Soldering pots

[MohiZ]

On a few of my projects (distortions with many pots mainly) I've had a problem where sometimes when I roll down for instance the volume knob, the lug 1 of which is connected to ground, the volume suddenly increases. The pot might work fine for the most part of its rotation, but when I reach a low enough setting, the volume suddenly springs right back up to maximum. Sometimes this also happens with other pots, and the problem is sometimes fixed by resoldering the ground connection.

Why is this? It's as though the ground connection suddenly stops working when too much of the signal is going to ground. It's really confusing because the connection IS working almost if not completely normally except when I turn the pot down enough. It's hard to measure this problem with a ohmmeter, and I'd like to find some definitive answer to this. I am using lousy quality pots but somehow I doubt that's the only reason. Does anyone else have this problem?

I also ran into this peculiar problem: I had a 22 k-ohm log pot, and it had a similar fault. When I measured resistance between pot lugs 3 and 2, the resistance behaved normally for the whole rotation of the pot. BUT when I measured the resistance between lugs 1 and 2, the resistance started to decrease from 22 kohms, but when it reached around 17 kohms, it sprang back up to 22 kohms and then continued to decrease from that value. Also when I measured the resistance between lugs 1 and 3 (which I think should remain at 22kohms at all times), it was either 22 kohms or 30 kohms depending on where the pot was set. It blows my mind how this is even possible  On top of that, when I removed the pot and measured it again, it seemed to be perfectly normal. Can this be because of bad solder connections or should I really switch to better quality pots?

Ps. sorry for the long post!

[cpnyc23]

What manufacturer's pots are you using?

-chris

[MohiZ]

I don't know the maker, there's no text on the pots except for the value. What I do know they're the cheapest ones I found. They're made of a black plastic that melts really easily when soldering, with a case of metal and super long plastic rods that I've been cutting to proper lenght for the knobs. I'm obviously not going to buy these ones anymore, but.. hmm... I just can't believe it could all be because of the pots. 

[petemoore]

should I really switch to better quality pots?
 The main benefit to doing that is it will tell you...how much difference higher quality pots make.
 In your circuit, the amount of circumstance involved with pot rotation immediately makes the pots suspect.
 In the case of the 22k pot measuring 30k, this is wierd...contact trouble with the probe, a meter that is reading funny? [I carry a spare and hope one of the two plays straight guy enough to tell me the other meter is joking], or something wierd with the pot, it happens.
 In the case of the 17k jumps to 22k and then drops...that's wierd too, and certainly sounds like a pot fault. If I needed that 'spot' for adjustment I'd change it, some 'wierd but otherwise pretty much working' pots have been known to be left at their post, doing what they do.
  Using thin-ish wire, and pre-tinning the stripped end, then using high-ish heat to quickly heat the lug so it can begin cooling before the plastic gets too soft is required with plastic pot cases, heat sinking the lug at the potbody is another option.
 

[MohiZ]

I have to try and be more careful with the soldering in the future. But I guess the thing that baffles me the most is that sometimes the ohmmeter shows completely consistent values for the pot during its whole rotation, but still when I plug the device in, there is a weird discontinuation at some point of the pot's rotation. Sometimes the problem fixes itself somehow and sometimes I'm unsure as to how to make it work. I haven't tried changing all of the pots that are acting up yet, because it seems strange to me if this was just because of the pots. But what do you think? And this has happened to me with several pots in two different pedals.

Of course, I could just try changing them all, but that would be tedious as all hell what with all the wiring, and it wouldn't necessarily even help. I guess I'm hoping that somebody would tell me it's definitely not the pots, because that would save me the trouble  like that's gonna happen.

[MohiZ]

After some further investigation I've come to the conclusion that the pots I used are just really that bad. Even though I tried to be careful with them, I'm now having to replace three of the six pots in my Dr. Boogey due to some discrepancies in them. For instance, the volume pot had a resistance of 83 kohms between lugs 3 and 2 in the maxed out position (should be zero), causing the output volume be rather low. I've been debugging the circuit for a long time in vain, but at least now I know the cause! I'll never buy those pots again, either 

As a sidenote: does it usually harm the pots to solder stuff to the backs of the pots? In my high gain projects I've taken a habit of grounding all the backs of the pots.

[cab42]

I came to a similar conclusion a while ago. Unfortunately it was the only type of pots I could get locally, so it was easy just to go down and buy one when I didn't have patience to wait for an internet order. I'm amazed how bad they were.

Since then my local shop has closed, so now I'll have to buy the pots on the internet anyway!

Carsten

[MohiZ]

For me it was the same reason, a cheap local place to get them! But luckily I can get much better quality ones at another electronics store, albeit they do cost more, too.

[Electric Warrior]

you get what you pay for