ADDAC System - 506 VC Stochastic Function Generator

by Sam Chittenden

ADDAC System - 506 VC Stochastic Function Generator

ADDAC System's 506 VC Stochastic Function Generator is a mouthful of a module name. Fitting, as the module is packed with functionality and dense with control options.


Weighing in at 20HP, the 506 follows ADDAC's utilitarian aesthetic and despite every square millimeter of panel being used for something, the module feels ordered and is very user friendly. The 506 is an officially-licensed expansion on the Stochastic Function Generator from Teia. Teia's version was a 2-channel model while ADDAC has expanded the 506 to four channels. However, ADDAC has not made a straight clone. In addition to the expanded channel count, they have overhauled the microcontroller and added some well thought out utility functions to each channel.

ADDAC describes the 506 as a "Quad Analogue Core Envelope Generator and Slew Processor with digital control". And at first glance it looks to be a fairly standard AD envelope generator–albeit one with more than the average output options. The trick up its sleeve is the unit’s onboard random generators which can be used to modulate the 506's Rise and Fall settings.


Each of the 506's four channels feature a CV signal input (trigger, gate, or voltage to be slewed), a Gate out (high while the envelope is in its rise stage), and End of Rise (EOR) and an End of Fall (EOF) outputs which are configurable per channel–via jumpers on the back–to emit either a trigger or gate during each respective stage. In addition to each channel's envelope out, the 506 offers two separate mix outs: an average of all four channels and a summed version. All six outputs are available simultaneously, which really provides for a ton of control options in your system.


Sweetening the package is the inclusion of attenuverters and offset controls for each channel. Coupled with each channel's curve pot (to adjust between linear and logarithmic) these utilities make it easy to dial in each envelope's response and level and greatly streamlines integrating each output's CV into a patch.

The 506's operation is further controlled by a series of four toggle switches (again per channel). You can choose between Trigger and Slew (whether the input at the Signal In jack will trigger the envelope or be slowed down based on the channel's Rise and Fall settings), Loop or One-Shot envelope behavior, and a speed range for the channel's Rise and Fall controls–selectable between Low, Medium, and High. The fourth switch is a Lock, which allows each channel to have it's various parameters set independently.


The Rise and Fall times for the function generator are set by a group of four controls: Rise Time Minimum, Rise Time Maximum, Fall Time Minimum, and Fall Time Maximum. Each channel's Rise/Fall settings can be independently or interdependently set depending on each channel's Lock switch, and the Rise/Fall settings are CV controllable via their respective input jacks (and attenuverters!). Each minimum/maximum pair specifies the range within which the random generators will adjust the respective time. If the maximum time is less than the minimum time the channel's random generators will not have any effect on the stage time. So if you want a standard Attack/Decay envelope or a simple LFO just dial the Rise and Fall maximums to zero. But where's the fun in that? The 506's randomization feature really elevates it from the crowd and makes it a module that will reward the intrepid synthesist again and again.


Using the 506 as a triggered, one-shot envelope is straightforward. As with a standard envelope generator, any trigger or gate will kick off the envelope's Rise, hold at the maximum voltage level (adjustable via the Offset and Amplitude controls) as long as the gate is open, and Fall once the gate is closed. The 506 makes it easy to add some variation to a patch by dialing in subtle, random changes in envelope times with the respective Maximum knobs.


Chain a few (or all!) of the 506's channels together by patching the EOF Out of one to the Signal In of another and output a complex, randomly evolving envelope from the Summing Mix Out. Thanks to the simultaneous availability of each channel's signal, you can utilize each stage of the chain to modulate another component of your patch at the same time.


Need some LFOs in your system? Bored of your tried-and-true triangle or sine wave? With period times that stretch from audio rate frequencies to creeping cycles up to six minutes long, the 506 has got your back. Add some random variation in a channel's Rise and Fall time, offset or attenuate the signal to taste, and that stagnant tone you've patched up will jump to life.


There is also fertile territory to be explored when pushing the looping 506 up to audio rates. Dialing in a 4-note chord and playing around with various randomization settings makes for some fantastic drones, alien speech, bubbling blips, and screaming, wild noise. It doesn't have to be crazy though. Using the CV ins for Min and Max allows a level of pitch control. While the 506 doesn't track V/Oct, it isn't too hard to get some passable melodic lines out of it.


In Slew mode, the 506 is great for adding subtle glide/portamento variations to a sequenced melody or bass line, or for lagging or softening some CV before piping it off to another part of a patch.


With the amount of inputs and outputs available, the 506 begs for some self-patching. Generating complex envelopes or LFOs is a blast and endless variations can be explored by plugging various EOR, EOF, and unused channel output signals back in to different parts of the module.


The 506 also has a 2hp-wide expansion module available that adds trigger inputs for each channel's random generator (allowing the generation of a new randomization value mid-cycle) as well as 4 CV outs for the random voltages produced by each channel.


ADDAC has created a compelling and fantastically enjoyable function generator in the 506. The randomization adds wonderful variability to the signals produced and the inclusion of dedicated utility functions only further the module's usefulness. I'm not one to complain about the inclusion of "too much stuff" in a module, but those who value spaced out controls may find fault with the decidedly cramped real estate. I will admit I found the toggle switches pretty close together and more than once I inadvertently flipped a switch or two that I didn't intend to. However, these small irritations pale in comparison to the utility provided, the creative applications to be had, and the sheer fun of it all. The ADDAC 506 VC Stochastic Function Generator (phew!) will find its way into most of my patches from here on out.


20HP 200mA +12V 150mA -12v

Price: 340€, Expander 90€


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