BP-4 bass preamp

The basic advantage of this preamp is that it uses special JFET based circuitry (instead of an operational amplifier, like many preamp manufacturers do) which behaves very similar to the tube.

Operational amplifiers, when overdriven (which happens at the beginning of nearly every tone), get into the saturation. They need some time to recover (recovery time) and the circuit doesn't work as expected during this short time. The result is that we lose the signal - the beginning of the tone. The tube (and this preamp) doesn't behave like this and when it is overdriven, it softly distorts the sound by the second harmonics, which is an octave and it doesn't matter. And the first signal after the peak is immediately played (no recovery time).

This picture shows how it works.

Another question is tone controls. Many preamps use the Baxandall tone control. It works like this:

But, tone controls for the bass are different. Treble for bass is not the same frequency as treble for guitar, cymbal, voice or saxophone. It is similar with the bass control. OK, 50Hz - 100Hz boost, but everything under 40Hz should be cut. No speaker (and bass box) will play it and there will be unpleasant interferences with the frequencies from the bass drum (kick). My tone controls are designed "musically", not "technically", and it works :-)

The following picture shows how: