Home |
Search |
Today's Posts |
#1
Posted to rec.audio.tubes
|
|||
|
|||
Is AC balance more important or DC balance?
Every time I hear the Kevin Johnston song, "Rock'n'roll, I gave you
best years of my lie/all the sunny Sunday afternoons/all the moonlit summer nights", I am reminded of Herb Reichert's confession a dozen or so years ago that he wasted the best years of his life chasing AC balance in PP amps. Just now I have spent weeks making sure my latest balanced PP amps are *truly* DC balanced. So, which do you think is more important, AC balance or DC balance? Andre Jute "The noted vacuum tube hi-fi designer, cyclist, music collector and critic, author, economist, psychologist, soldier and advisor to statesmen worldwide has made his home in the vicinity for many years." -- from his hometown's website |
#2
Posted to rec.audio.tubes
|
|||
|
|||
Is AC balance more important or DC balance?
In article . com,
Andre Jute wrote: Every time I hear the Kevin Johnston song, "Rock'n'roll, I gave you best years of my lie/all the sunny Sunday afternoons/all the moonlit summer nights", I am reminded of Herb Reichert's confession a dozen or so years ago that he wasted the best years of his life chasing AC balance in PP amps. Just now I have spent weeks making sure my latest balanced PP amps are *truly* DC balanced. So, which do you think is more important, AC balance or DC balance? DC balance is far more important than AC balance. Good DC balance maximizes power supply rejection and minimizes potential saturation problems in the output transformer. AC balance, I'm not sure why anyone would be overly concerned with AC balance. Regards, John Byrns -- Surf my web pages at, http://fmamradios.com/ |
#3
Posted to rec.audio.tubes
|
|||
|
|||
Is AC balance more important or DC balance?
"John Byrns" AC balance, I'm not sure why anyone would be overly concerned with AC balance. ** Huh ?????? So you LIKE lotsa 2nd harmonic non linearity and consequent IM generated ? ....... Phil |
#4
Posted to rec.audio.tubes
|
|||
|
|||
Is AC balance more important or DC balance?
Andre Jute wrote: Every time I hear the Kevin Johnston song, "Rock'n'roll, I gave you best years of my lie/all the sunny Sunday afternoons/all the moonlit summer nights", I am reminded of Herb Reichert's confession a dozen or so years ago that he wasted the best years of his life chasing AC balance in PP amps. Just now I have spent weeks making sure my latest balanced PP amps are *truly* DC balanced. So, which do you think is more important, AC balance or DC balance? Both are important. DC offset causes the OPT iron to be partially dc magnetised so with ac signal it can magnetise closer to saturation, and because a PP tranny has no gap it doesn't take much dc to muddy the waters. AC balance is less critical, because the gm of tubes could be different. So with exactly equalised ac drive voltages, each output tube still won't do an equal amount of work on the load. So adjusting the balance of the ac for least THD can be done to make sure equal ac current production occurs. This will give the best 2H cancellations. Its a complete PITA to have to connect distortion test gear to listen to music. The fact is that most pairs of output tubes are close enough to convey a large benefit of 2H cancellations even despite their differences, so that even if you end up with as much 2H in the output as 3H, its mot much of a worry. Quad -II amps have a single damn cathode resistor, and when the KT66 tubes age its common to find one tube with 30mA, and cool, and the other with 90mA and with some red on the anodes, and the sound is ghastly. Placing individual RC networks for each output tube is the most sensible thing to reduce the DC imbalance. Tubes that balanced badly with one Rk will be found to be within 5% with say 470 ohms and 1,000 uF. This also has an effect om the gm. Gm rises with Ia, so a tube biased higher than another also may have higher gm. Although its not essential to always use matched pairs/quads of tubes, it does help. I have never bothered to try to provide an ac balancing pot in any amps because one could sit there swinging the balance pot while listening to music and not hear the slightest changes to the sound. At low levels of 1 watt average from 20 watt AB amps, the ac balance doesn't need to be perfect. Its class A operation, and inherently its going to be OK. Patrick Turner. Andre Jute "The noted vacuum tube hi-fi designer, cyclist, music collector and critic, author, economist, psychologist, soldier and advisor to statesmen worldwide has made his home in the vicinity for many years." -- from his hometown's website |
#5
Posted to rec.audio.tubes
|
|||
|
|||
Is AC balance more important or DC balance?
Hi RATs!
****, Andre! Just put in Alan Blumlein's garter circuits and get on with your life. We have not got forever, you may have noticed It is a simple circuit. If you don't use electrolytic caps, it is damn near fool proof http://www.tubecad.com/2005/May/blog0046.htm Blumlein may even have understood as much about electronic circuits as Eyeshadow! (If not Professor Hat Trick ...) _____ John Broskie is a delight, even if he is thinking too fast to build circuits and actually listen SPICE cadets may truly understand the theory and such, but some of us old RATs only want Ear Magic or Death! Mr. Blumlein gives you Ear Magic for the price of four resistors and two caps (per channel). John Atwood heard my old Heathkit A7 with the Blumlein bias circuit and it was clearly superior to the huge 300B SE I got as damaged freight for under a hundred bux. The A7 doesn't even have the audiophile square corner wiring harness ... it does have a pair of tin foil and Teflon coupling caps, and a simplified signal path. I don't require tone controls nor source switching. ( I can not pass up this fine opportunity to point out that Mssr. Atwood used a shared R/C to cathode bias two power tubes in one of his early designs. ) Mssr. Turner knows a dedicated cathode bias network sounds better than a shared network. Perhaps he could spare a couple passive parts to determine in Mssr. Blumlein had a clue or anything (And Eyeshadow, if you ever actually ever build a tube circuit, this is a simple circuit to determine if you really are deaf, as well as rude and arrogant.) ____ While in this fine mood and enjoying something almost like energy, let me vent a bunch of miscellaneous rants from my decades playing Ear Toy Evil Scientist: 1. Electrolytics are cheap. Not good. Expensive electrolytics are expensive, not good. Replacing electrolytics with oil caps is good, not cheap. Replacing electrolytics with free oil caps is approaching the gates of Heaven. 2. There is not much useful stuff to be learned from commercial circuit designs. Engineers can do it perfectly, but, to get paid, they must do it the cheapest that is barely tolerable. "Quality" in manufacturing means "all the same", not "Good". "Good" is what those goddam users want. F**k 'em! 3. Everybody hates everybody else. Please don't take it personally, you moron! 4. Newsgroups are the toilet walls of our world. At least now you can't smell the inspiration ... 5. How do you get good bass from a 3" driver in a small box? Bull****! It is advertising drool. Quit reading ads, you may actually cheer up. 6. My wife hears things in the recorded pianist's technical approach she does not find acceptable, no matter what I have just done to the system We had to sell her grand piano, long ago, due to the turbulence of the engineering job seas. I shall never live that down. 7. A circuit which delivers the most power from a given tube may, or may not, deliver the finest sound. It just ain't fair ... 8. Meters are wonderful. Not great music critics, but, easy to read ... 9. I am running out of energy. So is the Universe. It had such great potential, and it wastes it all getting bigger, and thereby, emptier. Happy Ears! Al |
#6
Posted to rec.audio.tubes
|
|||
|
|||
Is AC balance more important or DC balance?
"Patrick Turner" wrote in message ... I have never bothered to try to provide an ac balancing pot in any amps because one could sit there swinging the balance pot while listening to music and not hear the slightest changes to the sound. At low levels of 1 watt average from 20 watt AB amps, the ac balance doesn't need to be perfect. Its class A operation, and inherently its going to be OK. I like to include one, though few people seem to be able to hear the difference between 0.1% and 1% :-)) Iain |
#7
Posted to rec.audio.tubes
|
|||
|
|||
Is AC balance more important or DC balance?
Iain Churches wrote: "Patrick Turner" wrote in message ... I have never bothered to try to provide an ac balancing pot in any amps because one could sit there swinging the balance pot while listening to music and not hear the slightest changes to the sound. At low levels of 1 watt average from 20 watt AB amps, the ac balance doesn't need to be perfect. Its class A operation, and inherently its going to be OK. I like to include one, though few people seem to be able to hear the difference between 0.1% and 1% :-)) Iain But the 2H which is present due to unmatched tubes is usually much less than the 3H in a PP amp. Having a balance adjustment means another darn thing that can go wrong, and often in an anode circuit of a driver tube with dc flowing in a pot. I have seen the results and had to repair them, and usually its a case of removing the pot and replacing it with fixed resistors to ensure equal balance with a given tube type such as a 6SN7 in a LTP driver/phase splitter which does not have ccs tail. Subsequent replacements with other 6SN7 will all give very close balance. Even with most old output tubes, the 2H is low. If there is an SE input tube before the LTP which has been balanced to equality, then the 2H of the input tube is included at the output. often reversing the positions of output tubes will make the 2H less due to cancelations. But trying to unbalance the ac drive to have output stage 2H cancel previous stage 2H seems mad. Better to make the amp have low thd to begin with, and the mild NFB will reduce all THD OK. Patrick Turner. |
Reply |
Thread Tools | |
Display Modes | |
|
|
Similar Threads | ||||
Thread | Forum | |||
How important is it to balance my speaker connections? | Pro Audio | |||
How to Adjust Balance on JL 300/4 Amp | Car Audio | |||
WTB: BRYSTON 10B PRO (Balance) SUB | Marketplace | |||
WTB: BRYSTON 10B PRO (Balance) SUB | Marketplace | |||
System balance for LP? | Audio Opinions |