ASR module is running!

[Haible_Juergen#Tel2743]

Hi!

After some minor difficulties, I got my Analogue Shift Register
Module running this morning!
I *love* playing with the second VCO following the first one
with a delay of two keystrokes - independent of the time
between the strokes! (I found a delay of 2 clock pulses
musically more interesting than just a delay of one pulse,
'cause when I am playing melodies, two adjacent notes
often form dissonant intervalls.)

Problems during construction:
(1) The pulses for the different sample&Hold stages may
not overlapp by any means! I got this warning from the
list before I started building; thanks again, You helped
me save much time. I did a redesign with another monoflop
between each stage to provide a secure and well defined
gap between the sample pulses.
(2) I made a great mistake with my S&H design. I wanted
to use a S&H with overall feedback to gain maximum accuracy,
but I didn't prevent the input opamp from saturating. The
effect was this: Everything worked fine for increasing
input voltages. But as soon as a decreasing voltage should
have been held by closing that n-channel JFET switch,
the input opamp's output went to the negative rail and made
the FET conduct again. I looked in Tietze/Schenk and found
the cure: Two diodes and a resistor clamping the first opamp
within +/-.7V of the sampled output voltage.

It's still only the naked pcb, no complete module. So wait
a few weeks before You ask for schematics (;->). Just had
to share this moment of first success with You all (after a
rather frustrating loooong night yesterday)!

JH.


PS.: As I have borrowed the idea (not the circuit!) from the
wonderful Serge catalogue, I can only recommend this
Serge Modular to all non-builders who want to have a
powerful Patchable. These guys have nice ideas!