P-bass tone control makes almost no difference.

[NachoConde]

Hello TB,
I recently acquired a p-bass (not fender) for very cheap. Its an old instrument, from the 70s if I am not mistaken. I decided to take it to a local guitar shop (not the big national guitar store but the tiny local one where the guy knows what he's actually doing as he's been repairing/playing guitars for years). He suggested I get the pots replaced as the ones on the bass were a bit worse for wear. He did the job and everything seemed to be working fine, but for some reason the tone knob makes almost no difference now. It's turned more into a treble on/off switch. For about 90% of the turn it sounds exactly the same, then for 10% it just takes away all the treble and gives a nice deep sound.
Don't get me wrong, I think that both sounds are great, but I want to have the things in between as due to this it has essentially become an instrument lacking in versatility.

Here's a sound clip of me fiddling with the tone knob as I play some stuff. You will be able to hear that theres only really 2 distinct tone settings. (Note: This is the bass straight into my interface, no EQ, effects, preamp, nothing but the raw tone):

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[Stealth]

Open up the bass and check the writing on the tone pot. If it says something like B250K or B500K (the letter B is the key) that means you have a linear tone pot - you might want to swap it for a logarithmic (A250K or A500K) which should give you a more useable tone sweep.

 

[NachoConde]

I just checked, the volume says B500K and the tone says A500K, any ideas of what else it could be?

 

[i_got_a_mohawk]

Switch in a linear pot for the tone and see how you find it.

 

[NachoConde]

Here's a couple of pics of the wiring:

 

[SamanthaCay]

Try it in a higher powered rig and see if there is a difference.
Audio taper pots generally work a little better in higher gain situations.

You can get different tapers liner, audio, logarithmic and reverse tapers.
Each will be best suited for a particular situation, so consider where you want your best tone and try it there first.

 

[Nev375]

Yeah, that looks incorrectly wired to me.

 

[NachoConde]

Yeah, that looks incorrectly wired to me.

It seems as though the guy at the shop wired it just as it was wired before, as you can kind of see here:

Also one thing i forgot to mention is that the way the pot works seems to be reversed. As in to cut the treble you have to go clockwise and to turn it up you have to go counter clockwise.

 

[SamanthaCay]

Yeah from the pics I can tell you that it is definitely wired weird, although the only thing wrong there is that the ground is on the wrong side of the tone control thus the reason it is reversed.

Edit:
To clarify by weird I mean not your typical setup for volume & tone.
There are a lot of different ways you can wire a passive v&t circuit and get the same results and most people go with one that is more typical like the way a Fender is wired for example.

 

[NachoConde]

I dont really mind the fact that it is reversed to be honest, but the lack of tone versatility is what worries me.

So then, what can I actually do to fix the issue? Just try a different type of pot? Change the wiring?

 

[SGD Lutherie]

The fact that the pots are wired up backwards, and the tone control is an audio taper means that the taper is going the wrong way, which is why you are having this issue.

Wire it up like this:

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[NachoConde]

Alright, I'll try doing that and report in once its done to let you know whether or not it worked. Thanks for all your help!

 

[SamanthaCay]

Like I said earlier, try it in a higher powered rig and see how it sounds, and to be more specific try it in all your desired setups and then decide if you need more versatility because it will behave differently in different situations.

 

[SamanthaCay]

The fact that the pots are wired up backwards, and the tone control is an audio taper means that the taper is going the wrong way, which is why you are having this issue.

Wire it up like this:

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That's a great point I hadn't thought of that.

 

[gfaulkner]

The capacitor is incorrect ,a .475 or .5 is suitable for bass.The cap which looks original would be more suitable in guitar.

 

[SGD Lutherie]

The capacitor is incorrect ,a .475 or .5 is suitable for bass.The cap which looks original would be more suitable in guitar.

You mean .047µF or .05µF. That's a .1µF which is larger, and was used on the vintage Fenders. It cuts the treble out at a lower frequency.

I prefer the .047µF caps myself.

 

[gfaulkner]

My bad,yes .047 or .05.

 

[the mojo hobo]

Changing the cap will change the tone, which the OP says he likes. I like the .1µF cap in a P bass myself. The tone pot being wired backwards is the problem.