The Jerkster Chaos Circuit

I’ll soon publish photos of this module.   The first interesting patch I’ve created with it is demonstrated in this recording.  You are listening to a collection of modules set up to create a random harmony, using the CGS Infinite Melody, two MOTM-310 VCOs, two MOTM-440 filters.  The Modcan Dual Quantizer keeps it on pitch, and the Dual Oakley ADSR-VCA modulates the notes.  All of that is pretty standard.  The interesting part is what the Jerkster does:  First, it provides a chaotic vibrato applied to the filters.  The X and Y outputs (which look fantastic on the Veeblefetzer displays) are used for these.  The Z output is patched to a comparator to produce a random trigger for a sample and holds that also modulate the filter cutoff frequencies.  The random trigger is divided by factors of three and four to gate the envelopes.  The Jerkster is itself controlled by a third sample and hold.

This is unusually mellow for a chaotic patch.  Realize that the chaotic aspect of it is in controlling the rhythm of the notes, as well as in the varying vibrato.  This is aleatoric and runs without intervention.  You hear one of the many scales available from the quantizer.  The 5th-Octaverb effect from the MPX-1 is used here, as well.

For the second recording, I added the CGS Bi-N-Tic Filter in series with the MOTM-440. This lends a much darker, bassy timbre with the special strangeness of the Bi-N-Tic.

R10UE-10

These are nice, strong cases that hold 20U width of MOTM modules.  I outfitted them with Synthesis Technology MOTM-19A mounting rails.  One of the cabinets has a Power One HAA15-0.8-AG +/-15 volt supply, and the other a Power One HTAA-16W-A triple voltage supply with +5V.  These use MOTM-960 and MOTM-990 power distribution boards, respectively.

The depth worked out nicely, with plenty of room in front of the supply for normal MOTM modules.  There’s even enough clearance for a Stooge 3-pot long bracket (below).

I built the power supplies into aluminum box enclosures for safety, so that no 120V AC wiring is exposed.  The box and cover are Digi-Key parts 377-1028-ND and 377-1047-ND.  I found a combination AC inlet, power switch and fuse, Schurter IEC320 AC I, (Mouser 693-4304.6090) for $9.00.  It takes the same type of fuses as the MOTM-900/950 (Littlefuse 0239.800HXP for USA), but fuses both sides of the AC line so you need two.  The enclosure is mounted on a 3U high blank aluminum rack panel.  The whole unit is just another rack-mountable item.  It’s essential to use an aluminum panel, not steel, because of the machining required to cut the large rectangular hole for the power connector.  I drilled 20 small holes in the enclosure to allow some ventilation, and the whole box being fastened to a big panel also provides conductive heat dissipation, which I hope will be sufficient.  On the HAA15 supply the jumpers labeled VW1 and VW2 near the output terminals have to be cut to change from +/-12 to +/-15 volts (thanks to Paul Schreiber for this tip).

Each section the dual MOTM-480 handles one audio signal from the above.  Bandpass outputs are used.  Resonance is set high (8).  FM is applied with two slow sinewave LFOs from a MOTM-380.

This patch also has spatial modulation.  Headphones are recommended!  A stereo cross-panner is patched up, consisting of two MOTM-190 VCAs, two channels of an Oakley Multimix, and my own Matrix mixer.  The Multimix inverts the signals, which are mixed back with the originals so as to phase-cancel when the VCA is at unity gain.  The result is that each signal pans left to right, inversely from each other.  Control for the VCAs is the Blacet EG2070 in LFO mode with its two convenient 180-degree outputs, moving between zero to +5V.  The VCAs are in Linear response, as is the output of the EG.

Lastly, the Lexicon MPX-1 adds the Delay>Detune preset for post-processing.  This is a self-running patch.

Description:  Blacet Research Model DF2420 manually controlled state variable filters.  Two filters in a single 1U panel.

From the Blacet website:

Two high quality state variable filters in one handy package. Just the ticket for applications where voltage control is not required, such as formant filtering, basic percussion sounds or as a super tone control. Also useful as a clock source in “extreme” feedback mode! Use the filters separately, or with one input feeding both filters (mixed or separate outputs), or with two inputs mixed to one output. No extra mixers needed!

This is the fourth Blacet module that I’ve put into MOTM format this way.  It is very neat and tidy, the board mounting to the panel by the pots.  In a custom Front Panel Express panel.

Download Blacet Basic Manual

Front Panel Express FPD file

Quantity: 1

Description: Dual Tellun Lag Processor in a Bridechamber panel.

Tellun Project Page

Bridechamber Panel Page

The project is built on two MUUB-4 prototyping boards, stacked on top of each other on a Bridechamber 3-Jack bracket.

Here’s a picture of the top board, which has the power input connector. The big 4.7 uF yellow box capacitor (Mouser part # 1430-1475) fits on the upper right corner.  It is secured to the board with a Scotch double-sided foam square.  The jumpers that would have been underneath the capacitor were omitted and wires were soldered onto the capacitor lead.  All parts were placed according to the Tellun instruction manual for assembly with the MUUB-4.  One tricky bit was that the schematic diagram is generic and it happens that U1 and U2 are reversed from the MUUB numbering. The pinout of one of the op amps is also different from the schematic.  I wrote in the MUUB numbers on the schematic and corrected the pinouts as well, as an aid during assembly.

Below is a picture taken half way through construction.  The bottom board is in place and has been wired up to the jacks and pots. Notice the two electrolytic bypass caps lying down over the power connector area.  I used 2.2 uF values for these.  Incoming power is supplied by jumpers (red, white, and black) to the top board.  The MUUB board has convenient locations to connect power jumpers.  Note also that only the top board needs ferrite beads (Mouser part # 81-BL01RN1A1F1J are used here).

Below is a picture of the completed module, as seen from the side.  I chose Alpha carbon pots, partly for cost and partly because of readily available 1M log pots (Mouser part # 313-1500F-1M).  I bought 10 of these pots and matched them for value, as suggested in the Tellun manual.  I trimmed off the end of the Bridechamber bracket, which is very long.  The bracket has mounting holes that match the MUUB board.  Nice!

Here is a closeup of the sandwiched PC boards.  The capacitors fit snugly and actually contribute to the stability of the assembly.  You can see here the small cutout on the Bridechamber 3-jack bracket that’s needed to accommodate the nearest pot.