Can a pot be faulty but pass audio? Questions about autowahs

[moid]

Hello everyone

Brace yourselves: I built a working circuit! I don't want the shock to be too powerful for those of you who know my usual style of construction! OK onto my questions:

I managed to build a Comet Filter pedal today - first time I used it only one of the pots worked (the 1M lin pot) the other (100k lin) did nothing. I ran my audio probe over it and audio travelled into the pot and out of it, and I could the follow the audio through the circuit without any problems, but the pot did nothing when I adjusted it. The only issue I could think of is that this 100K pot was salvaged from an old circuit that didn't work (I'm getting low on parts, so decided to raid my box of circuits that never worked).

I replaced the 100K lin pot with my last new unused 100k lin pot and yay the circuit works (it's not the most dramatic filter, but it does work).

My rambling question is could a pot pass audio correctly, but not affect the circuit? I measured the old pot I removed with my DMM and it goes from 30ohms resistance to 104Kohms at either end of the sweep which doesn't seem odd to me, but should I just chuck this pot now as unreliable? I think I will... was the issue just my dodgy soldering?

I'm not sure if it matters, but here's the schematic and layout I used:





PS is there a simple circuit that could be added to the above that simulate one (or both) of the pots slowly turning, like an autowah? I was envisaging something like a LDR and an LED and some sort of IC? Any guesses what circuits to look at? Feel free to say no if this circuit can't be modified. If there are any interesting mods I could add to this before I box it that would be nice. Or if you know an autowah or filter circuit with a really slow and deep filter sweep that can have the speed of the sweep adjusted that would be interesting too. Thanks!

Hope you're enjoying this afternoon

[antonis]

My rambling question is could a pot pass audio correctly, but not affect the circuit? I measured the old pot I removed with my DMM and it goes from 30ohms resistance to 104Kohms at either end of the sweep

Did you measure pot with wiper & outer leg shorted or just with wiper "open" ??

[moid]

I connected the positive probe to lug 2 and the negative probe to lug 1 I think... if I should've chosen lug 3 I can try again.

[antonis]

Probes polarity doesn't mind..

What I'm trying to tell you is you may get expected readings between lugs 1 &  wiper and/or 3 & wiper but what counts in your circuit is wiper to be connected (short) with lug 1 or 3..
If wiper is "open", despite its good travel working, its resistance between lugs 1 & 3 should be remain constant (100K)..

[pinkjimiphoton]

yes, a smoked pot can still function sometimes over part of its throw. usually what happens is the  carbon track gets damaged, can actually light up and burn.  the pot will work, at least partially depending where the damage is cuz two of the three connections will usually still work... but when ya hit the "dead zone" it will either drop out completely and not work, or seem to jump around and do weird stuff.

if ya use a linear pot, say, and your meter, connect the leads to the center pin and one of the  outer pins. sweep the pot... you should see it change as you describe. if it changes smoothly, then try the other side.  do NOT expect the taper to look the same... the taper will often be a bit different depending on which side you use. if ya get a smooth sweep while watching the meter, the pot is probably ok. if it glitches, either throw it out, or mark it and save it for a variable resistor down the road somewhere.

[moid]

Thanks chaps! Well after slowing turning the pot while testing it, if I test wiper to lug 3 it goes from 5ohms to 20Kohms, then drops to 0 for a bit, then jumps to 40Kohms, proceeds OK to 60Kohms, drops to 0 again and comes back at 71Kohms and goes to 104K at the end...
Wiper to lug 1 starts at 30ohms goes to 8K, drops to 0, then rises quickly to 55K, is fine to 81K, drops to 0, then goes up to 84K and carries on to 104K

I think we can consider this pot to be toast. Alternatively, I may have the world's first tremolo circuit in a pot

[pinkjimiphoton]

tremolo in a pot.... i like it. i think i'd like mushrooms in my shampoo, too. 

[moid]

It's the only way to consume mushrooms. Having them gently massaged into your scalp under warm flowing water

[pinkjimiphoton]

oh, i dunno....  lol

[antonis]

You guys may consider yourselfs lucky enough 'cause there isn't any bald guy among moderators..