Bourns pots - which lugs are which?

[appar111]

I just picked up a couple of these to put in my guitar and a friend's:

http://www.tubesandmore.com/scripts...levclients/cemirror/ELEVATOR.FXP?item=R-VB-SL

It has 3 lugs, but they're a different pattern than a traditional CTS style pot. Two are next to each other, but the other lug is off by itself.

Which lug is the ground, which is the "in" lug and which is the "out" lug? Is the one that's off by itself the ground lug?

Also, aside from figuring this out, is there anything else I need to know?

According to the spec sheet:

http://www.bourns.com/data/global/pdfs/82.pdf

...there's supposed to be a lockwasher, a hex nut and a solder lug washer, but neither of the two I got (new, from Allparts) have the solder lug washer. Should that have come with them, and is it required to get everything grounded properly?

If anyone can give me a "Bourns pots for Dummies" crash course, it'd be appreciated.

thanks!
J.

 

[ratherdashing]

Re: Bourns pots - which lugs are which?

There's no such thing as a "ground" lug on a pot. They have one lug for each end of the track (the resistive material), and one lug for the wiper (the part that moves across the track).

On a CTS or Alpha pot, the left and right lugs are the ends of the track, and the center lug is the wiper.

On the Bourns, I'm pretty sure the two lugs on the bottom are the track, and the top one is the wiper. I am not 100% certain of this, but if you have a multimeter it should be easy to test. Put the probes on two of the lugs and turn the shaft. If the resistance changes while you turn, one of the lugs is the wiper. If the resistance does not change, the other one is the wiper.

 

[appar111]

Re: Bourns pots - which lugs are which?

Thanks for explaining that! I'm a noob when it comes to the construction of a potentiometer, much less the Bourns pots.

I don't have a multimeter, unfortunately.

So, if the one off by itself is the wiper lug, and the other two lugs are the end of the track, would it make any difference which one I used to wire the pickup to, and which one I used for grounding purposes?

 

[SabbathFan0220]

Re: Bourns pots - which lugs are which?

ratherdashing nailed it. On the Bourns box style pots, ignore the fact that the lugs are staggered. When you look at it from the bottom, the three lugs are in the same arrangement they always are on CTS or Alpha. The middle one is the wiper. Why the middle lug is mounted at a different height than the others...I have no idea.

The pot is supposed to come with a solder lug lock washer. Although I ordered some Bourns 95 series pots and they didn't come with any either. The solder lug is just to ground to if you're using the pots in an unsheilded guitar (or pickguard with no foil). This is rarely the case...I've never seen a pickguard without foil. Your guitar should be properly shielded anyway.

http://www.bourns.com/data/global/pdfs/bourns_82_and_95_grounding_appnote.pdf

As for which wire goes where, it depends how the pot is being used. Is this a volume pot? Tone pot? Something else?

EDIT: I just saw that the model 82 pots don't have the lugs arranged like the model 95 pots. I believe the one at a different height is still the wiper though. On the model 95 pots, the lugs are numbered. Numbers 1 and 3 are the track ends and number 2 is the wiper. Maybe there is a label on your pots as well?

 

[appar111]

Re: Bourns pots - which lugs are which?

I'll check-- I think the lugs were numbered (it's very small print!). So I'd just use the #3 lug to ground things to.

This guitar actually doesn't have shielding on the pickguard (it's an allparts guard), but we'll have to add it at some point. Next string change (and after my buddy picks up some foil shielding) I can just run a wire to a regular washer and then ground that wire to lug #3.

thanks for the advice, guys!

 

[Stratman]

Re: Bourns pots - which lugs are which?

Bourns pots are internally wired 1, 2, 3 same as other pots. Look for the very small number imprinted on the top of the pot.

Looking from the top

3 --MWMWMWM -- 1
........... ^
........... ^
........... 2

Sorry for the crude illustration!

It is my understanding that since Bourns pots are internally grounded that the normal "Solder to the pot's metal back" does not apply.

To quote Bourns....

POTENTIOMETER DESIGN
Most standard guitar potentiometers have a rear metal cover that is used as the ground. The rear cover is actually grounded to the metal bushing and the metal shaft. The potentiometer must be designed with a good internal ground to eliminate noise. Some potentiometers lack good internal ground resulting in a “scratchy” sound when the shaft is rotated. This phenomenon can be mistaken for a “dirty” potentiometer even if the part is perfectly clean.

Bourns® Model 95 Premium and Model 82 Vintage Guitar Potentiometers are internally grounded to eliminate unwanted noise. In addition to the internal ground, these potentiometers are designed with high-grade ceramic elements with a conductive polymer resistance ink. The specific audio taper incorporated into these potentiometers provides a desirable gradual increase in output without “dead spots,” or areas of sudden level increase that may be encountered with standard potentiometers. Together, the element and a multi-finger wiper system produce true sound while minimizing the effects of unwanted noise, providing the guitarist with many years of service.

BUT what is confusing is this information from Bourns' model 82 datasheet...

"One lockwasher, one mounting nut, and one solder lug washer is shipped with each potentiometer"

 

[appar111]

Re: Bourns pots - which lugs are which?

Update-- the lugs were in fact numbered, the #2 lug was the wiper lug, but it was the #1 lug, not the 3, that was the lug to use for grounding.

The cool thing is, I used the #3 at first, and the volume knob action was reversed-- the volume was all the way up when the pot was all the way down, and as I turned the knob up, it lowered the volume. Nice if you have a left handed guitar and need a new pot!

I actually saw an allparts "lefthanded guitar volume pot" the other day at a guitar store. Couldn't one "make" their own by switching which lugs they use on a regular pot? i.e. switching which two end lugs you wire the ground and the lead to?

 

[ratherdashing]

Re: Bourns pots - which lugs are which?

Update-- the lugs were in fact numbered, the #2 lug was the wiper lug, but it was the #1 lug, not the 3, that was the lug to use for grounding.

The cool thing is, I used the #3 at first, and the volume knob action was reversed-- the volume was all the way up when the pot was all the way down, and as I turned the knob up, it lowered the volume. Nice if you have a left handed guitar and need a new pot!

I actually saw an allparts "lefthanded guitar volume pot" the other day at a guitar store. Couldn't one "make" their own by switching which lugs they use on a regular pot? i.e. switching which two end lugs you wire the ground and the lead to?

Volume pots are not linear, i.e. the resistance doesn't change evenly all the way across the track. If you reversed the end lugs the volume would increase very slowly at first, then suddenly increase at the end.

With a linear pot (which are usually used for tone) you can swap the lugs with no issues.

 

[appar111]

Re: Bourns pots - which lugs are which?

what type are the Bourns pots? Because the volume change was gradual (yet reversed) when I had the ground wires on the wrong lug.

 

[SabbathFan0220]

Re: Bourns pots - which lugs are which?

The Bourns 82 series are audio taper.

 

[Stratman]

Re: Bourns pots - which lugs are which?

http://www.mylespaul.com/forums/pickups/76246-bourns-pots-2.html

Seymour and Frank get Kudo's from Bourns....