[sdiy] Digital control

[Johannes Öberg]

Thanks for your help guys!

Are the Mbase01 schematics available somewhere, or does anybody know
how they implemented the DCR's? How did the Polysix or other early
patchmemory synths do it?

The digital resistor chips are to expensive for me unfortunately. If I
would try to build a digitally controlled analog synth (of course,
this is more like dreaming than considering) I would need alot of
digitially controlled "pots". What's the _cheapest_ way of doing this
with an acceptable reproducability and resolution (say at least 6
bits) ? IIRC the old polysynths used to use a single D/A going into
these crazy mega-sample'n'hold chips, going into VCR's. Are these
SnH's still an alternative? Can't it be done in a simpler way, if one
accepts poorer stability or something?

The other alternative seems to be multiplying DAC's, but this can't be
a cost-effective way of doing it, can it? Or did I misunderstand? I'm
believing you mean that I should use one DAC per pot. It sure seems
compellingly simple enough though.

Shouldn't it be possible to use a totally el-cheapo method, something
like a single transistor as the VCR and either a giant sample'n'hold
thing or perhaps even the old one-bit-D/A from the microcontroller? Or
am I totally naive? Any linearity problems could be compensated for in
software, methinks. As most of the 'digitally controlled resistors'
would replace pots for non-timecritical stuff (like Attack rates) slow
settling time (or what it's called) due to slow samplerate for the D/A
wouldn't be a problem.

/Johannes