.The circuit board for this project has now been discontinued. Ready made modules maybe still available from Krisp1.com.
The OMS-820 is a companion module to the MOTM-820 voltage controlled lag processor. It adds powerful new features to the superb Synthtech module. No component changes are needed to the MOTM module, and the two modules are connected together by just one removable connector hidden behind the front panels.
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With this module you can make the MOTM-820 into a voltage controlled LFO with variable waveshape. Or you use it to make a powerful voltage controlled envelope generator, with manual set and preset modes. You will be amazed by the uses you can find for this module.
1. LFO
When the mode switch is turned to LFO, the output(s) of the MOTM module will oscillate between +5V and -5V. The rise time of the waveform will be set by the UP control and the fall time will set by the DOWN control. The frequency will change according to the settings of both UP and DOWN. You can also change the rise and fall time together with the UP/DOWN control on the MOTM. You can easily make saw, reverse saw, and triangle type waveforms. The LIN/LOG pot on the MOTM will alter the shape of the waveform by introducing the usual non-linearites of the exponential rise and decay.
Top frequency is 1KHz or so, whilst the lowest frequency is so low I got bored waiting for one cycle!
2. EG mode
When the mode switch is turned to EG, you get a voltage controlled AD/AR generator and more besides. This section has four sub-modes. These are selected by two switches: AD/AR and Gated/Resetable.
The envelope generator can be triggered by two means, either a gate input as normal ADSRs, or a push button, SET, on the front of the OMS-820. When in AD(attack-decay) and Gated mode, the output of the MOTM-820 will then rise until +5V is reached, whereupon it will fall back to zero. Rise and fall times are governed by the MOTM-820 of course, and fully voltage controlled. Removal of the gate signal will cause the decay phase to start prematurely. Standard A-D EG behaviour.
Switch the unit to AR (attack-release) and gated mode, and the output will rise to +7V or so, and stay there until the gate is released. Standard A-R EG behaviour.
For either of the above modes, pressing the RESET switch will start the decay or release phase regardless of the gate's condition. The RESET input has NO effect in this mode.
Switch to AD and Resetable mode. The MOTM output will now rise to a +5V peak when the gate input goes high or the SET switch is pushed. It will then fall back to zero automatically. Removing the gate has no effect on the output. This is 'one shot' mode. However, the output may be forced to decay prematurely by pressing the RESET push button, or by use of the RESET input. A positive signal of above 1V or so will activate reset.
Switch to AR and Resetable mode. The MOTM output will rise until +7V is reached whereby it will stay there indefinitely, or until the RESET button or RESET input is activated.
Remember that all rise and fall times are controlled by the pots on the MOTM820 and OMS820. And can be varied from 1mS to well over two minutes.
Four LEDs are included on the front panel. Two of these will indicate the status of the gate and reset inputs. Another will show the EG's status. A fourth LED, a bicolour type, will give visual indication of the final output signal.
The OMS-820's two pots pots together with the MOTM's own pots, control the rise and fall time. This will enable you to set a time of say, 1 sec with the OMS-820's pots and then introduce a modulation signal. The depth of which is controlled by the MOTM's pots.
The OMS-820 and the MOTM-820 are connected together by one 4 way 0.1" connector. It can be simply removed if the modules need to come apart at anytime. The wires from the connectors are simply soldered to sepcial key locations on the MOTM-820. No component changes are required to the MOTM-820 at all.
The rear of the earlier issue 1 OMS-820. The issue 2 boards are similar in size but use the superior Spectrol 248 or BI TT pots.
Project Downloads
Construction Guide Our handy guide to building Oakley DIY projects
Parts Guide Our handy guide to buying parts for Oakley DIY projects
Links to schematics are available to purchasers of the PCB or module and will be sent via e-mail when the board(s) are shipped.
Front Panel database
A Schaeffer front panel can be made for a 1U wide OMS-820 module . The database can be found here. To read this file you will need a copy of 'Frontplatten designer' from Schaeffer. The program also features on-line ordering, so its now even easier to buy your panels from Scheaffer.
The company are based in Berlin in Germany and will send out panels to anywhere in the world. Delivery to the UK normally takes around ten days. For North American users you can also order your Schaeffer panels from Front Panel Express.
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