[sdiy] Oberheim OB-8

[Kevin Lightner]

>Don't excuse yourself for an opinion Kevin, when it's based on facts. ;-)
>It seems necessary to repeat this pot-cleaning message once in a 
>while, even though it should be common knowledge by now. Many still 
>consider Radio Shack spray cans as the magic solution, just like the 
>manufacturer wants us all to believe.
>I've been spending half my life preaching that spraying (of any 
>kind) will not do any good. It's the only available quick-cure when 
>a pot suddenly develops a problem on stage or in the studio, and the 
>recommended thing to use in a situation like that, but replacing the 
>pot should be the next thing shortly after that.
>Better safe than sorry.
>
>Senso

There *are* some situations where spraying will help in the long 
term, but it's not the panacea that many believe. With some Rolands 
and Moogs for example (JP8, MPG80, Rogue, etc, etc) the rubber dust 
covers dry up and fall into the sliders. In this case, a flushing is 
a decent idea. If the wiper or resistive area is damaged though, 
obviously this won't help.

On OB8s, Sems and many other Oberheims, the resistive element is a 
thin layer applied to a backing material or phenolic piece. The 
higher values like 1meg are very thin and can come off with a spray.

On Minimoogs, I usually replace pots and always do when tuning is concerned.
The resonance pot is a 50K rev audio taper and is difficult to find, 
especially in a high quality type style.
So, I will often open these and attempt a manual cleaning. It also 
helps gauge what use the machine has seen, since the thickness of the 
wiper can be observed.
Mil-spec pots are usually pretty easy to find though, as they've 
adhered to many standard specs over the years. Finding split, 
half-moon or serated shaft pots is often much more difficult.
Also, I can't tell you how many pots I replace where someone drilled 
a hole in the back to allow the solvent in. Very often the pot or 
wiper assy is damaged or metal bits have scored the element.

But with many synths that come here, the boards are actually washed. 
I haven't seen any pots adversely affected by some pressurized hot 
water (soft water here.) I blow them out with an aircompressor and 
relube them, of course. With this method, exposed pots very often 
need no additional attention and haven't seen a harse solvent or 
runny lube. It may sound drastic, but often it's the kindest 
treatment they've seen in years, when done right.

Btw, here's a pic of two Arp 2600 slider shells.
The one on the left *was* sprayed repeatedly with a top quality 
industrial solvent.
The one on the right was disassembled, cleaned with acetone and 
polished with metal polish and a Q tip.
Guess which one feels better after lubing and reassembly ;-)

http://www.synthfool.com/rb2600ba.jpg

Here's a pic of what Cramolin can do to Ody slider contact wipers.
Plating came right off.

http://www.synthfool.com/cramolindamage.jpg




-- 
Regards,
Kevin Lightner

Myself: http://www.synthfool.com
Service and sales: http://www.moogmusic.com/service.php
Sales: http://www.cluboftheknobs.com