Dual RVG Module
The Dual Random Voltage Event Generator (Dual RVG) is a faithful replica of the vintage EMS Random Voltage Generator. It is an all analogue design which generates two separate random voltages that can be timed either from the internal LFO or from an external clock. However, one of the most interesting features is that varying amounts of randomisation can be added to the internal clock rate with the Time Vary control - so with this we can randomise time period in addition to voltage.
The TR-IN input allows an external clock to be used instead of the internal LFO. When the LFO is stopped two new random voltages can be generated with each press of the manual Trigger button.
We have added many useful features that were not present on the original design, including Level and Offset controls for both outputs, adjustable Slew on Output 1, control of internal LFO run / stop from an external Gate signal, control of LFO rate using an external CV, and the LFO output is brought out to the front panel as both a Sawtooth and Triangle wave and both of these waveforms are skewed as Time Vary is added to the LFO rate. We have also added a gate output that produces a gate for each internal clock pulse, and this gate length changes in proportion with the time variance. The duty cycle of the gate can also be varied from 1% to 99%.
Module Width: 14hp
Module Depth: 26mm (Including power lead)
Current Usage: 95mA Positive, 70mA Negative
Product Information
We have taken the original EMS RVG design and re-created it in Eurorack format, and added many extra features that make it a considerably more useful in a modern day modular system, but of course it can also be used with other synths too and with a suitable conversion cable it can be used with the original EMS VCS3 and Synthi A or Synthi AKS.
Limited Edition
The Dual RVG will be available with either a Black (Dark Edition) or Silver front panel. Just like the original EMS RVG the circuitry uses vintage unijunction transistors for both the ramp and hold and LFO circuits, these are quite rare and we have only obtained enough UJT's to build a limited number of modules, Therefore the Dual RVG module is being released as a once only, strictly Limited Edition of 250 units worldwide.
Introduction Video
Here's a short video that covers the main features and illustrates some uses of the Daul RVG module.
Usage notes:
Due to the idiosyncratic vintage circuitry of the original EMS Random Voltage Generator there are a few unusual characteristics in the operation of the Dual RVG that it may be useful to know to help you to get the best from this unique module.
The LFO FREQ control has an effective range from positions 4 through to 10, and a "dead" range from 0 through to 4. However, it still covers the full range of 0.2 Hz to 20Hz that was possible with the original vintage RVG, this behaviour is due to the type of UJT's that we have used along with the extra circuitry needed to implement voltage control of LFO frequency. The rate of the internal LFO can be voltage controlled by patching an external CV to the FQ-CV input and the amount of external CV fed to the LFO is attenuated by the FQ-CV control. When using an External CV the upper range of the internal LFO can be extended up to around 45Hz, so this is an extended range that is not possible with the original vintage RVG.
The GATE output is only available when the RUN switch is ON (down). When the RUN switch is set to OFF then no GATE output is available. This also applies if a gate signal of +3V or higher is patched to the RUN-GT input when the RUN switch is OFF. This will route the internal LFO clock to the random voltage section and the Time Vary function will also work, however in this configuration it is not routed to the gate circuitry and therefore no gate signal will be available from the GATE output
The TIME VARY function is only active when the internal LFO is used, it does not work when an external clock source is used rather than the internal LFO. This is because the TIME VARY control applies a random voltage to the rate of the internal LFO, so obviously if the RUN switch is set to OFF and an external Clock is patched to the TR-IN input the random voltages will be changed with each external clock pulse received, however the TIME VARY control will not have any effect on the timing of the random voltages V1 & V2 as the internal LFO is no longer being used as the clock source.
When the RUN switch is set to off the RAMP and TRIANGLE waveforms are still available from the front panel outputs, and the frequency is still controlled by the LFO FREQ control - however the LFO is disconnected from the random voltage selection circuitry and the LED indicator will no longer display the rate, instead it will monitor the external clock. This is deliberate, as it allows the internal LFO to be used independently from the Random voltage section.
The onboard sample and hold system for the V1 and V2 random voltages is implemented with analogue S&H circuitry based around a Unijunction Transistor and a low loss hold capacitor. This circuitry is required to "hold" the random voltage generated for V1 and V2 between clock pulses. Leakage of charge from the hold capacitor through the Unijunction Transistor causes this held voltage to drift either up or down with time and this can be noticeable when long hold times are used, for example when very slow LFO rates are used or the RUN switch is turned off. We have (rather laboriously!) hand selected the UJT's for best performance, but even so there will be a small amount of drift over time and this may be worse on one channel than the other. This was obviously also the case with the original EMS RVG unit, however we have used a better pcb layout and also fitted a high impedance FET opamp as a hold capacitor charge buffer so the sample and hold performance is improved against the vintage RVG that it is based on.
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