The BP-1 preamps for bass and GT-1 for guitar are characterized by very small dimensions, coming very handy to carry or to be inserted in the pedalboard. In addition, it has a side bracket for rack installation in studio applications.
In the flat position, the two knobs for low and high frequencies do not provide any type of emphasis, maintaining the tone of the pickups unchanged.
By turning both controls clockwise, you will get a boost for the corresponding frequency band.
Furthermore, the control for high frequencies can simulate the closing of a passive tone if it is turned counter-clockwise from the flat position.
The BP-2 preamplifier is the expanded version of the BP-1, as it has the same configurations for the treble and bass knobs and the same response, with the addition of 2 switches for further actions on low and high frequencies.
When positioned downwards, you will get a "surround" cut to the bass driver, ideal for the use of 5-string basses, and a high-frequency cut on the treble driver.
Positioned upwards, you will get a mid 70's cut to the bass driver for an enhanced punch and a cut on the mid-high frequencies for the treble driver.
Finally, a third switch allows you to have a gain on the output volume from the preamp with "1x" and "2x" options.