[sdiy] TB303 Slide

[Mattias Rickardsson]

On 26 May 2012 02:23, Tim Stinchcombe <tim102 at timstinchcombe.co.uk> wrote:
>> Does the R2R DAC in the TB 303 feeding the glide capacitor directly
>> actually achieve constant glide time regardless of the voltage span
>> between notes. (ie: glide time from 1V to 1.83V is the same
>> as from 1V
>> to 2V?)
>
> Yes. The output resistance of the DAC is always 100k, regardless of the
> voltage, and so the time constant with the 220n (C35) is 22ms - thus after
> about 60ms the slide is complete, no matter how large or small the voltage
> change was.

I guess it's "constant" glide time?

What I mean is... that it's an ordinary exponential RC charging curve,
having longer times for bigger steps, never completing the slide? :-)

A glide from 1 V to 2 V is shorter than a glide from 0 V to 2 V. When
gliding from 0 to 2, it goes quicker at the start and by the time it
passes 1 V the rest of the glide is identical to a glide from 1 to 2.
So the time is indeed longer... The glide time is just "constant" in
the sense of reaching within a certain percentage (say, 90%) of the
total glide distance - but no such percentage can be considered a
*complete* slide for all different distances. :-)

/mr