preamp onboard

Posted on Feb 5, 2014

After the unexpectedly big success of my JFET bass preamp I decided to build an onboard version. For a Jazz Bass-like instrument, I had to get along with three controls, maybe some switches if I used push-pull pots. Further, I wanted the functions of the knobs unchanged (vol - vol - tone) and, if possible, use the original pots. This preamp featur

preamp onboard
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es independent buffer stages for both pickups, a "Big Muff" style tone control with switchable mid cut and a gain/buffer stage for the output. The source resistors R2, R5 and R11 have to be selected according to the FET (and the supply voltage). Connect a 5k pot instead of the source resistor and adjust for maximum non-clipping signal at the drain. Then disconnect the pot, measure its resistance and put a resistor with the closest value available into the circuit. I use this preamp for my acoustic bass to mix two piezo pickups (Underwood/Realist). For this purpose, I changed P1 and P2 to 2M5. First impression: The mid cut function is too strong/not necessary for double bass, and the pickups are out of phase. Thinking about a phase switch. No problems otherwise, works great.

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