[mike s]

On Tuesday, April 5, 2011 11:24:28 AM UTC+1, Patrick Turner wrote:
On Apr 3, 9:04*pm, mike s wrote:
On Apr 2, 1:16*pm, Andre Jute wrote:





On Apr 1, 9:23*pm, Newbie wrote:

It seems well known that negative feedback can reduce lower order harmonics, but
increase the higher order ones.

Can anyone direct me to references that show how this happens with mathematical
analysis? *Perhaps a paper in the journal of the AES, or elsewhere; on the web,
perhaps?

Here's an article to help you distinguish between added-on negative
feedback and natural negative feedback.http://www.audio-talk.co.uk/fiultra/...dre%20Jute.htm

This article explains why added-on negative feedback is a bad thing in
tube audio if you have really good speakers; it focuses on how the
higher harmonic artifacts are added.http://www.audio-talk.co.uk/fiultra/...dre%20Jute.htm

More articles on Harmonic Distortion on the KISS Amps site, available
through those pages.

This in intriguing in that what Jute has re-invented or re-created is
pretty much exactly the type of amplifier that Harold Black was faced
with in the 1920s when he invented negative feedback. *So it would be
interesting to hear from someone with such an amplifier as to what
happens if negative feedback is employed.

Certainly well designed and built valve amplifiers can perform
superbly as domestic audio systems without negative feedback. *Though
building two with exactly matched characteristics for stereo can be a
(not unrewarding) challenge. *Of course before the signal reaches the
domestic system it's been through many other higher performance
amplifiers, all of which will employ NFB.

My own system has no global NFB in the output stage, but it uses push
pull triodes, driven by another pair of triodes, so it's hardly worth
it. *And I like the "traditional" sound.http://mike.wepoco.com/Home/retro-ge...ers/Building-a...


What exactly was "traditional" sound?

My shorthand way of saying I'm not an audiophile. I decided I would build a copy of a 1930s hobbyist amplifier for a mix sentimental reasons - my grandfather was a "set builder" and from him I first learnt about radio and electronics, and curiosity - how good or bad were such amplifiers? So I had already decided that I would accept whatever sound it created, of course I wasn't fool enough to bring it straight into the living room.


In 1925, reproduced sound was mostly pretty damn awful mainly because
transducers such as microphones and speakers and recording discs were
so woefully limited in their ability to create hi-fi. Triode
amplifiers could always be easily made without global NFB and to be
able to perform flawlessly compared the other crappy gear which was
used.


1925! Wow, you're an old one. What you say is true, but is also why that period between the wars is so interesting. It begins with battery valves driving high impedance horn loudspeakers with metal diaphragms and by 1939 we have excellent permanent magnet speakers, even concentrics, and electrostatics, along the way were energised types and some really wacky stuff. Ribbon microphones were being used by the better broadcasters, etc. TV is developed, as was FM, stereo, radar and electronic computers. Even colour and 3D TV were demonstrated before WWII was over. The quality of recordings in another matter - I believe that in the UK early radio was more about live broadcasting than the endless replaying of popular tunes scratched into discs, folks had their own wind up gramophones for that vice.

The amplifier I chose to build was the one Williamson chose as the starting point for his seminal amplifier with global NFB.

I do have a few 1930s speakers, but wouldn't want to listen to them everyday, but I'll bet that there are plenty that are better than many of today's speakers, such as those used with computers. Instead I have a pair of 1960s Mordaunt Shorts with Kelly ribbon tweeters that I rather like. Perhaps not modern audiophile standard, but better than high street stuff, and cheaper.

But now we have had hi-fi discs since vinyl days. The mics and
speakers and record cutters, FM transmiters, and digital technology
etc have quite low distortions, so the amp needs to perform better
than the worst generic crappy tube stuff which was used in 1925. There
were crappy triode amps. The WE movie theatre amps were not so hot
IMHO.

There has always been plenty of damn awful tubed audio electronics
available at a cheap price for those who wouldn't know hi-fi even it
it bit them on the arse.


Sure there were always bad electronics, and there still are, but the amplifier Cocking designed in 1934 was still being used in top end radiograms of the 1950s by Dynatron and and RGD. Which is a good thing as it created lots of British PX4 (PP3/250) push pull amplifiers for today's collectors in Asia, like the the Dynatron LF59.

Patrick Turner.

Michael Saunby

http://mike.wepoco.com has more info on my old electronic stuff.

[Patrick Turner]

On Apr 6, 4:27*am, mike s wrote:
On Tuesday, April 5, 2011 11:24:28 AM UTC+1, Patrick Turner wrote:
On Apr 3, 9:04*pm, mike s wrote:
On Apr 2, 1:16*pm, Andre Jute wrote:

On Apr 1, 9:23*pm, Newbie wrote:

It seems well known that negative feedback can reduce lower order harmonics, but
increase the higher order ones.

Can anyone direct me to references that show how this happens with mathematical
analysis? *Perhaps a paper in the journal of the AES, or elsewhere; on the web,
perhaps?

Here's an article to help you distinguish between added-on negative
feedback and natural negative feedback.http://www.audio-talk.co.uk/fiultra/...dre%20Jute.htm

This article explains why added-on negative feedback is a bad thing in
tube audio if you have really good speakers; it focuses on how the
higher harmonic artifacts are added.http://www.audio-talk.co.uk/fiultra/...dre%20Jute.htm

More articles on Harmonic Distortion on the KISS Amps site, available
through those pages.

This in intriguing in that what Jute has re-invented or re-created is
pretty much exactly the type of amplifier that Harold Black was faced
with in the 1920s when he invented negative feedback. *So it would be
interesting to hear from someone with such an amplifier as to what
happens if negative feedback is employed.

Certainly well designed and built valve amplifiers can perform
superbly as domestic audio systems without negative feedback. *Though
building two with exactly matched characteristics for stereo can be a
(not unrewarding) challenge. *Of course before the signal reaches the
domestic system it's been through many other higher performance
amplifiers, all of which will employ NFB.

My own system has no global NFB in the output stage, but it uses push
pull triodes, driven by another pair of triodes, so it's hardly worth
it. *And I like the "traditional" sound.http://mike.wepoco.com/Home/retro-ge...ers/Building-a...

What exactly was "traditional" sound?

My shorthand way of saying I'm not an audiophile. I decided I would build a copy of a 1930s hobbyist amplifier for a mix sentimental reasons - my grandfather was a "set builder" and from him I first learnt about radio and electronics, and curiosity - how good or bad were such amplifiers? *So I had already decided that I would accept whatever sound it created, of course I wasn't fool enough to bring it straight into the living room. *



In 1925, reproduced sound was mostly pretty damn awful mainly because
transducers such as microphones and speakers and recording discs were
so woefully limited in their ability to create hi-fi. Triode
amplifiers could always be easily made without global NFB and to be
able to perform flawlessly compared the other crappy gear which was
used.

1925! *Wow, *you're an old one.

How'd ya work that out?

I'm 63, a 1947 model, and my old man was a 1912 model, so 1925 radio
and audio transmission along a path involving microphone based on
telephone evolution, early triode amps and horn speakers was being
done by the time my dad was only 13, a kid, and my grad dad about
maybe 40. Ancient history.


What you say is true, but is also why that period between the wars is
so interesting. *


I couldn't agree more. I am prsently working on a 1935 5 valve radio,
6D6, 6A7, 6B7, 75, 42, 80 tubes.
Built with the pride of my grandfather's generation. ****ing riddled
with design shortcomings though and giving 120Hz to 2.5kHz audio
bandwidth for AM and SW. Even in 1935, nobody could escape being
ripped off when they spent 4 months wages on a fancy floor standing
radio which had had the performance drained out of if by bean counters
and dalled brained engineers who refused to believe humans could
enjoy
music better if the resonse was 20Hz to 20kHz.

3kH ike ruldIt begins with battery valves driving high impedance horn
loudspeakers with metal diaphragms and by 1939 we have excellent
permanent magnet speakers, even concentrics, and electrostatics, along
the way were energised types and some really wacky stuff. *Ribbon
microphones were being used by the better broadcasters, etc. *TV is
developed, as was FM, stereo, radar and electronic computers. *Even
colour and 3D TV were demonstrated before WWII was over. *The quality
of recordings in another matter - I believe that in the UK early radio
was more about live broadcasting than the endless replaying of popular
tunes scratched into discs, folks had their own wind up gramophones
for that vice.

In 1963, my mother bought a new "hi-fi" stereo set at ridiculous
expense made by Kreisler. It featured a lousy TT with ceramic cart,
and a tube line up of 6AN7+6AN8 for the AM radio, no FM, Oz didn't get
FM until 1970s.
The audio amps were 1/2 12AX7 for phono amp with quite incorrect RIAA
filter, 11/2 12AX7 audio driver for
one output tube, 6BQ5, and maybe1/2 a 12AX7 for a really crummy tone
control circuit. Everything was crummy, sub standard. The 6BQ5 was in
pentode and global NFB was 3dB. Rola speakers were attrocious but at
least gave 93dB/W/M so quie dinner time listening was possible. But
there was no real bass, and above a watt it wasn't too hot, like using
a low powered guitar amp for hi-fi.

Nobody gave a **** about distortion and noise. Hum was tolerated and
pots crackled when you touched them.
The level of performance was no better than 1935, and in fact probably
worse.
Mum junked her junky Kriesler by giving it to me. I demolished the
cabinet for firewood and used the chassis electronics to develop my
ideas and to learn what I could dould, and identify what to never do,
ie, copy what the buffoons of the aidio industry were churning out to
sell at great expense to cashless gullible women like my mum. I added
more turns to the OPT sec to increase the interleaving because it was
just a single P winding wound over a single first on sec. The S-P-S
interleaving reduced leakage L and increased OL BW. I used the
increased sec turns for local cathode FB like in Quad-II but SE, and
then added another gain stage and applied about 18dB NFB, so about
20dB more FB than in the original amp. I built a pair of speakers with
far more solid boxes than were used for most of the utter rubbish
being sold to ppl everywhere.
The end result was glorious full range sound and a grand piano sounded
grand. I then worked on the AM radio to get 8kHz of BW instead of a
lousy 2.5kHz by reducing the Q of IF transformers.
Quad made pretty good super het AM tuners but all Quad gear was only
available to rich people, or 0.1% of Australians in 1955, and 95% of
them wrere uncultured rabble, and had little real interest is fine
music.

So although many things were possible by 1939, **** all people had any
access to the realisations of what was possible in theory until about
1970.

The amplifier I chose to build was the one Williamson chose as the starting point for his seminal amplifier with global NFB.

The Willy amp IS GOOD, but was a sub-optimal design designed to save a
resistor here or a capacitor there which was the symbol of parsimony
which dominated so much manufacturing after 1939. Almost all
manufacturers after 1939 laughed their lungs out when they saw Willy's
plans for an amp. You can still hear the echoes in the old factory
offices, "Nah, we don't need to do it like this!, we'll be ROONED if
we try to make this ****, OH MY GORD! how can our fellas wind OPT like
that?!" So, whatever Willy said was ignored by 95% of manufacturers.
What finished up in most ppl's was a pair of EL84 instead of KT66 in
triode and bloody awful OPTs, nothing remotely like Willy's
recommendations.
IOW, Leak 2020. Mullard 510.

I do have a few 1930s speakers, but wouldn't want to listen to them everyday, *but I'll bet that there are plenty that are better than many of today's speakers, such as those used with computers. *

I get a few PC speakers to repair, this week a pair of Gallos with
each speaker having 2 x 1.5" drivers in 3"dia metal spheres plus a
kind of SE electrostatic panel bent into a U between the two spheres.
It made perfectly awful sound very badly coloured. I was given an old
1994 Metz TV which had such bad sound I removed all speakers, and I
use the sound outlet from set-top box to a passable SS hi-fi amp from
1975 and a pair of passable VAF bookshelf speakers with flat wide BW
and little colour.

Instead I have a pair of 1960s Mordaunt Shorts with Kelly ribbon
tweeters that I rather like. *Perhaps not modern audiophile standard,
but better than high street stuff, and cheaper.

Exactly.

But now we have had hi-fi discs since vinyl days. The mics and
speakers and record cutters, FM transmiters, and digital technology
etc have quite low distortions, so the amp needs to perform better
than the worst generic crappy tube stuff which was used in 1925. There
were crappy triode amps. The WE movie theatre amps were not so hot
IMHO.

There has always been plenty of damn awful tubed audio electronics
available at a cheap price for those who wouldn't know hi-fi even it
it bit them on the arse.

Sure there were always bad electronics, and there still are, *but the amplifier Cocking designed in 1934 was still being used in top end radiograms of the 1950s by Dynatron and and RGD. *Which is a good thing as it created lots of British PX4 (PP3/250) push pull amplifiers for today's collectors in Asia, like the the Dynatron LF59. *

I have a deep IRREVERANCE for most old reverred designs including
those by Leak, Quad and most others because whenever I have set out to
make a decent amp I could get better measurements than any of these
supposedly good makers, and get better music. I guess the Rolls Royce
of 1932 was a shirt and trouser load better than the 1921 model
Rolls. But you can't own a Rolls. It owns you. And while most ppl
could only motor in what what they could a Ford, if you owned a Rolls,
you Rolls alone.

My father was a vet and he did house calls to sick animals just like
doctors used to call around to see a sick child. The good old days -
for the medicos, and boy, you needed a fat wallet to fetch a vet or a
doc to the house. But anyway, in 1956 I do recall my father's
wonderment with a snooty pair of groovers with a sick dog who had a
decent TT with magnetic PU and a decent home brew amp with 807 output
tubes which were very cheap for 25 years after WW 2 if you bought them
at Army Disposal stores where lots of excess production for a longer
WW2 was disposed of to the general public. One friend bought an 800W
RF transmitter, all tubed, army green, perfect condition, and made
like the text books said, real good AM performance. He's still got
it.

Anyway, the LP plus decent TT, home brew 807 amp and some decent home
brew speakers got you excellent sound by about 1955, if you knew what
you were doing, but 99% of everyone was techically illiterate.


Patrick Turner.

Michael Saunby

http://mike.wepoco.comhas more info on my old electronic stuff

I like your collection of old stuff. Part of my work is getting old
stuff to work properly. The radio I have on bench now has a little
tiny cheap nasty dial 3" in dia like those at your website only worse.
The formed perspex? plastic has yellowed and dulled, I am not sure if
I can fit a bit of glass instead. There is no brand, so the radio
was probably made by furniture maker who bought the radio chassis and
speaker to fit to his woodwork to sell a pretty thing to a bloke who
had just won at the horse rarces and who wanted to give something nice
to his missus so 'e could getta root.
The real rich blokes bought much more elaborate radios with 6 foot
long cabinets, big (****ing awful) Colaro TT for 78 plays at one end,
7 band AM radio at the other end, and a drink cabinet in the middle.
The drink cabinet was mirror lined to make it look like there was more
booze in there than there really was. Maybe the guy got two roots,
he'd remember the first, but was too drunk to recall the second, and
who cared about the sound?
But its how the "baby boomer" generation was conceived.

Patrick Turner.