Pot Q

Goober1206 · #1 06-03-2010, 11:52 PM

I've been learning about wiring and such, but lately been focusing on pots. I don't understand something. On some diagrams I see the hot signal going into the middle lug out of the three of a basic volume pot and on some it goes into one of the side lugs. Same with tone pots. Also, with tone pots, I see the input but where's the out? Basically, on a volume pot, and on a tone pot, I don't unerstand why the wires go where they go, and where exactly they should go. I'm confused. Shine a light?

bongomania · #2 06-04-2010, 12:21 AM

The middle lug is the wiper, and it defines the resistive value between the wiper position (knob turn) and each "end" of the resistor. So for example with a 250K pot with the knob turned about 1/4 of its rotation, you could reasonably expect that there would be about 60K resistance between the middle lug and one outer leg, and about 190K between the middle lug and the other outer leg. It usually doesn't matter whether you consider a side leg to be the input or the output--it's the same series resistive value either way. The one exception I can think of is if you are connecting different circuits to both outer legs, and if the output just goes to ground (as in a tone pot). In that esoteric case, you'd want the wiper to be the output to ground.

And with a tone pot, all it does is drains a portion of the signal off to the ground, so there is no output per se.

Goober1206 · #3 06-04-2010, 12:27 AM

How would I wire a concentric volume/tone pot? I have two of them, on for each pickup on my jaguar. The volumes seem to work, but after turning maybe half an inch down, it seems to kill the signal. And the tone knobs don't seem to do anything. Thanks for the help bongo, I sorta got that lol

bongomania · #4 06-04-2010, 01:55 AM

Concentric pots are really just two regular pots stacked one on top of the other. So you actually follow the exact same wiring diagram as a normal two-pot setup. Check out the wiring diagrams at StewMac and Seymour Duncan, they are super helpful and easy to follow.

SGD Lutherie · #5 06-05-2010, 11:41 AM

When you see a one pickup bass, like P bass, or a Gibson Les Paul, the pickups are wired to the outside lug. When you turn the volume down, you are shunting the output of the amp to ground. On two pickup instruments like a Les Paul, turning down one pickup shuts off both. You can't get much blending going on.

On a bass with two pickups like a Jazz bass or Rick, the pickups go to the center lug. Turning off one pickup doesn't not turn off the other, so you can blend the two signals better.

The downside is you get a little more treble loss when you turn down the volume.