Odp: [sdiy] DAC for MIDI2CV

[Tony Allgood]

> I've seen in Tony Allgood's MIDI DAC that he uses 10n polyester caps
with precision opamps (at least for the pitch), although I've read that
polycarbonate and polypropylene caps have lower leakage.

I used polyester because they didn't show any measurable improvement
over polypropylene. The refresh rate is 31.25KHz in the midiDAC and the
sample window is comparatively large. There's only eight channels and I
think we use pretty much all the time allocated to that channel to
charge the cap. Trevor Page could give you more details here. There is a
small dead time before we open the 4051 to each of the caps to let the
DAC output op-amp stabilise.

Having said that I think that polypropylene would offer an improvement,
although by how much its hard to tell. Rapid sell low voltage
polypropylene at around 40p each.

Regards,

Tony Allgood                       Penrith, Cumbria, England

Oakley Sound Systems                     www.oakleysound.com
Modular projects            www.oakleysound.com/projects.htm