[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

[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. -

[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

[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.

[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

[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 ;-)

[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]

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.

[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

[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.

[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 ;-)

[Arny Krueger]

"Patrick Turner" wrote in message

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.

That's nuts.

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

Anybody can scribble equations on paper.

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.

Niche products don't define technology.

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

I pointed a friend of mine who has written several books about audio and a
number of AES conference papers and JAES articles at the site, and he
basically said that Cheever was nuts. Oh, there's a kernal of truth to some
of what he says, but a lot of it is way off the deep end.

[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.

[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.

[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.

[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.

[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.

[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.

[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]

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.

[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]

Arny Krueger wrote:

"Patrick Turner" wrote in message

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.

That's nuts.

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

Anybody can scribble equations on paper.

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.

Niche products don't define technology.

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

I pointed a friend of mine who has written several books about audio and a
number of AES conference papers and JAES articles at the site, and he
basically said that Cheever was nuts. Oh, there's a kernal of truth to some
of what he says, but a lot of it is way off the deep end.


Whether Cheever is nuts or not doesn't change what we have to work with
for
most of us; I for one will not adopt a carefree anything goes attitude
to
THD and IMD just because one guy says i am not measuring things
properly.

Anyway though, nothing YOU have said prooves Cheever IS NUTS.
I remain open minded, and I don't believe what I hear is all down to
what we know we can measure so far.

Why is it so that many ppl need subtitles for opera sung in english,
but other ppl understand it all, and have no trouble humming along as
well?
Hearing and people's brains vary somewhat enormously.
I cannot see why the brain may not indeed screen out much of the signal
its gets from the
microphone functions in our ears.

A brain is a seriously wonderful development in evolution, and I don't
underestimate
its unique sub-conscious abilities to tailor sound signals to however it
wants to
in real time to enable information for best survival to register as fast
as possible.

But alas I am no audiologist, and no expert, and I doubt I could
easily construct test gear for TAD tests, and then demonstrate to a
sceptical audience that
TAD evaluation methods were truly valid.

I recall that when someone said the Earth went around the Sun,
a certain religious organisation took a very dim view and cut the guys
ears off.

The organisation was begun by Jesus Christ, a liberated thinker of his
time,
and you'd think his followers would also allow some free thoughts.

How about you guys permitting free thought without calling someone nuts?

Patrick Turner.

[Phil Allison]

"Arny Krueger"
Phil Allison wrote:


** 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.


** Precisely - as anyone with even a modicum of insight into audio
electronics has long known.

Unless they are complete dopes or terminally asleep.

Guess who qualifies for both .... ?



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


** Shame the speakers I listen to ( Quad ESL63s ) have virtually no audible
THD or IM whatever.

Small wonder they so sound " lifeless " and " boring " .......

Maybe a nice SET harmonic enhancer will improve things ....



....... Phil

[Arny Krueger]

"Patrick Turner" wrote in message

Arny Krueger wrote:

"Patrick Turner" wrote in
message


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

I pointed a friend of mine who has written several books
about audio and a number of AES conference papers and
JAES articles at the site, and he basically said that
Cheever was nuts. Oh, there's a kernal of truth to some
of what he says, but a lot of it is way off the deep
end.

Whether Cheever is nuts or not doesn't change what we
have to work with for most of us; I for one will not adopt a carefree
anything
goes attitude to THD and IMD just because one guy says i am not measuring
things properly.

I agree with that.

Anyway though, nothing YOU have said proves Cheever IS
NUTS.

I long ago quit trying to dissuade true believers with logic and science.
The point is that with electronics, its possible to get all measurable forms
of distortion so low that the fact that THD and most forms of IM are
suboptimal measures is irrelevant. Even with all their suboptimalities, get
them low enough and you're done.

And, while some tubed equipment has enough nonlinear distortion that the
Geddes-Lee results can apply, it is also possible to get the nonlinear
distortion in tubed equipment low enough so that it doesn't matter.

The logical justification for the Gedees-Lee papers is not electronics, it
is transducers particularly speakers.


I remain open minded, and I don't believe what I hear is
all down to what we know we can measure so far.

Patrick, given that you eschew bias-controlled listening, that has to be
true. Prejudice and bias can have very strong effects on listeners.

Why is it so that many ppl need subtitles for opera sung
in english, but other ppl understand it all, and have no
trouble humming along as well?

Preferences and training.

Hearing and people's brains vary somewhat enormously.

The brain is the most powerful organ in the body.

I cannot see why the brain may not indeed screen out much
of the signal its gets from the microphone functions in our ears.

It's not a matter of *may*, its a matter of *does*. If the brain studied
only waveforms, MP3s wouldn't work as well as they do.

[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

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

[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.

[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.

[Patrick Turner]

TT wrote:

"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

Peter Stein is just a man, and no man alive can gurrantee safe passage
through a marriage, and when his came to an end, his wife and all the
lawyers
involved settled so they each got half the family wealth under
Australian Family Law,
and this included the ME company. That's how I understand what went
wrong.
Divorce can easily wreck the family business, and its hard for someone
to climb back up to where they were.

So in case we may think Peter's amp production failed because of design,
we should all consider the real reason, and one so many of us can
sympathise with.

Its remarkable Peter may still be trying to re-establish; most of us at
his age would
retire to something else after 30 years in the business, and just enjoy
the fishing.

Its really difficult to make any business last a long time, and Peter's
25 years
deserves a darn medal. I dunno how he could have structured his business
so
it could not have closed over a divorce, but then all such businesses
require an interested
head persona to keep them running, and its simply not easy in Oz
with imports and absurd customer expectations pressing always towards
business unviability.
Australia has a large history of failed audio industry enterprizes.
But then the list of cafes and restaurants that went broke just last
year
probably outnumber all the audio businesses ever started.

You can all nit-pick Peter's achievements, and sure there are
better/worse amps than ME,
but give the man a fair go please!

Patrick Turner.

[Patrick Turner]

John Byrns wrote:

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.

What i do know is that for present AM and FM transmissions in Oz the
waves must remain compatible for existing analog receivers to
decode audio from the RF carrier waves, and the recovered audio cannot
be more linear than the transmitter modulator permits,
and so I have assumed modulators have inbuilt means to use NFB to
ensure modulation is as linear as possible. Engineers have told me but
I admit I have not seen ths latest transmitters' schematics and analysed
them.


If you want to build a really low thd RF oscillator with say an AM
function
to allow between say 0% and 100% modulation levels of a tone, its not
hard to
make one up which uses NFB to linearize the modulation to an extent
where
the receiver demodulation THD/IMD will always be higher, unless
rather extraordinary measures are taken with RF and IF amplifications
and AM detection methods.

With the very simple methods used in tubed superhet receivers,
THD of 5% isn't uncommon, but its not because of the transmissions
which imho are better than ever much of the time.
One may argue id MP3 pop music is worse than old analog transmissions
direct
from a record groove, or tape, but the challenge of linearizing
transmissions remains.

Anyone who really knows about radio transmissions like to comment?

Patrick Turner.



Regards,

John Byrns

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

[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

[Arny Krueger]

"Patrick Turner" wrote in message

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.

Patrick, that's one way to always be right - change your statement after it
has been responded to. You only barred loop feedback in the statements I
responded to. Now, you've changed your story quite extensively.

This is simply not possible with a solid state power
amplifier where you MUST use extensive local FB such as emitter
follower connection

Emitter followers are prohibited but cathode followers are OK? LOL!

and local current FB to linearize the signal.

Pardon me while I decline to get hyper about five cent resistors.

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

But you must use external loop FB.

Nope.

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

Emitter resistors are loop feedback? On what planet? They are an example of
local feedback.

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

You kept piling on nonesensical distinctions after I responded.

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

I never said you did, Patrick. But you don't seem to have a problem with
changing your story after its been responded to.

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.

That's interesting. Would that be what most people call local feedback, or
was it really loop feedback?

Have you analysed the ME schematics?

I only know what Trevor tells me.

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.

So how long are you going to stick by this new story, Patrick?

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.

As you say Patrick, there's no problem with applying feedback.

[Eiron]

Patrick Turner wrote:


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.

So your example of an SS amp produces 5% THD without feedback,
yet you say that to produce less than 10% is extremely difficult.
I needn't go and measure anything, I'll just use your example to
show that you are being very silly.

--
Eiron.

[Arny Krueger]

"Patrick Turner" wrote in message


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.

This is true only if you design SS amps in accordance with Patrick's rules
for intentionally designing crappy amps.

It's possible to optimize a SS amp for good open loop performance. This
isn't done very much because it would be a really stupid thing.

In essence, what Patrick is telling us is that the only way he can come up
with a favorable comparisons between tubed and SS amps is to force the SS
amp to be designed in accordance with 2 sets of stupid rules.

The first stupid rule of Patrick's is that the SS amp must be designed
without loop feedback.

The second stupid rule of Patrick's is that the SS amp must be designed
without local feedback of the usual kinds.

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.

This would work for either tubes or transistors. You don't see a lot of
tubed amps with 60 dB NFB for two reasons:

(1) It's hard to get enough excess gain with tubes to sacrifice 60 dB or
gain, no matter how good the reason.

(2) Tubed amps tend to have too much phase shift to have 60 dB NFB and still
be stable.

I am speaking about the facts of the engineering.

Subject to some absolutly crazy rules.

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

It works for either tubes or transistors.

[TT]

"Patrick Turner" wrote in message
...


TT wrote:

"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

Peter Stein is just a man, and no man alive can gurrantee
safe passage
through a marriage, and when his came to an end, his wife
and all the
lawyers
involved settled so they each got half the family wealth
under
Australian Family Law,
and this included the ME company. That's how I understand
what went
wrong.
Divorce can easily wreck the family business, and its hard
for someone
to climb back up to where they were.

So in case we may think Peter's amp production failed
because of design,
we should all consider the real reason, and one so many of
us can
sympathise with.

Its remarkable Peter may still be trying to re-establish;
most of us at
his age would
retire to something else after 30 years in the business,
and just enjoy
the fishing.

Its really difficult to make any business last a long
time, and Peter's
25 years
deserves a darn medal. I dunno how he could have
structured his business
so
it could not have closed over a divorce, but then all such
businesses
require an interested
head persona to keep them running, and its simply not easy
in Oz
with imports and absurd customer expectations pressing
always towards
business unviability.
Australia has a large history of failed audio industry
enterprizes.
But then the list of cafes and restaurants that went broke
just last
year
probably outnumber all the audio businesses ever started.

You can all nit-pick Peter's achievements, and sure there
are
better/worse amps than ME,
but give the man a fair go please!

Patrick Turner.

Well said Patrick and I'm sure Peter will appreciate your
kind words.

BTW it is always a pleasure to correct Arny ;-)

Cheers TT

[Patrick Turner]

Arny Krueger wrote:

"Patrick Turner" wrote in message

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.

Patrick, that's one way to always be right - change your statement after it
has been responded to. You only barred loop feedback in the statements I
responded to. Now, you've changed your story quite extensively.

This is simply not possible with a solid state power
amplifier where you MUST use extensive local FB such as emitter
follower connection

Emitter followers are prohibited but cathode followers are OK? LOL!

and local current FB to linearize the signal.

Pardon me while I decline to get hyper about five cent resistors.

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

But you must use external loop FB.

Nope.

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

Emitter resistors are loop feedback? On what planet?


Emitter resistors are used in many SS amps as local
applications of series current NFB to linearize the otherwise appalling
voltage linearity
of BJTs. They also raise the effective base input resistance,
appallingly
low without such NFB.
These local NFB apps ARE local LOOP FB.
Do not try to evade the issue that it is impossible to build
a listenable bjt amp without loop NFB of some kind, or external NFB of
any kind.

NOW READ ME CAREFULLY, ARNY, A TYPICAL 6SN7 DOES NOT NEED ITS CATHODE
RESISTOR TO BE UNBYPASSED
TO PROVIDE LINEARISING LOCAL NFB, YOU GOT IT!!?

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

You kept piling on nonesensical distinctions after I responded.

You keep lying arny, and acting like slime, and your reputation follows
you.

Somehow, you expect us to agree BJT amps can be made without NFB, but
they cannot.



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

I never said you did, Patrick. But you don't seem to have a problem with
changing your story after its been responded to.

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.

That's interesting. Would that be what most people call local feedback, or
was it really loop feedback?

TWO LOOPS OF LOOP FB, YOU GOT THAT!!

Have you analysed the ME schematics?

I only know what Trevor tells me.

well, you would be PIG IGNORANT if you relied on information about
how amplifiers worked from Trevor Wilson.

The fact is you just made absurd allegations about ME amps without
knowing the facts about how they worked,
or without seeing a schematic. This makes you a pig brained fool arny.

And No, I won't enlighten you by sending you a copy of the schematic.
Find your bloody own copy.

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.

So how long are you going to stick by this new story, Patrick?

Its the same old story, and I will stick by it. Get used to ppl thinking
you are just plain dull.

Patrick Turner.

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.

As you say Patrick, there's no problem with applying feedback.

[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. -