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

[TooManySynths]

> 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.

Do you mean C8?

> 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.

Aha, now we're getting somewhere.  Have you looked at
the envelope with a scope?  My tests suggest that the
cap will discharging as soon as voltage is applied,
but, will discharge at a slower rate. The input has to
go to ground before the cap will recharge. Therefore
the envelope won't have a truly flat top but a slow
decay followed by a fast decay. Am I missing
something?  Also, I just assumed that d8 and d9 are
garden variety 1n914 or so, ok assumption?

Nevertheless, the kick is definately fatter when the
gate pulse to the envelope is longer.

For what it's worth, I have a 909, I don't really want
to build the 909 kick.  What I want is to recreate the
characteristics that make it thump like a bitch and
apply that to other kick sounds.  

More questions:

1)What is the nature of the Accent CV. Is it positive,
negative? 0 to X, -X to Y? 

2) Do Q8 and Q9 only serve to extract a pulse for the
Attack portion of the sound?

3) Q3 appears to be NPN and Q8 appears to be PNP,
correct?  

4) Q12 seems to be providing VCA functions, albiet, a
dirt simple one.  Does that contribute signifactly to
the "shape" of the sound?

Thanks
Daryl

> 
> Colin f
> 


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