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P Bass Tone pot acting like volume...

Toso2121

Toso2121

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Jan 28, 2016
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#1
I have a 70's Fender P bass that has always been one of my favorite workhorses. One day the sound got real thin out of the blue. The volume knob still worked but the tone knob acted like a volume as well. Very thin, weak, and trebly sound. I figured a pot failed or something. I just decided to rewire everything and ordered new CTS 250 pots and cloth wire, orange drop cap. The pickups remained and I just rewired everything else newly in place. I used a standard P Bass set up wiring diagram. I have wired several Jazz basses and P Basses before so It's not my first time around. Everything looks good and after plugging up, things sound pretty much the same. Thin, trebly, and the tone pot acts like volume. it doesn't roll off highs. I have never encountered this.

Any ideas? Did the pickup fail? Seems odd, but I have some other pickups around that I may swap to try that next. Just wanted to see if anyone had any ideas...
 
#3
jeffmensch said:
That is really weird. I'm thinking you're on the right track with suspecting the pickup. Swap it out and see what happens.
Click to expand...
Thanks. That's the plan. It was interesting to see that crappy 70's plastic wiring inside. Cheap pots too. It's funny, that is one of my favorite P Basses, but they sure didn't go long on quality in the 70's.
 
#4
It does sound like a pickup problem.

A common failure is a bad connection where the coil wire connects to the pickup terminal (typically an eyelet). Reheating, and adding a bit of fresh solder, can often fix it if that's the case. Even better is to wick or vacuum off the old solder before resoldering.

Just have to be very careful, as the magnet wire (coil wire) is very fragile.

-
 
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#5
megafiddle said:
It does sound like a pickup problem.

A common failure is a bad connection where the coil wire connects to the pickup terminal (typically an eyelet). Reheating, and adding a bit of fresh solder, can often fix it if that's the case. Even better is to wick or vacuum off the old solder before resoldering.

Just have to be very careful, as the magnet wire (coil wire) is very fragile.

-
Click to expand...
Thanks. I didn't actually remove the pickup covers and examine them. I will do that today. I will try your idea, then swap pickups. Thanks.
 
#7
A failed pickup would not make the tone work as a volume pot. I know you replaced the pot and cap but I would still check ALL ground connections and if that didn't reveal anything wire straight to the pot before I spent money on pickups
 
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#10
line6man said:
This problem almost certainly has nothing whatsoever to do with the pickup.

It is usually caused by either a leaky capacitor or a capacitor that has been shunted. Check your wiring to see if there are any shorts near the tone control, and if possible, replace the capacitor.
Click to expand...


A shorted or leaky tone cap would still allow the pickup to work though, at least when set to "10".

And the pickup doesn't work; the sound is weak.

A very high resistance in one of the pickup connections can cause the tone control to heavily load down the pickup, and make it weak overall..

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#13
I wired the pickup to the input jack and the pickups sound great. Therefore it has to be in the wiring. I have checked it all by sight and it looks fine. I am just going to go back and rewire and test everything with a multimeter as well.
 
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#14
A check with a multimeter is usually the fastest way to detect wiring issues. At least you know now that the pickup is working as it should. I would wire up the volume control next and move on to the tone control if that works correctly. If the tone control acts as a volume control then either the capacitor is shorted (this can be easily detected by measuring across the cap - it should read infinite ohms, if it reads zero it's shorted and must be replaced).

Good luck,
Stephan
 
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#15
darkbluemurder said:
A check with a multimeter is usually the fastest way to detect wiring issues. If the tone control acts as a volume control then either the capacitor is shorted (this can be easily detected by measuring across the cap - it should read infinite ohms, if it reads zero it's shorted and must be replaced).

Good luck,
Stephan
Click to expand...

Yup. This.
 
#16
Well, thanks to everyone for all the help. The problem is now solved! I checked each pot and the capacitor. Everything checked out with a multimeter. I wired the pickup straight to the jack and it sounded fine. When everything was soldered back together, the same problem appeared. Thin tone, limited range and travel of each pot, and the tone pot acted like second volume. Talk about crazy. I checked the wiring a third time. It ain't that hard, but a grown man was about to cry. The next step was to take the pickup covers off and look at them. Instead, I removed the pickup and replaced it with a Fender Custom Shop '63 P Bass pickup that I had sitting in my workshop. BOOM!!!!
It was the freakin pickup all along! Sigh...
Now this '79 P Bass, which was always one of my favorites, sounds amazing! All new CTS pots, crappy 70's wire replaced with cloth push back wire, new cap, and that great pickup. This once great bass is just awesome now. I thought I was fixing a guitar but now have an even better instrument that I never expected.

I think I may look at those '79 pickups,... or just toss em. LOL
 
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#18
TheArchitect said:
A failed pickup would not make the tone work as a volume pot.
Click to expand...

line6man said:
This problem almost certainly has nothing whatsoever to do with the pickup.
Click to expand...
sorry guys, this is precisely backwards. a busted coil wire will cause this exact thing, a pickup that still works but now sounds thin and the tone knob turns into another volume knob.

the tone knob thing is the first check for an open coil wire. (it's capacitance that's letting the pickup still produce some sound, so the tone pot's cap will kill that sound entirely if you let it.)
Toso2121 said:
I removed the pickup and replaced it with a Fender Custom Shop '63 P Bass pickup that I had sitting in my workshop. BOOM!!!!
It was the freakin pickup all along! Sigh...
Click to expand...
yep.
 
#19
walterw said:
sorry guys, this is precisely backwards. a busted coil wire will cause this exact thing, a pickup that still works but now sounds thin and the tone knob turns into another volume knob.

the tone knob thing is the first check for an open coil wire. (it's capacitance that's letting the pickup still produce some sound, so the tone pot's cap will kill that sound entirely if you let it.)

yep.
Click to expand...
Thank you. I definitely learned.
 
#20
walterw said:
sorry guys, this is precisely backwards. a busted coil wire will cause this exact thing, a pickup that still works but now sounds thin and the tone knob turns into another volume knob.

the tone knob thing is the first check for an open coil wire. (it's capacitance that's letting the pickup still produce some sound, so the tone pot's cap will kill that sound entirely if you let it.)

yep.
Click to expand...
So how did it work wired directly to the jack?
 

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