Home |
Search |
Today's Posts |
#1
Posted to rec.audio.tubes
|
|||
|
|||
Distortion products
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. |
#2
Posted to rec.audio.tubes
|
|||
|
|||
Distortion products
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. |
Reply |
Thread Tools | |
Display Modes | |
|
|
Similar Threads | ||||
Thread | Forum | |||
Distortion products | Vacuum Tubes | |||
crimestoppers products | Car Audio | |||
Guide to old B&K products | Pro Audio | |||
Toft Products | Pro Audio | |||
Telefunken USA - many new products !?! | Pro Audio |