny Krueger wrote:

"Eeyore" wrote
Arny Krueger wrote:
"Kevin McMurtrie" wrote in message

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.

The low voltage rating takes this device out of
consideration for serious audio amps for home or
professional use. It may or may not be up to snuff for
automotive use.

Try coming up with a relevant example - something that
can take at least 100 volts.

More like 230-250V !

Well, yes, now that they are so easy to obtain.

I was trying to make things easy for him.

In fact we built a lot of pretty good power amps with 60-90 volt parts, back
in the day.

That was a while back ! Even 2N3773s were good for 140V IIRC. I still have half
a tray of them somewhere from when I used to replace crap transistors with
something that would handle the job and not go phut.


Graham

[Eeyore]

John Larkin wrote:

Eeyore wrote:
Kevin McMurtrie wrote:
"Arny Krueger" wrote:
"Eeyore" wrote
Kevin McMurtrie wrote:
Damon Hill wrote:
RichD wrote in

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.

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.

These are NOT used in audio amps.

Learn something about LATERAL mosfets that were designed for audio. I've already
given part number and links to data sheets.

That doesn't really matter. The transfer function only needs to be
continuous so that you can close a loop around it, and the fet needs
to be able to stand the peak power dissipation. That can easily be
done with vertical "switching" type fets. A modern FLOOD architecture
[1] works great with most any kind of fet. Lots of things have changed
in the last few decades.

John

[1] Of course you've never heard the term before. I just invented it.

Fine. Can you elaborate some more on it ? Laterals have some truly lovely features
for audio. The only downside being a slightly highish Ron. Not really a problem when
(as I have) used as many as 6 in parallel (12 mosfets per channel / 24 per amp). They
also match beautifully with no need for source balance resistors (so some of the Ron
loss 'goes away').

Graham

[Eeyore]

Don Pearce wrote:

Eeyore wrote:
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).


High gain bandwidth products are important for a good reason. If you can
keep device phase shifts well up in frequency, the dominant pole (I know
you didn't implement one specifically, but I'm sure it was still there)
can also move up in frequency.

Yes, there was ultimately one after the initial pole-zero which as you know
helps keep phase response (and therefore margin) under control.


That means that global feedback will
carry on working instead of disappearing towards the top of the audio
band, at which point it has usually changed to local feedback in the
voltage amp, leaving output stage non-linearities uncorrected.

Interesting. In the distant past, I've toyed with seperate feedback paths from
both those points.

Graham

[Eeyore]

MooseFET wrote:

Bewa Mosfets like the STW55NM60 have a decreasing threshold
voltage for increasing temperature. This means that biasing them to a
low idle current isn't so easy.

Indeed. You'll need lossy ballast resistors. Laterals are different that
way.

Graham

[Fred Bartoli[_2_]]

Eeyore a écrit :

"Mr.T" wrote:

"Fred Bartoli" " " wrote

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.
But isn't that part of the problem, producing Mosfets with identically
symmetrical characteristics in N-ch and P-ch ?
Of course good circuit design can compensate for many such factors, so the
final result is what is important, not some evangelical belief, IMO.

Fred is thinking of push-pull transformer coupled arrangements. He needs to
advance about 4-5 decades.


Uhhh?

What I wrote is just basic maths.
Try a pencil and paper...

That's one reason I never call modern amps push-pull but complementary
symmetry instead.

Graham



--
Thanks,
Fred.

[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.

[Eeyore]

Fred Bartoli wrote:

Eeyore a écrit :
"Mr.T" wrote:
"Fred Bartoli" " " wrote

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.
But isn't that part of the problem, producing Mosfets with identically
symmetrical characteristics in N-ch and P-ch ?
Of course good circuit design can compensate for many such factors, so the
final result is what is important, not some evangelical belief, IMO.

Fred is thinking of push-pull transformer coupled arrangements. He needs to
advance about 4-5 decades.

Uhhh?

What I wrote is just basic maths.
Try a pencil and paper...

Try measuring one !

Graham

[Kevin Aylward[_3_]]

it.

Not at all in any remote way shape or form.
Don't you at least agree there are many similarities between 1/f
noise and offset?


Actually, I do. By and large, they amount to the same thing. Its all low
frequency variations. For example, if one designs a chopper amp to get low
offset, it also kills/corrects for 1/f noise as well. If one has 1/f
problems in an system, one immediately thinks about using a chopper..well I
do any way...


Kevin Aylward
www.anasoft.co.uk
SuperSpice

[Phil Allison]

"MooseFET"
Vladimir Vassilevsky


1) With FETs, it is simpler to control bias current, because of the
negative dependency from the temperature. That simplifies the life.

Bewa Mosfets like the STW55NM60 have a decreasing threshold
voltage for increasing temperature.


** Every switching MOSFET made has a negative gate threshold voltage tempco.

Equates to a VERY positive drain current tempco.

Many times more severe than a BJT.




...... Phil

[Kevin Aylward[_3_]]

RichD wrote:
On Sep 18, "Kevin Aylward" 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.

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.

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.

Do you have any experience designing audio amps?

er... yes...e.g.

http://www.studiomaster.com/1984%20-%201986.htm

"This was the amplifier pro sound companies were waiting for; many buy up to
100 units. "

Which did you use?

Right now I use a few, one of which is a studiomaster AX2500 (750+750),
which I did not design. I also have a Behringer 1280S mixer/amp, and a
Carlsbro (600+600) PA..and a.etc...etc...

Kevin Aylward
www.anasoft.co.uk
SuperSpice

[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

[Eeyore]

Eeyore wrote:

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

Oops THREE. I forgot Kevin Aylward.

Graham

[Kevin Aylward[_3_]]

Eeyore wrote:
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 ?


It has just occurred to me, that you probably live quite close to me. I
live in Stevenage now, just a tad away from the old Luton hunting grounds. I
would say a joint visit to the pub for some Guinness might not go amiss.

Oh.. check out my current venture. Available for
bookings...www.blonddee.co.uk


Kevin Aylward
www.anasoft.co.uk
SuperSpice

[John Larkin]

On Fri, 19 Sep 2008 15:28:33 +0100, Eeyore
wrote:



John Larkin wrote:

Eeyore wrote:
Kevin McMurtrie wrote:
"Arny Krueger" wrote:
"Eeyore" wrote
Kevin McMurtrie wrote:
Damon Hill wrote:
RichD wrote in

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.

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.

These are NOT used in audio amps.

Learn something about LATERAL mosfets that were designed for audio. I've already
given part number and links to data sheets.

That doesn't really matter. The transfer function only needs to be
continuous so that you can close a loop around it, and the fet needs
to be able to stand the peak power dissipation. That can easily be
done with vertical "switching" type fets. A modern FLOOD architecture
[1] works great with most any kind of fet. Lots of things have changed
in the last few decades.

John

[1] Of course you've never heard the term before. I just invented it.

Fine. Can you elaborate some more on it ? Laterals have some truly lovely features
for audio. The only downside being a slightly highish Ron. Not really a problem when
(as I have) used as many as 6 in parallel (12 mosfets per channel / 24 per amp). They
also match beautifully with no need for source balance resistors (so some of the Ron
loss 'goes away').

Graham


An opamp per fet, closing a local loop, feedback from the fet source,
makes each fet look like a perfect unity-gain, fast, zero-offset
device. Opamps are cheap, but fets and heat sinks are expensive. Power
all those gate-drive opamps from a DC-DC converter floating on the
output node; DC/DC bricks are cheap nowadays, too. Do a simple output
current limit for fast overloads and back that up with a digital fet
power dissipation simulation that provides the real protections. That
will optimize the hell out of the power supply, fets, and heat sink,
giving a lot more safe power for the buck, especially in
complex-signal non-sinusoidal apps like audio and NMR gradient
drivers.

Use a bunch of smaller fets rather than a few big ones; that speeds
things up and spreads the heat out across the heat sinks better.

For the audio version, use two "hot" heat sinks, with no insulators
under the fets.

Include full BIST. It's worth it for the savings in production test
alone.

The output stage will be so quiet and linear that no overall feedback
is needed or helpful.

The audiophools will hate this.

John

[Kevin Aylward[_3_]]

Eeyore wrote:
Kevin Aylward wrote:

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

This link seems to be bad. I did find this though

http://divinecables.co.uk/mains-powe...i-power-cable#

All I can say, is that I am still stunned..and shocked...shocked and
stunned...all I said was that I was taller than Jesus, not that I was bigger
than Jesus...


Kevin Aylward

[Eeyore]

Kevin Aylward wrote:

Eeyore wrote:
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 ?

It has just occurred to me, that you probably live quite close to me. I
live in Stevenage now, just a tad away from the old Luton hunting grounds. I
would say a joint visit to the pub for some Guinness might not go amiss.

Sounds ok to me. I'm in St Albans. Will contact you off group.


Oh.. check out my current venture. Available for
bookings...www.blonddee.co.uk

OK will do. I know someone who might even book you.

Graham

[Eeyore]

Kevin Aylward wrote:

Eeyore wrote:
Kevin Aylward wrote:

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

This link seems to be bad. I did find this though

Works here.


http://divinecables.co.uk/mains-powe...i-power-cable#

All I can say, is that I am still stunned..and shocked...shocked and
stunned...all I said was that I was taller than Jesus, not that I was bigger
than Jesus...

I'd like to start a movement to have all these liars and fraudsters shut down.

Graham

[Kevin Aylward[_3_]]

Eeyore wrote:
Kevin Aylward wrote:

Eeyore wrote:
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 ?

It has just occurred to me, that you probably live quite close to
me. I live in Stevenage now, just a tad away from the old Luton
hunting grounds. I would say a joint visit to the pub for some
Guinness might not go amiss.

Sounds ok to me. I'm in St Albans.

Yeah, just down the road...16.7M according to the AA. Although with a
suggested time of 20mins, obviously, the AA don't know how to drive...

Will contact you off group.

Look foward to it. My phone # is on my websites.



Oh.. check out my current venture. Available for
bookings...www.blonddee.co.uk

OK will do. I know someone who might even book you.

Oh.. nice...

Kevin Aylward