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You can try this, but it’s much easier to buy a 12 to 16 bit D/A converter. Basically the problem you’re trying to solve, D/A converter accuracy, has already been perfected by IC designers over the last 20 years.
John Loffink
jloffink@...
-----Original Message-----
From: J. Larry Hendry [mailto:jlarryh@...]
Sent: Tuesday, February 19, 2002 10:45 PM
To: MOTM List
Subject: Re: [motm] Quantizing
I have l long been thinking about a quantizer. My thought process was that a very accurate circuit could be built in the 8 bit format IF one used a ADC to get the digital quantities, but avoided the 8 bit DAC by going completely analog on the output. Then each of the 8 elements could be trimmed accuracy so when you added the elements each together you would have much greater than the accuracy expected from a 8 bit DAC. I can see Paul shaking his head and sighing at me right now. But, I have been thinking seriously about a replacement for the 822 when those PCBs are gone that uses pots instead of rotary switches. So, trimmer count would be considerable less. Of course, then your basic circuit is a quantizer. I have done no development yet because of other projects, my need to learn more, and the (cough, cough) significant stock of 822 PCBs I would like to make a dent in first. :) And, I fully admit to knowing almost nothing about it and being significantly under-qualified for the job. So, I'll probably play with it anyway.
On a related question, where would one normally expect the analog out to track the input relative to step points. To simplify the example, let's assume 1 volt steps. Would the output be desired to change from 1 to 2 volts at 1.5 or 1.9999 on the input? I don't see that is really matters. But, I am still pretty ignorant on the subject.
Seems the 8 bit DAC might be fine for a mono synth and single oscillator, but would never do where oscillators might beat together. I have a couple of the PAiA 8 bit MIDI 2 CV 8s that I use with stuff other than my MOTM modular. For my mono synths (like my Micromoog) that 8 bit resolution seems to be OK.
Larry