The Red Light District - another PP EL84 amp - Page 59

ttan98 · 20th November 2009, 05:29 AM

Sy,

I think you must have looked into using the voltage regulator, LM317 as a current sink, I see nothing wrong with using it.

Did you shelf the idea? Any particular reason why?

SY · 20th November 2009, 08:43 AM

As a current sink for what? The output stage? If so, it's a not-so-good idea. It makes the overload recovery much worse, is unsuitable for AB operation, and the LM317 is a pretty mediocre (OK, downright lousy) current sink at high frequencies. What you want there is a constant voltage sink, and one which recovers instantaneously and without incident after overload. The LEDs fit the bill perfectly.

Some people use a current sink that's heavily bypassed, but again, this is an approach that severely compromises overload recovery, not to mention passing the output signal through some big, ugly electrolytic caps.

Yvesm · 20th November 2009, 09:18 AM

Quote:

Originally Posted by SY

. . . not to mention passing the output signal through some big, ugly electrolytic caps.

weinstro · 20th November 2009, 12:52 PM

SY,

I'm just starting out here, but this is extremely intriguing. As long as I'm still in the "paper tiger" phase, what should be my expectations with the RLD driving my 86-87 dB @ 1w, 4 ohm, small vented two-way loudspeakers?

I doubt these were optimized for a tube amp. My "reference" amp is a Marantz MA-5, which is 120W, solid state.

Thanks!

SY · 20th November 2009, 12:57 PM

Small room, I hope.

120W for those sounds about right.

Now if you have some Quad 57s...

weinstro · 20th November 2009, 06:47 PM

Quote:

Originally Posted by SY

Small room, I hope.

120W for those sounds about right.

Now if you have some Quad 57s...

Maybe 14' x 20'. Should I be thinking of paralleled outputs, bi-amping, or just plain bigger?

SY · 20th November 2009, 06:49 PM

Bigger. Much bigger. That's a 100 watt room/speaker setup ya got there.

ttan98 · 20th November 2009, 09:08 PM

The series resistance of LED is by no means negligible, besides 5-6 LEDs in series, the total resistance adds up.

Nowadays one can get high quality caps from Panasonic eg Silmic or FM series, in AC mode the series impedance to gound is negligible. I see no reason not to use bypass caps. At the end of the day, design is compact and does the job well.

SY · 20th November 2009, 09:16 PM

Other than blocking, which is a very serious problem, and the Achilles' Heel of nearly every self-biased output stage. And the sonic problems (real and imagined) of having that big electrolytic directly in the output stage signal current path.

The impedance of the arrays is about 4-5R, pretty negligible. And common mode to boot. And flat as far out as I can measure, certainly not the case for LM317s nor big honkin' electrolytics.

TheGimp · 21st November 2009, 02:52 AM

Well, I finally finished reading this thread start to finish. It took three days off and on.

I was going to try a LM317 current source for the Sven 6P1P, but now I think I'll try LEDs instead.

Thanks to all who contributed to this thread.

20th November 2009, 05:29 AM	#581
ttan98 diyAudio Member Join Date: Apr 2006 Location: Melb	Using LM317 as Current sink Sy, I think you must have looked into using the voltage regulator, LM317 as a current sink, I see nothing wrong with using it. Did you shelf the idea? Any particular reason why?

20th November 2009, 08:43 AM	#582
SY Tetsujin diyAudio Moderator Join Date: Oct 2002 Location: Austin, TX	As a current sink for what? The output stage? If so, it's a not-so-good idea. It makes the overload recovery much worse, is unsuitable for AB operation, and the LM317 is a pretty mediocre (OK, downright lousy) current sink at high frequencies. What you want there is a constant voltage sink, and one which recovers instantaneously and without incident after overload. The LEDs fit the bill perfectly. Some people use a current sink that's heavily bypassed, but again, this is an approach that severely compromises overload recovery, not to mention passing the output signal through some big, ugly electrolytic caps. __________________ "We all feel like that, Reggie, now and then, especially when Spring is upon us, but few of us would care to put it on our cards." — Sir Archibald Clerk-Kerr

20th November 2009, 12:57 PM	#585
SY Tetsujin diyAudio Moderator Join Date: Oct 2002 Location: Austin, TX	Small room, I hope. 120W for those sounds about right. Now if you have some Quad 57s... __________________ "We all feel like that, Reggie, now and then, especially when Spring is upon us, but few of us would care to put it on our cards." — Sir Archibald Clerk-Kerr

20th November 2009, 06:49 PM	#587
SY Tetsujin diyAudio Moderator Join Date: Oct 2002 Location: Austin, TX	Bigger. Much bigger. That's a 100 watt room/speaker setup ya got there. __________________ "We all feel like that, Reggie, now and then, especially when Spring is upon us, but few of us would care to put it on our cards." — Sir Archibald Clerk-Kerr

20th November 2009, 09:16 PM	#589
SY Tetsujin diyAudio Moderator Join Date: Oct 2002 Location: Austin, TX	Other than blocking, which is a very serious problem, and the Achilles' Heel of nearly every self-biased output stage. And the sonic problems (real and imagined) of having that big electrolytic directly in the output stage signal current path. The impedance of the arrays is about 4-5R, pretty negligible. And common mode to boot. And flat as far out as I can measure, certainly not the case for LM317s nor big honkin' electrolytics. __________________ "We all feel like that, Reggie, now and then, especially when Spring is upon us, but few of us would care to put it on our cards." — Sir Archibald Clerk-Kerr


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20th November 2009, 12:52 PM	#584
weinstro diyAudio Member Join Date: May 2003 Location: California	SY, I'm just starting out here, but this is extremely intriguing. As long as I'm still in the "paper tiger" phase, what should be my expectations with the RLD driving my 86-87 dB @ 1w, 4 ohm, small vented two-way loudspeakers? I doubt these were optimized for a tube amp. My "reference" amp is a Marantz MA-5, which is 120W, solid state. Thanks!

20th November 2009, 09:08 PM	#588
ttan98 diyAudio Member Join Date: Apr 2006 Location: Melb	The series resistance of LED is by no means negligible, besides 5-6 LEDs in series, the total resistance adds up. Nowadays one can get high quality caps from Panasonic eg Silmic or FM series, in AC mode the series impedance to gound is negligible. I see no reason not to use bypass caps. At the end of the day, design is compact and does the job well.

21st November 2009, 02:52 AM	#590
TheGimp diyAudio Member Join Date: Aug 2009 Location: Johnson City, TN	Well, I finally finished reading this thread start to finish. It took three days off and on. I was going to try a LM317 current source for the Sven 6P1P, but now I think I'll try LEDs instead. Thanks to all who contributed to this thread.

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