"Don Pearce" wrote in message
...
On Wed, 4 Nov 2009 08:32:19 +1100, "Trevor Wilson"
wrote:


"Don Pearce" wrote in message
...
On Wed, 4 Nov 2009 07:52:21 +1100, "Trevor Wilson"
wrote:


"Don Pearce" wrote in message
...
On Wed, 4 Nov 2009 07:06:02 +1100, "Trevor Wilson"
wrote:


"Pete" wrote in message
...
I am looking to build an amp for home theatre/hifi use.
currently have an amp using Hitachi's default design for mos fets
from
the
'80's ( 2sk49 2sj50 I think ). It is used with a tagmclaren av32r
and
ipl
acoustics tl4 speakers at the front and Ariston ( small black
tubular
things that sound quite good ) at the back.

I plan using LM4702 but have three options for the output stage.

bipolar
SAP15P and SAP15N
2SA1943 and 2SC5200
mosfet
2SK1530 and 2SJ201

I know I'm inviting WW3 but would there be any differance in sound
between
them ?

**Depends on implementation. The MOSFETs, of course, will always sound
like
MOSFETs - dull, boring, undynamic and compressed. The 2SA1943/2SC5200
devices are amongst the most advanced, lowest distortion output
devices
developed. The SAP15s are easy and convenient to implement, but you
run
the
risk of using a device unique to a single manufacturer. Once that
manufacturer deletes them from the product line-up, you'll be screwed
for
spare parts later on. Personally, I like the 2SA1943/2SC5200 devices,
Collectors coupled to the load.

Compressed?

**Yep.

You can of course produce a transfer characteristic to
back this up?

**Negative Tempco of gm.

As far as I am aware it is perfectly possible to produce
a MOSFET design without a trace of compression - which would of course
show up as an unimaginably huge distortion figure.

**What can I say? It what they sound like, when operating in low bias
Class
A/B. When operating in high bias Class A/B or Class A, they show no
signs
of
compression. At low currents, they suck. Ask anyone who has taken the
time
to do a double blind listen. I have. Many times. Shockers.

Negative tempco makes no difference. The gain of a power amplifier is
set by a pair of feedback resistors. Provided there is sufficient open
loop gain available (and we must assume there is) there can be no
compression. The system will perform at constant gain up to the
clipping point just like any amplifier.

I presume you are treating this as an interview for a job reviewing in
Stereophile?

**I doubt that. I have been critical of Stereophile many times. I have
also
performed several DBTs involving MOSFET amps and BJT amps. The first was
way
back when Perreaux first burst onto the scene with their MOSFET amps. I
wondered at what I was hearing, so I set up a Phase Linear 400 amp for
comparison. The Phase Linear was determined (not just by me) to be much
more
dynamic sounding. The only MOSFET amps I've heard which do not suffer this
problem are those manufactured by Pass Labs.

Tell me about your blind listening experiences with MOSFET amps and BJT
amps.

We're discussing compression, which can be measured objectively -
please don't try to divert the discussion onto the metaphysical. Show
me compression.

**DBTs are not metaphysical. They allow REAL differences to be heard. Tell
me about your experiences with DBTs between MOSFET and BJT amps.


--
Trevor Wilson
www.rageaudio.com.au

"Trevor Wilson" wrote

**DBTs are not metaphysical. They allow REAL differences to be heard. Tell
me about your experiences with DBTs between MOSFET and BJT amps.

I'd be interested to know how these DBTs were conducted. How many listeners
did you use?, how were they recruited, how much did they know about the
purpose of the test? etc.

David.

"David Looser" wrote in message
...
"Trevor Wilson" wrote

**DBTs are not metaphysical. They allow REAL differences to be heard.
Tell me about your experiences with DBTs between MOSFET and BJT amps.

I'd be interested to know how these DBTs were conducted. How many
listeners did you use?

**10. I arranged for a person who had no knowledge of which amp (he was no
present at set-up time) was which to throw the switch, whilst keeping a
record of which position the switch was in at each change. I set the
equipment up and was present for the test, but took no part.

, how were they recruited, how much did they know about the
purpose of the test? etc.

**They only knew that there might be a change in the system when the light
changed from green to red. The listeners were all those who considered
themselves to be audiophiles. They were not 'people off the street'. I was
already familiar with the listening preferences of each. They were tested in
groups of two, over a period of several days.

I performed the test, because I heard about these "new" (back in the early
1980s) MOSFET amps and how wonderful they allegedly were. I was surprised at
how bad they sounded, despite glowing reviews in places like Stereophile. I
decided to recruit others to see if their perceptions agreed with mine. They
did. All listeners reported similar findings. The MOSFET amps sounded
'compressed' and lacking in dynamics.


--
Trevor Wilson
www.rageaudio.com.au

In article , Trevor Wilson
wrote:

"David Looser" wrote in message
...
"Trevor Wilson" wrote

**DBTs are not metaphysical. They allow REAL differences to be heard.
Tell me about your experiences with DBTs between MOSFET and BJT amps.

I'd be interested to know how these DBTs were conducted. How many
listeners did you use?

**10. I arranged for a person who had no knowledge of which amp (he was
no present at set-up time) was which to throw the switch, whilst
keeping a record of which position the switch was in at each change. I
set the equipment up and was present for the test, but took no part.

So the person throwing the switch did know which choice (A or B) they had
made at each time? That means the result isn't double-blind. The point of
double blind is that *noone* involved in either running or taking the test
has *any* idea which - A or B - is being presented at the time.

Where was the 'switch'?

, how were they recruited, how much did they know about the
purpose of the test? etc.

**They only knew that there might be a change in the system when the
light changed from green to red.

Which "light" controlled how?

The listeners were all those who considered themselves to be
audiophiles. They were not 'people off the street'. I was already
familiar with the listening preferences of each. They were tested in
groups of two, over a period of several days.

I performed the test, because I heard about these "new" (back in the
early 1980s) MOSFET amps and how wonderful they allegedly were. I was
surprised at how bad they sounded, despite glowing reviews in places
like Stereophile. I decided to recruit others to see if their
perceptions agreed with mine. They did. All listeners reported similar
findings. The MOSFET amps sounded 'compressed' and lacking in dynamics.

Raw data of results? Statistical analysis and outcomes in terms of levels
of confidence, etc?

Which 'amps' did you try? What were the details of the level matching,
avoidance of clipping/saturation etc?

How did you establish the results *were* a basis for conclusions about one
form of transistor versus another rather than being a problem with some
specific designs or devices?

Given all the work, where did you publish the results? Since your results
seem to run contrary to all the published results I've seen - and I suspect
would have been welcomed by many 'subjective reviewers' I would expect them
to have been eager to have them published.

The problem is that you've only now given us your selected recollections.
Not the evidence anyone else would need to see if what you say stands up as
a conclusion.

Slainte,

Jim

--
Please use the address on the audiomisc page if you wish to email me.
Electronics http://www.st-and.ac.uk/~www_pa/Scot...o/electron.htm
Armstrong Audio http://www.audiomisc.co.uk/Armstrong/armstrong.html
Audio Misc http://www.audiomisc.co.uk/index.html

"Jim Lesurf" wrote in message
...
In article , Trevor Wilson
wrote:

"David Looser" wrote in message
...
"Trevor Wilson" wrote

**DBTs are not metaphysical. They allow REAL differences to be heard.
Tell me about your experiences with DBTs between MOSFET and BJT amps.

I'd be interested to know how these DBTs were conducted. How many
listeners did you use?

**10. I arranged for a person who had no knowledge of which amp (he was
no present at set-up time) was which to throw the switch, whilst
keeping a record of which position the switch was in at each change. I
set the equipment up and was present for the test, but took no part.

So the person throwing the switch did know which choice (A or B) they had
made at each time?

**They knew whether it was A or B, but not which amp was which.

That means the result isn't double-blind. The point of
double blind is that *noone* involved in either running or taking the test
has *any* idea which - A or B - is being presented at the time.

**True enough. I never claimed that the test was perfect.


Where was the 'switch'?

**In different room to the speakers systems being listened to.


, how were they recruited, how much did they know about the
purpose of the test? etc.

**They only knew that there might be a change in the system when the
light changed from green to red.

Which "light" controlled how?

**The light in the listening room.


The listeners were all those who considered themselves to be
audiophiles. They were not 'people off the street'. I was already
familiar with the listening preferences of each. They were tested in
groups of two, over a period of several days.

I performed the test, because I heard about these "new" (back in the
early 1980s) MOSFET amps and how wonderful they allegedly were. I was
surprised at how bad they sounded, despite glowing reviews in places
like Stereophile. I decided to recruit others to see if their
perceptions agreed with mine. They did. All listeners reported similar
findings. The MOSFET amps sounded 'compressed' and lacking in dynamics.

Raw data of results?

**Lost in the mists of time. The results were 100% anyway.

Statistical analysis and outcomes in terms of levels
of confidence, etc?

**The participants picked which amp was playing 100% of the time.


Which 'amps' did you try?

**Phase Linear 400(b) and Perreaux 2150.

What were the details of the level matching,
avoidance of clipping/saturation etc?

**I installed level pots in each amp and matched levels to within 0.1dB or
better. Prior to the testing, I used my CRO (Tek 465b) to ensure that the
amps never reached Voltage limiting with the music used for the test. The
main volume control was marked with a line and instructions that it always
remain below that line (Voltage limiting). In my prior testing, I found that
normal listening levels rarely exceeded 15 - 16 Volts RMS.


How did you establish the results *were* a basis for conclusions about one
form of transistor versus another rather than being a problem with some
specific designs or devices?

**I didn't, though I've noted (informally) that most (all?) Class A/B MOSFET
amps exhibit similar sonic issues to those I heard several decades ago.


Given all the work, where did you publish the results?

**It was for me and to prove a point to some of my sceptical clients. As you
have already discovered, the test was hardly rigorous enough to publish.

Since your results
seem to run contrary to all the published results I've seen

**Do they? Can you cite where a DBT was performed using a Phase Linear vs. a
Perreaux?

- and I suspect
would have been welcomed by many 'subjective reviewers' I would expect
them
to have been eager to have them published.

**Subjective reviewers tend to avoid DBTs.


The problem is that you've only now given us your selected recollections.
Not the evidence anyone else would need to see if what you say stands up
as
a conclusion.

**Indeed. Perhaps you may care to relicate my test?


--
Trevor Wilson
www.rageaudio.com.au

"Trevor Wilson" wrote

**They only knew that there might be a change in the system when the
light changed from green to red.

Which "light" controlled how?

**The light in the listening room.


Why a light? It's existence reduces the validity of your results. The
listeners should not only not know which amp is 'A' and which 'B'. They
should not know whether, at any given time, they are listening to 'A' or
'B'. Listeners will often give a preference when asked to compare 'A' to 'A'
or 'B' to 'B' because they think there *ought* to be a difference! Ideally
they should not even know that the test is a comparative test of amps
(rather than say sources or cables).

David.

In article , Trevor Wilson
wrote:

"Jim Lesurf" wrote in message
...
In article , Trevor Wilson


So the person throwing the switch did know which choice (A or B) they
had made at each time?

**They knew whether it was A or B, but not which amp was which.

That means the result isn't double-blind. The point of
double blind is that *noone* involved in either running or taking the
test has *any* idea which - A or B - is being presented at the time.

**True enough. I never claimed that the test was perfect.

But the above means that the test can't be established as blind. So the
results could easily be for reasons other than the one you asserted. i.e.
nothing to do with 'MOSFET' being any different to 'Bipolar' as classes of
o/p device. Thus your evidence isn't reliable as a basis for your belief.


Where was the 'switch'?

**In different room to the speakers systems being listened to.

No. I meant where in the experimental system?


, how were they recruited, how much did they know about the
purpose of the test? etc.

**They only knew that there might be a change in the system when the
light changed from green to red.

Which "light" controlled how?

**The light in the listening room.

Controlled *how*?

Raw data of results?

**Lost in the mists of time. The results were 100% anyway.

That has no assessable meaning without knowing how many times the test was
done, if the same material was used, conditions of tests, etc, etc.

Statistical analysis and outcomes in terms of levels
of confidence, etc?

**The participants picked which amp was playing 100% of the time.

Problems as above.

I could easily say "I spent 2 mins listening to one amp, then 1 min
listening to another. I could hear they were different. 100% right." Alas,
as evidence that would be worthless.

Are you not aware of the various proceedural and other flaws that can spoil
a test even when 'blind'? e.g. the flaws with the Stereophile tests they
did at a show some years ago?


Which 'amps' did you try?

**Phase Linear 400(b) and Perreaux 2150.

What were the details of the level matching,
avoidance of clipping/saturation etc?

**I installed level pots in each amp and matched levels to within 0.1dB
or better. Prior to the testing, I used my CRO (Tek 465b) to ensure
that the amps never reached Voltage limiting with the music used for
the test. The main volume control was marked with a line and
instructions that it always remain below that line (Voltage limiting).
In my prior testing, I found that normal listening levels rarely
exceeded 15 - 16 Volts RMS.

How did you establish that *current* limiting never occurred? My experience
with o/p fets from days of yore is that they were far more prone to this
than bipolars.

How did you monitor for any current limiting or clipping *during the
tests*? The problem here is that real-world speakers can be more demanding
of current that you might be aware when playing music.


How did you establish the results *were* a basis for conclusions about
one form of transistor versus another rather than being a problem with
some specific designs or devices?

**I didn't, though I've noted (informally) that most (all?) Class A/B
MOSFET amps exhibit similar sonic issues to those I heard several
decades ago.

Afraid that is an opinion, not assessable evidence.


Given all the work, where did you publish the results?

**It was for me and to prove a point to some of my sceptical clients. As
you have already discovered, the test was hardly rigorous enough to
publish.

Since your results
seem to run contrary to all the published results I've seen

**Do they? Can you cite where a DBT was performed using a Phase Linear
vs. a Perreaux?

Sorry. I thought you were claiming that *MOSFETS* sounded different as a
class of device to *Bipolars*. Are you now *only* saying that the Phase
Linear sounded different to 'a Perraux'?

So are you making no claim wrt this being a general result for the two
types of output device regardless of the choice of individual device type
or circuitry?

- and I suspect
would have been welcomed by many 'subjective reviewers' I would expect
them to have been eager to have them published.

**Subjective reviewers tend to avoid DBTs.

I wonder why? :-)


The problem is that you've only now given us your selected
recollections. Not the evidence anyone else would need to see if what
you say stands up as a conclusion.

**Indeed. Perhaps you may care to relicate my test?

You are offering to send me a Phase Linear and 'a Perraux' so I can do this
with no costs to myself?

If so, then I still would have some problems. One is that I can't
'replication your test' because you haven't actually defined all that was
involved and given me your raw data, etc so I could see if I could either
match what you did, or spot any flaws that would make a repeat pointless.
If I did the test differently, then I might not replicate your results for
that (unknown) reason.

Or are you asking me to (again) compare different amps using a better
defined method which might differ from the one you used?

If the latter, it is something I have done many times in past decades. The
results in general were that neither I - nor others I tried them on - could
relaibly tell one amp from another. i.e. they/I showed no ability to do so
with statistical reliability.

Only exceptions were when there was a measureable difference like one amp
was clipping/saturating or the gain levels or frequency response were
sufficiently different.

Yes, I did experiment with MOSFET amps. I found they worked OK provided you
could ensure the circuit drove them without allowing RF bursts, and you
kept within their limited current range. I preferred bipolars because I
personally found them easy to use, and they could provide large peak
currents, etc. So seemed to me more suited to real music.

And I'm afraid that these days I don't think it would be fair to do such a
test simply using my own ears. Afraid I am now too old for that to be
reliable. So I'd need to line up a set of listeners generally younger and
more alert than myself. Would you be paying for any of this?

Slainte,

Jim

--
Please use the address on the audiomisc page if you wish to email me.
Electronics http://www.st-and.ac.uk/~www_pa/Scot...o/electron.htm
Armstrong Audio http://www.audiomisc.co.uk/Armstrong/armstrong.html
Audio Misc http://www.audiomisc.co.uk/index.html

"Jim Lesurf" wrote in message
...
In article , Trevor Wilson
wrote:

"Jim Lesurf" wrote in message
...
In article , Trevor Wilson


So the person throwing the switch did know which choice (A or B) they
had made at each time?

**They knew whether it was A or B, but not which amp was which.

That means the result isn't double-blind. The point of
double blind is that *noone* involved in either running or taking the
test has *any* idea which - A or B - is being presented at the time.

**True enough. I never claimed that the test was perfect.

But the above means that the test can't be established as blind.

**Like I said: It was not a perfect test.

So the
results could easily be for reasons other than the one you asserted. i.e.
nothing to do with 'MOSFET' being any different to 'Bipolar' as classes of
o/p device. Thus your evidence isn't reliable as a basis for your belief.

**It is not a belief. The test was constructed in an attempt to verify what
I and others had already informally noted as having heard.



Where was the 'switch'?

**In different room to the speakers systems being listened to.

No. I meant where in the experimental system?

**At the speaker terminals of the amplifiers. The switches were relays.



, how were they recruited, how much did they know about the
purpose of the test? etc.

**They only knew that there might be a change in the system when the
light changed from green to red.

Which "light" controlled how?

**The light in the listening room.

Controlled *how*?

**By the person throwing the switch. He also controlled the lights. The
lights merely indicated a POSSIBLE change in amplifier.


Raw data of results?

**Lost in the mists of time. The results were 100% anyway.

That has no assessable meaning without knowing how many times the test was
done, if the same material was used, conditions of tests, etc, etc.

**I understand and have acknowledged the imperfect nature of the test.


Statistical analysis and outcomes in terms of levels
of confidence, etc?

**The participants picked which amp was playing 100% of the time.

Problems as above.

I could easily say "I spent 2 mins listening to one amp, then 1 min
listening to another. I could hear they were different. 100% right." Alas,
as evidence that would be worthless.

**Indeed. Except that the listeners were able to correctly identify each
amplifier perfectly.


Are you not aware of the various proceedural and other flaws that can
spoil
a test even when 'blind'? e.g. the flaws with the Stereophile tests they
did at a show some years ago?

**I am now, but was not then. If I were to perform a similar test today, I
would certainly be doing things very differently.



Which 'amps' did you try?

**Phase Linear 400(b) and Perreaux 2150.

What were the details of the level matching,
avoidance of clipping/saturation etc?

**I installed level pots in each amp and matched levels to within 0.1dB
or better. Prior to the testing, I used my CRO (Tek 465b) to ensure
that the amps never reached Voltage limiting with the music used for
the test. The main volume control was marked with a line and
instructions that it always remain below that line (Voltage limiting).
In my prior testing, I found that normal listening levels rarely
exceeded 15 - 16 Volts RMS.

How did you establish that *current* limiting never occurred?

**I didn't. In fact, when using the Quad ESL63 speakers (I also used KEF
104.2 speakers), I suspect that both amps would have experienced current
limiting at some point.

My experience
with o/p fets from days of yore is that they were far more prone to this
than bipolars.

**Indeed. However, the current limiting of MOSFETs has always tended to be
more benign than BJTs (depending on how the BJT current limiting is
employed).


How did you monitor for any current limiting or clipping *during the
tests*?

**No. As I previously stated though, I checked the music, prior to the test
with my CRO and did not note any significant issues. Yes, I am well aware of
how transient the nature of current limiting can be and, thus how current
limiting could have occured.

The problem here is that real-world speakers can be more demanding
of current that you might be aware when playing music.

**Indeed. OTOH, the KEFs were chosen for a couple of reasons. One is the
extensive use of Zobels throughout the crossover and the consequently
relatively smooth 4 Ohm load presented. The ESL63 was not as easy to drive.
In fact, the differences between the two amps was far more profound with the
Quads, than with the KEFs.



How did you establish the results *were* a basis for conclusions about
one form of transistor versus another rather than being a problem with
some specific designs or devices?

**I didn't, though I've noted (informally) that most (all?) Class A/B
MOSFET amps exhibit similar sonic issues to those I heard several
decades ago.

Afraid that is an opinion, not assessable evidence.

**Indeed. Hence the inclusion of the word: "informally".



Given all the work, where did you publish the results?

**It was for me and to prove a point to some of my sceptical clients. As
you have already discovered, the test was hardly rigorous enough to
publish.

Since your results
seem to run contrary to all the published results I've seen

**Do they? Can you cite where a DBT was performed using a Phase Linear
vs. a Perreaux?

Sorry. I thought you were claiming that *MOSFETS* sounded different as a
class of device to *Bipolars*. Are you now *only* saying that the Phase
Linear sounded different to 'a Perraux'?

**Nope. Those are the two amps I tested. I have not performed any tests
since. All listening has been done on a much more informal basis.


So are you making no claim wrt this being a general result for the two
types of output device regardless of the choice of individual device type
or circuitry?

**The measured performance of both amplifiers significantly exceeded the
limits of human hearing WRT frequency response, THD, IMD et al. Both amps
had roughly similar power output capability. Certainly, the topology of both
amps is somewhat different, but the big differences lie in the use of
different technology output devices.



- and I suspect
would have been welcomed by many 'subjective reviewers' I would expect
them to have been eager to have them published.

**Subjective reviewers tend to avoid DBTs.

I wonder why? :-)


The problem is that you've only now given us your selected
recollections. Not the evidence anyone else would need to see if what
you say stands up as a conclusion.

**Indeed. Perhaps you may care to relicate my test?

You are offering to send me a Phase Linear and 'a Perraux' so I can do
this
with no costs to myself?

**Nope. Both amps are common and cheap.


If so, then I still would have some problems. One is that I can't
'replication your test' because you haven't actually defined all that was
involved and given me your raw data, etc so I could see if I could either
match what you did, or spot any flaws that would make a repeat pointless.
If I did the test differently, then I might not replicate your results for
that (unknown) reason.

**Fair enough.


Or are you asking me to (again) compare different amps using a better
defined method which might differ from the one you used?

**That would be a possibility. If you feel that it might be constructive to
do so.



If the latter, it is something I have done many times in past decades. The
results in general were that neither I - nor others I tried them on -
could
relaibly tell one amp from another. i.e. they/I showed no ability to do so
with statistical reliability.

**You have directly compared Class A/B MOSFET amps with Class A/B BJT amps?


Only exceptions were when there was a measureable difference like one amp
was clipping/saturating or the gain levels or frequency response were
sufficiently different.

**Sure.


Yes, I did experiment with MOSFET amps. I found they worked OK provided
you
could ensure the circuit drove them without allowing RF bursts, and you
kept within their limited current range. I preferred bipolars because I
personally found them easy to use, and they could provide large peak
currents, etc. So seemed to me more suited to real music.

**Indeed. In the early days, BJTs provided significantly more current for
much less money. Not so much today. MOSFETs capable of delivery large
currents are relatively cheap.


And I'm afraid that these days I don't think it would be fair to do such a
test simply using my own ears. Afraid I am now too old for that to be
reliable. So I'd need to line up a set of listeners generally younger and
more alert than myself. Would you be paying for any of this?

**Not a chance. If you are sufficiently motivated you will do what I did. If
you are not, then you won't.


--
Trevor Wilson
www.rageaudio.com.au

"David Looser" wrote in
message
"Trevor Wilson" wrote

**DBTs are not metaphysical. They allow REAL differences
to be heard. Tell me about your experiences with DBTs
between MOSFET and BJT amps.
I'd be interested to know how these DBTs were conducted.
How many listeners did you use?, how were they recruited,
how much did they know about the purpose of the test? etc.

In the end you've got to go to Australia to see Trevor prove his point. I've
been down this road with him before in his anti-loop-feedback days.

"Arny Krueger" wrote in message
...
"David Looser" wrote in
message
"Trevor Wilson" wrote

**DBTs are not metaphysical. They allow REAL differences
to be heard. Tell me about your experiences with DBTs
between MOSFET and BJT amps.
I'd be interested to know how these DBTs were conducted.
How many listeners did you use?, how were they recruited,
how much did they know about the purpose of the test? etc.

In the end you've got to go to Australia to see Trevor prove his point.
I've been down this road with him before in his anti-loop-feedback days.

**Perhaps you missed my last post to you.

Here it is:

---
**I'll make it easy for you. Locate an old Phase Linear 400(b) and an early
Perreaux amp. Set up a DBT between the two and ask the listeners what
differences they feel they can hear (if any). Let me know what results you
find. Both amps are plentiful and cheap, so the test should be an easy one.
Both amps use ****-loads of global NFB, minimal bias current and primitive
topology so the only major differences are related to the output devices
used.

Take the time to listen for yourself. You might be surprised. I was.
---

Both amps were readily available in the US (and other places) and should be
very cheap and easy to obtain. No need to travel to Australia.

--
Trevor Wilson
www.rageaudio.com.au