For those of you in the Spector Club, you all know this as the old "smadder set-up." Simply put, the BTC system is vol/bal/stacked bass and treble. The EXB circuit is the fourth knob. Rolled all the way off, it does nothing. When you start rolling it up, it creates a mid scoop while simultaneously boosting the lows and highs. It's a cool preamp set-up and I've left it all wired for a quick install - not that these EMG quick connects are difficult at all.
Great condition - only 15-20 hours of use.
You can hear the system reviewed by Jaymi here:
http://www.youtube.com/watch?v=dvouvHz_cgc
The whole system would cost you $136 new. I'm asking $65 shipped.
Paypal and CONUS only please.
BTC System
For EMG pickups only, the BTC System features a pre-wired balance control (blend) and master volume with the bass and treble on a concentric pot. BTC Controls and Systems are the most widely used bass EQ Systems in the world. Approximately 12db of cut and boost are available for bass and treble and all controls are center detented to assure quick return to normal tone settings. A dual-dip switch is mounted to the PC Board that lets you program the high end frequency response four different ways so you can choose the sound that's right for you. These systems use the latest in surface mount technology, are extremely quiet, and require very little current from a 9 Volt battery
http://www.emgpickups.com/products/index/137/146/4
EXB
The EXB is an unconventional equalization control for bass that increases the low and high frequency regions while reducing the midrange simultaneously to provide the gain and punch that bass players want. Slap players will especially appreciate its superior clarity and percussive quality. Similar in design and construction to the EXG, this unit is compact and will fit into most EMG equipped instrument control compartments without any modification. Instruction and wiring diagrams are included for easy installation
http://www.emgpickups.com/products/category/146/4 
