uneven pots

[heavyfunkmachin]

hi all,

i´ve got a jazz bass, and the volume pots on it are "uneven", i meant. its like 50% of the volume was between 0 and 9, and then from 9 to 10.... boom, the other 50% just like that... so its hard to control the volume, i just leave it in 10 and do it trough the amp or volume pedal, but i fell silly about it... is this normal? i mean, its due to some kind of electric thing i dont get, or are they just ****** mexican pots i should get change?

please, help.

thanks.

 

[newfuture]

They may not be logrithmic (audio taper) pots. That would be strange, but possible.
Open the bass and look for the value of the pots. They might be stamped into the back cover, or printed on the top of the pot, so you might need to take it off the control plate. They should read 500k (or 250k) and have an 'A' next to the numerical value. If it's 'B', then it's a linear pot and you'd probably want to change it.

 

[heavyfunkmachin]

that´s the thing, it has an A on it, so... what can I do? where´s the deal??

i have a log pot that behaves like a linear pot???

 

[ctmullins]

Hmm. I would recommend removing the pot and checking the resistance with a multimeter through the sweep of the wiper. But that's prolly too much trouble to be practical. Chances are that it's just a bad pot.

 

[SGD Lutherie]

that´s the thing, it has an A on it, so... what can I do? where´s the deal??

i have a log pot that behaves like a linear pot???

Log taper focus most of the volume at the last 10% of the rotation, which is exactly what you are hearing. Linear taper gives you what ever you have the knob set at, so half way is really half way, but that doesn't always sound right to the ear.

I think the issue is they are cheap pots with a poorly done audio taper.

Some audio taper pots really switch between two linear tapers to approximate a log taper.

 

[walterw]

that´s the thing, it has an A on it, so... what can I do? where´s the deal??

i have a log pot that behaves like a linear pot???

no, that's just an audio volume behaving like an audio volume on a bass. put some "B" (linear) volumes in there and it will be much more even.

(i'm really surprised at the conventional wisdom around here suggesting the opposite, but that dramatic drop from 10 to 8 is what audio volumes do! you can put one on an ohmmeter and watch the numbers drop really dramatically from 10 to 7, then even out at a much lower level from there to off.)

 

[LoveThatBass]

If you have an ohmmeter if it is a linear taper pot you can read between one of the outside wire lugs and the center wire lug (wiper). Slowly and at a consistant rate turn the pot shaft and watch the ohmeter. (note: an analog ohmeter with a needle pointer will do best in showing the rate of change as you turn the pot but a digital will work also). If the needle moves (or resistant changes at a constant rate) you have a linear pot. If it is first slow then speeds up or is fast then slows down on rate of change then it is most likely an audio taper. Audio taper (originally logarythmic taper) was designed to counter the human ears way it hears volume changes (logartythmically) meaning the change in volume is not linear or consistant. A Linear taper pot for Volume only will cause a fast rate of change say at first then slowing quickly to nothing. What you are describing sounds as if you have a linear taper pot for the volumes.
Also another factor that can cause this. Depending on the type pickup being used such as a Fender single coil for example typically works best with 250K pots. You have much better control of volume and tone than if you use a 500K which, again depending on the pots in question (single coils) will have more of a turn on turn off switch effect. I have tried this and came to this conclusion. I like 250K pots better for single coils and 500K for Humbuckers. The one exception being Fender P pickups. I think 250K work better for both P and J style pickups.

 

[heavyfunkmachin]

so... everybody is saying different things... the real question is how can the neck pickup work great being a 250k A (altough its also a switch) and the neck pickup have a dramatic increase from 8 to 10 being also a 250k A... when both are connected to single coils (jazz bass)...

i bought new pots because the mexican ones i had did THIS EXACT THING... what do i have to do to get an even volume pot??? trial and error? is there a mystery??

(p.s. i dont have an ohmmeter)

and by the way, i understand that log pots are made logaritmic to sound more even than linear since the human hear hears in a "logaritmic way"... so... 250kA should be the more even stuff I can get my hands ond, isnt it? and they are CTS, not cheap ones.... what do i do?

 

[SGD Lutherie]

Have you tried plugging your bass into another amp, and does it do the same thing? Also, are you plugged into anything else before the amp?

If two sets of pots are doing the same thing, then you might be plugging your bass into something with an input impedance that's too low.

I've used both audio and linear pots for volume over the years and I don't have that effect where it's acting like a switch.

I did have a pan pot who's taper I wasn't crazy about, so I smoothed out the taper a bit by adding a resistor between the wiper (middle lug) and the "hot" lug on the pot. For a 250K pot I think I used a 100K resistor.

 

[heavyfunkmachin]

wherever I plug it, whenever i plug it, neck volume/switch behaves normal (sustained volume increase) and the bridge volume desnt (little difference form 1 to 7, then great increase from 8 to 10). the volume pot its a fender cts with 250k A stamped on it, so it´s a log pot...

i replaced the original mexican pots (cts also) because of this... i dont understand, the neck vol/switch its great and as far as i know its also a log switch... did i get 3 bad pots in a row??? (the 2 origgial mex and the new bridge one???) i did something wrong???? i didnt solder anything to the "top" of the pots in order to not overheat them... im kind of desperate.... is this a scratch and win?? do i just buy pots and pots until i get one that behaves properly?????? can i put any more question marks???????? ( )

 

[SGD Lutherie]

i didnt solder anything to the "top" of the pots in order to not overheat them...

How did you make the ground connection to the lug on the volume pot?

To solder on the back of a new pot, just scratch up some of the metal in one place, heat it up for a second or so and melt a little solder on the back in a nice smooth patch. Not a lump. Then tin your wire and you will be able to solder them together easily with just a little solder.

 

[walterw]

wherever I plug it, whenever i plug it, neck volume/switch behaves normal (sustained volume increase) and the bridge volume desnt (little difference form 1 to 7, then great increase from 8 to 10). the volume pot its a fender cts with 250k A stamped on it, so it´s a log pot...

i replaced the original mexican pots (cts also) because of this... i dont understand, the neck vol/switch its great and as far as i know its also a log switch... did i get 3 bad pots in a row??? (the 2 origgial mex and the new bridge one???) i did something wrong???? i didnt solder anything to the "top" of the pots in order to not overheat them... im kind of desperate.... is this a scratch and win?? do i just buy pots and pots until i get one that behaves properly?????? can i put any more question marks???????? ( )

it's possible that one pot has a different audio taper than another. (some are designed to be more extreme, others are a little closer to linear.)

it's likely that that push-pull is a "B" rather than an "A", which means it's linear. just get a linear volume for the other pickup and you'll be done with all this angst.