Wiardgroup

To pick up where Doc left off...

Actually we have to go back a little. The Buchla Model 266 
"Source of Uncertainty" has a quantized voltage output formed by 
a shift register and a couple of resistor analog to digital 
converters.

Somehow I ended up clocking it with an audio signal, and that 
sounded pretty good (like the video game sound chips). So the 
shift register from the 266 with the resistor DAC was added to 
the classic VCO and forms the RAND output. It's the same as the 
2^n output with n always at six. The 300 series already contains 
a Source of Uncertainty built into every Classic VCO (Your 
Welcome!).

The SOU shift register is fed back with an exclusive OR gate in a 
thing called a "pseudo random shift register".  Now Doc came up 
with the very clever idea of loading the shift register from a 
random data source formed by a comparator sampling a white 
noise generator. This makes the data "truely" random compared 
to "pseudo" random.

Bernie Hutchins published a design in Electronotes called the 
"Pseudo Random Tone Wheel" or PURTWEE (EN#106 Pg. 3). 
That design started with a pseudo random shift register and 
used that data to load a "tone wheel" which was another shift 
register, clocked at an audio rate, which could be recycled or 
loaded with a new bit under probability control.

Bernies original design did NOT contain it's own VCO and used 
6 chips for the noise source, 9 chips for the tone wheel, 24 chips 
for the probability control and 3 summers for a total of 42 ICs for 
the original PURTWEE design.

I realized that by using Doc's idea of generating random data 
using a comparator and white noise source, we could drop the 
PURTWEE component count down to 6 ICs and actually do a 
better job. Since the redesign was SO major, and we are using 
an actual white noise source, I felt it was appropriate to change 
the name from "Tone Wheel" to "Noise Ring" (get it?).

The last step was to add a VCO to the design for customer 
convenience, and a new ultra wide range VCO was developed 
for the purpose.

To summarize, the module is a Tone Wheel in wolfs clothing. A 
hybrid of the MIC Rube Goldberg Function Generator, 
Electronotes Pseudo Random Tone Wheel animator and the 
Buchla Source of Uncertainty. "Noise Ring" seemed good since 
RGFGPURTWEESOU does not pronounce well.

Shortly I will be doing a write up on the 2 hardware 
configurations and other possible modifications you can do at 
home.