While not specifically synth related, this features a neon lamp multivibrator, ostensibly for the purposes of creating a suboctave signal to mix in with the straight signal. In this device, it more or less just creates a different type of distortion, albeit a cool one.
The housing is from a fried computer power supply.
Youtube clips to follow shortly:
This is, of course, based on Eric Barbour’s designs, with a few twists.
I built a separate sine/square wave oscillator and have put an input jack on the front of the ring mod for input of any carrier signal.
Basically, the first jack is the straight signal input. It feeds a 6ej7 pentode, then the volume pot below the jack, then pin 6 of the sheet beam tube.
The second jack is the carrier input, which feeds 1/2 of a 12ax7, a volume pot, the second 1/2 12ax7, then the beam deflection pins.
The top switch takes the straight input and switches it to the carrier circuit, cutting off the carrier input. This creates some weird and useful sounds, especially in conjunction with the bottom switch, toggles the value of the 12ax7’s first cathode resistor bypass cap between 10 uf and .01uf.
The third pot is screen voltage control for the sheet beam tube and the last jack and pot are output.
I have built a few of these in the past, and after reading of the death of Michael Waisvisz last week, I decided to use my last 709 to build this:
Due to the woofer in a ported enclosure with a tweeter, this thing is way more efficient(louder) than most crackleboxes with a small speaker. There is a significant amount more bass as well.
I installed a line out, for stadium use.
It runs on two 9 volt batteries(in parallel, so they last longer).
The contact points are pennies.
Based on the Eric Barbour schematics from the cgs synth website. Now I just have to build a keyboard controller, though it mangles my guitar quite nicely.
It contains a noise source, 2 VCO’s, 1 VCF, 1 VCA and a 2 channel mixer(from the old RCA tube book).