[sdiy] TB-303 clone

[harm jansen]

Hi there,

I'm working on a tb-303 clone for hobby purposes and I
ran into some small things:

I don't want to use large potmeters for the control of
the analog part such as the Piher potmeters that
available in europe. My main problem with the Piher
range is that the stereo potmeter that is necessary is
twice the thickness of the single potmeters which
makes it impossible to mount the potmeters on a pcb
and then to a enclosure. The single potmeters would be
too low relative to the ecnlosure for mounting them
with screws.
I looked around and I saw that quite some companies
like Roland use Alps potmeter. These see really neat
because they are snap in types. But the problem is
that I can only find them in two values : 10k and
100k.
And for the TB you need 1M and 50k. I don't want to
redesign the analog part.
So I was wondering if anyone knows if anyone knows if
Alps has more values in this range? And if people know
if there are other companies that have small potmeters
that can be mounted on a pcb and that have a
stereopotmeter version with the same thickness.

Another question I have is about the matched pairs in
the 303. The SC1583 and SC2291 are getting pretty
scarce these days and I want to replace these with CA
3046 arrays. I was planning on using one array for the
VCO and using a transistorised heater scheme to keep
the temperature in the VCO at a constant elevated
temperature. Has anyone done this before ?
And I want to use one array for the VCF if possible. I
want to do this by replacing the output diff. amp
(around Q21) with an opamp.
Is this possible and if yes why didn't Roland do this
then in the first place? Is there a problem with
common mode rejection in older opamps and is that why
they only used opamps in the SMPS and the CV buffer ?

If anyone could answer these question I would be most
happy.

Robert



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