Help With Alps Volume Pot Noise

JimOfOakCreek · 30th April 2011, 08:22 PM

Can someone help me with this peculiar issue?

I replaced a cheap 100K Ohm volume pot on an tube amplifier kit with a 100K Ohm Alps Blue Velvet volume pot. With the Alps volume control at the extreme ends, near the most quiet and near the most loud, I get a slight hum with a noise, a sort of rushing sound.

Between those extremes the Alps volume control is dead quiet.

The original cheap volume pot had a similar issue but less pronounced.

This was an S5 Electronics K12G kit. I did remove two 0.22uf DC blocking caps in line with the two inputs.

TubeManiac · 30th April 2011, 08:29 PM

you can try 100ohm grid stopper. or put the DC blocking caps back.

ilimzn · 30th April 2011, 08:29 PM

You might have an oscillation problem, as well as a ground issue. The residual resistance of the Alps in both extreme positions is only a few tens of an ohm, unlike cheap pots where it's 10x more, which may account for the less pronounced effect with the cheap pot. For an experiment try connecting a ~1k resitor in series getween the pot wiper and the amp input, and report what happens.

Michel · 30th April 2011, 11:48 PM

Make sure there is no measurable DC on the pot. If DC is present, you will always have the kind of noises you describe.

30th April 2011, 08:22 PM	#1
JimOfOakCreek diyAudio Member Join Date: Apr 2007 Location: Oak Creek, WI	Help With Alps Volume Pot Noise Can someone help me with this peculiar issue? I replaced a cheap 100K Ohm volume pot on an tube amplifier kit with a 100K Ohm Alps Blue Velvet volume pot. With the Alps volume control at the extreme ends, near the most quiet and near the most loud, I get a slight hum with a noise, a sort of rushing sound. Between those extremes the Alps volume control is dead quiet. The original cheap volume pot had a similar issue but less pronounced. This was an S5 Electronics K12G kit. I did remove two 0.22uf DC blocking caps in line with the two inputs. __________________ HiFi - Jazz - Wine

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30th April 2011, 08:29 PM	#2
TubeManiac diyAudio Member Join Date: Feb 2010	you can try 100ohm grid stopper. or put the DC blocking caps back.

30th April 2011, 08:29 PM	#3
ilimzn diyAudio Member Join Date: Feb 2005 Location: Zagreb	You might have an oscillation problem, as well as a ground issue. The residual resistance of the Alps in both extreme positions is only a few tens of an ohm, unlike cheap pots where it's 10x more, which may account for the less pronounced effect with the cheap pot. For an experiment try connecting a ~1k resitor in series getween the pot wiper and the amp input, and report what happens.

30th April 2011, 11:48 PM	#4
Michel diyAudio Member Join Date: Nov 2004 Location: L'Assomption, QC	Make sure there is no measurable DC on the pot. If DC is present, you will always have the kind of noises you describe.