It’s my attempt to build a famous 808 cowbell drum module. I must say, it sounds like nothing else (including real cowbell). I made some mods in original circuit – some of them are well known:

• decay mode – lets you choose between 2 decay times: “original” and shorter one,
• filter mod – changes output filter characteristics for more sound variation,
• 2 generator settings – “original” and user defined (with additional front panel knobs),
• the circuit uses 7805 voltage regulator instead of transistor circuit.

Schematics should explain everything.

The main difference is that 4 generators are used – 2 work as original, tuned squarewave source, 2 other are user tweaked. You can choose with switch which one you want to use – this way distinct cowbell sound will never be lost. PCB is designed for use with eurorack synth standard – +/- 12 V power supply via 2×5 goldpin header. PCB size is around 98 x 46 mm, it will fit vertically behind eurorack module front panel. Better quality PCB shot is added as attachement at the end of the post, along with BOM.

I etched the PCB using Bungard FR4100X160/3500 laminate with light-sensitive coating – very quick and reliable method. One 160 x 100 mm piece costs below 3 euro. Big “minus” sign on the PCB near the power connector (left PCB side) shows where negative voltage comes.

Finished drum module looks like this. A always, I used Alpha 16 mm pots and gold plated jacks. Two blue box type trimmers serve as frequency controls for “original” generators.

The small PCB on the back side of the panel holds the trigger LED. It is glued to potentiometers – not very elegant solution. The small caption on every potentiometer really helps while wiring.

And how its sounds? Nothing like cowbell 🙂

If you want to build one for yourself, here are all necessary project files. Happy DIYing!

Jack

Big thanks for Marek, for his photo session!