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-   -   Split Feedback (http://www.diyaudio.com/forums/solid-state/3558-split-feedback.html)

sdman 14th May 2002 03:18 AM

Split Feedback
 
Wrinkle your brows on this one guys.
Looks rather interesting.
www.altmann.haan.de/splif_page/

GRollins 14th May 2002 03:41 AM

Well, for one thing, a "non-inductive resistor" is hardly a good stand-in for most real world loudspeakers. You could start a prolonged argument as to whether the guy's logic is flawed on this point. I'm just noting this in passing.
You're losing power when you remove a pair of output devices. In the case of one pair, when you add a pair to act as proxies, you're going to load the power supply down; possibly with dire consequences.
I'd question some amplifiers' stability when faced with modifications to the output stage.
Assuming that you can get the thing to work (for this, I'd recommend designing an amp from the ground up, rather than modifying an existing one), I have no doubt that it sounds different...but does it sound better?
Sounds like sophistry to me.

Grey

jam 14th May 2002 05:05 AM

A very interesting idea. He is actually compensating for non-linearities in the output stage (with feedback) but the reactive nature of the load will not affect the the feedback loop.

Might be a good, idea the only problem I see is the output stage (not in the feedback loop) has to be large to maintain a low output impedence.

This might make a good comparison to a circuit with nested feedback loops.

Jam

Ren Hoek 14th May 2002 09:49 AM

His idea is not new. I bet your friend Nelson Pass knows this one, man.

Ren

Nelson Pass 14th May 2002 09:00 PM

Actually I have not encountered this, although it is
an interesting and imaginative idea.

Of course it won't correct for things that a real life
load will do, but then again we aren't always looking
for that either.

Pete Fleming 15th May 2002 05:05 AM

I have also never seen this idea before and think it has great merit

jan.didden 16th May 2002 08:37 PM

I looked at it, I wouldn't say interesting, rather weird. Look at the schematic under 'this is it':
He uses feedback to linearize the output of the block 10. Due to the nature of feedback, this will result in the input to '10' to be heavily distorted. Then he uses this heavily distorted node to feed the stage that drives the speaker. And claims it sounds much better....
As I said, weird.

GRollins 16th May 2002 10:40 PM

I've been mulling this over and it might be interesting to pursue for drivers that present a purely resistive load, i.e. ribbons, planars, etc. I still don't like the idea of modifying an existing circuit, but a from-the-ground-up design might be interesting.
Hmmm...wonder if it's too late to stick this into the Aleph-X...

Grey

Greg Erskine 17th May 2002 10:25 AM

I though it sounded plausible until I saw another one of his pages.

www.altmann.haan.de/tubeolator/default.htm

Think this will work?

Greg

Nelson Pass 17th May 2002 07:02 PM

I guess Altmann is more than a one idea guy. :)

It strikes me that the SPLIF amp will work better if you
can presume matching between the output stages, and
if you adjust the load of the fed-back stage to look like
the speaker load.


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