Noisy volume controls in old receivers

[jackinnj]

here I am plagued with noisy controls in the Pioneer SX838 which I purchased prechildren (now they are getting married! -- I carried this unit from Harvey Electronics to my office on 53rd Street on a hot summer day). I am wondering whom else out there hasn't given thought to the following solution to the noisy and failing volume controls in these great, power receivers -- something I have mentioned before. Use the existing control to drive the input to a serial ADC and use the ADC to drive a digital pot from ADI (www.analog.com). SMT, the real estate would be about 0.3 sq inch. Any comments?

[cowanrg]

just clean the pot and it will be back to normal. very simple to fix. its just dirt and grime in the knob itself.

[jackinnj]

the pots in the pioneer are almost impossible to get to to clean -- I've done it.

I think that the "dirtiness" in some small measure is due to forced-air cooling and heating -- which blows around a lot of dust, even with an electrostatic cleaner on the furnace. Thus the problem recurs.

[roddyama]

Hi Jack,

The “dirtiness” is usually due to oxidation. I will periodically go on a pot turning binge (once every few month) to “wipe” the oxidation away. This is not to say the force air heating and cooling has nothing to do with it, it is certainly a contributor. Most of my equipment is more then 20 years old and is still working fine with this routine.

Rodd Yamas***a

[MRehorst]

Noisy pots are often caused by DC getting to the pot via a leaky coupling capacitor. Check for electrolytic coupling caps and replace them with new ones. Film caps should be OK.

MR

[G]

Wouldn't it be easier to just replace the pots with some high quality plastic film pots? Why add more devices to the signal path?

[Neutron Bob]

The best solution I have seen is called Stabilant 22A, if I remember correctly. You have a litttle oxidation on the wiper surface. I think it was sold under the name "Tweek" years ago.

I just looked the juice up for you: http://www.stabilant.com/bccomp.htm

I think this clears up the air regarding Sumiko's sale of the product years ago. It is used today (22A) in VW/Audi electrical systems. I can assure you, unless you are dealing with very low signal or RF applications, it's the best thing since the invention of pre-sliced bread!

Use the genuine article. You'd be amazed at how well it works in potentiometers. If you are into camera repair, especially "heavy brass" vintage cameras (with analog computers for exposure control), the technicians swear by it.

Bobby

[MRehorst]

Originally posted by G
Wouldn't it be easier to just replace the pots with some high quality plastic film pots? Why add more devices to the signal path?

You misunderstood. I suggested replacing a defective capacitor that is already there (assuming it is there). IF the problem is DC on the pot due to a leaky coupling cap, replacing the pot will not solve the problem.

MR

[roddyama]

Hi Bobby, Jack,

Here’s what we had in the early 80’s. The stuff is called Cramolin. It was marketed by monster cable and then went to Craig Industries. It appears to be a German company as can be seen by its home page; yeah, the stuff is still around. I think in spray form.
http://www.cramolin.de/

Rumor has it that Craig was sited by the USEPA for the propellant they were using in the spray cans and blamed it on the anti-oxidant ingredients. This allowed them to change the formula and market it under the same name (reported to be less effective and probably cheaper).

I did use the stuff on my connectors, but it difficult to get at the Alps type sealed pots. It will go through my connectors again once I figure I have the system where I want it, and I know it will stay that way for a while.

Here’s a photo of the stuff.

Rodd Yamas***a