808 Clave Synthesis
The 808 clave is a very simple circuit. It’s just a single bridged-T oscillator. It doesn’t pass through any filter or VCA.
On the 808, the Clave and Rimshot share some components. In the block diagram above, you can see the clave in black and the rimshot in cyan. IC20 is the a bridged-T network.
A bridged-T circuit creates a quickly decaying oscillator pulse by exploiting an op amp’s need to balance its input voltages (+ and -). If you want to understand more about how this works, I’d recommend watching Moritz Klein’s video explaining his kick drum circuit.
Page 14 of the 808 service manual shows a diagram listing the frequency and decay times of all of its sounds. The clave (C) is set at 2500 Hz, which corresponds to D#7 +8 cents, with a decay time of 25 ms.
Because of its simplicity, this is an easy sound to reproduce.
Basic Clave on a Fixed-architecture Monosynth:
1: Set one of your oscillators to use a sine or triangle wave. Tune it to D#7.
2: Turn all other oscillators down in the mixer so you only hear one oscillator.
3a: Set the filter to low-pass, then raise the filter frequency to its maximum so no sound is cut or filtered out.
3b: If your synth supports it, try using a bandpass filter, You should set it to a fairly high centre frequency.
4: Set filter resonance to zero.
5: Lower the filter FM/ENV amount to zero.
6: Set the VCA envelope to have an immediate attack, no sustain, and a very fast decay. Adjust the decay time to taste. It should be long enough that it isn’t just a click, but fast enough that it produces little to no tail.
Self-resonating Clave on a Fixed-architecture monosynth:
1: Turn all oscillators down in the mixer.
2: Turn the synth's volume down (protect your ears), then raise the filter resonance to maximum until it starts self-oscillating.
3: Tune the filter frequency to D#7.
4: Lower the filter resonance until it stops self-oscillating. Raise synth volume back up.
5: Increase the filter FM/ENV amount. Playing a note should briefly trigger the filter into self resonance.
6: Set the filter and VCA envelopes to have zero attack time, a fast decay, and zero sustain. Adjust the decay times. It should be more than a click, but not long enough to have a noticeable tail.
On a Modular or Semi-modular:
Ingredients:
- A self-resonant filter.
- A trigger source.
Optional:
- An exponential AR envelope.
- A VCA.
1: Raise the filter resonance to maximum. It should start self-oscillating.
2: Tune the filter frequency to D#7.
3: Lower filter resonance until it stops self-oscillating.
4: Patch the trigger to either the filter's audio input, or the filter's FM input (try both).
5: When you fire a trigger, it should briefly push the filter into self resonance.
Optional:
If you want a longer decay, send the trigger to an envelope with zero attack and a fast exponential decay. Then patch the envelope to either the filter FM, or the audio input.
If the filter generates a lot of noise, run it through a VCA.
Further Reading
Pg. 6 has a brief description of the combined clave/rimshot circuit (RS/CL).
Pg. 7 has a block diagram (top right, under the BD).
Pg. 9 the circuit (bottom right).
Pg. 14 has a chart displaying the frequency, and decay time (C).
Synthesizing Cowbells & Claves (SOS)
Gordon Reid explains how to reproduce classic cowbell and clave sounds. Scroll down to get to the clave.
Designing a simple analog kick drum from scratch (Youtube).
Moritz Klein, the designer of the Erica Synths EDU DIY Kick Drum, describes how the module works, including the functioning of a bridged-T oscillator.