PS Audio Preamp clean-up-Scratchy Volume/switches

mmadden28

I have a nice PS Audio 5.0 preamp that had a nasty scratchy sound whenever I changed the volume.

I was going to resolve that issue by doing a quick spray with some switch/potentiometer cleaner while I did the full cleanup on the unit to include cleaning and treating all the RCA jacks with DeOxit, etc. When I opened the preamp, I was surprised to find that the Volume potentiometer was essentially sealed, so there was no way for me to spray anything in there to clean it out. :frown:. Then I noticed a couple screws on it. Cool, I can take it apart and do a real cleaning job on it.

This is what the Volume control (potentiometer or POT) looks like--this is a stock pic as I forgot to take a pic of it before I disassembled it (or reassembled for that matter).

It's a Nobel 100k dual audio pot, apparently a quality part. This is no plastic case-its metal, and thick at that. Each channel is its own circuit board, Nice! Unfortunately Nobel stopped making these back in '97 or something like that and are hard to source. At least they can still be found for about $50 each. I never could fathom why a volume control could cost $50, but after seeing the build construction of this, now I see why. I can also see why higher end audio equipment can demand higher prices (assuming of course it's using quality components in side.

It was not easy to take apart because it was soldered to a board--ultimately I was successful in taking it apart but it was a feat. I was out of desoldering braid and was unsuccessful using just a solder sucker so I had to do it without removing the pot from the board--It would have been so much easier had it not been soldered to the board though.

What follows are a bunch of pics for your viewing entertainment...

Pic of the back of it with the model/value-.:


..with the back cover removed


A few shots with the wiper visible and also all the dirt and grime. No wonder the thing is scratchy.




..with the wiper removed


Above was all just one channel--getting to the other wiper was a feat.
Here's a shot of the other channel:



I gave it a good clean with some contact cleaner and a gentle brushing:



And then cleaned with Deoxit, gently wiped, and followed up with Deoxit Gold:


And "How ya like me now!?!?" - Ahhh nice and clean--What a difference huh? Looks almost brand new (except for the wiper wear marks)


I also cleaned the wipers for each channel as well, being very careful not to bend any of them. Then I reassembled the pot.

I went on to clean the entire preamp, sprayed all the dust and such off the board, and cleaned and treated all the RCA jacks. I also cleaned a few other switches as well. I'll post those pics here shortly.

When I restored the unit back to working condition and powered it up in the rig, the volume control was now PERFECT-not a noise :cool: Well worth the time and effort.

mmadden28

A quick shot of the rest of the preamp after a quick spray cleaning along with a gentle brushing.

mmadden28

And here are some pics of the multi position switches tha also got a bath. These are also of higher quality and able to be at least partially disassembled. I couldn't find a part #, but these are Lorlin PT rotary switches.

Note the ball bearings and spring. they are used inside the 'blue' control part that was removed. It allows for detents for selecting different inputs. A good solid 'click' with these switches. (Note: Don't lose the ball bearings--there's nothing like searching for one for about 20 minutes. :redface:)



The contacts and wiper contact are both in this almost sealed unit. Unfortunately I was unable to disassemble this any further as its sort of riveted together.:


So I had to gently pull the clear plastic cover back while I sprayed the contact cleaner in, and followed up with Deoxit so it could do its job. I tried to pseudo brush the contacts by passing a peice of paper between the contacts and the contact wiper to remove any heavy residue or oxidiation. Then I rinsed again with contact cleaner and finally a quick short burst of Deoxit Gold.


And a side by side:

Note the heavy oxidation on the traces and the lack of it inside behind the clear plastic. Even though its not a true seal, it apparently has prevented the inner contacts from also oxidizing. :cool: I guess these are the Silver contact plating version.

The end result isn't as dramatic as the Volume pot, but there is a difference, especially where the contact wiper slides.

I hadn't noticed any stray noises when switching prior to cleaning but I figured I might as well do it all and do it right if I am going to do it at all ya know? :cool:

ben62670

Nice tedious clean up Bro!

George Grand

Nice preamp.

mmadden28

Thanks Ben.
----
It is isn't it George? I picked it awhile back up from some audio nut.
By the way I did build a power supply for this--Scott McGowan had sent me the Service Manual and schematic for it. I didn't put it in an enclosure yet, its just hooked up haphazardly right now. It's one of those 'let me get this hooked up and see how it works and then never get around to it' kind of things ya know? And Damn, the transformer could power a full size amp--holy crap. I'll post those pics to as soon as I put it i an enclosure.
It's running pre and phono-pre duties for the Yammy TT and Carver Amazing Plats setup right now.