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:
Wavering Drone
This was made with the Modular Tetrazzi amplitude-modulating itself and going through a pair of MOTM-490 filters being swept by LFOs. Tetrazzi is controlled by the Wogglebug.
Before Tsunami
Uses the Modular Tetrazzi as a linear FM modulation source for the Zeroscillator in “no bias” mode. A thick drone arrives from the Synthesis Technology e340 Cloud Generator and later departs.
Tetrazzi Ditti
Example use of the Modular Tetrazzi as a sound generator, driven by other modules. In this patch a simple pattern generator drives four MOTM-800 envelope generators, each of which is patched to one Tetrazzi VCA input. The inverted out of the MOTM-800 came in handy to drive two of the VCAs panning in the opposite direction. The pattern generator clock also drives three sample and holds, which patch to the four Tetrazzi VCO CV inputs. With that running I played around with the UPTON, DONTON, UPMOD, and DONMOD pots, and flipped the range switches. The recording is straight from the Tetrazzi VCA outputs. No other processing!
Modular Tetrazzi
After I received my Ciat-Lonbarde Tetrazzi Organ, I spent a lot of time delving into its design. I wanted to understand it as well as possible in order to be able to play it well manually. By design, Ciat-Lonbarde instruments are intended for play, as in fun, and their operation is to be joyfully discovered, rather than coldly reasoned out. I like to play, but my brain also likes to figure out. I used the paper circuit diagram, together with the schematic diagrams provided by Peter Blasser, and conducted my own experiments. These then were my starting points.
Shown above is Peter B’s schematic for one of the four Tetrazzi oscillators. It is an ingenious design for a voltage-controlled sawtooth/ramp oscillator, where the up and down rates are separately voltage controlled. Not only are the rates under VC, each VCO has two modulation inputs, one for up (UPMOD) and one for down (DONMOD), that are hard-wired internally to come from the other VCOS. The internal patch looks like this:
UPMOD cross connections: [1 -> 4; 4 -> 3; 3 -> 2; 2 -> 1]
DONMOD cross connections: [4 -> 1; 4 -> 2; 2 -> 3; 2 -> 4]
The depth of modulation for UPMOD and DONMOD are under voltage control, all four being simultaneously controlled. The different topologies for these two internal patches is the reason behind the different sound experienced for UPMOD vs DONMOD. Did I just reveal a secret? No, it is discoverable to anyone who takes the time to understand the paper tetrazzi. If you click this image, save the GIF, and print it, you will have the paper Tetrazzi.
Functional Structure
The Tetrazzi consists of the following circuit elements:
- Four VCOs with VC up and down ramp, plus a solid state switch for additional modulations from node space
- Four “scroll” generators, track and hold circuits for establishing initial frequency and wave shape for each VCO
- Stereo VCA with inputs to each channel from each of the four VCOs, controlled by touch-sensitive piezo sensors
- A matrix of connections called node space for patching additional cross-modulations
The Tetrazzi Organ, built into the lovely wood case, provides the following means of manual control.
- Initial pitch and wave shape (the scroll) are set randomly by a red button, one for each VCO.
- UPTON pot controls the rate of rise, all VCOs
- DONTON pot controls the rate of fall, all VCOs
- UPMOD pot controls the depth of modulation for the rise rate, all VCOs
- DONMOD pot controls the depth of modulation for the fall rate, all VCOs
- Four wooden bars with piezo sensors attached control the stereo VCA
- Node space connections are made by touch or jumper wires
I took note that the pot wheels simply provide a voltage source. I also noted that the scroll circuit simply provides a voltage. And that the piezo electric sensors are voltage generators. What I’ve done is to create a modular package for the Tetrazzi in which all of these voltage-control inputs are interfaced to standard modular levels through panel jacks.
I modified the scroll circuit on the board. The scroll is now disabled. The CV input goes into the on-board op amp where the scroll voltage used to go. I used the XRS pad for a resistor that brings out the individual VCO output. The SCR pad, originally for a capacitor, was used for a 100K terminating resistor. See details by clicking on the schematic.
Adapter Circuitry Schematic
I designed interface circuits for
a) mixing CV from a panel pot with an external CV (8 of these),
b) buffering the VCA outputs up to modular level,
c) buffering the individual VCO outputs up to modular level,
d) creating a mix of all four VCO saw/ramp outputs,
e) creating a mix of the four pulse outputs that go into node space.
The CV input buffers also have the job of limiting the CV to the Tetrazzi board to safe ranges. My design provides the following features.
- Pots for UPTON, DONTON, UPMOD, DONMOD, plus an attenuated CV input for each
- Pots to replace the scroll, one for each VCO, plus an attenuated CV input for each
- Four attenuated, AC-coupled CV inputs to replace the bars for controlling the VCA
- High/low range switch for each VCO
- Individual output for each VCO at 9 v p-p, bipolar
- Left and Right VCA outputs, bipolar
- Averaged sum of all the individual outputs (9 v p-p), bipolar
- Mix of the node space pulse outputs, scaled for modular use (nominally 10 v p-p, adjustable), bipolar
- Banana jack patch bay for the node space outputs (red) and inputs (blue)
So many patching possibilities exist I can’t describe them all now. I will make MP3 posts soon. I may also make a video demonstration. Some things I’ve already tried that work well include patching an external LFO into the frequency inputs for vibrato or into the VCA inputs for stereo panning. An envelope generator into the VCA control inputs works pretty much as expected. And now it’s possible to tune the VCOs together with pots instead of randomly.
CONSTRUCTION
Here’s the Tetrazzi board (purchased by itself, assembled but I had to add the power components) with only the power input wired up for testing with the prototype adapter board. Look closely and you can see the eight 1/8-watt resistors I added near the button connectors. The circuit modifications were minimal, but I did have to cut some traces to disable the scroll circuit and bring out the individual outputs.
Here’s my adapter board, wired up on a prototyping board in the classic manner.
The back of the board with wiring. It’s all hand-soldered, folks.
I built a jig from a piece of plywood to mount the two boards next to each other for the prototyping phase.
Panel assembly and wiring of the panel.
Wiring to the Tetrazzi board. Some go to MTA connectors that hook to the adapter board and some go to the panel.
The Tetrazzi board installed and wired up to the panel.
Final assembly.
Untitled A
Reading about Pierre Schaeffer, founder of musique concrete, and his ideas of acousmatics and the sonorous object.
a) The sonorous object is not the instrument that was played. b) The sonorous object is not the magnetic tape. c) The magnetic tape can contain a number of different sonorous objects. d) But the sonorous object is not a state of mind. Sonorous objects can be clearly described and analyzed.
Listen to this recording. Do you hear sonorous objects? Do the sonorous objects have any reference beyond themselves? To how they were made? To other things that come to your mind when you listen? It is called Untitled A, because otherwise I cannot think how to give a title to a recording unless it either 1) refers to how it was made, 2) refers to something it reminds me of, or 3) is just whimsical nonsense. Schaeffer believed that the sonorous objects can be clearly described and analyzed. I wonder why I’d want to do that. I’d rather just listen.
Broken Silence
The primary chance parameters are pitch, tempo, loudness and duration. Modules include VCOs, VCAs, VC EGs, VC LFOs, a VC clock divider, sample and holds, and a frequency shifter. No filters or software effects were used. It is a self-running patch recorded directly to MP3.