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Old 23rd August 2008, 02:27 PM   #11
Manu is offline Manu  Europe
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Location: Vienna, Ostrich
Thanks a lot for responding my questions.
I thought there were sort of rule of thumb concerning res value related to pot value, like R Res = Pot R or little less, or so.
But I see it is not that trivial...

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Old 24th August 2008, 04:21 AM   #12
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Originally posted by analog_sa
Unfortunately the shunt connection is also a bit contoversial: per example Peter Daniel, whose opinions i hold in high regard is not a fan.

The series resitor value is a compromise between the lowest load that the preceding stage can drive and the highest output impedance of the attenuator acceptable.

Regarding the wiper issues which Mr Pass mentioned, one way to minimise the effect is a constant resistor between wiper and ground at around x10 the pot value. A high input impedance stage following the pot like a tube or a fet also helps.
Remember the basics of Thevenin equivalence. A pot with distortion
doesn't get better just because it goes to ground. People think that
if a component is not literally in series with the signal path, then it's
all better. It's not.

When you load the wiper, you change some characteristics, but in
doing so you can exacerbate its distortion.

vocabulary word for the day: Exacerbate

usage example: If you exacerbate, you'll go blind. (Stop when you
just need glasses.)

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Old 24th August 2008, 08:35 AM   #13
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Originally posted by Nelson Pass

vocabulary word for the day: Exacerbate

usage example: If you exacerbate, you'll go blind.

It would have worked in my case if there was a threat of going deaf.

The loading addresses a different distortion mechanism, maybe the two are self-cancelling at a sweet spot?
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Old 26th August 2008, 12:52 AM   #14
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Originally posted by Nelson Pass

People think that if a component is not literally in series with the signal path, then it's all better. It's not.

I've fought this same conceptual battle for years. The basic idea seems to be quite seductive considering how hard it is to dissuade people once they've got it in their heads.
The only analogy I've ever found to work is that of a photographic negative vs. a positive. Most people, when they think of a picture, think of a positive. Nothing wrong with that. It's pretty much the way we see the world on a day to day basis and it seems intuitively obvious. But if you look at a photographic negative, you'll see that it contains all the same information, just reversed, dark for light. But to say that it lacks the information is incorrect. It's only a matter of whether it's additive or subtractive.
I admit that this does not convince everyone--it's just the best analogy I've been able to come up with so far.
My definition of 'in the signal path' is if I can see signal at a given point with an oscilloscope. If there's a signal, then from my point of view it's having some sort of interaction with the music we hear.

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