[sdiy] I need a 909 kick circuit analysis

[Colin Fraser]

> -----Original Message-----
> From: owner-synth-diy at dropmix.xs4all.nl
> [mailto:owner-synth-diy at dropmix.xs4all.nl]On Behalf Of TooManySynths
> Sent: 09 September 2001 14:12
> To: synth-diy at dropmix.xs4all.nl
> Subject: [sdiy] I need a 909 kick circuit analysis
>
> I looked through the archives and I can't seem to find
> much detail on the 909 kick.  I have a schematic of
> the kick (sidenote, none of the 909 schematics links
> work, are they on line somewhere?) and I'm trying to
> make some sense of it.
>
> In  particular, how is the VCO working, and what is
> the role of Q11? I see that it bridges C4 with R51 on
> what appears to be the start of the trigger. I'm
> assuming the trigger is a positive going pulse.

It's for oscillator sync.
If you didn't have the oscillator synced by the trigger pulse, sometimes you
might trigger the sound when the oscillator is at zero, other times when
it's near it's peak.
Trigger it at it's peak and you'll get an audible click (like Hammond organ
key click).
Years ago I built a bass drum module from a SSM2045 filter with resonance
full up to act as a sine wave oscillator - it suffered from a seemingly
random click at the start that I didn't pin down until I built a 909.

> Also is the "Attack" circuit simmilar to other drum synths.
> What I mean is, I see that they are injecting noise
> into the "Attack" circuit, does "Attack" just control
> the level of a noise blip.  I haven't touched my 909
> in a while and it's not sitting in front of me.

'Attack' is a mixture of a click - the sound of the beater hitting the drum
skin, and a burst of pink noise - shell resonance.
Believe it or not, they were actually trying to synthesize a realistic bass
drum sound ;-)

Colin f