DAC accuracy

[Tony Allgood]

The DAC-08 is available in higher spec'd types. If you do use the DAC-08
use this part. The ordinary dac-08 is only 1/2LSB accurate. Clock it
with a counter and look at those errors. Even if you use just seven or
six bits those errors are audible in a polyphonic system, and are easily
measurable with a cheap voltmeter. If you set it up for 83mV per note
and are using the 7 top bits, then one LSB represents half of this. Half
of that, ie. the spec'd error, will be +/-20.75mV. This is a goodly
proportion of what you are trying to get within 0.2% to. Tim Orr
(designer of EMS stuff and transcendent synths) reckoned that ten bit
accuracy was important. I am not just looking at the spec sheet either.
I have just tried to tune my 3340 based polysynth using a dac-08. It
doesn't work, octaves do not produce 1V differences across the keyboard,
even if you get it right down the bottom it doesn't at the top. It can't
its a DAC-08, a cheap and cheerful little dac and nothing else. If you
do get get your DAC-08 to sound good, then you are lucky. I wasn't.

Regards,

Tony Allgood, Cumbria, UK

Rack mounted moog filter and the TB3030 SuperBassline projects:

http://aupe.phys.andrews.edu/diy_archive/schematics/oakley/