Wed Jan 12 18:34:26 EST 2011
Prophet 5: A/D and D/A resolution
I found the Prophet 5 service manual, as it is a nice example of a
digitally controlled analog instrument. Made me think: maybe high a/d
resolution isn't so necessary for storing patches: approximate
settings are just fine. It's when D->A is used for continuous control
that problems arise.
The prophet uses 7 bits for most CVs. and 14 for the frequency CVs to
allow for fine tuning. Tuning happens in octaves.
The Prophet uses a single 16 DAC for both D/A (synth control) and A/D
(potentiometer readout), combined with CD4051 ($30 Tayda, $50
Futurlec) analog muxes and sample-and-hold circuitry.