Analog Modular

PugixWelcome 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:

Beats On Drugs

The Beats patch with parameters driven by Quantisise, plus digital delays from MPX-1.  In collaboration with David Linton.

Live Beats Rehearsal

Here’s a rehearsal for something I could perform live.  I call it ‘Beats’.

Rollz-5 Schematics

rollz-5-pcb-frontThis is the Rollz-5+ PC Board by Meng Qi.  The circuits follow fairly closely the original paper circuits, designed by Peter Blasser.  I am building it with modifications of my own to make it more modular.   Here’s the back side of the board.

rollz-5-pcb-backI’ve drawn schematic diagrams for all of the circuits and added my own modifications to the drawings.  The Rollz-5 circuits are early, non-voltage-controlled versions of the ones that ended up in the Plumbutter.  While Plumbutter schematics are available (see previous link), I haven’t been able to find normal schematic diagrams for the Rollz-5.  Peter B. provided the paper circuits only, which are pictorial graphics of the circuit layouts.  I drew my schematics referencing those graphics and checking against the Meng Qi board shown here and against the Plumbutter schematics.  (There may be mistakes on my diagrams, so be warned.)


rollz-5-avdogAVDog is made up of three internal ‘modules’.  An envelope generator, made from a filter set to a very low frequency, drives a transistor VCA that gates a simple audio oscillator.  ‘Inpulse’ triggers the envelope.  I’ve added four features.  A dual-ganged pot replaces the ‘x’ resistors, so you can control the period of the envelope.  The oscillator has a separate output jack, plus a switch into the VCA so you can cut it off.  Finally I added an auxiliary input to the VCA.

Also show is one of the 3-Roll Rollz circuits (which is unrelated to the AVDog).


rollz-5-2-roll-lfoI bread-boarded up the Roll circuit and played around with it.  I made 2-, 3-, 4-, and 5-roll versions.  I found that the odd number ones oscillated at ultrasonic frequencies (~100 KHz), and I didn’t want those.  I found that a 2-roll produced a nice LFO.  I added a positive pulse output (like Plumbutter) and an LED driver by Ken Stone.  The two ‘nodes’ still have jacks.  I’m building all eight Rollz identically, but with different value capacitors.  These are the rhythm generators.


rollz-5-gongGong is a low-pass filter, combined with a circuit to ring it.  Interestingly, this gong circuit is different from both the paper gong and the gong in Plumbutter.  The PC board has places for two 2M trim pots, but I will use a ganged panel pot, so that you can adjust the filter frequency.  I’ve also added an auxiliary input, so you can patch any of the other modules through it.


rollz-5-x4-ultrasoundUltrasound is a switch-capacitor filter with an internal high frequency oscillator.  If you build this PC board, you should add the missing 22K resistor to ground to each circuit.  I’ve added an output jack with 10K series resistor for the H.F. output (this is the yellow banana jack on Plumbutter).

 Output Mixer and Voltage Regulator

rollz-5-output-mixerPlumbutter has an output mixer with pots for Gong, AVDog, and Ultrasound that mix each one of the pair to left and right outputs.  Rollz-5+ has 12 audio modules (4 each of those just mentioned), so I designed this output mixer to be similar to Plumbutter.  There are six ganged pots.  Each pot sends a pair of the same type of module to both right and left.  The connections to the mixer aren’t shown on the individual schematics above, but they will tap off just ahead of the series resistor going to the corresponding output jack on the panel.

I’m including a 7809 voltage regulator.  This takes a 12V wall wart supply input.  I am not building the Vactrol voltage starvation circuit that’s on the PC board.


I’m planning to build this behind a clear acrylic panel, so that the PC board will show.  The pots will all be panel-mounted.  More details to follow.


Studio 2014

Finally, after almost a whole year of residing in boxes, wrapped in anti-static bubble pack, the 5U modules have been unpacked and installed into the five main walnut cabinets. Big thanks to Charles Brandon Howes for assistance in unpacking and setting up. Since I had used the power supply from one of the 5U portable cabinets for my Quantisise project, the 20U of modules in the left portable cabinet are without power. Portable cabinets on the right hold the 5U/BugBrand/CGS Serge, and the mixing and effects are beneath.


The table holds the four Ciat-Lonbarde instruments, left to right:  Tetrazzi Organ, Cocoquantus, Plumbutter, and Sidrazzi Organ.  The patch cords are in a Pomona rack to the right.


Here’s the workbench, in the midst of bread-boarding Meng Qi Rollz5 circuits for an upcoming project.

Finally a closeup of the main cabinet. It’s laid out a little differently than previously. The ZO came to the center again. And the lower cabinet has some small-knob modules.

Installation at ReHappening 2014

How can I describe The {Re}Happening? Such a unique event. Many simultaneous performances of music, dance, multimedia, all taking place from 6 PM to midnight on April 5, 2014, held in what is now a summer campground near Black Mountain, NC.  I was honored to be selected to make an installation.  Thank you, {Re}Happening!  The setting for my installation was in a cabin, reached by climbing several flights of wooden steps at night in the dark.  My cabin was at the top level, and I was surprised at the number of people who made that climb!  Thanks to Diana and my friends David Linton and Vincent Wrenn, the setup went smoothly.  David and Diana took turns minding it, while I ducked out to hear Vincent’s performance on his monochord.  On my return I was astounded to find the cabin nearly filled with people surrounding The Influencer and taking turns playing with it.  It seems that a large measure of the fascination it held was the mystery of the relationship between it and the sound.  Everyone seemed to be having fun and the whole thing was so much more well-received that I had ever expected.

Here’s a short video of getting it set up, with David helping out.

Here’s Vincent Wrenn trying it out.

And here’s Claire Elizabeth Barratt trying her hand.

I’ll briefly describe the patch, for those interested.  Two Buchla 258J clone VCO modified sine waves are mixed into the Bugbrand Frequency Shifter.  Downshift into one MOTM-490 VCF, upshift through the BugBrand digital delay into a second MOTM-490 VCF.  Each VCF through a CGS Tube VCA to the outputs, left and right.  Three sample and holds are triggered by the CGS Slope Detector by motion on one axis of The Influencer.  These steps select new pitches for the VCOs and a new rate for the frequency shifter.  One axis of the Influencer modifies the VCF cutoff frequencies (each inverted from the other) and the second axis modifies the CV of the VCAs (also in an inverse relationship).  The result is fairly playable, because a rapid motion of the Influencer will generate new pitches, but slow motions will only change the filters and loudness.  Players seemed to pick up quickly on the filter and level effects, while seeming to be a bit mystified by the random pitch changes.  No one needed to understand how it worked to be able to play it.

Finally, here’s a recording of one of the audience (unknown) playing it.

The Influencer


I propose a live, interactive installation in which sound is generated in real time by analog synthesis equipment that I have designed and built for this type of work. It is intended for interaction with an audience in a space with some acoustic isolation, such as a small room, but which is open in such a way that people wandering by may be drawn in by hearing it. A visual aspect is provided by the appearance of the equipment, including indicator lights monitoring electrical activity.

The work will generate sound patterns by means of oscillators inter-modulating in a complex manner, being modifiable by audience participation. It will proceed automatically, on its own, until affected by some interaction. The intent is to delight the audience with sights and sounds and by the experience of discovering the impact of their own actions. The work has no designated length, can run for as short or as long as desired, and can be scheduled into any time slot. People can come and go as they please.

That was the proposal I wrote to apply for the 2014 {Re}Happening event at the former site of Black Mountain College in North Carolina.  At the time of writing I did not have the interactivity part worked out.  Then I learned that a friend, Stephen Thomas Barnwell, was building a magnetic table joystick controller.  He had seen an idea found on the Internet.  I decided to build my own variation.  I call it The Influencer, because while technically it is a control device, I like to think of it as influencing rather than controlling the patch.

My build puts all the circuitry into a 3x4x5 inch aluminum box, supported by 3/8-inch galvanized pipe over a 16-inch wok fastened to a wooden table.  The circuit buffers each pot of the 2-axis joystick and provides range and offset pots for tweaking the outputs.  I set it to approximately +/- 4.5 volts.  Two standard nine volt batteries power it from within.  With on-off switch!  A 1/4-inch TRS jack for an insert cable feeds the two voltages to the synthesizer.

influencer-box-joystickinfluencer-box-potsinfluencer-box-insideI pondered different ideas for the pendulum shaft, which had to be detachable for transport.  The simplest idea worked.  It is just a 5/8-inch wooden dowel, drilled down the center and filed to make a pressure-fit with the joystick handle.  (A later version included some weights at the bottom to increase momentum.)  A magnet is screwed onto the end.  Various small magnets placed into the wok cause attraction or repulsion, depending on the polarity.  It works well enough, but I want to raise the support and make the shaft longer.  I made two of the pendulums in case one broke, which was precient.  The first one was accidentally pulled off the shaft too many times during the event and lost its friction fit.

My wife, Diana Brewster, tricked it out with foliage, a green and white color theme, and lights!  An excellent idea, since I am short on visual presentation.  Here’s a little video of a trial run in my studio.  The next post will have video and sound from the {Re}Happening installation.