Jazz Bass Blend Pot Wiring

Endpin

My skills are more in the woodworking and fretwork departments. I can solder well enough but have no great knowledge of circuits. I mostly build and work on acoustics in my spare time, which doesn’t require any electronics knowledge! I’m sure this will come across as a bit thick to many of you!

I’ve just done a refret on a jazz bass, which has had a blend pot added at some point. The owner has asked me to take a look at the circuit while I’m at it. None of the three controls; master volume, blend, master tone, seem to have a very good sweep to them and are a bit on/off. The volume pot is an audio taper, not sure about the tone (don’t know how to measure this).

The circuit doesn’t seem to look like any other diagrams I’ve seen online. 

What can I do to improve the taper of the three pots in the circuit?

here is the circuit;

I’m not sure of the value of the yellow component as this is tucked in close to the longer one next to it.

ICBM

The yellow component is another cap, in parallel with the silver one - this will produce an unusefully large cap value almost regardless of what the extra one is - even .1uF is at the upper end of the sensible range. This will not be helping the tapers of the volume and tone pots. If you turn it round you should be able to see the value, but the first thing I would do is simply remove it (which will enable you to see the value anyway!), not least because it's a [heresy alert] crappy old cap which may well be out of value or leaky. [/heresy]

Everything else does appear to be wired correctly, so it's either that, just that the pot tapers aren't very good (many modern ones aren't, even from good manufacturers) or that it's plugged into too low-impedance an amp input (eg one designed primarily for active basses), which also messes up the tapers.

Funkfingers

It might help to know whether the CTS pots are 250k, 500k or 1Meg. The latter will behave in the "very on/off" manner described. 

A balance pot would normally be two linear taper tracks. In theory, this should provide a smooth and proportional transition between the signals of the two pickups.

In reality, with passive Jazz Bass pickups, there is a fairly limited portion within the travel of a balance pot where the blends sound good. This is why I tend to stick to the traditional VVT control circuit. 

Bridge PU up full. Neck PU rolled back until I hear a comb filtering honk. Thereafter, extract no end of tonal variety entirely through playing technique alone.

Endpin

Thanks so much. I’ll see about replacing the two caps with one of a known value. Perhaps first just snipping the yellow one to see what difference it makes.