solder-side pots

[rutabaga bob]

Have come across several layouts lately that use board-mount pots attached from the solder side.  I've used straight-pin top mounted pots a few times, but never the 90 degree pots from under the board.  I build with single-sided perf.  Any advice, or a couple of pix?

[Phend]

Here is a Small Bear link
https://smallbear-electronics.mybigcommerce.com/single-gang-16mm-rt-angle-pc-mt-long-pin-linear-audio/

[idy]

Those that Phend linked to are long pins, the shorter ones are more common.

"All" the PCBs I have bought are like that: 90 degree pots mounted on the "back" of the board. Otherwise they would have to clear components.

Could you show us what you are looking at?

The "straight pin" ones I have used a few times... I think Tayda's boards use them.

[ElectricDruid]

Yeah, I always design things this style as well. Here's a couple of examples:




These both use the more common short-leads version of the right-angled Taiwan Alpha pots. Which Small Bear also have:

https://smallbear-electronics.mybigcommerce.com/single-gang-16mm-right-angle-pc-mount/

[rutabaga bob]

Forgive my lack of clarity.  I know what they are; what I need is some advice or pix about soldering them in, since the perf I have is not through-hole plated.  It's plain phenolic on one side, with pad-per-hole on the other.  Any trick to install, since the slender pin part won't be solderable?

[idy]

You are asking about inserting the pots from the back... so instead of soldering to the slender part you will have to solder to the fat part?

I notice that the wide part of the pin is also wide enough to touch the adjacent unused pad...

Options include using a drill bit and get rid of the two in-between pads?
Filing the pins?
Using a jig when soldering so the pins don't go all the way to the hilt? They seem plenty long enough. I have done this on boards where the pots need to line up with rotary switches.

[antonis]

It should be almost impossible 'cause you'll have to solder all three lugs after pots mounting/securing on enclosure..
(unless, of course, you've obtained the ultimate hole-shaft-pads alignment during drilling..)

[GibsonGM]

I also build everything on perf, and have come across this too - I just never bothered to work up a solution; I avoid this kind of pot.

I wonder if it would be possible to take a small rectangular piece of perf and flip it over, super glue it to the area where you want the pot and attach it, so the pads are "up".  Of course, this means filing or otherwise making the pot legs longer to go thru the extra material.  They are usually too wide for perf holes anyway as Tom's pics seem to show.  Then you could solder on the component side the way a 'real' PCB is made.  Use jumpers to bring the pot legs over to where they need to be.   It might work...or maybe would just be too MUCH work!  Depends on if having them on the back side really makes the build, I suppose...you'd gain a lot more room that way!

Antonis just beat my post - and his observation is extremely important, too....

[Govmnt_Lacky]

On multiple occasions, I have just used the solder LUG style pots and attached/soldered bits of resistor leads to the lugs to use as "legs" and then just soldered the "legs" to the pads.

[ElectricDruid]

Forgive my lack of clarity.  I know what they are; what I need is some advice or pix about soldering them in, since the perf I have is not through-hole plated.  It's plain phenolic on one side, with pad-per-hole on the other.  Any trick to install, since the slender pin part won't be solderable?

I've done this a few times. The trick is to not push the pots all the way down. The pot's pins are a very tight fit in perf holes which actually helps, since it'll generally stay in place while you solder it. You want a couple of mm of the narrow pin showing on the trackside, so you can solder to that. This also keeps the broader part of the pots leg away from touching other tracks. I don't know that I'd entirely recommend it, but it's ok for prototypes and it's certainly not impossible.

[rutabaga bob]

Thanks for the suggestions.  I will try and link to a layout shortly. 

[marcelomd]

Hi!
Make sure you test everything BEFORE soldering, the pots, because that's the last thing you'll do on the solder side.
I'll just leave a suggestion of using regular pots and attaching them with wires. This way you can move the. Around a bit.

[rutabaga bob]

http://effectslayouts.blogspot.com/2015/10/zvex-mastotron.html

Here's the example.  The little intro paragraph talks about using the 90-degree-leg pots.

EDIT: I thought about flipping the board over; this would allow me to solder the pins properly.  Not sure about installing components, though.

[Phend]

I have used a spacer between the pot and board as an aid for soldering. Yes these 90 pots have a wider lug that can span across the holes which may cause a short, so spacing is needed. Then from a cad layout I make a very accurate hole template for locating the pot mounting holes. The pot holes in the template are small, on center, which I then drill to size after removing the template. A drill press is handy for this.

[rutabaga bob]

Nice!  What is the thickness, approximately?

A wrinkle: I have read that, on such inverted-pot layouts, the pots are supposed to go in/on last.  That wouldn't allow a spacer to be clamped; might not allow a spacer, period.

Thanks!  I like it!  Might use this with my board-flipping idea.

[Phend]

That is an example, the black plastic is .125 inch thick. But any spacer thing could be used, need not be clamped, fingers might work in a pinch, pun, just get one lead soldered then do the rest. Note that any leads, wires, components that might be under the pot will be difficult to work with, fix or replace. So try to leave the areas under the pots vacant. I didn't, PITB to change anything under there. I also used those plastic dust caps on the pots, so 1/16 inch spacer could be used (see picture). In order to get the holes in the right spot on a metal box, an accurate cad layout is needed to make a template. Shown is my next project in cad, accurate. And an example of a template with 1/16 inch dia holes which I will used to locate the pot holes and switch in a box. Drill 1/16 then open them up to 9/32 or 5/16.

[ElectricDruid]

+1 agree, the pots are *last* and you need to be pretty sure everything else is good before you put them on because it's going to to be a b!tch to fix it afterwards if it's not.

I've never really bothered with the spacers - like I said, the pins are tight enough that you can just get it set right, then solder it. You do need some sort of insulation in between though. I like a bit of overhead transparency plastic for that, but that's only because I've got a pile of it hanging about and no-one has used overhead projectors in at least twenty years, so it's otherwise useless!

[rutabaga bob]

Well, as you can see at the linked example, there are connections under there.

I messaged the guy who makes the layouts, but I don't think he will get back to me anytime soon.