The Artec MB-1 is an ingenious solution to the problem of combining piezo-electric pickups with the standard magnetic pickups in an electric guitar. These pickup types typically cannot be combined because of the impedence differences - the value of controls (volume and tone) that an electric guitar works effectively with is very different from that which a piezo works with.
The MB-1 works to buffer the output of the magnetic pickups to match the output impedence of the piezo. The circuit has a preamp to bring the very low output of a piezo up to the correct level to match with the magnetic pickups. Upon the PCB there are three trimpots to adjust the (left to right) magnetic pickup gain level, piezo pickup gain level, and magnetic pickup treble control. There are two mini toggle switches that switches the phase of your piezo (so that it combines with magnetic pickups of any phase), and pickup selection (magnetic, both, piezo).
The MB-1 has four potentiometers - one volume and one tone for both the magnetic and piezo pickups. It has one input for the magnetic pickup that requires soldering (that and the 9v battery clip are the only soldering required), so it is preferable in the majority of cases to put the magnetic pickup input after any pickup switching you may have. There is also a 2.5mm jack socket to plug your piezo into. The output is split into multiple different jacks and an XLR balanced output. it has a piezo output, a magnetic output, and blended output from a jack and the XLR (which is phantom power).
To simply the circuit, any of the output jacks can be unclipped from the PCB. Both mini toggles can also be unclipped - this leaves the circuit permanently in piezo and magnetic blended mode. Both tone potentiometers can also be removed to have the circuit function as if they are at half way (magnetic pickup treble can still be adjusted by the trimpot though). It can be used minimalistically with 2 volume potentiometers and a single jack. This set up would work similarly to a Jazz bass with no tone control.
Potentiometer shaft width: 9mm