Model 2111 Random Voltage Source

The Slightly Nasty Model 2111 Random Voltage Source allows you to easily incorporate elements of randomness and chance into your modular patches, either clocked to some sort of external trigger (such as a clock or gate pulses), or free-running via the internal voltage-controlled clock. It provides three different flavours of noise signal, three random voltage outputs plus a slewed variant, random logic, clock output and a clock-synced ramp output.

The noise is available in White, Dark, and Light variants – White is flat across the spectrum, Dark emphasises low frequencies and rolls off the top end, and Light rolls off the bass frequencies and emphasises the high frequencies. This is particularly useful for making multiple percussion voices, as well as allowing noise to be directly mixed into a patch without tying up a filter.

The random voltages are generated by feeding random voltages into the input of a shift register and then generating the outputs via two scrambled 6-bit resistor-ladder DACs to create one of 64 possible output voltages. Outputs A and B are mostly independent from one another, output “A-B” is the difference between the two and has a somewhat different (more centre-weighted) distribution, as well as being available in a linearly-slewed variant for smooth random modulation.

The Voltage-Controlled Clock increases the versatility of the module by providing useful timing functionality, and the ability to create interesting random timing signals by feeding the unit’s random outputs back into its own Clock Rate input. The timing core of the clock is broken out to the RAMP output as a 0-5v ramp signal that allows for interesting synchronised modulation when using the 2111 as a master clock (Note that this output will always follow the internal clock, even when using an external clock source). The Clock can run into audio rates as well, to create interesting voltage-controllable noise effects.

The two logic outputs on the 2111 are the Clock output, which is self explanatory, and the Random Logic output – which follows the first bit of the shift register and is useful as a random two-state modulation source, a random gate/trigger signal for envelopes etc., or an Atari 2600-style digital noise signal.

Due to the use of an 8-bit shift register to convert the noise signal into clockable static voltages, the randomness of the 2111 is somewhat unusual. While it is impossible to predict exactly what the next value will be, the fact that each clock pulse introduces only one new binary bit into the register means that any given output value can only be followed by one of two possible subsequent values. This means that certain patterns will reappear as similar bit strings travel through the register on different occasions.



Current Documentation (v1.0 Rev A):

Model 2111 Construction Manual

Model 2111 Schematics

Model 2111 BOM