Potentiometer - bushing length is a wee bit shy?!

[funkgang49]

Yes, gents, length does matter!

Just starting a new build and drilling holes for the control panel pots. I was planning on using insulated shoulder washers to allow each pot to be grounded to its respective star grounding point instead of the chassis. The chassis is .090 thick aluminum and I will be ordering an etched plastic faceplate from BNP lasers.

Problem is that when dry fitting all of my junk drawer pots (a mix of various value Alpha and CTS) I couldn't find a pot that had a bushing length sufficient to clear the chassis plus the thickness of a faceplate and still have enough bushing clearance to thread the retaining nut onto!

I know, I know, it sounds like a personal problem - I'm feeling a little short changed right now. Thing is that none of my pots had recently been swimming in a pool.

Any suggestions?

[Deric]

The Mojo branded CTS are usually long enough. Not available in a ton of values though...

[Ron Worley]

PEC

[Gaz]

Bourns pots from Apex Jr. are good for 1/16" faceplates and .100" chassis. They are actually a little longer even than PEC.

Also Mojotone Alpha Pots (the ones they make to imitate CTS pots)

[M Fowler]

You need to read the pots specs. Needs to have a thread length of 3/8 inch.

I use CTS from Mojotone or Alpha for Mojotone.

[rp]

I was planning on using insulated shoulder washers to allow each pot to be grounded to its respective star grounding point instead of the chassis.

The case isn't grounded to the circuit part of the pot, ie the track, unless you make it so soldering tabs to it or a bus soldered along the back of the pots. No real need for insulated washers and no need to solder any tabs to the back of the pot. I assume that's your goal, isolate the pots and run a bus soldered to them? Much easier to run each ground from the pot lug to your chosen ground point with a wire run, and that way you can be more specific with your grounds too. You can also run the bus only connected to the ground tabs but not the cases, if you have at least three tabs it should be plenty of support. But screw all that, if you ever have to replace a pot the bus thing is a PITA, individual wire ground runs are better IMO. And if a nut is a little loose you don't thundering noise as in fenders.

If you are thinking belt and suspenders, isolating the pots and not soldering a bus along the back, I wouldn't. You want the case of the pot to go to mains ground (chassis) rather than float for best shielding I would think, could even be dangerous isolating the case from mains ground if a hot wire ever came loose and made contact the shaft would have voltage on it.

[pdf64]

Agree, the pot cases may be seen as just screening extensions of the chassis, and unrelated to the amp's 0V arrangement.

[sliberty]

I thought that all of the "better" pots had bushings that were 3/8" x 3/8". No?

[funkgang49]

Thanks everyone!

I will run a wire from each pot lug to be grounded to its respective chassis ground point:
Volume 1&2 to V1 ground point
Treble & Bass to V2 (Cathode Follower) ground point
VVR ground to Main Ground Point

and lose the shoulder washers for the Pots. Now there is plenty of bushing length!

again, as always, size does matter!

By the way, I got the Mojotone CTS-style pots - great price. I'll give 'em a try.

Thanks pdf64, rp!