"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