MOTM-120R Sub-Octave Multiplexer

MOTM 120R Sub-Octave MultiplexerFrom the Synthtech website:

The MOTM-120 is based on an article in Electronotes, updated with improved and added features.

The MOTM-120 contains two four-stage sub-octave dividers, a digital multiplexer, and four digital ring modulators. It operates in one of two modes, SUB and CROSS.

In the SUB mode a single input is fed into the A IN jack. A four-bit binary counter is clocked with the input signal. This generates the lower four sub-octaves. These are then mixed by individual pots along with the input signal. A switch selects either the original source mixed in or a squared version of the input.

In the CROSS mode both A and B input signals are required. Each is divided into their respective sub-octaves and then each corresponding sub-octave is digitally ring modulated with the other. If A IN is audio, but B IN is from a LFO, you hear a 16-cycle pattern of the sub-octaves getting multiplexed in. As the B IN signal is raised into audio frequencies, the results are huge chordal timbres with lively beat frequencies.

The Tellun DB-120R daughterboard adds these features:

  • Switchable AC/DC coupling for the outputs
  • A +/- 5V pulse output for each sub-octave
  • Weighted sum output STAIR for staircase wave generation

MOTM-120R panel photo by Scott Juskiw

MOTM 120R Back

MOTM 120R Side


3 Responses to MOTM-120R Sub-Octave Multiplexer

  1. Richard Mechling says:

    Hello Mr. B
    Just a call for help… for suggestions in using Cynthia’s SUBMUX DELUXE, which I see you had a hand in developing ? Can’t seem to get anything useful out of it. Hope you have the time to reply !

  2. Richard says:

    Hi RM,

    The MOTM-120R can be used as an audio signal processor, or as a control voltage generator. If you’re trying to get cool audio processing, try patching two VCOs into A and B and using the CROSS mode. Use the MIX or STAIR outputs with AC coupling. For an example of what that can do, listen to this:

    For voltage generation, use an LFO as a clock into the A input, select the SUB mode and DC output coupling. Using the four mix pots, you can create a complex repeating sequence. The STAIR output produces a rising sequence of voltages. Use the SUB1 – SUB4 outputs as triggers for envelop generators to get a new note every 2/4/8/16 ticks of the input clock.

    As far as my contribution to the design, I made a prototype version of what became the Tellun DB-120R circuit. Scott Juskiw then created the DB-120R PC board, based on my circuit. (I have upgraded my prototype board to a DB-120R board.) The circuit is very simple. Cynthia Webster had offered the MOTM-120 packaged into a Modcan format and was inspired to create the SUBMUX DELUXE, which is no longer available from Cyndustries, so you are lucky to have one. However, anyone can still buy MOTM-120 parts from Synthesis Technology and a DB-120R board from Tellun and do this for themselves, providing they can find or make the panel. I am lucky to have a genuine Stooge MOTM-120R panel.

    Richard B.

  3. Pingback: MOTM-120R Sub-Octave Multiplexer « Steve Force Music

Leave a Reply

Please use your real name instead of you company name or keyword spam.