The cause of the Bazz Fuss "synth like" sounds?

[janus]

Hello all,
I just built a bass fuzz, put it in an altoids tin, and love the sound-- especially the synthy sounds when it decays. I was wondering if anyone could tell me what causes that to happen?. I've been reading all the electronics books I can find but I'm not experienced enough to figure it out. thinking it might be the diode? I used a 3.3uf cap on the input and was really happy with the sound..
Thanks


Brian