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Old 15th August 2011, 10:35 PM   #1
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Default Shunted pot?

I tried this mod on an amp I'm repairing at the moment - it was fitted with an alps blue 250k. Anytime i've tried these in the past i've always found them to be "veiled". So I thought I'd try the shunt and am very impressed by the result.

Anyone else done this & what have you thought of it?

Details: Shunt Pot Volume Control for Better Sound and/or Gain Reduction - World-Designs-Forum



Fran
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Old 16th August 2011, 10:54 AM   #2
DF96 is offline DF96  England
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This seems to be a bad idea, as it deliberately puts signal current through the lowest quality resistance in the circuit: the wiper-pot contact. In the normal arrangement, this contact only has to supply the tiny input current for the next stage. It also changes the load on the previous stage which might vary the LF response, depending on the capacitor at the output.

So the most likely outcome is a small increase in distortion, and volume-dependent LF response.
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Old 16th August 2011, 11:46 AM   #3
Mooly is offline Mooly  United Kingdom
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The article mentions, and to me this is the best bit, that by choosing a metal or carbon series resistor the sound can be made "warmer" or "brighter and clearer". Perhaps a series chain of MF and CF resistors could be employed to tweak the result even more...

DF96... I think spot on with your observations.
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Old 16th August 2011, 12:49 PM   #4
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Yes, all fair points indeed.

But have any of you actually tried it?
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Old 16th August 2011, 12:50 PM   #5
DF96 is offline DF96  England
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Yes, choose your favourite type/amount of distortion. Instead of swapping resistors, it would be much more user-friendly if people adopted Wavebourn's idea (in a thread which I can't be bothered to search for) of a knob to adjust 'musicality' by varying the amount of low-order distortion.

Quote:
But have any of you actually tried it?
No, why would I want to try a bad idea? Should I try to deliberately oxidise my plugs and sockets, just to see what it sounds like?

Last edited by DF96; 16th August 2011 at 12:52 PM. Reason: expand
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Old 16th August 2011, 12:59 PM   #6
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Quote:
Originally Posted by DF96 View Post


No, why would I want to try a bad idea? Should I try to deliberately oxidise my plugs and sockets, just to see what it sounds like?
OK, valid reasons why you don't want to go there.

Moving along swiftly so, has anybody else tried it?

Fran
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Old 16th August 2011, 01:23 PM   #7
AndrewT is offline AndrewT  Scotland
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The pot can and is replaced by a bank of switched resistors.
That is a topology that some will have tried.
I have when I require only a limited range of SPL adjustment.
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Old 16th August 2011, 02:22 PM   #8
kevinkr is offline kevinkr  United States
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Quote:
Originally Posted by woodturner-fran View Post
OK, valid reasons why you don't want to go there.

Moving along swiftly so, has anybody else tried it?

Fran
Yes, and despite the valid technical objections I find it sounds significantly better than the Alps Blue 250K does used in the conventional sense. That said I would consider it a band-aid on the path to acquiring a better pot or stepped attenuator.

Something to bear in mind is that the load impedance presented to the source varies dependent on setting so it is important that the source have a much lower source impedance to avoid potential inter-actions.. (distortion and LF response issues)

This shunt connection is pretty SOP for balanced inputs FWIW..

Andrew's suggestion is a good one for the situation where the required gain range is relatively limited.
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Old 16th August 2011, 07:46 PM   #9
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Kevinkr: your experience matches my own. Like you I wantt o replace it with a stepped pot, but my normal first choice was out of stock, so I wanted to try this in the meantime. I'm surprised by what I hear!

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