Onboard preamp troubleshooting

[Phil m]

Hey guys, I have run into a wiring problem on one of my customer's bass so tought I'd ask the electronics Experts over here

I've installled an Aguilar OBP-3 preamp inside of a Jazz Bass clone I built, I must have installed about a dozen of these preamps in the last couple of years without a hitch, unfortunately i'm now stuck, here's the schematic used



As can be seen I added a passive tone pot to it, I've also wired a few of these with this schematic in the past without a problem, the difference this time is that i used a Fender 250k/500k dual concentric pot for both the volume and the tone controls



I essentially wired all the ground wires to one star ground and sent that to the jack. Frm the tone pot drawing, i soldered the cap to one lug then the other bit of the cap to the casing (same side casing as the lugs making sure not to touch lower casing for the other part of the pot) and then sent a ground wire from there to the star ground.

Here's the problem, absolutely everything in the circuit works fine as it should work besides the tone control. From turned up full on to about 1/3 of a turn nothing happens to the sound (tone doesn't work) then once turned the pot back to that 1/3 the sound goes dead on the bass, volume shuts completely off.

The top part of the pot (volume knob) works fine, just the lower part of the pot, the tone doesn't work

Any ideas anyone? I'm at wits end here and need to send this bass back to its owner...

[J M Fahey]

Sorry but I don't understand why you added a passive tone pot, which is a poor obsolete solution, to a preamp which has powerful active bass/mid/treble controls.
That said, you sound like the tone cap is shorted .
Measure the resistance from the center lug of the tone pot to ground, at all points of rotation, with the yellow wire you marked lifted.
You should get always infinite resistance.
Post results.

EDIT: why did you cross out the wire grounding the blend pot?