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Old 10th April 2005, 01:11 AM   #11
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Uhhh...

Compression is noted, and the first thing you suspect...are *coupling capacitors*!?

Yeesh, what are audiophools writing about these days!? omg...(trails off mumbling)

No, compression comes from resistance. One way is power supply resistance, another is bias. A PP amp played side by side with an SE amp may be perfectly balanced at low volume, but the SE drops out at higher SPL due to the output stage beginning to cut off, moving operating point towards class AB, increasing current draw - subsequently increasing bias voltage, which reduces gain. In the case of PS resistance (excessively lossy inductors or intentional resistance), plate voltage sag occurs, though not as significant as the amplified effect at a self-biased cathode.

Fixed bias inherently does not compress as much for this reason.

All in all, I'm with SY. You get the most out of things LOUD. My Metallica collection knows this.

Tim
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Old 10th April 2005, 02:37 AM   #12
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Quote:
Originally posted by SY
Sound engineer? Your problem is probably more related to the volume control knob and its setting. Sound engineers listen to things LOUD. A wimpy little tube amp in a home setting won't satisfy them.
Slow down hot dog! When I get home from my columns of JBL VerTec line array, digital crossovers (can't believe hi-fi guys use those things by CHOICE) and mega-watt amplifiers I switch on my Darling. Only thing that keeps me sane!

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Old 10th April 2005, 02:50 AM   #13
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Old 10th April 2005, 08:08 AM   #14
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Kathodyne,

like Tim (Sch3mat1c) already said, go for fixed bias.
Besides his arguments it will sound better cause you loose the 220uF electrolytic out of the signalpath.
No matter what TriodeDick says, fixed bias is better and sounds better.

Back to your problem, did you check your output trans. ?
Is it 6k primary ? did you connect it right ?
I spoke to another dutch diy some time ago who also build this amp and he was very disappointet with the sound. He found out that for one thing his output transformer had the wrong primary impedance. Don't remember where and how he got it, but it's worthwhile to check this.

Dick.
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Old 10th April 2005, 12:28 PM   #15
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hi,

@sch3matic(@dj middelkoop for the trannies)
Well... i changed a lot to this amp. output transformers from 10k that caused oscillation to 6k that don't. upto this new splitter stage...and the power supply.
I got some REAL good technical help from mattijs de vries (www.machmat.com)
to be honest i'm just a beginner with not so much technical background and the only thing i hadn't changed where the coupling capacitors
And after reading how they can affect bandwidth....i made an assumption....
but after reading some more it seems you can just 'set' them at where they begin altering, usually dis is thone way above 20khz and somewhere around 10 to 20hz...

I am led to think this has been properly done in anna's first design so (assuming) even with these new tubes it wouldnt give a dramatic difference

@robert morin
I know now that (if i understand mattijs's explanation). the lm317 at the cathodes of the 5965 provide an almost infinite rk. The choice is to use litlle current into a big load...so that the load line gets more horizontal... and it doesn''t matter much where the tube is being biased...

changing the bias point of the 5965 didn't help, it merely got things running quite hot:
The biggest mentioned here are:

- remove autobias which puts a big elektrolytic in the signal
* ok worthwile AND nice to try...the auto-fixedbias design from www.machmat.com (diy-kit)

- use ccs with a transistor.....(or tube???!!!) instead of the lm317


It seems i now know what i have to be doing!! buy stuff!!!!

Thanx a lot!


:- my: guess....within 6 years....NO part of Anna will have been in the original one -:
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Old 10th April 2005, 01:21 PM   #16
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Ok you're making progress here.
Try the fixed bias from Matthijs.
Matthijs is very knowledgable, following his advise will shurely help.

You're right with the coupling caps, the values are ok, leave them for now.
When your amp start sounding better you can try other brands to hear the sonic impact.

I don't use the 317 for CCS but use transisitors or (mos)fets.
So I cannot tell you if this will make an improvement.

Dick.

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:- my: guess....within 6 years....NO part of Anna will have been in the original one -:
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Old 11th April 2005, 05:59 AM   #17
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The first thing I would be doing is changing C4 and C5. Spend a bit of hard earned cash on some 470uF/100V Blackgate Standards.

As noted above cathode bias is always going to impart a "compressed" sound compared to fixed bias - me, I like it that way and have converted a couple of amps from fixed bias back to cathode bias. Make sure that YOU don't like it that way before paying any attention whatsoever to your audio engineer friend.

Cheers,
Ian
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Old 11th April 2005, 09:56 AM   #18
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Hi!,

Thank you all for your tips!

This morning i tried something else....i removed the 100ohm resistors from g2....

Well believe it or not, but this did do something....it clears up!
just to remove something!!

this in combination with the automatic fixed bias module which will arrive next week will do a lot of good, i'm sure!
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