Whats a Good 6L6 circuit? - Page 3

hacknet · 24th April 2004, 09:16 PM

one question, i recall EC8010 saying that David Hafler solve some oscillation problems by increasing the coupling capcacitors. the original issue uses a 0.25uf cap and the "revised" a 0.22uf. could i be a smart **** by putting 0.47uf?

EC8010 · 24th April 2004, 09:43 PM

I've been searching desperately to find the article (I think it was Hafler), but I just can't seem to find it I have a feeling that the coupling capacitors were made quite a bit bigger, perhaps 1.5uF.

SY · 24th April 2004, 09:50 PM

Quote:

Originally posted by EC8010
I've been searching desperately to find the article (I think it was Hafler), but I just can't seem to find it I have a feeling that the coupling capacitors were made quite a bit bigger, perhaps 1.5uF.

Hafler and Keroes, Audio Engineering, reprinted in Audio Anthology v2, "Ultra-Linear Operation of the Williamson Amplifier".

Quote:

from Hafler and Keroes

The low frequency time constants of the original circuit's interstage coupling networks were the same for both such networks. This is not particularly desirable in a feedback amplifier... Increasing one pair of coupling capacitors from 0.05uF to 0.25uF... increases the low frequency stability margin at nominal increase in cost.

EC8010 · 24th April 2004, 10:31 PM

SY: Thank you for that. I "knew" it was a factor of 5:1, hence my guess at 1.5uF!

analog_sa · 24th April 2004, 11:21 PM

Hacknet

Andy's suggested circuit is much better than a Williamson. That is if you want to build a modern sounding amp and not just something of historical value.

Going as far back as the sixties amp builders noticed the Williamson plays better in mono than stereo. Lots of NFB keeps the sound strictly in the speakers, kills dynamics and soundstaging and together with the excessively repetitive use of 6SN7 produces cold and boring (for a tube amp) mids.

fdegrove · 24th April 2004, 11:37 PM

Hi,

Quote:

Lots of NFB keeps the sound strictly in the speakers, kills dynamics and soundstaging and together with the excessively repetitive use of 6SN7 produces cold and boring (for a tube amp) mids.

As an example:

I have a PP 2A3 amp that uses only local FB, no global loop whatsoever...
The soundstage that little amp can throw is little short of amazing.

With any decent recording you can plunk the speakers down, even only 4-5 foot apart, you just can't tell the sound comes from those speakers.
That's not to say the amp is perfect, it isn't.
For what it cost me however it's a joy to listen to.

Cheers,

arnoldc · 25th April 2004, 01:58 AM

Quote:

Originally posted by fdegrove
[B]I have a PP 2A3 amp that uses only local FB, no global loop whatsoever...
The soundstage that little amp can throw is little short of amazing.

Hi Frank, i've been wanting to make a PP 2A3 and been contemplating on the JE Labs PP 2A3. However, I want to try one of yours. Is that at all possible? Share the schematic or is this a commercial amp?

hacknet · 25th April 2004, 02:34 AM

hmm... williamson or not williamson...

i`ll have a look and see what i decide on... the rest look quite game on a williamson.

andyjevans · 25th April 2004, 10:44 AM

That's not to say the amp is perfect, it isn't. For what it cost me however it's a joy to listen to.>

That's exactly my response to taking off the global feedback loop - joy! The sound just makes you like it - happy pills. Haven't got a clue how this effect measures, but I was just grinning when I heard the sound without feedback. If I'm reading the language correctly, others seem to have a similar response. Not to say that others don't grin when they add feedback - I'm sure this happens too.

hacknet · 25th April 2004, 01:02 PM

what trans did you guys use? i`m considering a tamura or a custom winder.

24th April 2004, 09:43 PM	#22
EC8010 diyAudio Moderator Join Date: Jan 2003 Location: Near London. UK	I've been searching desperately to find the article (I think it was Hafler), but I just can't seem to find it I have a feeling that the coupling capacitors were made quite a bit bigger, perhaps 1.5uF. __________________ The loudspeaker: The only commercial Hi-Fi item where a disproportionate part of the budget isn't spent on the box. And the one where it would make a difference...

24th April 2004, 10:31 PM	#24
EC8010 diyAudio Moderator Join Date: Jan 2003 Location: Near London. UK	SY: Thank you for that. I "knew" it was a factor of 5:1, hence my guess at 1.5uF! __________________ The loudspeaker: The only commercial Hi-Fi item where a disproportionate part of the budget isn't spent on the box. And the one where it would make a difference...

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24th April 2004, 09:16 PM	#21
hacknet diyAudio Member Join Date: Nov 2002 Location: sg	one question, i recall EC8010 saying that David Hafler solve some oscillation problems by increasing the coupling capcacitors. the original issue uses a 0.25uf cap and the "revised" a 0.22uf. could i be a smart **** by putting 0.47uf?

24th April 2004, 11:21 PM	#25
analog_sa diyAudio Member Join Date: Aug 2002 Location: Sofia	Hacknet Andy's suggested circuit is much better than a Williamson. That is if you want to build a modern sounding amp and not just something of historical value. Going as far back as the sixties amp builders noticed the Williamson plays better in mono than stereo. Lots of NFB keeps the sound strictly in the speakers, kills dynamics and soundstaging and together with the excessively repetitive use of 6SN7 produces cold and boring (for a tube amp) mids.

25th April 2004, 02:34 AM	#28
hacknet diyAudio Member Join Date: Nov 2002 Location: sg	hmm... williamson or not williamson... i`ll have a look and see what i decide on... the rest look quite game on a williamson.

25th April 2004, 10:44 AM	#29
andyjevans diyAudio Member Join Date: Sep 2003 Location: London	That's not to say the amp is perfect, it isn't. For what it cost me however it's a joy to listen to.> That's exactly my response to taking off the global feedback loop - joy! The sound just makes you like it - happy pills. Haven't got a clue how this effect measures, but I was just grinning when I heard the sound without feedback. If I'm reading the language correctly, others seem to have a similar response. Not to say that others don't grin when they add feedback - I'm sure this happens too.

25th April 2004, 01:02 PM	#30
hacknet diyAudio Member Join Date: Nov 2002 Location: sg	what trans did you guys use? i`m considering a tamura or a custom winder.

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