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


**Depends on implementation. The MOSFETs, of course, will
always sound like MOSFETs - dull, boring, undynamic and
compressed.

Sounds like more of the same "every amplifier sounds different religion
that Trevor has been entertaining many of with for years and years.

**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.


--
Trevor Wilson
www.rageaudio.com.au

"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.

On Wed, 4 Nov 2009 08:47:13 +1100, "Trevor Wilson"
wrote:

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.


Stop changing the subject. Either there is compression as you claim,
or there is not. Show me evidence of compression.

d

"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

"Don Pearce" wrote in message
...
On Wed, 4 Nov 2009 08:47:13 +1100, "Trevor Wilson"
wrote:

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.


Stop changing the subject. Either there is compression as you claim,
or there is not. Show me evidence of compression.

**I cannot. Try the test and let me know what you hear. Perhaps you will
have a different explanation. Negative tempco of gm is the only thing that
makes sense to me.


--
Trevor Wilson
www.rageaudio.com.au

On Wed, 4 Nov 2009 09:12:59 +1100, "Trevor Wilson"
wrote:


"Don Pearce" wrote in message
...
On Wed, 4 Nov 2009 08:47:13 +1100, "Trevor Wilson"
wrote:

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.


Stop changing the subject. Either there is compression as you claim,
or there is not. Show me evidence of compression.

**I cannot. Try the test and let me know what you hear. Perhaps you will
have a different explanation. Negative tempco of gm is the only thing that
makes sense to me.

We are discussing one single parameter - compression. Once you start
with nonsense like seeing what you hear, you are no longer able to
isolate that parameter - you hear the sum of everything. And of course
mixed in with your "just listen" thing is all your bull****tery with
terms like "more dynamic". This is meaningless drivel, and the
standard recourse of the charlatan trying to claim superior skills of
discernment to the average man. It won't wash. You made the claim, now
substantiate it or withdraw it.

d

"Pete"

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 ).

** Those are Hitachi's famous TO3 pack " lateral " mosfets as used in many
famous hi-fi and professional power amps.

They are extremely easy to use, exceptionally rugged and have NO issues
with biasing or bias stability. Plus they will share current automatically
when used in parallel.


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

bipolar
SAP15P and SAP15N
2SA1943 and 2SC5200

mosfet
2SK1530 and 2SJ201


** Those Toshiba numbers are NOT lateral mosfets at all - but switching
types with a low gate voltage threshold.

Such devices do not have any of the desirable characteristics of the Hitachi
laterals.

Biasing is a pig, thermal runaway is just itching to happen.


..... Phil

"Don Pearce" wrote in message
...
On Wed, 4 Nov 2009 09:12:59 +1100, "Trevor Wilson"
wrote:


"Don Pearce" wrote in message
...
On Wed, 4 Nov 2009 08:47:13 +1100, "Trevor Wilson"
wrote:

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.


Stop changing the subject. Either there is compression as you claim,
or there is not. Show me evidence of compression.

**I cannot. Try the test and let me know what you hear. Perhaps you will
have a different explanation. Negative tempco of gm is the only thing that
makes sense to me.

We are discussing one single parameter - compression. Once you start
with nonsense like seeing what you hear, you are no longer able to
isolate that parameter - you hear the sum of everything. And of course
mixed in with your "just listen" thing is all your bull****tery with
terms like "more dynamic". This is meaningless drivel, and the
standard recourse of the charlatan trying to claim superior skills of
discernment to the average man. It won't wash. You made the claim, now
substantiate it or withdraw it.

**I'm uncertain of what you are demanding I withdraw. Are you demanding that
I withdraw my theory that pertains to why MOSFET amps sound so bad? Or are
you demanding I withdraw what I and others hear?

Given the problems that many people hear with MOSFET amps, I proferred a
theory. I cannot validate that theory. If you have an alternate theory to
explain what people hear, then please present it.

As for claims of "superior skills of discernment", I make no such claims. My
hearing is just average. Anyone with average hearing will easily discern the
problems I speak of. I suggest you conduct your own test and confirm.
Perhaps you will develop a more credible theory.


--
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.