Banjo Processor

Pitch-to-Voltage Convertor

An analogue synthesizer interface built around a five-string banjo

When The Peasant built the first SynthCase project, a keyboard was not included, as playing one is not something that he has ever learned to do. However, The Peasant is a banjo player, and so thought that it would be very interesting to use a banjo to control the analogue synthesizer. A number of years ago a pitch-to-voltage convertor circuit board, designed for guitar use, was purchased from fellow DIY enthusiast Harry Bissell. This pcb only used the bottom three guitar strings to extract the CV output, and so it was decided to expand the board to work with all five strings on the banjo. The board was designed to output CV, envelope, and triggers, and also included a built-in bass synthesizer. A special hex pickup was required to deliver individual string outputs to the circuitry.

During the design phase, "feature creep" reared it's ugly head, and the final project ended up including a preamp/mixer section, using the hex pickup and an input for a regular banjo pickup. Some extra functions were added to the bass synth, and some quasi sawtooth outputs were added courtesy of another small pcb from Mr. Bissell.

Below is the case chosen to be used for this project. This was an obsolete pager battery charger, and was just the right size!

Next the front panel was designed. This was a color 300 dpi drawing created on the computer.

The drawing was emailed to a printer, who printed and laminated it using low gloss laminate.

The laminated drawing was then used as a guide for drilling all of the holes in the front panel.

After drilling and deburring the holes, the drawing was attached to the front panel using 3M type 77 spray adhesive. Then the holes for the the front panel parts were cut out of the drawing using an exacto knife.

Finally, all of the front panel controls, connectors, and LED sockets were mounted, completing the front panel.

Now the internal construction and wiring can begin. Here you can see the main PV circuit board, the small sawtooth pcb on the bottom right, an unpopulated perf board for expanding the PV circuit to five channels, and the power supply partially completed. The preamp/mixer circuits will be mounted on the front panel.

Here you can see the first of two preamp/mixer boards completed and wired to the front panel. The second preamp/mixer board in the rear of the picture is about 2/3 completed. This part of the project was designed using all discrete FET circuitry except for the tone controls.

In this picture, the preamp/mixer circuitry is complete and working. The PV expansion perf board is fully populated, the power supply completed, and the PV wiring has just been started.

At last, all of the wiring has been completed, the circuitry has been tested and calibrated, ready to go!

And now the experimentation in the new musical genre of "Analogue Banjo Synthesis" can begin!!

Check out The Peasant's SynthCase and SynthCase 2 projects!