Tele tone controls (circa 1972)

[ragtweed]

Back when Fender introduced the Deluxe, Custom & '72 Thinline they used 1 meg pots due to the wide range humbuckers, but I've noticed after looking at several wiring diagrams that the middle leg on the tone pots is always jumpered to one of the outside legs. Does this affect the value (resistance) of the pot?

[gaddis]

Not really. The value of the pot represents the resistance between the outer two terminals. Also it represents the maximum resistance obtained between the inner terminal and either one of the outer terminals. Pots can be used as three-terminal devices in which the pot behaves like two variable resistors, but are often used as just two terminal devices which implements just a single variable resistor. In this case the inner terminal and one of the outer terminals are used. If you short the unused terminal to the inner terminal in this case, you end up with essentially the same circuit. There must be some small advantage to doing this, but frankly it escapes me. Don't know if I explained that too well...

[ragtweed]

I'm still a little perplexed as to why they jumpered the wiper to one of the outside legs.

[chuckocaster]

just a different way of doing it, like how on early les pauls they wired the pup to the middle lug and then on later they went to the outside... granted that achieves the ace frehley strutter effect.

[gaddis]

I'm still a little perplexed as to why they jumpered the wiper to one of the outside legs.

Draw yourself a little circuit diagram of a pot with just the center terminal and one of the outer terminals wired up. You will see that what you have is just a simple variable resistor that changes value from zero ohms to whatever resistance the pot is rated at.

Now draw a similar diagram but with the center terminal jumpered to the previously unused terminal. You essentially still have the same variable resistor since the other half of the pot's resistance that has now come into play is shorted out by the jumper.

So what's the difference? Well, the only thing I can think of is that if the wiper of the pot makes intermittent contact with the resistance material, you would get different results in either case. In the first case if the wiper loses contact you end up with an open circuit. In the second case if the wiper loses contact you end up with a resistance equal to the rated pot resistance. Probably the lesser of two evils.