Had a Wiard Noisering in for repair. This was a very interesting not just because of its technical interesting design but also it is quite rare and seems to have a trace back to some “god like” synth designers.
Background
The noise ring and the earlier Wogglebug is the logical evolution of a classic Buchla Source of Uncertainty circuit.The Wogglebug is a random voltage generator, originally designed by Grant Richter of Wiard Synthesizers. Designed for the Wiard 1200 synthesizer system.
Image Front
Image Rear
Block Diagram
Operation
The best description was found the Modwiggler forum.
Roycie Roller » Thu Dec 10, 2009 2:57 am
In one position you hear the Noise Ring operating as normal.
This is a great description of what’s actually happening in the NR (i think written by Dr. Mabuse, posted by Babaluma in the Wiard 1200 series info thread)
“The Wiard N.R. uses analog noise at a basic source point in it’s algorithm, but never directly. This noise is never sampled by an sample/hold circuit, in fact there are no sample/hold circuits in the N.R and this is a fundamental distinction. (It will help to consult the N.R. block diagram, at this point) You may already know how a shift register works but for anyone who doesn’t, i’m going to use the analogy of a conveyer belt with room for 8 people….
In the N.R., analog noise is used to tickle the threshold of a comparator, the comparator flips on and off producing either ‘someone’ or ‘no one’. depending on the state of the comparator. This person/non-person stands OFF the conveyer belt waiting for a signal. The signal comes from the clock. The clock is also a 2-state device. We’ll call them ‘tick’ and ‘tock’. Remember that the clock is not steady. It varies with a CV. This is important. When the clock is in a ‘tock’ state , nothing happens. The conveyer belt doesn’t move and no one steps on. The N.R.’s output is static. But when the clock switches to “tick” the conveyer belt moves one step and if the comparator was tickled to it’s ‘someone’ state, someone steps aboard. If it was in ‘no one’ state the conveyer moves one step with an empty place. On the next tick the conveyer lurches forward and if anyone was in the last (8th) position they get dumped off. Another thing happens at each tick, the DAC takes a snapshot of the pattern of occupied and unoccupied places on the conveyer, and based on that pattern it sends a voltage to the output, a different voltage for every different pattern, Thus as the two devices, comparator and clock, go on flickering , the conveyer gets loaded with different patterns that SHIFT on each tick. This cycling of patterns is the heart of the N.R.’s method, and this is very close to the classic function of a digital shift register.
But there are some twists! And one of the more brilliant twists that Grant conceived is depicted in the block digram by the line marked ‘old data’ feeding the “solid state switch’ . This is controlled by the ‘Change’ control. As the ‘Change’ control vector decreases, the chances INCREASE that the passenger who was just dumped off the end of the conveyer will get another turn and move right back to the front of the conveyer again and prevents any ‘new’ passengers (from the flickering comparator) from boarding. The effect of this is a ‘circular’ buffer wherein the pattern repeats ad infinitum until ‘new’ passengers are re-introduced by increasing the change control. At slow clock rates this results in cycling patterns. At audio clock rates the effect is a clearly discernible pitch. The wonderful thing about this is that the change control vector is continuous and thus, at audio frequencies, random audio (noise) will start to organize itself into a pitched tone. The ‘between states’ are sublime (to my perverse ear, anyway) and if you descend into chaos again , when you morph to pitch the next time there’s no guarantee that you’ll get the same wave as before. Please forgive me for editorializing, but the resulting patterns are exquisite!!! i’m sorry to confess my fetish, but that’s just the very definition of my personal idea of a good time!”
In the other position, i think (but not totally sure) the jumper inverts the ‘passengers’ on their way back to being re-fed through the Shift Register.
Switching between the two as the NR runs gives you a mix of sound at the outputs at audio rate. As cv’s, they are much more complex patterns.
You don’t even need to wire a switch to try it, just change the jumper position
There are a limited number of good resources on-line about these modules
https://web.archive.org/web/20060614161137/http://www.wiard.com:80/1200/NR/Noise_Ring.html
https://www.modwiggler.com/forum/viewtopic.php?t=59128
Falstad Simulation
From the block diagram and operational description a simulation of the unit was possible using the excellent Falstad circuit simulator.
The simulation is not perfect and the controls are very sensitive (Not range limited pots so there is a sweet spot to get it to function as expected)
Repair
So the module came in non functional. Some reports of the Two Main IC being replaced (poorly positioned) So replaced those as a matter of course.
Finally found that yes all ICs had there respective +15V and -15V inputs but everything had latched up high.
In the end after a few measurements of all chips supply pins I found that there was NO 0V connection. On closer inspection the PCB pad had been lifted away and there was no 0V going to the Top copper side pad and the via next to the pad. Must have pulled away when the reported dropping of the module happened.
Noise Circuit
One interesting issue was the noise circuit. When the PCB was tapped with an insulated object you could “hear” the response in the white noise generator output and the pattern / sequence would change as well.
Replaced the Noise transistor and also the PCB gain pot still without much difference.
After a bit of research into the issue the Ceramic capacitor in series is to blame. The ceramic capacitor is creating a Microphonics effect.
See link below:
https://en.wikipedia.org/wiki/Microphonics
This effect is were the ceramic film acks like a pizeoelectric microphone which is pickeup by the high gain (x200) noise generator amplifiers.
I see now on some later images of the Noisering they fitted a resistor in series and not a capacitor. Also a film capacitor might also lessen the effect. I spoke to the customer and agreed whats a bit more noise in a noise circuit.
When the unit is tapped it does change the noise generator and you can hear the regular sequences change slightly but it does add to the modules charm.
Clock in & Mods
Once the unit was repaired and working the customer wanted a Clock in mod and also to make use of some of the additional expansion socket outputs.
There is a great section on this modification on the modwigger forum written by the great and very helpful Tim Stinchcombe
So the modification would be normally sone on the front panel but the customer wanted a little 1U panel fitted. Also we agreed on 1 Switch for Clock IN enabled and then 3 additional Expansion signals.
1U panel and 9way socket for easy disconnection for fitting into rack,
Clock IN waveform Internal clock switched to external clock (signal generator)
Example waveform taken from expansion port.
Summary:
This was a pleasure to work on such a module and also understand the operation of the noise ring. The repair and modifications itself was not complex BUT trying to understand the operation was somewhat mind-blowing especially in the chaotic parts when the unit self oscillates in some feedback loop.
I do have some hand drawn circuit diagrams and one day will try to capture them into a schematic and BOM to help others. Get in touch if you need more information…
Thanks again to my customer Theo for entrusting me with this repair.
Satori Synthesis 
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