[sdiy] Since it's 9/09, it's time for more 909 questions :)

[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 20:13
> To: synth-diy at dropmix.xs4all.nl
> Subject: [sdiy] Since it's 9/09, it's time for more 909 questions :)
>
> Thanks for the help so far with the 909 kick circuit.
> I have been working on recreating the VCA envelope and
> I think I have been going on an false assumption.
>
> So, what I want to know is how wide is the trigger
> pulse that feeds into R1.  I suspect that it is at
> least as wide as the flat portion of the top of the
> VCA envelope, but I'm not sure.

All 909 trigger pulses are 2ms.
In the bass drum, the trigger pulse charges C7. While C7 is charged, Q3
turns on Q4. Q4 applies the accent CV to Q8.
The size of C7 determines the length of the flat top of the envelope - the
decay phase doesn't start until C7 is discharged enough to let Q3 adn
therefore Q4 turn off, removing the accent CV from C8 and allowing it to
discharge thru the pot.

Colin f