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Andre Jute Andre Jute is offline
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Default 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

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John Byrns John Byrns is offline
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Default 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/
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Phil Allison Phil Allison is offline
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Default 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


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Patrick Turner Patrick Turner is offline
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Default 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

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tubegarden tubegarden is offline
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Default 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




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Iain Churches Iain Churches is offline
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Default 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



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Patrick Turner Patrick Turner is offline
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Default 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.
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