The Red Light District - another PP EL84 amp

[ttan98]

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]

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]

Originally Posted by SY

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

[weinstro]

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]

Small room, I hope. 120W for those sounds about right.

Now if you have some Quad 57s...

[weinstro]

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]

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

[ttan98]

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]

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]

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.