[Patrick Turner]

While surfing around the web for
any decently measured THD or IMD measurements
carried out on pentode tubes, I came up wuth very little of interest
that at least I didn't know a lot about already.

There is more mention of triode THD and some about IMD.

Some of what i found was up to the standard of the 1950s
RDH4 examinations of THD and IMD, and basically nobody
has provided the well set out analysis
of a typical 6AU6 including the schematic,
and with levels of THD products from 2H to 10H
as they rise in level for the progressive rise of fundemental F.

So we really only know that THD and IMD exist in devices, and that
it all rises with output levels and load values.

But while looking around Google under 'pentode distortion measurements'
I came across a thesis drafted up by one Mr Daniel H Cheever, posted at

http://web.mit.edu/cheever/www/cheever_thesis.pdf

Here he talks about the increase in harmonic trash within a signal
caused by NFB.
You all thought NFB reduced the trash, but he has other ideas supported
by
his calculations and observations fairly well
presented.

But his conclusions must be considered in the context of his ideas
presented about the Total Aural Disconsonance figure of merit, or TAD.

Basically, he seems to be saying the sound we hear is distorted by the
ear which is a very non
linear microphone, but the brain filters the harmonics out, but where
an amp produces harmonics, ( or speakers, microphone, or other device
)then
unless the relationship of the harmonics relate
to what a brain does with harmonics, it affects the sound far more than
we think using accepted methods,
and an SET amp can thus sound a heck of a lot better than a high NFB amp
using bjts.

He has a lot of mathematics to proove his point, or tend to proove it at
least.

He cites samples of new tube amplifiers costing many thousands made by
CJ and others
where the use of loop NFB has been reduced drastically.

So what do people think about My Cheever's thoughts?

Patrick Turner.

[Eiron]

Patrick Turner wrote:

But while looking around Google under 'pentode distortion measurements'
I came across a thesis drafted up by one Mr Daniel H Cheever, posted at

http://web.mit.edu/cheever/www/cheever_thesis.pdf
snip
So what do people think about My Cheever's thoughts?

********, and illiterate ******** at that.
Apparently he got an MSc. for it!

--
Eiron.

[John Byrns]

In article ,
Patrick Turner wrote:

http://web.mit.edu/cheever/www/cheever_thesis.pdf

There's 87 pages in that thesis that must be read before one can form an
opinion. I wonder what Arnie thinks about all this. I wonder is the
"TAD" is the same "new" distortion testing methodology that was
discussed in this group a couple of years ago?


Regards,

John Byrns

--
Surf my web pages at, http://fmamradios.com/

[tubegarden]

Hi RATs!

Local in ear and head and body distortions becomes a 'known value' to
some of us. When modified by a cold or something, the world sounds
funny. Even beloved recordings on a favorite system become strange.

None of this matters to the meter readers. They think everything is
simpler than it sometimes appears and that everything important is
'out there'.

Some is. Some is 'in here' and some is 'not fully known'.

We fling cowpies at each other on newsnets and internets. It is jolly
good fun. What we think we know about what others' hear is the true
nonsense. We don't care We form opinions as we type them ...

Happy Ears!
Al

[Eeyore]

tubegarden wrote:

Hi RATs!

Local in ear and head and body distortions becomes a 'known value' to
some of us. When modified by a cold or something, the world sounds
funny. Even beloved recordings on a favorite system become strange.

None of this matters to the meter readers. They think everything is
simpler than it sometimes appears and that everything important is
'out there'.

It *is* simple. But complicated too ! ;~)

Graham

[Sander deWaal]

John Byrns said:


http://web.mit.edu/cheever/www/cheever_thesis.pdf


There's 87 pages in that thesis that must be read before one can form an
opinion. I wonder what Arnie thinks about all this. I wonder is the
"TAD" is the same "new" distortion testing methodology that was
discussed in this group a couple of years ago?


There has been some discussion about this thesis in the past.

The usual outcome: those who like tubes agreed with most of it, those
who loathe tubes disagreed with most of it.

--

- Maggies are an addiction for life. -

[Arny Krueger]

"Sander deWaal" wrote in message

John Byrns said:


http://web.mit.edu/cheever/www/cheever_thesis.pdf


There's 87 pages in that thesis that must be read before
one can form an opinion. I wonder what Arnie thinks
about all this. I wonder is the "TAD" is the same "new"
distortion testing methodology that was discussed in
this group a couple of years ago?

There has been some discussion about this thesis in the
past.

The usual outcome: those who like tubes agreed with most
of it, those who loathe tubes disagreed with most of it.

Typical of Sander's overly-confrontational approach to technology he can't
properly understand.

[Sander deWaal]

"Arny Krueger" said:

"Sander deWaal" wrote in message

John Byrns said:


http://web.mit.edu/cheever/www/cheever_thesis.pdf


There's 87 pages in that thesis that must be read before
one can form an opinion. I wonder what Arnie thinks
about all this. I wonder is the "TAD" is the same "new"
distortion testing methodology that was discussed in
this group a couple of years ago?


There has been some discussion about this thesis in the
past.

The usual outcome: those who like tubes agreed with most
of it, those who loathe tubes disagreed with most of it.


Typical of Sander's overly-confrontational approach to technology he can't
properly understand.


ROFL!!

That's why I design amps for a living, and you fix computers and work
on your "usenet career", hmmm? ;-)

--

- Maggies are an addiction for life. -

[Arny Krueger]

"Sander deWaal" wrote in message

"Arny Krueger" said:

"Sander deWaal" wrote in message

John Byrns said:


The usual outcome: those who like tubes agreed with most
of it, those who loathe tubes disagreed with most of it.


Typical of Sander's overly-confrontational approach to
technology he can't properly understand.

ROFL!!

That's why I design amps for a living, and you fix
computers and work on your "usenet career", hmmm? ;-)

You design amps for a living, Sander?

Do tell!

[Iain Churches]

"Sander deWaal" wrote in message
...
"Arny Krueger" said:


Typical of Sander's overly-confrontational approach to technology he can't
properly understand.


ROFL!!

That's why I design amps for a living, and you fix computers and work
on your "usenet career", hmmm? ;-)

--

Sander. I had a very similar confrontation with Arny on the subject of
classical music recording (which it what I do for a living) Discussion
regarding our relative skills ended abruptly when someone sent me
one of Arny's choir recording efforts. I did not know whether to
laugh or cry, and have not been able to take him seriously since
that moment.

I am sure he is very good at fixing second hand computers though
(but then so is my ten-year old nephew)

It would be interesting to see some of Arny's hombrew tube amps.
Hopefully he will post a link.

Iain

[Arny Krueger]

"John Byrns" wrote in message

In article ,
Patrick Turner wrote:

http://web.mit.edu/cheever/www/cheever_thesis.pdf

There's 87 pages in that thesis that must be read before
one can form an opinion. I wonder what Arnie thinks
about all this. I wonder is the "TAD" is the same "new"
distortion testing methodology that was discussed in this
group a couple of years ago?

The only "new" credible nonlinear distortion methodology I know of was the
work of Geddes and Lee.

http://www.aes.org/e-lib/browse.cfm?elib=12465

http://www.record-producer.com/learn.cfm?a=3651

http://forums.soundandvisionmag.com/...ssage.id=72717

http://www.gedlee.com/downloads/THD_.pdf

etc.

[Ian Bell]

Patrick Turner wrote:

While surfing around the web for
any decently measured THD or IMD measurements
carried out on pentode tubes, I came up wuth very little of interest
that at least I didn't know a lot about already.

There is more mention of triode THD and some about IMD.

Some of what i found was up to the standard of the 1950s
RDH4 examinations of THD and IMD, and basically nobody
has provided the well set out analysis
of a typical 6AU6 including the schematic,
and with levels of THD products from 2H to 10H
as they rise in level for the progressive rise of fundemental F.

So we really only know that THD and IMD exist in devices, and that
it all rises with output levels and load values.

But while looking around Google under 'pentode distortion measurements'
I came across a thesis drafted up by one Mr Daniel H Cheever, posted at

http://web.mit.edu/cheever/www/cheever_thesis.pdf

Here he talks about the increase in harmonic trash within a signal
caused by NFB.
You all thought NFB reduced the trash, but he has other ideas supported
by
his calculations and observations fairly well
presented.

But his conclusions must be considered in the context of his ideas
presented about the Total Aural Disconsonance figure of merit, or TAD.


For more recent work (2005) along very similar lines but with slightly
different conclusions see http://www.gedlee.com/distortion_perception.htm

Ian

[Phil Allison]

"Ian Bell"

But while looking around Google under 'pentode distortion measurements'
I came across a thesis drafted up by one Mr Daniel H Cheever, posted at

http://web.mit.edu/cheever/www/cheever_thesis.pdf

Here he talks about the increase in harmonic trash within a signal
caused by NFB.


For more recent work (2005) along very similar lines but with slightly
different conclusions see http://www.gedlee.com/distortion_perception.htm



** Meet the NEW load of ********...

Same as the old load of ********.


( Apologies to Pete Townshend )




........ Phil

[Ian Bell]

Phil Allison wrote:


"Ian Bell"

But while looking around Google under 'pentode distortion measurements'
I came across a thesis drafted up by one Mr Daniel H Cheever, posted at

http://web.mit.edu/cheever/www/cheever_thesis.pdf

Here he talks about the increase in harmonic trash within a signal
caused by NFB.


For more recent work (2005) along very similar lines but with slightly
different conclusions see http://www.gedlee.com/distortion_perception.htm



** Meet the NEW load of ********...

Same as the old load of ********.


( Apologies to Pete Townshend )


To be fair to the gedlee work, it is properly scientific, makes no
distinction between tubes and SS and did include a good sized sample of
double blind tests.

Ian

[Phil Allison]

"Ian Bell"
Phil Allison wrote:


But while looking around Google under 'pentode distortion measurements'
I came across a thesis drafted up by one Mr Daniel H Cheever, posted at

http://web.mit.edu/cheever/www/cheever_thesis.pdf

Here he talks about the increase in harmonic trash within a signal
caused by NFB.


For more recent work (2005) along very similar lines but with slightly
different conclusions see
http://www.gedlee.com/distortion_perception.htm



** Meet the NEW load of ********...

Same as the old load of ********.


( Apologies to Pete Townshend )


To be fair to the gedlee work, it is properly scientific, makes no
distinction between tubes and SS and did include a good sized sample of
double blind tests.


** The problems with it are to do with underlying assumptions and relevance.

It ain't relevant to anything in modern audio electronics.

( Save for a few wackos with SET amps maybe. )


BTW

I assume you got the Pete Townshend reference ;-)




...... Phil

[Patrick Turner]

Phil Allison wrote:

"Ian Bell"
Phil Allison wrote:


But while looking around Google under 'pentode distortion measurements'
I came across a thesis drafted up by one Mr Daniel H Cheever, posted at

http://web.mit.edu/cheever/www/cheever_thesis.pdf

Here he talks about the increase in harmonic trash within a signal
caused by NFB.


For more recent work (2005) along very similar lines but with slightly
different conclusions see
http://www.gedlee.com/distortion_perception.htm



** Meet the NEW load of ********...

Same as the old load of ********.


( Apologies to Pete Townshend )


To be fair to the gedlee work, it is properly scientific, makes no
distinction between tubes and SS and did include a good sized sample of
double blind tests.

** The problems with it are to do with underlying assumptions and relevance.

It ain't relevant to anything in modern audio electronics.

It would seem it is beyond Phil's abilities to constructively
point out the errors of Mr Gedlee and Cheever their entourage agents.
Merely claiming these guys are irelevant to electronics isn't enough
to substantiate shrill howls of ******** etc.

Patrick Turner.

( Save for a few wackos with SET amps maybe. )

BTW

I assume you got the Pete Townshend reference ;-)

..... Phil

[Arny Krueger]

"Phil Allison" wrote in message

"Ian Bell"
Phil Allison wrote:


But while looking around Google under 'pentode
distortion measurements' I came across a thesis
drafted up by one Mr Daniel H Cheever, posted at
http://web.mit.edu/cheever/www/cheever_thesis.pdf

Here he talks about the increase in harmonic trash
within a signal caused by NFB.


For more recent work (2005) along very similar lines
but with slightly different conclusions see
http://www.gedlee.com/distortion_perception.htm



** Meet the NEW load of ********...

Same as the old load of ********.


( Apologies to Pete Townshend )


To be fair to the gedlee work, it is properly
scientific, makes no distinction between tubes and SS
and did include a good sized sample of double blind
tests.


** The problems with it are to do with underlying
assumptions and relevance.
It ain't relevant to anything in modern audio electronics.

True, as it is pretty trivial to build electronics that are sonically
transparent.

Geddes and Lee's work does have application to loudspeakers, which are
Gedde's major area of interest.

[Patrick Turner]

The Score So Far,

one says
"********, and illitertate boolocks at that",

two asks,
" ..I wonder what Arnie says?"

three says
"we get weird sound when we get a cold and we type opinions as we type
them.."

four says
that the thesis favoured tube amps at the expense of SS amps,

five said
....."might explain why the empirically arrived at minimum level
necessary for 'undetectable distortion' changed dramatically when
transistors replaced tubes, though."
And five also said a lot of other things which proved he had more
understanding of what Cheever said
about ears, ear distortions and brains.

six said
"For more recent work (2005) along very similar lines but with slightly
different conclusions see
http://www.gedlee.com/distortion_perception.htm

I had a look at that but don't have time right now to read Gedlee's
1.6MB dissertation,


and seven said,
"** Meet the NEW load of ********...
Same as the old load of ********.
( Apologies to Pete Townshend )

Without immediately knowing what relevance Mr Townshend has,
I am at a loss to comment.



TAD, ot Total Audio Discononance is not to be confused with TID,
Transient Induced Distortion.



It seems to me Cheever tries to show that the ears will produce harmonic
voltages from the
hairs in the cochlea in your ear when a pure tone is used as a signal.
The brain he says, filters out the harmonics, and we hear the tone as
pure.

To me this defies common sense, because it implies the brain would do a
lot of filtering
with music or noise which is riddled with many harmonics.
Humans are notoriously erroneous creatures. God isn't perfect, let alone
understandable,
if we take a look at his creations over the millions of years or trial
and error.

But if Cheever is correct, and the brain does away with much of what the
ear microphones feed to it
then its easy to see how MP3 formatted sound gets away with it...

Anyone who has listened to the effects of clipping of clean sine wave in
an amp
would know what the threshold level is for THD of the tone; a 400Hz tone
seems to
suddently become "harder" sounding when the clipping becomes easily
visible on the CRO.
Pop music guitar players would say visibly undistorted sound is dull and
lifeless;
they set their levels so THD is 15% minimum most days...

But Cheever's treatise includes the effect of using NFB in an amp making
10% 2H, and this is not ******** at all; using say 8 dB of NFB around a
gain
stage with 10% THD with no NFB does not improove the sonics even though
the 2H is reduced a bit.

The phenomena of using a very mild amount of NFB, say 5dB to 14dB around
an amp with 10% open loop Dn
and its creation of other harmonics of a higher F has been well
documented in the past.

The past examiners of this phenomena have concluded that where open loop
THD was 10%, and there
was sufficient open loop gain present, ie, the amp wasn't clipping, and
still had considerable headroom
in its output and drive amp stages, then you simply need to apply a lot
more FB
and then all original open loop AND ARTIFACTS CREATED BY THE NFB are
reduced at a constant rate once NFB exceeded about
20dB, and this is shown in Cheever's graphs, if anyone here is able to
read a graph
by looking at it long enough.

Since many SS amps with NFB make THD 0.005% quite routinely at 1 dB
below clipping, and
perhaps 0.001% at say 2 watts, and that open loop THD at 1dB below clip
was 3% typically,
then just how does the ear and brain tell us something is drastically
wrong and make some listeners
go running to the shop for an SET amp?

Surely there have to be limits of audibility of distortion.
If it simply ain't there on the basis of it being totally inaudible if
played to listeners on its own
without the wanted undistorted sound, then how do we perceive the
distortion?

0.001% of say 4Vrms into 8 ohms, 2 watts, makes noise lower than an ant
walking
across the floor in front of the speakers.

I have heard music via SS amps which tend to make a noise similar to
people tearing up
paper in time with the music levels, but many SS amps just don't,
and are as clean as a whistle, so to speak, even clinically clean, too
darn clean in fact for
some listeners, and clean in an objectionable way compared to when they
listen to
a tube amp, which may measure 50 times worse, but nevertheless still
measure quite well with less than 0.04% THD for an SE amp,
and 0.02% for something PP.

I have found it quite easy to make a clean sounding SS amp, and several
that
sound ok when compared to class A tube amps of similar power ceilings
and
low THD at low levels used during continuous actual listening.

I could say that the use of very good passive filtering of rail supplies
in all the amps concerned leads to a clean sound, as well as a high% of
class A working
before the amp moves to class AB helps the NFB do its job.
In many SS amps the noise in the open loop signal is far greater than
the THD/IMD,
so much so that examining the output waveform on a CRO is marred with
hum levels,
even at high output levels.
Reducing the injected PS noise with careful filtering allows the open
loop
to actually be plotted and graphed.
Before NFB is applied many an SS amp then resembles
a giant phono amp which amplifies say 1mV of input to 25Vrms output at
100Hz with bandwidth rolling off
at 6dB/octave after some low F pole which can be as low as perhaps
100Hz.
The open loop response usually includes the local output stage emitter
follower NFB which equates to
typically 40dB of local loop series voltage NFB, ( the definition of the
variety of NFB is important ).
So the response and THD one sees is mainly that created by the class A
bjt input and driver stages.
And if anyone gets that to less than 3% at 25Vrms, they are doing well.
If they also have open loop bandwidth from say 20hz to 5kHz, they are
doing a lot better.

Having an open loop pole at 100Hz means that at if the global NFB is say
60dB at 100Hz, then at 1kHz, its 40 dB,
and at 10kHz its 20 dB, and by 100kHz, there is no effective NFB applied
because gain has dropped to unity.
Just as well, because we get stability more easily.

Its very easy to reduce the 3% of THD to 0.003% with 60dB of GNFB.
My view is that the this 60dB is more effective if there is a low amount
of noise in the signal to begin
with; the applied NFB has an easier task to perform, ie, cleaning out
the spuriae,
which if not cleaned out would leave things sounding worse, surely,
even if by some miracle, we could totally reduce PS noise,
and extend the open loop BW out to 20kHz?
Extending the open loop BW out to 20kHz isn't all that easy with bjts
because we'd have to use either global NFB around the voltage amp gain
stage/s
or have cascaded stages of gain each with its own local FB and when you
have
say 3 gain stages cascaded each not using much NFB, I cannot see how the
spuriae will not be better than if one simple effective GNFB loop is
applied around
ALL 3 cascaded stages.

Amplifiers without emitter follower output stages,
ie, common emitter outputs will have much more open loop THD,
and I cannot see how FB could be dispensed with at all, one other reason
being that
collector resistance like pentode anode resistance or drain resistance
in mosfets gives an amp
with output resistance far to high to be usable, and well above speaker
impedances.

Meanwhile, triodes are passable without any global NFB
and can operate in common cathode and still remain listenable,
and their internal NFB makes them able to have output resistance well
below speaker impedances.

A customer of mine maintains he prefers the sound
of a quad of 300B in PP for each channel without any GNFB.
The NFB is adjustable and he can make the comparisons easily
at the trun of a switch knob.

But we are stuck with distortion regardless of what we do, and the only
way
to avoid it is to attend live music, and where the instruments are NOT
amplified.

Nevertheless I'd swear I was at a concert when I listen to music from
the
local ABC Classic FM radio station here, despite the whole process of
recording onto a CD, replay, sending the signal to a satelite and back,
then encoding
it all to be able to re-constructed into stereo vi a multiplexed 100MHz
carrier,
in my humble all tubed FM tuner, which has switching diodes to create
the stereo,
and the less I tell you all about the process, the better.

My lounge room is never really the best seat in the theatre though,
mainly
because I'm at home, and not out, all dressed up for the occasion, with
friends,
and with the aura of the theatre and human togetherness affecting my
subjective senses.
But plenty of times my lounge room has brought me closer than the best
theatre seat ever could to a performer.
I have plenty of LPs recorded as far back as 1958 which
put me in the same studio room with the artists.

And this luxury is possible despite all that has been said about noise
and distortions.

Patrick Turner.

[Patrick Turner]

And in addition to what i said below, there was a brilliant series of
articles
in the 1978-1979 copies of monthly Wireless World on the way in which
low levels
of NFB can make the sound worse.
It was penned by one Peter Baxandall, his part 6 article appears in
Feb'79,
and has very similar graphs of the NFB effects on THD spectra as Mr
Cheever
has drawn, except that Baxandall's efforts look more plausible.
The math involved are at a level fit only for a masochist with lots of
time,
but Baxandall does manage to get the point across regarding applying NFB
and its effect on spectra in THD.
To avoid the worst of what Baxandall and Cheever are saying, it would
seem prudent to
ensuring open loop distortions before NFB is applied be kept well below
the
10% level they use in the examples for their analysis.

Fortunately, this is easily possible with triode amps, but
extremely difficult with any SS devices.

Patrick Turner.


The Score So Far,

one says
"********, and illitertate boolocks at that",

two asks,
" ..I wonder what Arnie says?"

three says
"we get weird sound when we get a cold and we type opinions as we type
them.."

four says
that the thesis favoured tube amps at the expense of SS amps,

five said
...."might explain why the empirically arrived at minimum level
necessary for 'undetectable distortion' changed dramatically when
transistors replaced tubes, though."
And five also said a lot of other things which proved he had more
understanding of what Cheever said
about ears, ear distortions and brains.

six said
"For more recent work (2005) along very similar lines but with slightly
different conclusions see
http://www.gedlee.com/distortion_perception.htm

I had a look at that but don't have time right now to read Gedlee's
1.6MB dissertation,

and seven said,
"** Meet the NEW load of ********...
Same as the old load of ********.
( Apologies to Pete Townshend )

Without immediately knowing what relevance Mr Townshend has,
I am at a loss to comment.

TAD, ot Total Audio Discononance is not to be confused with TID,
Transient Induced Distortion.

It seems to me Cheever tries to show that the ears will produce harmonic
voltages from the
hairs in the cochlea in your ear when a pure tone is used as a signal.
The brain he says, filters out the harmonics, and we hear the tone as
pure.

To me this defies common sense, because it implies the brain would do a
lot of filtering
with music or noise which is riddled with many harmonics.
Humans are notoriously erroneous creatures. God isn't perfect, let alone
understandable,
if we take a look at his creations over the millions of years or trial
and error.

But if Cheever is correct, and the brain does away with much of what the
ear microphones feed to it
then its easy to see how MP3 formatted sound gets away with it...

Anyone who has listened to the effects of clipping of clean sine wave in
an amp
would know what the threshold level is for THD of the tone; a 400Hz tone
seems to
suddently become "harder" sounding when the clipping becomes easily
visible on the CRO.
Pop music guitar players would say visibly undistorted sound is dull and
lifeless;
they set their levels so THD is 15% minimum most days...

But Cheever's treatise includes the effect of using NFB in an amp making
10% 2H, and this is not ******** at all; using say 8 dB of NFB around a
gain
stage with 10% THD with no NFB does not improove the sonics even though
the 2H is reduced a bit.

The phenomena of using a very mild amount of NFB, say 5dB to 14dB around
an amp with 10% open loop Dn
and its creation of other harmonics of a higher F has been well
documented in the past.

The past examiners of this phenomena have concluded that where open loop
THD was 10%, and there
was sufficient open loop gain present, ie, the amp wasn't clipping, and
still had considerable headroom
in its output and drive amp stages, then you simply need to apply a lot
more FB
and then all original open loop AND ARTIFACTS CREATED BY THE NFB are
reduced at a constant rate once NFB exceeded about
20dB, and this is shown in Cheever's graphs, if anyone here is able to
read a graph
by looking at it long enough.

Since many SS amps with NFB make THD 0.005% quite routinely at 1 dB
below clipping, and
perhaps 0.001% at say 2 watts, and that open loop THD at 1dB below clip
was 3% typically,
then just how does the ear and brain tell us something is drastically
wrong and make some listeners
go running to the shop for an SET amp?

Surely there have to be limits of audibility of distortion.
If it simply ain't there on the basis of it being totally inaudible if
played to listeners on its own
without the wanted undistorted sound, then how do we perceive the
distortion?

0.001% of say 4Vrms into 8 ohms, 2 watts, makes noise lower than an ant
walking
across the floor in front of the speakers.

I have heard music via SS amps which tend to make a noise similar to
people tearing up
paper in time with the music levels, but many SS amps just don't,
and are as clean as a whistle, so to speak, even clinically clean, too
darn clean in fact for
some listeners, and clean in an objectionable way compared to when they
listen to
a tube amp, which may measure 50 times worse, but nevertheless still
measure quite well with less than 0.04% THD for an SE amp,
and 0.02% for something PP.

I have found it quite easy to make a clean sounding SS amp, and several
that
sound ok when compared to class A tube amps of similar power ceilings
and
low THD at low levels used during continuous actual listening.

I could say that the use of very good passive filtering of rail supplies
in all the amps concerned leads to a clean sound, as well as a high% of
class A working
before the amp moves to class AB helps the NFB do its job.
In many SS amps the noise in the open loop signal is far greater than
the THD/IMD,
so much so that examining the output waveform on a CRO is marred with
hum levels,
even at high output levels.
Reducing the injected PS noise with careful filtering allows the open
loop
to actually be plotted and graphed.
Before NFB is applied many an SS amp then resembles
a giant phono amp which amplifies say 1mV of input to 25Vrms output at
100Hz with bandwidth rolling off
at 6dB/octave after some low F pole which can be as low as perhaps
100Hz.
The open loop response usually includes the local output stage emitter
follower NFB which equates to
typically 40dB of local loop series voltage NFB, ( the definition of the
variety of NFB is important ).
So the response and THD one sees is mainly that created by the class A
bjt input and driver stages.
And if anyone gets that to less than 3% at 25Vrms, they are doing well.
If they also have open loop bandwidth from say 20hz to 5kHz, they are
doing a lot better.

Having an open loop pole at 100Hz means that at if the global NFB is say
60dB at 100Hz, then at 1kHz, its 40 dB,
and at 10kHz its 20 dB, and by 100kHz, there is no effective NFB applied
because gain has dropped to unity.
Just as well, because we get stability more easily.

Its very easy to reduce the 3% of THD to 0.003% with 60dB of GNFB.
My view is that the this 60dB is more effective if there is a low amount
of noise in the signal to begin
with; the applied NFB has an easier task to perform, ie, cleaning out
the spuriae,
which if not cleaned out would leave things sounding worse, surely,
even if by some miracle, we could totally reduce PS noise,
and extend the open loop BW out to 20kHz?
Extending the open loop BW out to 20kHz isn't all that easy with bjts
because we'd have to use either global NFB around the voltage amp gain
stage/s
or have cascaded stages of gain each with its own local FB and when you
have
say 3 gain stages cascaded each not using much NFB, I cannot see how the
spuriae will not be better than if one simple effective GNFB loop is
applied around
ALL 3 cascaded stages.

Amplifiers without emitter follower output stages,
ie, common emitter outputs will have much more open loop THD,
and I cannot see how FB could be dispensed with at all, one other reason
being that
collector resistance like pentode anode resistance or drain resistance
in mosfets gives an amp
with output resistance far to high to be usable, and well above speaker
impedances.

Meanwhile, triodes are passable without any global NFB
and can operate in common cathode and still remain listenable,
and their internal NFB makes them able to have output resistance well
below speaker impedances.

A customer of mine maintains he prefers the sound
of a quad of 300B in PP for each channel without any GNFB.
The NFB is adjustable and he can make the comparisons easily
at the trun of a switch knob.

But we are stuck with distortion regardless of what we do, and the only
way
to avoid it is to attend live music, and where the instruments are NOT
amplified.

Nevertheless I'd swear I was at a concert when I listen to music from
the
local ABC Classic FM radio station here, despite the whole process of
recording onto a CD, replay, sending the signal to a satelite and back,
then encoding
it all to be able to re-constructed into stereo vi a multiplexed 100MHz
carrier,
in my humble all tubed FM tuner, which has switching diodes to create
the stereo,
and the less I tell you all about the process, the better.

My lounge room is never really the best seat in the theatre though,
mainly
because I'm at home, and not out, all dressed up for the occasion, with
friends,
and with the aura of the theatre and human togetherness affecting my
subjective senses.
But plenty of times my lounge room has brought me closer than the best
theatre seat ever could to a performer.
I have plenty of LPs recorded as far back as 1958 which
put me in the same studio room with the artists.

And this luxury is possible despite all that has been said about noise
and distortions.

Patrick Turner.

[Arny Krueger]

"Patrick Turner" wrote in message


To avoid the worst of what Baxandall and Cheever are
saying, it would seem prudent to
ensuring open loop distortions before NFB is applied be
kept well below the
10% level they use in the examples for their analysis.

Fortunately, this is easily possible with triode amps, but
extremely difficult with any SS devices.

False claim.

You just build the SS amp with enough local feedback to overcome the bad
design decision to avoid loop feedback. I've done it, and so can anybody
with reasonable circuit knowlege. A now-defunct Australian manufacturer
named I believe ME did it. It's not rocket science, just a waste of time,
effort, and good electronic components.

[TT]

"Arny Krueger" wrote in message
...
A now-defunct Australian manufacturer named I believe ME
did it. It's not rocket science, just a waste of time,
effort, and good electronic components.

I believe Peter Stein of ME Australia would take exception
to that statement. Not to mention Trevor Wilson when he
sees it ;-)

see http://www.me-au.com/

Maybe "hiatus" would have been a more appropriate
description than defunct ;-) He is in fact still
manufacturing and repairing.

Regards TT

[Patrick Turner]

Arny Krueger wrote:

"Patrick Turner" wrote in message


To avoid the worst of what Baxandall and Cheever are
saying, it would seem prudent to
ensuring open loop distortions before NFB is applied be
kept well below the
10% level they use in the examples for their analysis.

Fortunately, this is easily possible with triode amps, but
extremely difficult with any SS devices.

False claim.

You just build the SS amp with enough local feedback to overcome the bad
design decision to avoid loop feedback.

My claim was not false. The triode has NFB built in, and no external
LOCAL
or GLOBAL NFB is needed for a listenable outcome.

This is simply not possible with a solid state power amplifier
where you MUST use extensive local FB such as emitter follower
connection
and local current FB to linearize the signal.


I've done it, and so can anybody
with reasonable circuit knowlege.

But you must use external loop FB. You have never built a BJT based
amplifier
without some external loop NFB, such as the emitter follower connection
et all.

I am saying this is not necessary with triodes. There is a distinction
and please do not misrepresent what i said.

I have nothing against NFB as such, and use it routinely and afaiac, in
the interests of better musical
performance.

A defunct Australian manufacturer
named I believe ME did it. It's not rocket science, just a waste of time,
effort, and good electronic components.

ME amplifiers used a large amount of NFB around two consecutive stages
each containing a few sub stages.
Have you analysed the ME schematics?

I repeat again, you cannot have a BJT based power amplifier
unless you use a lot of external NFB in the way the device is connected.

The drain or collector resistance is way too high just like
the anode resistance of a beam tetrode of pentode to allow amplifiers
without
a lot of NFB, usually 20dB at least if the devices are working in class
A.

Patrick Turner.

[Eiron]

Patrick Turner wrote:

To avoid the worst of what Baxandall and Cheever are saying, it would
seem prudent to
ensuring open loop distortions before NFB is applied be kept well below
the
10% level they use in the examples for their analysis.

Fortunately, this is easily possible with triode amps, but
extremely difficult with any SS devices.

Now you're just being silly.
There's no reason why a solid state amp shouldn't have linear gain
stages and low open-loop distortion.

--
Eiron.

[Arny Krueger]

"Eiron" wrote in message


Patrick Turner wrote:

To avoid the worst of what Baxandall and Cheever are
saying, it would seem prudent to
ensuring open loop distortions before NFB is applied be
kept well below the
10% level they use in the examples for their analysis.

Fortunately, this is easily possible with triode amps,
but extremely difficult with any SS devices.

Now you're just being silly.

Agreed. I remember when Pat could say sane things about SS.

There's no reason why a solid state amp shouldn't have
linear gain stages and low open-loop distortion.

Agreed that there is nothing that necessarily stops a SS amp from having low
distortion before loop feedback is applied. However, the steps you take to
reduce open loop distortion, reduce the effectiveness of loop feedback.

Loop feedback has a lot of benefits and no practical disadvantages when done
right. It may take a degree in engineering with a concentration in
electronics or control systems to know how to do it right. That stops many
basement diddlers.

[Patrick Turner]

Eiron wrote:

Patrick Turner wrote:

To avoid the worst of what Baxandall and Cheever are saying, it would
seem prudent to
ensuring open loop distortions before NFB is applied be kept well below
the
10% level they use in the examples for their analysis.

Fortunately, this is easily possible with triode amps, but
extremely difficult with any SS devices.

Now you're just being silly.
There's no reason why a solid state amp shouldn't have linear gain
stages and low open-loop distortion.

In fact SS amps have appalling open loop performance, high THD/IMD,
poor phase shift character, lousy bandwidth,
and lots of noise, and perhaps appallingly high output resistance.
NFB reduces all the defects by the amount of NFB used, and typically
its 60dB, so that where you see that THD = 0.005% at a db below
clipping,
without NFB the same amp makes THD = 5% at the same power.

I am speaking about the facts of the engineering.

I have led myself to think NFB allows devices to sing
the way they were meant to.

But I also allow that other reasoning about amplifier behaviour
is worth consideration, but I am not about to throw out known techniques
that appear to work fine
so far..


Patrick Turner.

--
Eiron.

[KeithR]

Patrick Turner wrote:


And in addition to what i said below, there was a brilliant series of
articles
in the 1978-1979 copies of monthly Wireless World on the way in which
low levels
of NFB can make the sound worse.
It was penned by one Peter Baxandall, his part 6 article appears in
Feb'79,
and has very similar graphs of the NFB effects on THD spectra as Mr
Cheever
has drawn, except that Baxandall's efforts look more plausible.
The math involved are at a level fit only for a masochist with lots of
time,
but Baxandall does manage to get the point across regarding applying NFB
and its effect on spectra in THD.
To avoid the worst of what Baxandall and Cheever are saying, it would
seem prudent to
ensuring open loop distortions before NFB is applied be kept well below
the
10% level they use in the examples for their analysis.

Thats kind of interesting, I worked at the same establishment as Peter J in
the early 60s (I was an apprentice, he was THE senior circuit design
consultant). I met him on several occasions and went to a number of his
lectures. At that time he considered a good level of NFB to be essential,
his design for 10 watt EL84 amp published in Wireless World at the time
demonstrated this.

The advice that he gave then was to not bother too much about the amp, NFB
could get the THD low enough not to matter, put very big reservoir
capacitors in the PS to avoid power line droop on peaks (he was an organ
music fan), spend as much as you can on the cartridge and speaker (this was
mono days) because that is where most of your distortion is going to come
from.

Maybe he had a change of heart in his latter days, but when I knew him, the
application of NFB was the heart of his work.

[Patrick Turner]

KeithR wrote:

Patrick Turner wrote:


And in addition to what i said below, there was a brilliant series of
articles
in the 1978-1979 copies of monthly Wireless World on the way in which
low levels
of NFB can make the sound worse.
It was penned by one Peter Baxandall, his part 6 article appears in
Feb'79,
and has very similar graphs of the NFB effects on THD spectra as Mr
Cheever
has drawn, except that Baxandall's efforts look more plausible.
The math involved are at a level fit only for a masochist with lots of
time,
but Baxandall does manage to get the point across regarding applying NFB
and its effect on spectra in THD.
To avoid the worst of what Baxandall and Cheever are saying, it would
seem prudent to
ensuring open loop distortions before NFB is applied be kept well below
the
10% level they use in the examples for their analysis.

Thats kind of interesting, I worked at the same establishment as Peter J in
the early 60s (I was an apprentice, he was THE senior circuit design
consultant). I met him on several occasions and went to a number of his
lectures. At that time he considered a good level of NFB to be essential,
his design for 10 watt EL84 amp published in Wireless World at the time
demonstrated this.

The advice that he gave then was to not bother too much about the amp, NFB
could get the THD low enough not to matter, put very big reservoir
capacitors in the PS to avoid power line droop on peaks (he was an organ
music fan), spend as much as you can on the cartridge and speaker (this was
mono days) because that is where most of your distortion is going to come
from.

Maybe he had a change of heart in his latter days, but when I knew him, the
application of NFB was the heart of his work.


His methods for EL84 amps are just as valid now as they were in 1957.
Accountants in amplifier manufacturing companies never agreed with
people
like Baxandall if there was a cheap nasty way to do things and still be
able
to maintain high sales levels, and all companies reverted to lowest
common denominator crap.

He was right about carts and speakers, and this is still valid today.

In 1957, most speakers were 95dB efficent at 400Hz at least,
and needed little power to go loud.
So amplifier distortions were low, since 1/4 of a watt gave a very loud
89dB from each speaker at a watt, and distortion falls about
proportionately
to output voltage in a substantially class A amp, which nearly all 10
watt EL84 amps were in 1957,
such as the Leak 2020.

Carts varied, some were good, some attrocious, but the Denon MC103
invented in 1949
by Denon was pretty good, and is still good.
1957 speakers were universally crappy unless you were silver tailed and
could afford
ESL57.

Ever plotted a response from any mint condition dynamics from 1957?

I have, and all are quite attrocious. Science may have been very briefly
used to design them,
but during manufacture any semblance of conformity to the science used
in the design
was utterly abandoned, and the public was treated to eating ****
sandwiches for which
they paid a lot of money for. There is still plenty of rip-off right
now,
but in 1957, it was quite rampant, since it was an age of hope, and
fantasies
about purchasing satisfactions of desires for suburban consumeristic
bliss.
Realities shocked ppl, so they looked away.

The stereo Kreisler radiogram my mum bought for a queen's ransom in 1963
had
two 3 watt SE EL84 in pentode amps with
extremely poor circuitry, only 4 dB of NFB which didn't improve the
sound one bit, very inaccurate RIAA,
and the extremely poor Rola speakers were located at each end of the 5'
long floor standing cabinet.
The Rola speakers gagged when asked to make bass from the few new rock
and roll records
my sisters insisted in buying at my parents' great displeasure.
High levels of bass were rude and tasteless in 1957.
The speaker breakup and rising accoustic output when fed from what were
current source amps gave boost to lower and upper F to compensate
partially
for electronic response deficiencies.

The cabinet had a nice finish, and that was why mum was able to be
talked into buying it.
She could have bought a lot better, because she was married to my dad, a
professional man,
a vet, but he may have become upset anyway, because he had a terrible
temper,
and she needed to fear what reaction would occur if she spent too much.
Professional men knew that their wives could make life very financially
miserable without
very much effort in 1960. They earned, their wives spent.
Besides, my dad didn't like music, and couldn't dance.
Mum used to teach piano, and needed music, and why she married a bad
tempered musical clod like dad
remains a mystery. Maybe he was good in bed...
People were desperadoes by the dozen in the 1940s, they didn't wait, and
didn't think.

Buying a full set of Quad gear was simply right out of the question, and
was only for
judges and barristers and prime ministers, and was an utterly frivoulous
expense
because the value of hi-fi in most ppl's minds at the time was not high;
how could it be?,
because nearly everyone based their opinion of hi-fi on the utter
garbage they were being sold,
which was simply to extend simple mantle radio electronics into a
radiogram package.

People tried to buy a better looking lifestyle in 1957, or 63, whenever,
and only the really dogged types who were well educated knew of an
alternative
way of living. Some were condemned as being free thinking communists,
who shocked genteel
society by NOT immeditately marrying and settling down and buying what
was laid out for them
by Dodgy Bros entrepreneurs who only wanted one thing, their money.
I was one such shocking examples of the brash young men about, I waited
10 years before marrying,
and rejected most things others foolishly did, and it wasn't until
1976 I bought any hi-fi, a passable SS receiver. First TT was a Sansui
212, and with Shure M91ED MM.
I had lots of good parties with that lot. I have always built my own
speakers,
and have the pair I made 31 years ago, rebuilt twice now, but the bass
drivers are still wonderful.
The mids and trebs were quickly retired when I got some measuring gear
and some Vifa midranges in 1993.
The bass function sounds well if the response is curtailed to 250Hz,
anything higher as ppl did in 1970
sounded like strident mud, but ppl tried to not have to buy a good
midrange.
Bass surrounds for the 12" Foster bass drivers are woven cotton doped
with rubber, and have no signs
of deteriation. Its the only pair of speakers I have ever seen with such
a suspension system,
I must have spotted the superiority in '76 straightawy; I was an
observant young turk.
The two drivers cost $30 each, so about a weeks pay for the two, or
equal to spending $700 now.
It was worth it; you should have seen the other crap being sold!!!!
I went to a local district library in 1976 and copied the design for a
bass reflex
from RDH4, which I found on a shelf. When building anything, I thought,
study well first.
One needs a 3 way system for full range sound, IMHO.
If I had had more time in 1976, I'd have built my own tube amps. But I
was doubling the size of the house
I'd bought, and building all my own furniture. The silly young wife also
needed a fair amount of fixin,
so building amps as well all looked like too many ruined sundays, and I
had a reasonable wage,
and although most THOUGHTFUL ppl thought tubes were nice, they knew SS
could do near enough to what tubes did
if you didn't have the money or time....
The receiver was a 30W/ch Linear Design, I still have it but the Oz
company has gone broke a long time ago.
It cost $200 in 1976, but that was half the price of a supposedly better
Marantz receiver capable of the same power.
$400 in 1976 was about a month's pay, or equal to maybe $4,000 now, and
Marantz sure laughed all the way to the bank,
because by then Marantz were having things made very cheaply in asian
sweatshops.
I didn't like big business much either. **** Marantz is what i thought.
The 30 watts per ch was more than what I ever needed at a party, and
seemed like a lot of power then.
Neither myself or my friends were deaf.

Patrick Turner.

[Phil]

Patrick Turner wrote:


It seems to me Cheever tries to show that the ears will produce harmonic
voltages from the
hairs in the cochlea in your ear when a pure tone is used as a signal.
The brain he says, filters out the harmonics, and we hear the tone as
pure.

To me this defies common sense, because it implies the brain would do a
lot of filtering
with music or noise which is riddled with many harmonics.
Humans are notoriously erroneous creatures. God isn't perfect, let alone
understandable,
if we take a look at his creations over the millions of years or trial
and error.

But if Cheever is correct, and the brain does away with much of what the
ear microphones feed to it
then its easy to see how MP3 formatted sound gets away with it...

Our knowledge of how things work often leads, incorrectly, to
conclusions like, the "mind" turns the image on our retina around so
that we don't see the world "upside down." However, as infants, nothing
"told our brain" which side of our retina was up or down, so it simply
learned to perceive the world, correctly, when images of the sky landed
on what we KNOW, as adults, is the bottom of the retina. In the case of
pure tones, the ear sends a signal to the brain that includes harmonics,
but to our brain, that's what a pure tone sounds like! When we hear an
"impure" tone, our ears send different signals to the brain, and we hear
a difference, with no need -- and for that matter no way -- to "filter
out" the harmonics. Having never received a pure sine wave signal from
our ears, how would our brain "know" how to filter out anything? And why
would it want to? Is there a business where a company can brag that
"this brain filters out 99% of the ear's harmonics!"

In other words, we forget that as infants, our brain ADAPTED to whatever
signals our senses sent it, and those signals became standard, normal.
However, the idea that our brains ALWAYS hear harmonics makes it easier
to understand why harmonics don't bother people that much; instead of
hearing the difference between 0% and 5% THD, the signals to our brains
vary from, say, 5% to 7.2% THD (I think THD adds in an RMS manner, hence
the change of 7.2% instead of 10%), obviously a much less drastic change!

After a brief glance, it LOOKS like a good paper, the result of honest,
intelligent research, one worth using in amp design until either (1) you
find a better paper, or (2) you find various tricks and techniques that
add to and/or improve upon the techniques he proposes.

Phil

[Patrick Turner]

Phil wrote:

Patrick Turner wrote:


It seems to me Cheever tries to show that the ears will produce harmonic
voltages from the
hairs in the cochlea in your ear when a pure tone is used as a signal.
The brain he says, filters out the harmonics, and we hear the tone as
pure.

To me this defies common sense, because it implies the brain would do a
lot of filtering
with music or noise which is riddled with many harmonics.
Humans are notoriously erroneous creatures. God isn't perfect, let alone
understandable,
if we take a look at his creations over the millions of years or trial
and error.

But if Cheever is correct, and the brain does away with much of what the
ear microphones feed to it
then its easy to see how MP3 formatted sound gets away with it...

Our knowledge of how things work often leads, incorrectly, to
conclusions like, the "mind" turns the image on our retina around so
that we don't see the world "upside down." However, as infants, nothing
"told our brain" which side of our retina was up or down, so it simply
learned to perceive the world, correctly, when images of the sky landed
on what we KNOW, as adults, is the bottom of the retina. In the case of
pure tones, the ear sends a signal to the brain that includes harmonics,
but to our brain, that's what a pure tone sounds like! When we hear an
"impure" tone, our ears send different signals to the brain, and we hear
a difference, with no need -- and for that matter no way -- to "filter
out" the harmonics. Having never received a pure sine wave signal from
our ears, how would our brain "know" how to filter out anything? And why
would it want to? Is there a business where a company can brag that
"this brain filters out 99% of the ear's harmonics!"

Survival of the genes is a strong instinctive motivator.

Every natural urge is related to survival, and if brains filter audio
from the ears to get
a faster message with more meaning, then you know why; hearing something
quick leads to getting first
in a competitive world, so one learns to ignore noise, and probably
distortions.

But exactly how all that happens isn't my field of expertise and I ain't
an audiologist.
But I know the mechanism of hearing is complex, and unable to be
understood easily.
and exactly what happens to electrical nerve signals leaving the ear and
travelling to the brain
is quite beyond me.

But I'd suggest that just as many people have rather obviously variable
physiology,
they also have rather varying brain function and each sense we have
varies in ability
to the next person along.

I don't reject your assessment of what may happen in ppls heads above,
but it
would be hard for me to accept it all as text book knowledge either.

Cheever seems to say that harmonic nerve voltages are generated around a
pure tone that arrives at the ear.
The brain filters out the harmonics, and we know a pure tone when we
hear one,
or put it this way, when THD exceeds roughly 0.5% of 2H, we find the
impurity to be perceptible
in the middle of a scene where the brain has decided a tone is pure
after filtering out
ear generated harmonics.
So what tells a brain to do the filtering? some sort of FB network?

If Cheever is correct,( and he may well be complete ******** if some one
can proove it, )
then would you not think that the variablity in ppl's hearing would make
them
prone to picking up much varying threshold levels of THD?

So different blends of harmonics would be created in different
ppl's ears and filtered out variably in different brains.

I could never accept that ONE generic array of harmonics is generated by
all ppl.

Hence it would seem very difficult to use Cheever's TAD method
calibrated for
everyone, but suitable perhaps to no individual.

Where does he offer a ready made set of steps 1 to 10 to apply
to make amplifiers and transducers more faithfully present audio to our
brains?

For theories to be useful, they need to be applicable.

Some guys sitting around in cafes in 1933 were well on the way to
drawing up a future on table napkins for a world based on digital
information
transfer. But they saw many insurmountable obstacles that would delay
digital until about
1970, when fast large reliable devices became viable to make and use for
civilian productivity gains,
not just for appallingly wasteful and expensive military superiority.
BJTs were just terrific if left alone in vast numbers to count things,
1,00,1,1,1,00,00,1, and so on. Using tubes for this was stupid.


In other words, we forget that as infants, our brain ADAPTED to whatever
signals our senses sent it, and those signals became standard, normal.
However, the idea that our brains ALWAYS hear harmonics makes it easier
to understand why harmonics don't bother people that much; instead of
hearing the difference between 0% and 5% THD, the signals to our brains
vary from, say, 5% to 7.2% THD (I think THD adds in an RMS manner, hence
the change of 7.2% instead of 10%), obviously a much less drastic change!

And certain blends of harmonics have very different effects on us.
Related harmonics are what substantiate music, with a few bashes and
bangs and thumps added for
rythym, which sets the pulse racing, and makes the ladies hot to trot.
Music leads to dancing, and certainly drinking, then dancing leads to
inevitable sexual passions which overcome the fears of responsiblities,
and sex is had,
and love is a trip of falling helplessly, this is being human, and
reproducing.
But we spend many years away from being sexual, and we have spare time,
and some of us are
incredibly gifted with a sense of music that seems to come from nowhere,
but makes heroes
of people like Bach, Beethoven, Motzart, and many others, whose
arrangements of harmonics summon
up all sorts of deeper complex emotions well away from the simple
tom-tom
thrub of popular music and its primitive sexual dis-inhibitor function.

Pure tones are seldom heard in the natural world of sounds.
But occasionally somone pulls out a complex silver plated flute from a
leather bound case and we have
fairly pure tones, and we know it. Its magic. But where a japanese
master
reaches for his shakuhachi flute we know immediately what it is, and
isn't.
More magic.

Now if the sound of such instruments were to have the signature sound of
crossover distortions added to them,
many would hear the flutes as somewhat spoiled perhaps, and perhaps the
tiny % of SS crossover harmonics are much more
UNATURAL than the much greater added harmonics of the class A SET
amplifer.
Look how easy it is for so many ppl to so easily hear someone play a
slightly off key note.
If ppl have been to a primary school concert, there will be plenty of
off key events,
then less as the students become faster at adjusting frequencies
produced to match those around them.
off key need only be a few cycles per second, but we notice it severely.
One does not need to much 7H harmonic to be added into a C chord to make
the sound bad.
Of course we grow use to some harsh blends of harmonics. A saxaphone has
a very awkward blend.
Tom Waits tries to sing, and barely manages, but ppl buy his voice.

So ears and brains are extremely fickle in what they like or don't like.


After a brief glance, it LOOKS like a good paper, the result of honest,
intelligent research, one worth using in amp design until either

(1) you
find a better paper,

I keep an eye open even while i sleep. One never knows where some truth
may lie.
It's strange to say that truth lies, but initially it seems like it,
until we accept it.
Cheever's ideas seem to have no practical application, although probably
there is some truth somewhere in at least some of what he says about
brain interpretations of sound.

I am human, and have only my experience to guide me, and this includes
the
feedback i get from my clients for whom I have built amplifiers,
or occasionally built speakers, or re-engineered existing audio gear.

The present status quo of adhering to some pretty basic rules
such as maintaining 20hz to 20kHz BW, low THD/IMD at loud normal
listening levels,
low noise, and low amp resistance is not foolish, and leads to more
successes,
and few failures I can recall.

Intermodulation products are IMHO, the very worst products that can
become added to any audio signal.
THD is not itself a worry, since so many harmonics are present in music
that altering their relative levels
by a percent or two makes no detectable tonal change.
But IMD action whose cause relates to the device non liearity expressed
by THD numbers
creates the sum and difference frequencies created between every pair of
frequencies
to a mush of distracting noise unless limited to low levels prefereably
below 0.1%.
This is based on a simple standard 60+ year old test of using 4V of 80Hz
and 1V
of 5kHz, and the 5,080hz and 4,820Hz IMD tones created should together
be less than 0.1% of the 5kHz amplitude.
Its easier than you may think to measure this.

Its my belief that the amount and complexity of IMD created in tube amps
is more forgivable
that that found in many (but not all) solid state amps, ie, you can have
far higher measured IMD in a tube amp
than you can in an SS amp and get away with it without ppl condemning
the tube amp
as rough, harsh and hard sounding.
Natural intermodulation F are produced within instruments, and perhaps
tube amp mimic
instruments, and hence are more acceptable.
To limit IMD of SS amps, I believe they need all the NFB they can
muster, unless they are set up
in class A, and suddenly ppl find that a class A pair of mosfets need no
more NFB than a
pair of class A KT66 in a Quad-II.
I have tested this idea by secretly swapping a beautiful 50 watt class A
tube amp for a
300 watt mosfet based amp with a zillion dB of total NFB and the
gathered audiophiles never noticed, and when i said I had swapped over a
major component,
they couldn't pick what it may have been, and when told, and when i
switched back and forth
the differences could not be heard.
Both the SS amd tube amps cost about the same to make and weighed about
the same,
and had the same designer, as one dude later told me, so maybe this
explained the simularity in performances.
It was indeed a rare and enjoyable evening.
The tube amp had 0.02% THD and SS amp about 0.002% at levels used for
the evening.

This was one of my very real guiding experiences.

I can entertain Cheever's ideas. I am not threatened, my world has not
been made invalid,
I know what works, and a lot of what does not. Perhaps i can learn
something new, i hope,
some of the time.


Oustide my simple recipe which is achieved with science, discipline,
careful measurements,
and attention to natural simple linearity, almost anything goes, like
changing cables, capacitors, and
using Skakti stones on speakers. Things within the "anything goes"
department don't interest me much,
and I don't believe they make much difference, but if quackery in audio
leads people to better enjoy
the musical experience and with a passion at home then so be it, at
least they seem to know what does make them at peace,
while others seem not at peace, on the warpath, and worried excessively
about
meters and numbers.

My "better paper" is written here and in my website for all to read.

Lord knows what Mr Cheever would say if he read it.


(2) you find various tricks and techniques that
add to and/or improve upon the techniques he proposes.


Exactly, one can always build upon foundations laid by others.
Its almost completely impossible to be totally original in any field of
human endeavour
or interest, we as a species are becoming more connected each day and
more interactive,
and despite the protestations of the Chinese People's Communist Party
and the
Iranian Goverment's objections to the operation of the FREE Internet.
All these old world hegemonic old power huggers
will be swept asside in future, and advances made where some seemed
impossible.
It may of course doom us even sooner rather than later, because if the
all the worlds'
9 billion people in 20 years all want to live like little kings and
queens then we can only
wonder how the planet can afford ans sustain it all for countless future
generations.

But I digress. I rather admire Peter Walker's Quad II amplifier topology
for
output stages. It is foundational for me. I build amps with a similar
topology.
But I don't use pentode driver stages unless strapped as triodes,
because the pentode
has far worse distortion spectra than triodes, and a greater amount of
them.
So to use an EL84 as a driver tube in pentode mode it needs its own
local shunt loop NFB
to reduce pentode gain from a maxima of around 200 to 20 to make it as
linear as triode,
and even then the spectra is just the same as pentode but reduced, and
not as simple as triode strapping.
I like the EL84 used as a triode driver because it seems to make the
sound from
any following stage more dynamic. It should, the EL84 in triode is about
equal to having
5 halves of a 6SN7 in parallel, and just as linear.


However, i still have a few ideas to try, and it is to be remembered
that
pentodes at low levels have been considered no worse sounding in much
audio gear of the past,
including where Quad and Leak et all used EF86.
Andy Grove continued the pentode tradition in Quad 40 amps with the use
of 6SH7 pentodes
instead of EF86.
There are millions of EF80/6BX6 anhd 6EJ7/EF184 left in the world, none
are darlings of the
hi-fi cognescenti but what would they know? have they built any amps?
Do they ever solder anything?
Using EF86 or much more gutsy 6BX6 or 6EJ7 the same way can have similar
problems,
or similar benefits.....

I have not tried the local shunt NFB idea around the EL84 pentode as a
driver stage.
Its extra circuitry, and its giving in to the idea that yet more devices
solve a problem,
but maybe it just won't. Conrad Jonson and ARC and a perhaps McIntosh
have allowed their circuits to become probably too complex for the music
to survive optimally.
These amps seem to me like are monuments to designer cleverness with
numbers rather than
symbols of effective simplicity.


I am not sure i want to lay waste the Cheever empire to leave
bloodstained foundations
amidst ashes of his thoughts, but if his temple is wood, and rots with
age,
maybe I would build a firmer stonework ediface where people could
worship without regrets or guilt.

Surely this would be a more harmonious outcome.

Patrick Turner.



Phil

[Edward R. Morris]

God IS perfect. You are right on one statement. "Humans are notoriously
erroneous creatures".

Edward Morris

"Patrick Turner" wrote in message
...


The Score So Far,

one says
"********, and illitertate boolocks at that",

two asks,
" ..I wonder what Arnie says?"

three says
"we get weird sound when we get a cold and we type opinions as we type
them.."

four says
that the thesis favoured tube amps at the expense of SS amps,

five said
....."might explain why the empirically arrived at minimum level
necessary for 'undetectable distortion' changed dramatically when
transistors replaced tubes, though."
And five also said a lot of other things which proved he had more
understanding of what Cheever said
about ears, ear distortions and brains.

six said
"For more recent work (2005) along very similar lines but with slightly
different conclusions see
http://www.gedlee.com/distortion_perception.htm

I had a look at that but don't have time right now to read Gedlee's
1.6MB dissertation,


and seven said,
"** Meet the NEW load of ********...
Same as the old load of ********.
( Apologies to Pete Townshend )

Without immediately knowing what relevance Mr Townshend has,
I am at a loss to comment.



TAD, ot Total Audio Discononance is not to be confused with TID,
Transient Induced Distortion.



It seems to me Cheever tries to show that the ears will produce harmonic
voltages from the
hairs in the cochlea in your ear when a pure tone is used as a signal.
The brain he says, filters out the harmonics, and we hear the tone as
pure.

To me this defies common sense, because it implies the brain would do a
lot of filtering
with music or noise which is riddled with many harmonics.
Humans are notoriously erroneous creatures. God isn't perfect, let alone
understandable,
if we take a look at his creations over the millions of years or trial
and error.

But if Cheever is correct, and the brain does away with much of what the
ear microphones feed to it
then its easy to see how MP3 formatted sound gets away with it...

Anyone who has listened to the effects of clipping of clean sine wave in
an amp
would know what the threshold level is for THD of the tone; a 400Hz tone
seems to
suddently become "harder" sounding when the clipping becomes easily
visible on the CRO.
Pop music guitar players would say visibly undistorted sound is dull and
lifeless;
they set their levels so THD is 15% minimum most days...

But Cheever's treatise includes the effect of using NFB in an amp making
10% 2H, and this is not ******** at all; using say 8 dB of NFB around a
gain
stage with 10% THD with no NFB does not improove the sonics even though
the 2H is reduced a bit.

The phenomena of using a very mild amount of NFB, say 5dB to 14dB around
an amp with 10% open loop Dn
and its creation of other harmonics of a higher F has been well
documented in the past.

The past examiners of this phenomena have concluded that where open loop
THD was 10%, and there
was sufficient open loop gain present, ie, the amp wasn't clipping, and
still had considerable headroom
in its output and drive amp stages, then you simply need to apply a lot
more FB
and then all original open loop AND ARTIFACTS CREATED BY THE NFB are
reduced at a constant rate once NFB exceeded about
20dB, and this is shown in Cheever's graphs, if anyone here is able to
read a graph
by looking at it long enough.

Since many SS amps with NFB make THD 0.005% quite routinely at 1 dB
below clipping, and
perhaps 0.001% at say 2 watts, and that open loop THD at 1dB below clip
was 3% typically,
then just how does the ear and brain tell us something is drastically
wrong and make some listeners
go running to the shop for an SET amp?

Surely there have to be limits of audibility of distortion.
If it simply ain't there on the basis of it being totally inaudible if
played to listeners on its own
without the wanted undistorted sound, then how do we perceive the
distortion?

0.001% of say 4Vrms into 8 ohms, 2 watts, makes noise lower than an ant
walking
across the floor in front of the speakers.

I have heard music via SS amps which tend to make a noise similar to
people tearing up
paper in time with the music levels, but many SS amps just don't,
and are as clean as a whistle, so to speak, even clinically clean, too
darn clean in fact for
some listeners, and clean in an objectionable way compared to when they
listen to
a tube amp, which may measure 50 times worse, but nevertheless still
measure quite well with less than 0.04% THD for an SE amp,
and 0.02% for something PP.

I have found it quite easy to make a clean sounding SS amp, and several
that
sound ok when compared to class A tube amps of similar power ceilings
and
low THD at low levels used during continuous actual listening.

I could say that the use of very good passive filtering of rail supplies
in all the amps concerned leads to a clean sound, as well as a high% of
class A working
before the amp moves to class AB helps the NFB do its job.
In many SS amps the noise in the open loop signal is far greater than
the THD/IMD,
so much so that examining the output waveform on a CRO is marred with
hum levels,
even at high output levels.
Reducing the injected PS noise with careful filtering allows the open
loop
to actually be plotted and graphed.
Before NFB is applied many an SS amp then resembles
a giant phono amp which amplifies say 1mV of input to 25Vrms output at
100Hz with bandwidth rolling off
at 6dB/octave after some low F pole which can be as low as perhaps
100Hz.
The open loop response usually includes the local output stage emitter
follower NFB which equates to
typically 40dB of local loop series voltage NFB, ( the definition of the
variety of NFB is important ).
So the response and THD one sees is mainly that created by the class A
bjt input and driver stages.
And if anyone gets that to less than 3% at 25Vrms, they are doing well.
If they also have open loop bandwidth from say 20hz to 5kHz, they are
doing a lot better.

Having an open loop pole at 100Hz means that at if the global NFB is say
60dB at 100Hz, then at 1kHz, its 40 dB,
and at 10kHz its 20 dB, and by 100kHz, there is no effective NFB applied
because gain has dropped to unity.
Just as well, because we get stability more easily.

Its very easy to reduce the 3% of THD to 0.003% with 60dB of GNFB.
My view is that the this 60dB is more effective if there is a low amount
of noise in the signal to begin
with; the applied NFB has an easier task to perform, ie, cleaning out
the spuriae,
which if not cleaned out would leave things sounding worse, surely,
even if by some miracle, we could totally reduce PS noise,
and extend the open loop BW out to 20kHz?
Extending the open loop BW out to 20kHz isn't all that easy with bjts
because we'd have to use either global NFB around the voltage amp gain
stage/s
or have cascaded stages of gain each with its own local FB and when you
have
say 3 gain stages cascaded each not using much NFB, I cannot see how the
spuriae will not be better than if one simple effective GNFB loop is
applied around
ALL 3 cascaded stages.

Amplifiers without emitter follower output stages,
ie, common emitter outputs will have much more open loop THD,
and I cannot see how FB could be dispensed with at all, one other reason
being that
collector resistance like pentode anode resistance or drain resistance
in mosfets gives an amp
with output resistance far to high to be usable, and well above speaker
impedances.

Meanwhile, triodes are passable without any global NFB
and can operate in common cathode and still remain listenable,
and their internal NFB makes them able to have output resistance well
below speaker impedances.

A customer of mine maintains he prefers the sound
of a quad of 300B in PP for each channel without any GNFB.
The NFB is adjustable and he can make the comparisons easily
at the trun of a switch knob.

But we are stuck with distortion regardless of what we do, and the only
way
to avoid it is to attend live music, and where the instruments are NOT
amplified.

Nevertheless I'd swear I was at a concert when I listen to music from
the
local ABC Classic FM radio station here, despite the whole process of
recording onto a CD, replay, sending the signal to a satelite and back,
then encoding
it all to be able to re-constructed into stereo vi a multiplexed 100MHz
carrier,
in my humble all tubed FM tuner, which has switching diodes to create
the stereo,
and the less I tell you all about the process, the better.

My lounge room is never really the best seat in the theatre though,
mainly
because I'm at home, and not out, all dressed up for the occasion, with
friends,
and with the aura of the theatre and human togetherness affecting my
subjective senses.
But plenty of times my lounge room has brought me closer than the best
theatre seat ever could to a performer.
I have plenty of LPs recorded as far back as 1958 which
put me in the same studio room with the artists.

And this luxury is possible despite all that has been said about noise
and distortions.

Patrick Turner.

[Patrick Turner]

"Edward R. Morris" wrote:

God IS perfect. You are right on one statement. "Humans are notoriously
erroneous creatures".

Edward Morris

There is always one, maybe two, in every crowd
who hears a large amount about what he is here for then picks
on what is not so obvious, and of little concern to
us humans, ie, God's perfection.

I recall singing a line of a folksong, a long time ago,

"God does love me I don't think,
If he did he'd buy me a drink"

Apparently, if I were to believe the born again Christian Right
I should buy God a drink, although drink is not a correct type of gift,
not for any god, even when it looks like he needs a very stiff drink, to
get him
relaxed at such a hard job all day creating then managing the Universe,
and putting up with all the mistakes he made, and those of the sinners
he created.
All seems a bit pointless to make a universe with built in obsolesence,
that needs to spend billions of years before parts of evolve self
consciousness,
and being able to ask "why the **** it is all here God?"

The One True Truth is that God is unknowable, because He is infinite,
and we only have tiny teenzy weeny brains to comprehend Him, and all the
information NOT IN THE BIBLE
won't fit into such brains, so there's no need to try, you will fail,
and whether God is perfect or not
is mere conjecture, a social convention during pleasant discourse.

Ppl say God Is Perfect because they are placing a safe bet.
Better to Praise the Lord despite evidence he doesn't deserve it just in
case
you end up having to face Him later.
One won't get into heaven if you turn up after
spending one's time down here casting ill favour upon the Lord.
But I have never catowed before anyone and won't ever.
I don't care if I go to hell. Hell, I been told to go there
often enough...

Its like bad mouthing the bank manager. He darn well knows what you
think
and when you ask for a loan, you'll know why he said " NO."

I see the Universe as SNAFU.

Meanwhile, courtesy of Chance, autumn days here are glorious, long
bicycle rides are nice,
music is great, not much distortion to worry about,
women my age are a complete waste of time,
I'd like to be a little richer, but I don't mind povety.
Life isn't too bad, not even tree bad, and if God isn't perfect, I
understand,
because neither am I.

Patrick Turner.

[Edward R. Morris]

Patrick,
Since you pride yourself on being so smart; so intellectual, what other
sources do you have about God, other than the Bible?

Edward Morris

"Patrick Turner" wrote in message
...


"Edward R. Morris" wrote:

God IS perfect. You are right on one statement. "Humans are notoriously
erroneous creatures".

Edward Morris

There is always one, maybe two, in every crowd
who hears a large amount about what he is here for then picks
on what is not so obvious, and of little concern to
us humans, ie, God's perfection.

I recall singing a line of a folksong, a long time ago,

"God does love me I don't think,
If he did he'd buy me a drink"

Apparently, if I were to believe the born again Christian Right
I should buy God a drink, although drink is not a correct type of gift,
not for any god, even when it looks like he needs a very stiff drink, to
get him
relaxed at such a hard job all day creating then managing the Universe,
and putting up with all the mistakes he made, and those of the sinners
he created.
All seems a bit pointless to make a universe with built in obsolesence,
that needs to spend billions of years before parts of evolve self
consciousness,
and being able to ask "why the **** it is all here God?"

The One True Truth is that God is unknowable, because He is infinite,
and we only have tiny teenzy weeny brains to comprehend Him, and all the
information NOT IN THE BIBLE
won't fit into such brains, so there's no need to try, you will fail,
and whether God is perfect or not
is mere conjecture, a social convention during pleasant discourse.

Ppl say God Is Perfect because they are placing a safe bet.
Better to Praise the Lord despite evidence he doesn't deserve it just in
case
you end up having to face Him later.
One won't get into heaven if you turn up after
spending one's time down here casting ill favour upon the Lord.
But I have never catowed before anyone and won't ever.
I don't care if I go to hell. Hell, I been told to go there
often enough...

Its like bad mouthing the bank manager. He darn well knows what you
think
and when you ask for a loan, you'll know why he said " NO."

I see the Universe as SNAFU.

Meanwhile, courtesy of Chance, autumn days here are glorious, long
bicycle rides are nice,
music is great, not much distortion to worry about,
women my age are a complete waste of time,
I'd like to be a little richer, but I don't mind povety.
Life isn't too bad, not even tree bad, and if God isn't perfect, I
understand,
because neither am I.

Patrick Turner.

[tubegarden]

On Mar 21, 3:16?pm, "Edward R. Morris" wrote:


three says
"we get weird sound when we get a cold and we type opinions as we type
them.."


err, I typed: "we form opinions as we type them"

Not that anyone reads long posts

Just how much coffee do you guys drink?

Happy Ears!
Al (three)

[Patrick Turner]

tubegarden wrote:

On Mar 21, 3:16?pm, "Edward R. Morris" wrote:

three says
"we get weird sound when we get a cold and we type opinions as we type
them.."


err, I typed: "we form opinions as we type them"

Not that anyone reads long posts

Just how much coffee do you guys drink?

Happy Ears!
Al (three)

Yes but you unplug tubes after you've grown them in your garden,
and put them in bases like flowers in vases,
and its all a very nice day where you are isn't it Al,
and hang in there mate because they don't makem like they used to
anymore.


I like Italiano de grond coffee grounda in Ozza, lotsa bootifull
grinders here.

I make him up in de Mocca on de stove, she boil, she steam, she gurglo,
she hava a Roma, multo bella segnor, et segnoras.

Er sumtimes I putta de grappa in de cuppa, it give a bigga boosta to the
de life.

meanwhile, itta help de opinione de intelegenzzi, le tuba craftori.

Patrica Turnera.

[Doug Flynn]

"Patrick Turner" wrote in message
...

So we really only know that THD and IMD exist in devices, and that
it all rises with output levels and load values.

But while looking around Google under 'pentode distortion measurements'
I came across a thesis drafted up by one Mr Daniel H Cheever, posted at

Here he talks about the increase in harmonic trash within a signal
caused by NFB.You all thought NFB reduced the trash, but he has other
ideas supported
by his calculations and observations fairly well
presented.

But his conclusions must be considered in the context of his ideas
presented about the Total Aural Disconsonance figure of merit, or TAD.

So what do people think about My Cheever's thoughts?

Patrick Turner.

Here's what I think:

Pentodes = evil
Global negative feedback = the spawn of Satan
Digitial = the work of the Devil

Cheers. Doug ;-)

[Patrick Turner]

Doug Flynn wrote:

"Patrick Turner" wrote in message
...

So we really only know that THD and IMD exist in devices, and that
it all rises with output levels and load values.

But while looking around Google under 'pentode distortion measurements'
I came across a thesis drafted up by one Mr Daniel H Cheever, posted at

Here he talks about the increase in harmonic trash within a signal
caused by NFB.You all thought NFB reduced the trash, but he has other
ideas supported
by his calculations and observations fairly well
presented.

But his conclusions must be considered in the context of his ideas
presented about the Total Aural Disconsonance figure of merit, or TAD.

So what do people think about My Cheever's thoughts?

Patrick Turner.

Here's what I think:

Pentodes = evil
Global negative feedback = the spawn of Satan
Digitial = the work of the Devil

Cheers. Doug ;-)


R U Obsessed with the devil today or what, eh?

I hope Mr Rudd does not legitimise witch hunts when he's voted in.

I wouldn't like to see you become a 'group leader of alternative
thinking limiting agents'

Say a warm HELLO to all the NFB in your triodes tonight.

If you hate NFB so much, then why doncha try a pentode?

Patrick Turner.

[Doug Flynn]

"Patrick Turner" wrote in message
...

Say a warm HELLO to all the NFB in your triodes tonight.

If you hate NFB so much, then why doncha try a pentode?

Patrick Turner.

Now you're just being pedantic (or should that be pentode-antic?)

Doug ;-)

[paul packer]

On Mon, 19 Mar 2007 10:40:10 GMT, "Doug Flynn"
wrote:


"Patrick Turner" wrote in message
...

Say a warm HELLO to all the NFB in your triodes tonight.

If you hate NFB so much, then why doncha try a pentode?

Patrick Turner.

Now you're just being pedantic (or should that be pentode-antic?)

Doug ;-)

Careful. People have blown tubes thinking up worse jokes than that.

[Patrick Turner]

Doug Flynn wrote:

"Patrick Turner" wrote in message
...

Say a warm HELLO to all the NFB in your triodes tonight.

If you hate NFB so much, then why doncha try a pentode?

Patrick Turner.

Now you're just being pedantic (or should that be pentode-antic?)

Doug ;-)

Was not the five pointed star some kind of devilish symbol?

Five is definately an odd order number, like 3, and 7 and 9 etc.
Such a statement is meaningless, like saying even number devices like
diodes and tetrodes
and sexodes have even order distortions.

Anyway, the load for a pentode and many SS devices will determine the
harmonic spectra,
and who is to say that one particular load might not suit your ears?

If you hate pentodes, then you should have a reason.
Same goes for beam tetrodes I guess.

It is possible you are reason-less, in which case we wish you bon voyage
in your musical persuits, but please rememember that so many
of the vinyl treasures you like so much are chocablok full
of pentode and NFB artifacts because many of the very best old vinyl
analog recordings we hear
were the result of routine use of the highest safe amount of NFB
possible
around circuits having as much safe open loop gain as possible
using as few tubes as possible, which meant using shirtloads and bundles
of EF86,
perhaps a few 6SH7, 6AU6 etc.

Had the studios tried to use nice simple triode circuitry without any
global NFB,
its possible a few may have managed the low N&D by the time a record was
issued to the public,
but also perhaps unlikely. Certainly they were prone to buying what was
cheap, had all the bells and whistles,
and what needed the least sevicing.
And can you tell us if you are listening to a filthy recording produced
using all transistor based gear?

I think I prefer the sound of the radio stations that have NFB built
into their carrier modulators,
so that at the station a receiver module produces audio from the
radiated RF signal,
then compares that with the audio used to modulate the RF signal, and
applies an error signal to reduce
N&D to sub audible levels.
I am wondering if I would like the whole transmission done without any
loop FB,
or if I would like a cutting head propelled without NFB.

Maybe I will never be able to answer such questions fully, so my mind
can't allow the irrationality
of hate for a pentoad. And in fact I have too many good sounding EL34
based amps
even with EF86 input tubes which sound well to doubt that pentoads can
sound well.
Then I have listened carefully with Quad-II amps which I have revised
using all triode
drivers and pentode drivers and heard not a huge amount to complain
about,
especially after the circuit revisions I have performed on such amps.

I even like j-fets, but these critters have a square law transfer like a
pentoad,
but unlike a bjt, whose transfer is exponential, and one generating more
harmonic garbage,
for which more NFB must be used to reduce, allowable because the
transconductance
of the bjt is very high, so gain is high....

I place the priorities for good sound on the room, then speakers, then
programme source,
then source medium, then amplifiers and tube choice.
Choice of BJTs does not seem to make any difference, if I am to believe
the
discussions about bjt choices.
It is to be assumed the home electronics involved at least conform to
0.1% N&D max and full 20Hz to 20kHz BW and damping factor of 5 at
average levels
which isn't hard if that's only 1/2 a watt per channel.

I have heard exceptions where on one occasison a group of 15 audio
enthusiasts huddled in a room in a shop
witnessed the dramatic improvement in sound when a 23 watt SET amp was
used instead of a Gyphon 100 watt class A monster.

There would be plenty of occasions where the SET would be NBG, if the
level was high, and ear crushing
pop was selected into insensitive speakers.

Horses for courses.

Patrick Turner.

[John Byrns]

In article ,
Patrick Turner wrote:

I think I prefer the sound of the radio stations that have NFB built
into their carrier modulators,
so that at the station a receiver module produces audio from the
radiated RF signal,
then compares that with the audio used to modulate the RF signal, and
applies an error signal to reduce
N&D to sub audible levels.
I am wondering if I would like the whole transmission done without any
loop FB,

Did you actually check out what sorts of "carrier modulators" the
various radio stations were actually using, so that you can truthfully
say you have correlated the sound of the stations with the "carrier
modulators" they used? It's probably too late to do this experiment
today, what with digital modulation schemes having taken over the field.
Assuming that you actually investigated what sort of "carrier
modulators" were being used by the stations you preferred, as well as
those you didn't, how did you eliminate the possibility that it wasn't
the overall loop negative feedback that produced the sound you liked,
but was some other factor common to the transmitters using overall loop
negative feedback? I can think of one factor that is common to most
analog transmitters that didn't use overall loop negative feedback, i.e.
demodulated RF, that I suspect was more likely to have contributed to
your dislike of them.


Regards,

John Byrns

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