Analog Modular
Welcome to my DIY synthesizer website. The name Pugix (and the graphic toon) belonged to an online gaming character that I used to play and has nothing to do with synthesizers.
My most recent activity:
Dual Resonant Gate
Quantity: 2 panels (4 total)
This is the Resonant Gate designed by Craig Lee, based on the original low pass gate Don Buchla circuit. The complete discussion is on Muff’s message board.
There have been many variations on the low pass gate. All share the central concept of using a Vactrol in the signal path as an amplitude controller. Various options provide for different levels of feedback, or resonance. Most low pass gates make us of a manual switch to select the mode of operation. This one is different in that it features a voltage-controlled feedback, which is labelled Mode. The mode is variable from no feedback at all to feedback large enough to make the circuit self-oscillate. The Mode pot sets the initial level of resonance, which can be added to or subtracted from by an external Mode CV through a reversible attenuator. The initial frequency is set by a pot I labelled ‘FR’ for frequency. (This is labelled ‘Offset’ on the schematic diagram.) External CV of frequency also uses a reversible attenuator.
My panel uses the ‘small knob’ MOTM grid format, which allows me to fit two identical resonant gates into a single 1U wide panel. This choice required me to omit the second CV input that the PC board provides.
My Modification
A problem was reported about the resonance circuit. It turned out that due to a characteristic of the Vactrol response, the resonance level could fall off over time. (See the full discussion, linked above.) I solved this for myself with a simple modification that set the minimum resonance to greater than zero. This means that the plain VCA mode is no longer available, and there is still some resonance at the lowest setting of the Mode pot. That’s OK with me. I like some resonance in the module at all times. Here’s the backside of the completed module:
My modification consisted of determining a parallel resistor for the resonance Vactrol. I described the procedure for finding the value in the post listed above. The end result is a resistor soldered across the Vactrol leads on the top of the board. Detail:
Finally, here’s a short demo of the resonant gate. It is filtering a triangle wave. A MOTM-800 envelope generator is hitting the CV. The demo starts out with the lowest resonance with the gate all the way open. Then I bring up the CV and play around with the controls a little.
Party Horns
It was a small party. Cocoquantus + Morphing Terrarium, some envelopes and VCAs, S&H with glide for pitch. The coco quantussy petal controls the M.T. morph inputs and is detected by the CGS slope detector to make gates.
Sensitive Dependence
This is the cocoquantus patched back to itself and left to run. I used the configuration in which four of the five oscillators are patched in a circle. The name refers to the concept of sensitive dependence on initial conditions in chaos theory. The cocoquantus is a chaotic pattern generator. Set the initial conditions and it generates patterns. A tiny move of the chaos pot changes those conditions. I didn’t touch it during this recording. There is a lot of bass in this one. Use of tiny earphones may lose some of it.
Late Nite TV
I’m trying out different combinations of equipment with the cocoquantus. In this patch the quantussy oscillator cluster is patched into the MOTM 510 Wavewarper, back through the COCO delays, and then through the Lexicon MPX-1 to add echos (way overdone, of course).
Petal On Its Own
This week’s cocoquantus patch again utilizes the CGS Tube VCA as a timbre enhancer. This time not only do the coco outputs each pass through one of these, in addition I’ve taken quantussy triangle outputs over to the CGS VCA CV inputs. This makes for interesting timbres. I finally understood the workings of the cocoquantus’s chaos circuit. For a decade I’ve been trying out different aleatoric techniques. The cocoquantus exceeds my expectations for an aleatoric controller. To duplicate the quantussy section would require five VCOs and ten sample and holds. For this recording I used a chain of four out of the five oscillators and let it run on its own for the entire recording without intervention.
Could It Get Some?
The cocoquantus with two of its oscillators patched back into the coco inputs, patched through the Uhbik phaser VST plugin in Audio Mulch. I twiddled with the cocoquantus controls during the recording.