Official Luthiers Forum!

I have just completed a custom chambered body guitar and am having a issue with the master volume control and TBX tone control. I have attached a schematic diagram for those of you who are good at figuring complex wiring schemes. The guitar has 2 magnetic humbuckers and the LR Baggs T-Bridge with the Ctrl-X preamp. Also in the signal path is the Fender TBX tone pot. Everything works except for two little glitches. (1) The Master volume (500K Mojotone audio taper) is silent for about 1/4 of its travel and then the volume jumps on with little change to full rotation. This is true if it is just the magnetics on, just the piezo on, or both. (2) One side of the TBX works as it cuts out some of the bass, but it only works when the master volume is at full. The other side of the TBX has no effect on the sound. Just a note that most of the Control-X comes pre-wired including the mounted circuit board blend pot. I assume it is possible that the 500K master pot is bad, but before I start pulling things apart, I wanted to see if anyone saw other issues that might cause either or both problems. Thanks.

I don't understand the 150K resistor from the wiper of the master volume to the top of the pot. It seems to effectively shunt about 1/4 of the pot. Try unhooking one end of it (the cap can stay on or be unhooked also)

FWIW, the one time I put a piezo bridge in an electric guitar with two humbuckers I just brought it out in a stereo jack - I didn't try to blend or switch on the guitar. We split the cable with an A/B splitter and took each signal to its own input at the amp (and whatever effects wanted for each channel). The owner never really bonded with the piezo, I'll be interested to hear what you think of yours.

That is a treble bypass on the master volume across the input and output lugs. Prevents treble loss at low volumes on the pot. I can remove the bypass to see if that makes a difference. Thanks.

The Blend pot is pretty versatile. An one-the-fly mix allows you to dial in some nice tones. The piezo bridge is very bright, but when blended with the Filtertrons it gives them a nice "sparkle". The LR Baggs Control-X can be both mono or stereo. There is a little button that sits between the toggle and blend pot that allows the switch between stereo cabling or mono.