Doepfer

Hi Stu,

Since I had a set of TB-303 schematics open in front of me on my desk 
(been studying the filter), I thought I'd ponder this on a slow 
Sunday afternoon - but do I assume correctly that the Bass Station is 
largely based on the '303?. From what I've spotted so far, there 
doesn't seem to be much of a concept of 'sustain' on the 303, but I 
don't know it that well. In any case, the envelope mechanism is the 
usual charge/discharge of a capacitor, and since this is the same as 
the A-140, it must be different relative voltage levels between the 
two machines that account for the different bend/linearity of the 
envelope curve.

I think there might be some room for manoeuvre in terms of a 
straightforward change to the A-140: during 'decay' the charge drains 
away via a transistor, which slowly turns itself off as the 'sustain' 
level is reached. If this transistor was kept hard on, and switched 
off via a separate means (say a comparator, or a simple differential 
pair), the charge would continue to drain off faster for longer, and 
hence the decay curve would not end up so steep, thus going 'straight 
for the jugular' (taking liberties with your metaphor!). The biggest 
problem is that such a scheme might open up a myriad of possibilities 
of what is and isn't a good curve, and it might be hard to remove 
this subjectivity if it came down to chosing component values etc.

I guess there is also the possibility that the Novation envelope is 
not generated in real hardware, but done by software? I looked around 
for a set of schematics, but from comments on other forums it looks 
like they don't exist, so without a unit to look at, we get no help 
in establishing just *what* contributes to its envelope shape.

Thats my few pennyworth - perhaps others and Dieter might have some 
more ideas?

Tim

--- In Doepfer_a100@yahoogroups.com, "Stu Grimshaw" <grimshaw@...> 
wrote:
>
> while trying to approximate my favourite bass station sounds on the 
a100,
> i found the only thing i couldn't get near to was the adsr curves,
> which seem less exponential (vis a vis pitch perception) than the 
a140.
> 
> does anyone have any tricks to flatten out the curve ?
> 
> how are the adsr's from other firms in comparison ?
> 
> dieter, would there be no demand for an alternative adsr ?  the way
> the a140 slowly settles into the sustain level is brilliant for many
> things, but i could certainly also use a curve that makes straight 
for
> the bullseye, no messing.
> 
> cheers,
> 
> stu
>