"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