Sound generators

A collection of classic drum machine circuits as well as some newer designs are used as inspiration for the sound generators. Generators are not exact copies of the corresponding original circuit, they were modified as needed.

There are 10 sound generators. Because sequencer has only 6 voice channels + accent channel, sound for four channels is selectable. Each channel level can be controlled with level control knobs. Also each channel has one controllable parameter, tuning or decay time.

These drum machines are used as models for the sound generator circuits:

    - Boss DR-55: kick, snare, hi-hat, accent circuit

    - Korg KR-55: kick, snare, rimshot, claves, noise generator

    - Eric Archer's Andromeda Space Rockers: MK-2 hi-hat, MK-1 toms


The sequencer part is heavily based on Matt Sarnoff's 7400 contest entry for Dangerous Prototypes contest. This is very nice step sequencer circuit implemented completely with 7400/4000-series logic. It needed several modifications though.

Sequencer is 7 channel, 16 steps. Two 7 x 16 step patterns can be stored.


Housing is a Nordmende Fidelio table-top radio from 70's. Parts of the radio (audio amp, mains transformer) have been re-used in the drum machine.

Video showing the machine in operation:

Part of the sound generator boards ready. These are self-etched, because they are quite simple one-layer boards.

Sequencer boards, mostly 7400 and 4000-series logic, no microcontroller.

Drum machine internals fully wired up, waiting to be inserted inside the radio enclosure.

Full schematics and Eagle files can be found here:

A more detailed build log is in my electronics blog. If you are interested in understanding the circuits and the design decisions behind them, I recommend reading this build log:


Thanks for Eric Archer, Matt Sarnoff and unknown designers at Boss and Korg for great inspiration!