Here are two videos demonstrating functions of the F3DB. They present the results of my explorations of how the F3DB works from a black box perspective. The module has an odd input structure that I can’t understand without a schematic diagram (which I have requested). It’s quite unusual for an input to be usable as an output too! At least as an undocumented feature.

Pay particular attention to the input structure, in the lower left of the above diagram. Note the MIXER/DIST PRE/POST GAIN/CLIP jumpers (shown as switches). As I said in the build post, these must be set to the default PRE positions, going into the first AMP; any other setting actually does not work. Also note the GFB (Gain Feedback) switch and pot. Two different feedback loops are possible. The GFB loop routes the output of the input preamp back to its own input, when the GFB switch is ON. The second feedback path is via the Feedback Pot that controls the amount of signal from the output of the filter bank fed back to the input preamp.

The first video shows how the F3DB can self-oscillate. Both GFB and Filter Bank feedback are demonstrated.

Part 2 of the demonstration shows the F3DB processing an oscillator.