Wiring double-gang pot to stereo output jack

[magicdog]

Hi - my first post so be gentle with me...

I want to wire a dual-ganged pot (10K Lin) to a stereo board-mounted jack socket so it will pan an output signal between left and right.

I understand the pots need wiring opposite ways so one goes up in value as the other decreases but I'm confused about the jack socket end of things...can anyone shed some light on this or point me to a suitable article...?

TIA

[magicdog]

Plleeeease...anyone...? 

[Mark Hammer]

The wiper (middle lug) of each pot section obviously goes to the output jack.  One lug of each pot section goes to ground.  Since you want to set it up as a panning-type control, then that implies that whatever lug goes to ground on the one section, the opposite lug of the other section goes to ground.  Which leaves us with two unused lugs, and these make up the inputs for the two signals.

Here is the thing to keep in mind, though: volume pots are normally logarithmic, but wiring up a dual-ganged log pot will only give you a log response for one of the sections, not for the other.  This means that adjustment for the two signal paths will be uneven/unequal.  The best solution is to use a log/antilog pot, but since these are generally only available on special order, the next best solution is to use a dual-ganged linear pot, read the Secret Life of Pots article over at geofex, and adjust the taper of the two ganged sections with parallel resistors so that thay approximate a log/antilog response.  This will get you closer to the goal of having the "middle" position on the control be equal amounts of the two outputs.

Alternatively, in high-end audiophile equipment, when the goal is to have identical amounts of change for two channels be created, they use multi-position rotary switches and 1% resistors.  That's a lot of work though.

[magicdog]

Thanks for the advice Mark I'll head on over and check the parallel resistor trick 

[grapefruit]

I haven't tried it for panning but this is a similar way I usually do "balance" or "blend controls, but in reverse.

If the signal is coming from a buffered output (eg. an op amp.) Have two 4.7k resistors coming from the op amp. These go to either side of a single gang 10k pot. The wiper of the pot goes to GND. With the pot to one side, one output will be shorted to GND (no output) and the other will be only slightly attenuated and vice cersa. With the pot in the middle the outputs will be even, though half the level a single output would have been.

Stew.

[magicdog]

Hi Stew - thanks for that tip.

I have got it running so that it pans correctly but it's cutting out when both signals should be equal (middle of the pot arc) - I realise you may have described this scenario in your post but i am a complete novice at this!

I have the positive inputs to the dual-gang pot wired to the wiper (and working) - do I still need to attach a 4k7 resistor to each of the outer lugs on both pots?

Apologies for my ignorance...

[grapefruit]

Not quite sure what you're describing here. Are you trying to do it the way Mark said or the way I said? It sounds llike you haven't got it wired correct for either way...
Here's what I meant. (I haven't tested this and it does have to be fed by a low impedance output like an op amp or it won't work properly)

IN  ----//4.7k//----------------------- OUT LEFT
      |                      |
      |                      /
      |           pot       /    wiper
      |           10k      /-----GROUND   
      |                      /
      |                      / 
      |                      |
     ----//4.7k//-------------------------OUT RIGHT

[RedHouse]

grapefruit's diagram is how a pan-pot is normally wired.