The 808 Cymbal Drone Generator use six fixed frequency square wave oscillators.
The six oscillator cluster circuit came from the TR808 drum machine for creating cymbal sound and other metal plate sound,
in fact these are the harmonic frequencies of the sounds of metal plate.
Each of the six oscillators have a volume pot. and a 12 db low pass resonant filter, the filter cut-off can be controlled by the potentiometer or the cv input.