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Old 24th June 2010, 02:33 PM   #1
wwenze is offline wwenze  Singapore
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Default What happens if you put a resistor parallel to the potentiometer?

A hypothetical question: say I have a 100k volume control at the amplifier's input, it picks up noise due to its high impedance,

If I put connect a 10k resistor between input and ground before the transformer, lowering the input impedance seen by the source and noise, will this result in less noise?
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Old 24th June 2010, 03:29 PM   #2
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If u put across wiper & ground ..The LIN becomes a LOG potentiometer..
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Old 25th June 2010, 04:18 AM   #3
Enzo is offline Enzo  United States
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On the left under regular features, select the first one - FX Skils/How Tos, then on the resulting list scroll down to "The Secret Life of Pots." Read that article. It not only describes pots in detail, but it also gets into how adding parallel resistors in various ways can change the resistance tapers.
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Old 25th June 2010, 04:30 AM   #4
gootee is offline gootee  United States
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Quote:
Originally Posted by wwenze View Post
A hypothetical question: say I have a 100k volume control at the amplifier's input, it picks up noise due to its high impedance,

If I put connect a 10k resistor between input and ground before the transformer, lowering the input impedance seen by the source and noise, will this result in less noise?
Yes, it will lower the noise, because of the lower impedance. But then why not use a 10K pot?

Resistors also generate noise, all by themselves, with higher resistances generating more noise. So it would be good to always try to minimize the values of resistors, when designing for low noise, as long as other contraints do not cause you to sacrifice too much.
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Old 25th June 2010, 06:41 AM   #5
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Quote:
Originally Posted by wwenze View Post
A hypothetical question: say I have a 100k volume control at the amplifier's input, it picks up noise due to its high impedance,

If I put connect a 10k resistor between input and ground before the transformer, lowering the input impedance seen by the source and noise, will this result in less noise?
Don't forget that for noise purposes, the source output impedance must be considered as in parallel to the pot. Most sources (CD players, preamps) have at most a few 100 ohms output impedance, tube preamps maybe a few k max. So paralleling the 100k pot with 10k doesn't do anything for the noise.

Edit: I was talking about noise generated by the pot resistance. Re-reading again I think you mean external noise picked up. In that case the parallel resistor might work. But remember, with the pot in mid position, the resistance 'seen' from the amp (and seen by the external noise source into the amp input) is about 25k. That will not change with a parallel resistor.
Why not just try it? You can't break anything!

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Last edited by jan.didden; 25th June 2010 at 10:29 AM.
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Old 25th June 2010, 07:39 AM   #6
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I use a Technics SU-C800U preamplifier case and it's original potentiometer which i find very good. I changed everything else inside.
The original preamp layout also picked up noise when the pot's wiper was somewhere in the middle of the course.
I got around this problem by connecting the pot's metal chassis directly to the preamp metal chassis while the pot's ground pin connected to the audio ground only.
Also i added extra shielding wherever possible. hope this helps.
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