AW: Re: AW: Re: Idea for a CV quantizer
HJ2743 at denbgm3xm.scnn1.msmgate.m30x.nbg.scn.de
Fri Mar 8 01:53:00 CET 1996
> Oscillator running at roughly 100 KHz drives a divide-by-100 counter
Also a good idea! So the fast oscillator would reset the slow one.
But what exactly would be the advantage?
Anyway, I have decided to use a DAC now. Thanks to Joachim who
trades me a 12 bit DAC, it is the easiest way to go now. (Though I
would really have liked to try the other approach!)
I will make a slight change to the usual design, however:
Now what I want is a counter that cycles fast until the comparator
fires, and then rests on this number for some time. This could
be achieved with an Inhibit input at the counter. The comarator
triggers a monoflop. The monoflop controls both, the S&H stage
and the counter Inhibit. When the monflop falls back, the counter
goes on, until another input channel's comparator fires. This way
the sampling time / counting time ratio would be greatly enhanced!
I have made the schematics for this last night. I will build a dual
quantizer, i.e. 2 independent channels that share one counter and dac.
I use one LM339 quad comparator for the CV/staircase comparison
and the monoflops.
The DAC is an AM6012. The counter is a CD 4060, which has an internal
clock oscillator. The clock enable is made by simply forcing one pin
of the oscillator gates to High as long as either of the monoflops are
on. As the monoflops are made of comparators, they have a +/-15V
swing and can control the S&H FETs (BF245) directly, without level shift.
5 opamps are required. Two serve as S&H buffers (either two LF356's or
a LF353 plus network for driving capacitice cables), one as a I/V converter
for the DAC, and the remaining two are needed for a level shift between
the comparator and the DAC. Why a level shift?
For quantizing continuous signals (sequencer potentiometers ...) I
wouldn't need it, but if I drive the quantizer with a standard keyboard
voltage (for example to enhance the accuracy of my Kenton Pro-2),
the input voltage would just always fall on the thresholds. So a shift of a
quatertone would be appropriate.
This project is on paper only so far - so any ideas are still welcome,
but layout / results isn't yet available.
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