2hp Rnd module

This 2hp module is a random stepped voltage and gate generator.  I’m making a special post about it, because I think it has a unique design.  More needs to be said, than the following quote by the manufacturer.

Rnd is a random voltage generator and random gate source with an internal clock. The output is a quantized random voltage between 0V and 10V. The attenuator control provides fine-tuning of the random voltage.

This allows for a musically useful range to be defined. In addition, random gates are emitted from the gate output with an associated probability control while externally clocked.

Random, stepped voltages are typically generated in a modular system by patching three different modules together:  a noise source, a clock, and a sample and hold (S&H).  It is also typical to combine these features into a single module.  Sometimes a slewing circuit is added for portamento.  The Ultra Random Analog module combines all of these.  See the BugBrand Noise Crusher for another example.  And also see my Triple S&H.  There, I’ve linked to S&H modules in three different formats!

Sample and Hold theory

A Sample and Hold circuit is usually designed to be a control voltage generator (although at high clock speeds, can work as a bit crusher).  It takes two inputs and produces one output.

One of the inputs is a varying signal of any waveform and frequency, typically a white noise source.  The other input is a clock trigger or gate.  Whenever the trigger input receives a gate, i.e. a voltage crossing a threshold, at that moment the value of the signal input is transferred to the output and is held without changing, until the next trigger is received.  Some S&H circuits can function as a Track and Hold, meaning that in one state of the gate the input is followed (tracked) and held in the other, as shown in the above diagram.

2hp Rnd features

  • A random source that is not available on the panel for input to its S&H circuit
  • A voltage controlled clock
  • A gate output
  • A random, stepped voltage output
  • An amplitude control for the stepped output
  • An external clock input with Int/Ext switch

The VC clock can be used independently of the random function, when operating in the Internal mode.  This is a great feature!  Everyone needs more VC LFOs.

The gate output operates in two modes.  In the Internal mode it is the clock output.  A new gate is generated at the same time as a new voltage on the RND output.  However, in External mode, the gate output produces random gates, at a frequency determined by the Rate knob and CV.

Bonus:  If you patch the Gate output to the External Clock input, you can get a random stepped voltage at random times!

The RND output is stated to be quantized.  This means that the output is restricted to discrete random voltages.  It is not quantized to any musical scale.  The level of the RND output is adjustable by the AMP knob from zero to the max of 5 or 10 volts, as determined by a jumper on the PC board.  It is unusual to have an output level adjustment on a module, because other modules that would use the voltage often have attenuators on their inputs.  It turns out to be a useful function in this case, because of the paucity of attenuators on a lot of Eurorack CV inputs.


The 2hp Rnd module provides random stepped voltages, a VC clock, and random gates, all in a convenient and very small panel.


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