Volume Pot Wiring

[vastur]

Hi everyone,

Something is puzzling me. I was convinced that the normal wiring for a pot acting as a volume control is:

One side: Input
Other side: Ground
Middle (wiper): Output

So, the output resistance/voltage is always lower than the output and relative to the position of the pot.

Then, why are jazz bass volume controls wired as:

One side: Output jack/tone control
Other side: ground
Middle: Pickup

Like here:
http://www.seymourduncan.com/support...jazz_bass.html

Isn't the pickup the input and the output jack the output? So, it should be the other way around, right? (Middle: pickup / Side: output jack).

Please shed some light on where did I go wrong?

Thanx!
Vasco

[vastur]

"...So, it should be the other way around, right? (Middle: pickup / Side: output jack)."

I meant (Middle: ouput jack / Side: Pickup)

[Stan Hinesley]

Actually a volume pot can be wired either way but since the volumes on a Jazz bass are in series with each other, wiring them the way that you said would cause each volume pot to turn down both pickups.

~Stan

[vastur]

Actually, I though the jazz bass pickups were wired in parallel, right?

Like on the image bellow, it shows a jazz bass circuit. Basically, my question is, why are the pickups not connected to the top of the resistors instead of the middle, and the output to the two middles.

Maybe I'm missing something very basic here, please enlighten.

Also, I don't understand why doing it would make one knob control the volume of the two pickups, as you said..

Thanks!

[vastur]

One more to image to illustrate what I mean.

In my mind it would make more sense for the jazz bass circuit to be like this.
Why is the one above used instead?

[Stan Hinesley]

Originally Posted by vastur

One more to image to illustrate what I mean.

In my mind it would make more sense for the jazz bass circuit to be like this.
Why is the one above used instead?

If you'll notice in the drawing above the wipers are connected to each other so any change in one will affect the other.

A Les Paul is wired that way. This is why if you put the pickup selector in the middle position and turn one volume down it turns both pickups down. Many people swap the input/output wires on Les Pauls to get around this.

~Stan

[BassoProfondo]

I have a Spector that had passive EMGs with and active preamp using a V-V configuration, and looking at the pots with the contacts facing me, I have:

Output | Input(pickup) | Ground

I wired new active pups the same way and everything works the way it should. I don't think that it would matter if let's say the first two pins were switched, only the path through the pot would change.

[vastur]

"A Les Paul is wired that way. This is why if you put the pickup selector in the middle position and turn one volume down it turns both pickups down. Many people swap the input/output wires on Les Pauls to get around this."

Hmmmm... ok, I think I get it!..

The bottom line seems to be that you just can't connect two wipers in parallel (or a wiper with another resistor).
Otherwise, because the resistors are different, the current will take the shortest path to the ground (meaning the wiper in the lowest position). So, the lowest wiper will control both volumes.

So, when wiring volumes in parallel, you have to connect the output to both the top (one of the sides) of the pot, and not the wipers. And the pots must have the same value.

That would explain why a P-bass (1 volume) is wired with the output in the middle (wiper). And the jazz bass with the outputs in the side of the pot.

Am i close?

Then, another question: does it have any influence on the tone, which way a volume pot is wired? I heard if the pot is wired in reverse (input in the middle, like the jazz bass) it makes a higher treble cut, as you turn down the volume, because the pickup coil gets more loaded, and eventually short-circuited to the ground.
Is this true?

Thanks,
Vasco

[keyboardguy]

stewmac.com has excellent free articles on guitar wiring; Go to this site and click on:

Page 4: How is a volume pot wired?

All your questions should be answered there....


http://www.stewmac.com/freeinfo/I-4000.html

Regards,

Mike

[vastur]

Fantastic!

Thanks a lot. The mistery is revealed.

Vasco