Insulation Tip - When Using Right Angle PCB Mount Pots

[Steve Mavronis]

(I had posted about the following infomation back in May 2010 as a reply to another thread that is buried in here someplace you'd have to search for. I thought this tip deserved attention on its own.)

I like 16mm Alpha pots. I'm usng this type at the moment which also act as my PCB support mounting.

Right Angle PCB Mount Alpha Single-Gang Audio Taper 16mm



Note that this shorter leg version leaves you only 1/10" between the bottom of the pot and PCB plane. By the time you factor in solder points it's almost touching leaving about 1/3 of that gap left.

To get around this I add rubber insulation using this 3M Tremflex 2155 Rubber Splicing Tape which is 30mil thick (about 4 1/3 layers of electrical tape) and rated for 600V. That white covering is just for separation between the tape layers in the roll and peels off.  A 3/4" by 22 foot roll costs $2.40 at Home Depot if anyone is interested in using this too:



This tape doesn't have any adhesive surface. It is used to wrap electrical wires for insulation and the layers fuse into each other. To use it as pot bottom insulation, just out a disk of rubber from it by tracing with an exacto-knife around a jack washer as a template. It cut easy and is an almost perfect fit on the bottom of a 16mm pot. Use super glue that works with rubber and metal (some don't) and while holding the rubber pad in place lift up one half to add a drop of glue underneath, press it down and repeat with the other half.

Alpha also have a longer leg version but I wanted maximum room for top side PCB components, and with the short version the PCB rests half way down into a 1590B enclosure.

[dune2k]

Hi,
I used foam rubber  (that kind you get at DIY/craft shops) between the bottom of the pot and the solder side. Works nice for me and is a lot less work. Just cut it out at about the size of the the PCB/pots and stick it in there. Since it's a little higher it holds in place pretty nicely.

[davent]

Lee Valley sell a good selection of small, clear self-adhesive bumper pads that should work well for what you need to do.  http://www.leevalley.com/en/home/Search.aspx?action=n

dave

[Steve Mavronis]

A lot of these bumper pads are too thick. I have 3/100ths of an inch space to work within between the solder points and pot. I already have a whole roll of the 3M tape anyways. I could surface 1000's of pots with that.

[caress]

foam.  cheap, easy to work with and you can just jam it in there to fit the space you're working with.

[Steve Mavronis]

I'll stick with what I have. It looks more professional and lasts forever.

[Paul Marossy]

I've never needed any insulation with a PCB mounted pot. Once that pot is soldered on, it's hard to move anything. Especially if you have two or more of them soldered onto a PCB.

[GP]

I agree with Paul here.

Not to detract from Steve's suggestion but even a small air gap is a damn good insulator at pedal voltages. Surely, the solder side is the opposite side of the PCB from the pot body anyway... given the picture Steve posted, i can't see any opportunity for shorting unless you really try to short it out.

The other comment i wanted to make was on the use of superglue. Whilst i know the alpha pots are enclosed body, many pot types aren't and the last thing you want to go dropping on a pot is superglue in this case.

[Steve Mavronis]

That generic picture was from a parts store, not my board. I'm careful with glue (being a scale modeler too) only using a small drop away from the edges so it won't drip off the pot back. I would prefer something ready made like the "pot condoms" available from GuitarPCB.com but didn't want to add more shipping costs from yet another place to the mix with the 2 other places I need for all my parts. On my PCB the pots are on the back solder side where the points do come close to touching and I didn't want to take chances even though when they are bolted on the case it would bridge over them but close. You can see the leg pins sticking up in this photo (3 pins bottom left and 3 pins top right) from my pedal build, with the component side facing you:



If these short leg Alpha pots were on the component side it wouldn't be an issue although parts can't fit under them so you'd lose valuable board space making it impractical to do. I didn't want to use the longer legged angle mount Alpha pots to save vertical space. Plus I like to see the parts side and the exposed IC socket makes it easy for swaping or replacing the op amp.

[Paul Marossy]

That generic picture was from a parts store, not my board. I'm careful with glue (being a scale modeler too) only using a small drop away from the edges so it won't drip off the pot back. I would prefer something ready made like the "pot condoms" available from GuitarPCB.com but didn't want to add more shipping costs from yet another place to the mix with the 2 other places I need for all my parts. On my PCB the pots are on the back solder side where the points do come close to touching and I didn't want to take chances even though when they are bolted on the case it would bridge over them but close. You can see the leg pins sticking up in this photo (3 pins bottom left and 3 pins top right) from my pedal build, with the component side facing you:



If these short leg Alpha pots were on the component side it wouldn't be an issue although parts can't fit under them so you'd lose valuable board space making it impractical to do. I didn't want to use the longer legged angle mount Alpha pots to save vertical space. Plus I like to see the parts side and the exposed IC socket makes it easy for swaping or replacing the op amp.

Very similar to how Wampler Pedals typically does things. Pretty efficient way of doing things.