Clap-Raca handclap

Love it or hate it … its the infamous fake handclap drum machine sound from the Roland TR-808!  When a friend asked me to a module to recreate this sound, I studied the schematics and came up with a hybrid clap sound, with several extra tweaks and mods that Roland engineers might have added if they had room for more knobs.  It’s built into an old metal box for 35mm slides, and runs off of a tiny 9VDC power adapter.  The trigger input works with drum machine and sequencer trigger outputs, and also works with some types of drum pads.

 Clap-Raca (normal)

 Clap-Raca (external input)

The Clap-Raca has knobs for Filter, Group Timing, Volume, and (inside) Reverb Blend.  There’s also an external audio input; plug something in here and the internal white noise generator is replaced with whatever audio you want.  Its like a triggered noise gate w/ filter.  It adds that classic electro spank when layered with a snare drum.  Tweak the filter and timing, and it sounds more like a punchy finger-snap.

Comparing the TR808 and TR909 clap circuitry.

Roland’s handclap sound is made up of two elements layered together; the “strike” and the “reverb” portion.  The circuitry has different sections for these, and both are triggered simultaneously.  The strike is a fast envelope with four closely spaced peaks.  Both the 808 and 909 use a similar scheme to generate this envelope.  The strike envelope controls a VCA (using an OTA) to shape white noise.  Its multiple peaks simulate a group of people clapping.  The “reverb” part of the clap simulates sound bouncing off the walls of a room.  Its so minimal - the white noise source is high-pass filtered, and fed to an envelope-generator and VCA… but the VCA in this case is just one transistor. (Q37 on the TR909 schematic).

Noise Source

The noise source circuitry isn’t shown on the schematics above; its piped in from a central noise generator in the drum machine that also feeds the snare, maracas, toms, etc… the TR808 has an analog noise source (transistor junction noise) to generate the clap sound, while the TR909 has a digital noise source (feedback shift register) doing the same job.  I chose the analog route and used the TR808’s noise circuitry.  The obvious modification to do here is to cut the noise source wire and add an external input, which gives plenty of options; the ability to chop and filter an external sound.

Is this available?

As of Sept 2009 I am designing a production model of the Clap-Raca in a stompbox format.