Two VCOs. The first VCO provides a semi sawtooth/square with Sub FM modulated by an LFO for harmonic variation. The second VCO just provides a sine wave. The VCOs are two octaves apart.

The two VCOs are mixed and fed to a wavefolder to form the required waveshape, and thence to a ladder VCF with a 12db slope and a VCA, both modulated by seperate envelopes (could be one – but this provides flexibility if required).

The VCA uses keyboard velocity, but via the Exp Mod input (not the Vel Mod input).

Finally delay and reverb to taste with a stereo panned output.