BassDrum 606 sound-change

[Thomas Michaux]

Tom Verheyden wrote:

> ...
> FIG. 11:    --------/\/\----------
>             |        R2          |
>             |                    |
>             |---||----+----||----|
>             |   C1    > R1 C2    |
>             |         <          |
>             |--|\     v GND      |
>                |  \______________|____  Periodic wave out
>                |  /
> Pulse in ------|/
> 
> f = 1/(2pi*SQRT(R1*R2*C1*C2))
> 
> Q = SQRT(R2/R1)/(SQRT(C1/C2)+SQRT(C2/C1))

The BassDrum sound on the 606 is based on 2 bridged T-network filter
like the above.

I worked only on one of it made by the components :

R59 (R2) = 680 Kohms
R58 (R1) = 3.3 Kohms
C20 (C1) = 56 nanoF
C19 (C2) = 56 nanoF


Which gives orignally :

F=60 Hz
Q=10

What I made is doublin the Q factor to have a longer decay, whitout
modyfing the frequency F.

You just have to double the value of R2 and divide the value of R1 by 2.

Do do this I put a 680 Kohms resistor in serial with R59 and a 3.3 Kohms
resistor in parallel with R58.

So the new value after mods are :

F=60 Hz
Q=20

The decay seems to be longer but now the problem I got is evident : 
Q as increased so the sound level too, saturation comes faster.
What I'm searching to do is a kind of feedback just like the one on the
808.
Could someone help, anybody already tried to modify BD sound on the 606,
related experiences welcome.

Thanks.

Thomas.