[sdiy] Digital modular backplane - update

[John Slee]

On 31 March 2014 19:18, cheater00 . <cheater00 at gmail.com> wrote:
> This could be reconciled with presets by using a balancing topology - i.e.
> if the knob it putting out 1V, but the preset is 0.5V, then the DAC should
> put out -0.5V and those voltages should be added.

Pots have end-of-travel, unlike typical rotary encoders. So if your pot
is at 90% position (you turned it to ~9.0 on a scale of 1.0-10.0)  and
you want to increase the preset value by another 20%... you're stuck.

So it's either

(a) motorised pots/faders (do these introduce a bunch of noise?), or

(b) encoder + digital pot + some kind of position indicator (LEDs?)

or

(c) ordinary pots and no "balancing" as you describe it, a la Roland
Jupiter and probably countless other analog synths

Of these, (a) and (b) are going to be expensive (relative to decent
quality ordinary pots), (b) will require a more complicated design, and
(c) is just plain awful.

And then you have other inputs, such as toggle/rotary switches. I
suppose you could replace those with momentary buttons and some
kind of indicator. I'd prefer that most of the time actually.

Look, I get the desire for a better modular. I really do. But I think that
to do it a better path might be to ditch the analog parts almost entirely
and use DSP everywhere. Like Creamware/SonicCore's SHARC
systems, which are brilliant but lack the touchy-feely aspect of a real
modular.

It'll almost certainly be cheaper, and with the savings you can invest
in some spectacularly good DACs for the output stage, and for ADCs
if you wanted a module to process external signals. I'm not convinced
that repeatedly munging signals with ADC/DAC stages is going to
result in a great sound.

Got prototype?

John