Voltage Controlled Slope

Desperately trying to finish some new electronics before other tasks consume my attention… the latest module for my DIY synthesizer is something like a clone of the recently released Makenoise Maths, which is itself a riff on the Serge Dual Universal Slope Generator. I actually imagine it much more as a kind of analog computer to tell the truth.

It packs two Serge Voltage Controlled Slope Generators, a pair of bipolar “Attenuverters” with positive/negative offset and a series of “analog logic” functions behind a single panel.

In other words, it can create two different waveforms at low or audio rate, with voltage-controllable upwards and downwards slopes, and can perform a number of mathematical functions close to the original Serge “peak” and “trough” functions on these slopes. And yes, it can go into cycle mode by itself, to give me a basic LFO or VCO function.

First basic tests indicate it’s quite a monster! I tend to use one VCS to trigger the other, then cross-modulate the Exponential CV inputs through the Attenuverter, and use one of the Analog Logic outputs to drive a VCO. Instant chaos. It’s incredible to compare the very different flavors coming from the AND, NAND, OR or NOR outputs from the same two input voltages. This module and one or two VCOs would make a very complex little synth all by themselves.

A quick and dirty example of the above patch:

Voltage Controlled Slopes + Analog Logic test by macumbista

NAND drives one VCO, OR drives one LFO. LFO patched back to left-hand VCS “both” input, also to VCO FM, some other cross-modulations as well. Here’s a photo of the patch:


Rise CV / Fall CV / Both CV / Exp CV / Signal Input / Trigger Input


Rise Time / Fall Time / Rise CV / Fall CV / Linear-Exponential mode switch


End of Cycle Output / DC Output


DC Input


Positive-Negative Gain / Positive-Negative Offset


DC Out / Also linked to ANALOG LOGIC inputs


AND “tough” (lowest of two voltages) / NAND inverted “tough” / OR “peak” (highest of two voltages) / NOR inverted “peak” / Sum of two voltages / Inverted Sum of two voltages

The module was created using PCBs from Ken Stone/CGS synths. I love Ken’s boards to death. I used:

2 x CGS75 Voltage Controlled Slope

1 x CGS26 Analog Logic

3 x CGS04 DC Mixer

There’s really not much out there that can’t be self-built with them, if you’re clever with how you put them behind the panel. I’ll be putting a bunch of CMOS digital logic boards on order soon, and putting together a modular synthesizer super-computer in the spring! Hell, one could almost clone an original Serge with them.

Me, I’m not interested in “cloning” anything, thus the hand-stamped letters and general rough feel. Took some fiddling to get it running properly, but now that it does it’s fantastic.

I had a chance to play with a huge Serge system at CEM in Rotterdam a few months ago, and my main area of inquiry were the Dual Slope Generators there. Made some incredible feedback/chaotic synthesis stuff possible. Maybe I’ll find some audio examples from that session and post them later. Until then…

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One Response to “Voltage Controlled Slope”

  1. macumbista.net » Blog Archive » Grazie tanto, Padova! Says:

    […] Venice–not the wisest idea, to be sure–re-making the Macumbista Mini to include my new Voltage Controlled Slope/Analog Logic module alongside a Polivoks filter and output mixer (not unlike one of the Serge M-Class panels). […]