For some reason the tone knob on my P is causing a significant volume cut. It cuts the high end, but by the time it's rolled all of the way off, it's at about a quarter of the original volume. Any help here guys?
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P bass tone knob causing volume drop?
- Thread starter wshines1892
- Start date
First thing I'd do is head on over to Mr. Gearhead and get the wiring diagram for your model P bass. Link below.
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Double check against the diagram and verify the wiring is OK. While you have the pots / wiring exposed, get some "deoxit" cleaner spray and clean the pots. Radio Shack sells the stuff in small spray bottles.
If it's still messed up after that, my guess would be a bad tone cap or pot. However I've seen P bass PU's act up like that if one of the coils are going out. Since you said it's OK on the bass side of the tone control, the PU's are probably OK.
After you check the wiring diagram, post back here.
I've checked it against several diagrams, swapped out both pots, and tried two variations of the Precision diagram. The cap is the only thing that I have yet to replace, could that be the cause?
If you checked everything else then the cap is the only thing left. They normally don't go bad but I've seen em messed up by heat from using too high of wattage soldering iron. Also seen the leads look good but actually be loose internally.
Check the cap with a meter and see if it reads the right value. Wire the PU's straight to the jack bypassing both the vol and tone pots and make sure the PU's are OK. Double check your wiring again and be sure it's correct. The P is real basic wiring but I've messed it up once or twice over the years just by accident. Had one once where the lead from the tone cap to the pot wiper was getting bent a bit from the wiring when I put it back in the body causing it to short when moving the bass around on stage. Since then I always put a piece of heat shrink or elec tape on the cap lead.
- Aug 21, 2008
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Does it happen when your volume control is on full, or when it's turned down partway?
If it doesn't happen when the volume is on full, than that's normal, depending on how it's wired (inout or output of volume pot).
I replaced the cap and it's still happening :/ is this the pickup? it sounds fine wide open, it's just when I use the tone knob it drops, and it happens at full volume. If I were to wire it straight to jack, what would I listen for?
you just want to make sure that both coils have the same output. in other words the balance between strings is at pretty much the same volume overall.
Is your P bass is just a standard passive 4 string? If so are the pots both 250K audio taper pots, and your tone cap is a .05?
the cap is a 47 and yes, it's a standard passive 4 banger. As far as I can tell, the string balance is even. I'm thinking maybe I'll just go out and buy an entire new wiring harness for it, just to eliminate any variable that I may not be catching?
yes you could buy a fully assembled harness but if you already have the parts, I'd strip everything off. Then clean off all the old solder using a solder sucker, and then rewire using a 25 or 40 watt pencil type soldering iron and using this diagram for a standard P bass.
Pay close attention to both of the pots. There's a chance some solder may have dripped in there and messed up the carbon trace on the wiper inside. They should feel smooth all the way back and forth. If you feel even the smallest amount of drag or roughness - replace them.
If your bass is an American series, they have an extra black ground wire that solders to a lug that's screwed in to the body cavity.
Hope this helps.
I did notice the ground from the jack goes to the volume pot, and then a ground wire from the tone goes back to the top of the volume. Would that have anything to do with it?
Is that wire from the jack going to the top of the pot (meaning grounded), or to one of the lugs? Usually the ground wire from the jack solders to the top of the closest pot which would be the tone pot. Then another ground wire runs to the vol pot.
Think of the black ground wires as a loop where everything has to be grounded together. If you look at the drawing starting with the black wire from the pup's you can follow it through.
The black from the pu goes right to the case (or top) of the volume pot and is soldered there. The end lug of the volume pot is also soldered to the pot case so the signal from the pup's get dumped to ground and kills it so the volume control will shut off the output signal when you turn it all the way down. Another black wire for ground runs from the top of the vol pot to the top of the tone pot. Then a ground wire continues on from the top of the tone pot to the ground lug of the input jack. The black wire from under the bridge also gets soldered to the top of the tone pot. If you have the ground lug that's screwed into the body to tie into the shielding that wire gets soldered to the top of either pot so it's grounded. That completes the grounding circuit. Wire yours up exactly like that and your grounds should be wired right.
Now for the hot side. The white wire from the pup's goes to the first lug of the volume pot and another wire goes into the same lug and runs to the first lug of the tone pot. That gets the pu signal to both volume and tone pots. Then your tone cap gets one end soldered to the center lug of the tone pot and the other goes to ground on the top of the pot. (Make sure the wire from the cap that goes to the center lug doesn't touch any part of the pots case or any of the other lugs.) That cap bleeds some of the signal to ground and creates the bass / treble. The third lug of the tone pot is open, no wires connected, not soldered to ground. Then a final wire goes from the open center lug of the vol pot to the positive lug on the input jack which is the "tip" on the cable.
That's it. Wire everything up that way and it should work. If not remember, you might have a bad pot.
good luck
Alright, I've replaced both pots with completely new ones and same thing. I've swapped out the cap with 2 others I had lying around and nothing. I wired it directly to the output jack and it sounds totally fine. Is there a possibility that this is being caused by the jack? I followed the wiring diagram you posted to a T.
edit: I've tried a third capacitor that I pulled out of my main player, so I know it works, and it still it cuts the volume. This isn't a small cut either, this is a big difference going from full on to off.
edit: I've tried a third capacitor that I pulled out of my main player, so I know it works, and it still it cuts the volume. This isn't a small cut either, this is a big difference going from full on to off.
Now this one has me wondering
If all the parts are good the thing should be working. I think the jack is OK since you said it works when wired straight through. Was it working before and then it started acting up or is it a bass you just got that has this problem? Also are the PU's stock or aftermarket? From the way you describe it, it almost sounds like the PU's are going out of phase when you use the tone control. You could try reversing the PU leads, switching the white and black just to see what happens. I sure would like to know what the readings are on those two PU coils in case one is weaker.There are only a couple of ways the P is wired, the early style and later style. The early style is slightly different and uses the .1uf cap (which I like better) but does the same thing. Here's the drawing for the 57 and 62 versions.
I'm guessing I just have a weak/dying coil :/ I just thought to A/B with my warwick and jazz bass and it has a fairly weak output. The pickup in question is a Fender Original '64. I got a hold of the TBer I bought it from and we're working on a solution. Thanks for all of the help guys
That doesn't sound right, I'm sorry. If one coil fails you will have no doubt about it, it will be obvious.
Can you make a recording so we can hear the effect?
There is always some volume loss as you turn the volume down. How much perceived loss it will depend on the capacitor's actual value, and the type of pot will make it a sharp loss or a gradual one... but there is always a loss with a passive tone control.
