M4TM VCSlope

The VCSlope is M4TM's take on the classic Serge Universal Slope Generator. It's a fairly close copy of one of Serge Tcherepnin's designs, the voltage-controlled one, with a couple tweaks. These are currently extremely limited and not in the shop, so hit us up on Instagram or Discord if you want one, while we have them!

Users familiar with the exact version Juanito worked with will notice the lack of exponential/linear switches for the slope curves, the addition of an attenuator normalled to the output jack, and the addition of a "fall" gate that goes high while the signal is falling. Users not familiar with the exact slope generator which inspired this will be familiar with one or several modules which are slope generators. MakeNoise Maths is the most common, Buchla Rampage is another, and there's many other versions of "USG" or "DUSG" modules out there.

Let's get into the function of this module.

Top section first.

1) TRIGGER IN JACK

This accepts a signal which starts the module's slope generating procedure.

2) CYCLE SWITCH

Flip this toggle up to have the slope generating procedure retrigger itself at the end of the procedure

3) OUT JACK

The LED right next to this output jack shows when the voltage is high. It turns on at the end of the slope generation procedure, and stays lit for a part of the next cycle's rise time

4) FALL JACK

The LED above this jack lights when the slope signal is in its falling phase

Next section:

1) IN JACK

Here's an input jack which injects whatever signal you put there into the emitters of the four transistors which are the heart of this circuit. Transistor pairs can be challenging to understand, and this circuit has a pair of transistor pairs, which make it truly mysterious. The signal put into this jack will be acted on by the rest of the module's controls. An audio signal will make it through the circuit somewhat or completely low-pass filtered by the settings of the rate knobs. The signal will be unable to rise or fall faster than the rate knobs allow. A fast rise rate (counter-clockwise) and a slow fall rate (clockwise) will cause this module to become an envelope follower.

2) RISE JACK

This accepts a voltage which will increase the amount of the "curvedness" of the shape of the curve. So if the knob linked to the jack is set all the way clockwise to the logarithmic side, a higher voltage here will make the curve MORE logarithmic. If the knob is all the way counterclockwise, e.g. exponential, a voltage will increase the exponential curve. It's important to note that the slope curvedness will also affect the effective speed of the rise or fall. A more exponential shape will cause the rising slope to complete in lesser time, and conversely a more logarithmic curve will cause the slope to complete more slowly.

3) CURVE KNOB

This knob sets the curve of the rise time as discussed right above, with a straight linear slope showing up at the knob's 12 o'clock position. For a look under the hood: this knob is an attenuverter (weighted so that 12 o'clock gets that nice straight rise) that sits inside the slope generator's complex full-of-transistors feedback path. An attenuverter amplifies a signal from a little less than 2X at one end, and -8X at the other end, and amplifies it by zero (which is to say, the output of the attenuverter is zero volts). And all this is happening inside the slope generator's feedback loop. Whew.

4) RATE KNOB

This controls how fast the slope rises. Counterclockwise is fast, clockwise is slow. This setting interacts a great deal with the curve knob, so, for example, a quick rise time will be made quicker or slower depending on how the curve knob is set. The middle CV jack: bothCV jack Okay, this inputs a signal to BOTH the rise and fall time slope curve sections. Higher voltage here will increase the curve the curve knobs are set to.

The next section is the fall section, and the functions here are exactly the same as the rise slope controls, but they control the fall slope instead of the rise slope.

The V/OctCV jack:

V/OctCV jack Okay, this accepts a signal that sort of almost kinda will control the frequency of this module when it's switched to cycle mode to track the pitch of a 1V/octave CV. It's not accurate, for there's no calibration available and no temperature compensation. This module comes from a West Coast Synthesis tradition, which prefers esoteric performance devices like a Theremin or pressure control or strip or something. So the imprecision is a feature not a bug?????

The bottom section

1) ATTENUVERT IN JACK

Put any signal in here and it will be amplified by 1X or -1X, with 0X at the noon setting. The light under the potentiometer reflects the voltage going out of the output jack. This input is normalled to the slope generator's main output. This attenuverter can be used for any signal, of course, so you've got the option to use the main output for something and use the attenuverter to control any CV or audio rate signal you please.

2) -/+ KNOB

Here's the attenuverter control.

3) OUT JACK

Output for this little attenuverter circuit.

Output jacks along the right side:

1) THE ONE WITH A TRIANGLE WAVE CROSSING A LINE JACK

This output is a copy of the main output right below it, but voltage-shifted so that the output swings between about +5V and -5V. This is useful when using this module as a VCO or bipolar LFO.

2) OUT JACK

Here's the main output. It outputs a signal at about +10V peak. It's normalled to the attenuverter section below it, allowing it to be attenuated and inverted as desired.

That's the module from the front side!

We did it! Next, let's talk about two user-controllable settings on the back of the module.

There's one trimmer on this module. Turning the trimmer counterclockwise enough will stop the slope generator from functioning at all. Turning it clockwise allows it to work, and turning it more clockwise allows it to operate more quickly. I haven't tried to use this setting as V/Oct calibration but it might work that way.

There's one jumper which is labelled to allow the main output to be buffered or not buffered. If you choose the buffered jumper position, you'll be able to plug any cable in to the output and not affect the operation of the slope generator, even if you're patching that output to another output or even a full + or - power rail.

But the original circuit didn't have a buffer on the main output. If you patched the output to a typical input, the slope generator worked as intended, doing what it was supposed to do. But it was possible to patch the output to a gate or trigger or CV or audio signal to change how the slope generator behaved.

USAGE NOTES

Juanito says they’re a much better circuit designer than synthesist, and that the potential of this circuit (especially when used in multiples) is vast, vast indeed. Their favorite way to play with this circuit is use at least two modules, patch them basically randomly, set one or both to cycle, and let them generate some kind of chaotic series of surprising tones, bleeps, noises, squeaks, thumps. But if you want you can.....

Envelope Generator

Trigger or gate signal in the top trigger jack
Toggle switch set to off
Curve and rate knobs for rise and fall set as desired
Output from the main output (or attenuator)

Trigger/gate delay

Trigger or gate signal in the top trigger jack
Toggle switch set to off
Rise curve and rate knobs set as desired
Output from the main output (or attenuator)

VCO/LFO

Toggle switch set to cycle
Adjust rise and fall knobs as desired
Experiment with plugging a CV into any of the input jacks, see what happens
Output from either the bipolar or main output

VCF

Audio signal in the non-trigger input jack
Rise curve and rate knobs set as desired
Experiment with a CV into input jacks
Output from bipolar output

Envelope follower

Audio signal in the non-trigger input jack.
Toggle set to off.
Set rise rate knob all the way counter-clockwise
Adjust rise curve rate to about 12 noon, experiment for better results?
Adjust fall rate and curve knobs to match how much "release" you want on the envelope Output from main output

Transient extractor

Audio signal with transients into the trigger input jack
Toggle set to off
Output from trigger output jack