100m-ish Audio Delay

BBD based delay moduled based on the Roland 100m M-172

This Eurorack module emulates the Audio Delay function of the Roland-100m M-172 module.

The circuit has been modified to operate with Eurorack power supplies and signal levels, and to address other issues with the original circuit.

As the MN3004 BBD chip used in the original circuit is now rare, the PCB is designed to accommodate either an MN3004, or the much easier to obtain MN3007.

The PCB in theory also supports various other MN30XX and MN32xx series BBD chips though not all of these options have been tested so far.

The original specs for the Roland module are:
- Delay 0-7mS
- 30Hz – 20 KHz
- S/N 60dB
- Input: 10V 50K
- Output: 1K
- External CV: 10V max 50K

The module includes the original LFO circuit, where the output amplitude decreases with increased LFO rate:
- LFO range 0.04 Hz to 10Hz
- Amplitude:
o 10v p-p at 0.04Hz
o 400mV p-p at 10Hz

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