Potentiometer Problem

[Tom Krebs]

I have a Les Paul Special on my bench with P100 pickups. The wiring is an unmolested factory harness.

Problem: Both pickups selected. The bridge pickup volume works, But when it's set to about 8 the sounds starts to thin out up to 10. Roll it back down the normal full bodied sound returns???  

Tom

[Russell Vance]

Change the pickup hots to each of the pots (ie: swap them around) see if the problem goes with the change or stays where it is - if it stays it's (probably) the pot wiper lifting off the track or a dirty resistance track- replace it and repeat. I'm not a great lover of repairing or cleaning pots but you can if you wish and it's doable. I use Caig on vintage stuff that needs to stay. Rusty.

[Pierre-Antoine Roiron]

If you have independant volumes wiring (i.e. with both pickups on, you can roll one volume down and still have the sound of th other pickup), it's the standard behavior. You can hear the same "problem" on JazzBass, due to the lack of resistance between the picjup, so that when both full on, each one bleeds a little in the other instead of having all its current sent to the amp. Add a 47k resistor between each pickup and it's volume pot (serial).

[FRANK]

HEY I THINK I VE SEEN THIS BEFORE IS PIN 1 OR PIN 3 GROUNDED ON THE TONE POT? I HAVE SEEN PASSIVE ELECTRONICS DO THIS I BELIEVE RECENTLY PROBLEM BEING EVERYTHING SOUND BUT THE GROUNDS ON THE TONE POTS ?I DON'T KNOW THIS MAY HELP

[Tom Krebs]

Thanks Gentlemen. Pierre you nailed it! Resistors solved the problem.

[Pierre-Antoine Roiron]

Glad it worked!

[Russell Vance]

Pierre,
I sort of get this if you have different pickup values (in parallel, both fully on) maybe loading the circuit differently or maybe even having an impedance conflict. I'm also aware of the problem of not being able to fully turn off guitars configured with independent volumes which is a by-product of wiring for independent volumes.

But I'm a little lost as to why increasing the overall (serial) resistance value of BOTH the pickups by the same amount would be effective - I must say I'm a little confused here (which wouldn't be the first time for me!).

[Pierre-Antoine Roiron]

I'll try to explain this the way I understand it, but my English may be a little weak :
From the point of view of the bridge pickup, when both pickups are on, the bridge hot wire is linked to the neck hot wire, and sees the 500k (for example) value of the pot. The neck pickup is maybe 7k. SO as a bridge pickup I have the choice between making my way through the 7k pickup, or through the 500k pot. As I'm a well educated pickup, i use the "least resistive path" (I'm not sure of this translation) and send my power both through the neck pickup (because it's easy) and through the pot. This results in less volume though the pot, therefore through the output.
Putting a 47k between each pickup and its volume pot is enough to limit this phenomenon, without loosing pickup output significantly.
It's a very simplified explanation, because these are complex currents, but you get the feeling of it. Maybe... if I've been clear enough... is that clear enough?

[Cyrus Comiskey]

Wow! I've had this problem on my Fender PJ for years now and have learned to live with it, but no more! I'm gonna try this out this weekend. Thanx for the great info!

[Russell Vance]

Thanks Pierre, I need to think about this - I'll get back to you.R