There is a lot of misinformation regarding the TonePump preamp shipped with some Spector basses. There are a few reason for this:
- Early Spector documentation referred to it as a boost-only preamp,
- No center-detent on the controls,
- Preamp has a significant gain boost, even with EQ at minimum settings
The TonePump is an asymmetrical cut & boost preamp. This means while there is both cut and boost functionality, there is MORE boost than cut!
TECHNICAL DETAILS
The TonePump preamp is designed by Michalik Designs, and is the same as their BP-4 preamp: https://michalik.cz/bp-4
- Bass EQ Range: +14dB / -4dB @55Hz
- Treble EQ Range: +14dB / -12dB @ 6.5kHz
- Bass Potentiometer: C10K (Reverse Audio Taper)
- Treble Potentiometer: A100K (Audio Taper)
- Gain +12dB
FREQUENTLY ASKED QUESTIONS
Q: Is there a “flat” EQ position on the bass and treble pots?
A: Not really. The TonePump has a baked-on EQ profile that cannot be completely flat. With the bass and treble pots set at approximately 8 o’clock and 11 0’clock (see illustration below), the preamp is as close to flat EQ as it can be. Even at this setting, the (non-trim) TonePump will still be boosting and cutting certain frequencies and will be 12dB louder than the input level.
Q: The TonePump is really loud and overloading my pedals and amp. Is there a way to adjust this?
A: After 2008, the TonePump preamp added an adjustable trim pot. On these units turning the trimmer to approximately 30% will bring the TonePump output down to the level of a normal instrument.
Older TonePump modules do NOT have a trimmer, so there is no adjustment:
However, it is possible to modify the instrument wiring to insert a small trimpot between the TonePump output (purple wire in this diagram) and the jack as shown here:
Q: Can I replace the TonePump bass and treble pots with different values?
A: Yes, however different values will change how the preamp works.
- Same resistance, but different taper: The adjustment range will be and tuning will be the same, but how quickly the EQ changes as you turn the knob will be different. For example, if you replace the C10K bass pot (reverse audio taper) with a B10K (linear taper) pot, you’ll find the “flat” area is near 12 o’clock instead of around 9 o’clock.
- Different resistance: This will change the tuning of the preamp. The bigger the change from the original pots, the larger the deviation from the original cut and boost frequencies.
Q: Will the TonePump work at 18volts?
A: Although Michalik does not list 18volt operation in their specs, we did test this in the shop with a few TonePumps. The increased voltage improved the headroom slightly, and we did not experience any issues. That’s not an official endorsement; if you let out the “magic smoke” at 18volts, that’s on you! š
Q: My wire colors do not match the wire colors in drawings that I’ve found. How do I know I have the right drawing?
A: This seems to be pretty common! We recommend first looking at the number of wires coming out of the TonePump. For example, the drawing early in this page shows a “9 wire” TonePump. Then look for drawings with the matching number of wires.
Once you have a drawing, check your installation against the drawing. Some of the colors may match, but what you are looking for is where each wire goes. Do the bass and treble pot wires go to the same wire position on the preamp? Do the two input pot wires go the first 2 wires? Does the Red battery wire go to the same wire position?