Modular for the Masses VCSLope

Hello! You seem to have gotten a M4TM VCSlope module to build! Nicely done, let's get started.

First, what is this module? It's a tweaked version of a universal slope generator, explored fully by synthesizer design genius Serge Tcherepnin (he's still around -- we're Facebook friends, basically bffs). It's an incredibly versatile circuit that's the backbone of famous, popular Eurorack modules like Maths (and clones) and various other DUSG modules you'll see everywhere.

Second, what is this module? Yup, get it, I designed the prototype versions of this module as a way to understand the hype. A slope generator creates a voltage that slopes up, then down. It can retrigger itself, so it can be a LFO or a VCO. The rise and fall shapes are adjustable from exponential to logarithmic. In this version of the circuit, you've got voltage control over these slope shapes. An audio signal can be processed with the core of this circuit, which will limit how fast (and what shape) the signal is allowed to rise and fall by, which behaves like a simple low-pass filter. There's outputs for the retrigger signal, the "slope-is-falling" signal, a DC-decoupled signal, and the output signal. There's an attenuverter available, making voltage tweaks possible.

This circuit can be:

1. A VCO
2. An LFO
3. A simple envelope generator
4. An envelope follower
5. A transient detector / trigger generator
6. A VCF
7. other stuff I can't even think of right now

This circuit really shines when paired with a second one or more than just two. Crosspatching a bank of these modules together can yield surprising, complex, non-repeating generative soundscapes.

Here's what you'll need!

1. 1x VCSlope printed circuit board, with SMD pre-assembled
2. 1x VCSlope faceplate/panel for Eurorack
3. 3x red LEDs, SMD, 1206
4. 4x green LEDs, SMD, 1206
5. 5x blue LEDs, SMD, 1206
6. 2x whatever color 3mm LEDs
7. 2x whatever color LEDs, 3528
8. 1x bipolar 3mm LED
9. 1x 2x5 IDC pin header for Eurorack power
10. 1x 1x3 IDC pin header for "buffered or not buffered" also the jumper for it
11. 1x boxed multiturn trimmer 100K
12. 1x on-on micro toggle switch and nuts
13. 12x Thonkiconn style mono jacks and nuts
14. 2x RK097 Alpha style sealed potentiometers, 100K, nuts, washers, and knobs
15. 3x JuanitoPots, clear-shafted potentiometers, 100K

You'll also need a soldering iron, solder, maybe flux, snips, pliers, a stable worksurface, protection from the elements, some kind of light source...... a playlist? You know, all the stuff we all need to put together Eurorack modules.

Each jack has a square hold in the PCB under it. That's where the 1206 LEDs get installed, facing "down" so the light will shine through the jack. Pay attention to the LED polarity and the little silkscreen guide, and color if you choose to follow the M4TM standard (red = input, green = CV, blue = output).

Get some solder on one pad, put the LED in, and solder the other side!

May as well install the rest of the LEDs and the single bipolar 3mm LED as well. The square LEDs will go under where the JuanitoPots are going to go, and the bipolar LED goes in the bottom JuanitoPot spot, the one with a round hole. It's a bipolar LED, so you can install it either way BUT if you want it to be "red means negative" and "teal means positive", put the longer leg in the square pad.

I like to make sure the LEDs are going to work before moving on. Connect the PCB to a Eurorack power source (with a loose 2x5 pin header unless you want to install it in this step).

Whoah, look at that. I messed up and put one of the LEDs in backwards. I was able to remove it, turn it around, and poof it works now.

Install the pin headers and the trimmer, and trim the leads. Simple! Fun! Easy!

Put all the big parts in the PCB, including the pair of 3mm LEDs. When they're all in, and before soldering them, install the faceplate and put the nuts on the pots and jacks and switch to keep the torque of this step from putting stress on the solder joints.

When everything is in place, solder it all up! You can choose how far to put the LEDs through the holes -- I like to keep them almost flush.

Toss a couple knobs on the metal-shafted pots, and you're basically done! Time to do a smoke-test!

Plug your module in to a Eurorack power source and see if it works! The trimmer adjusts the speed of the rise and fall rate, and if badly adjusted, the module won't cycle.

Okay maybe it's time for a user manual.

Trigger and gate section:

1. the top left "trigger in" jack accepts a trigger, a spike of voltage.
2. with the switch in the down position, the slope generator will make one slope up and down of voltage when triggered, and then stop.
3. with the switch in the up, "cycle", position, the trigger will loop the up/down cycle, which will be free-running forever
4. the "out" jack is where the "end of cycle" trigger is presented. The LED next to it is an indicator for when the trigger out happens, but it stays lit longer than the trigger lasts, and has a little fade out. This is a feature from the original slope generator and I would have done things differently myself, but whatever.
5. the "fall" out jack and the LED above it are where you get (and can see) a high voltage when the slope voltage is going down. This signal stays high for the duration of the down-sloping voltage

Audio "in" jack

1. well... this is where you can put an audio signal into this module to have the slope generator process it. The knobs and control voltages will have an effect on the audio. Experimentation is vital to understand what this input means.

CV inputs on left

1. the "rise" and "fall" CV inputs affect what the slope shapes of the rising and falling sides of the voltage slope.
2. the "bothCV" jack sends a CV to both the rise and fall sides of the voltage slope
3. the "V/OctCV" input is the way you can control the rate of the slopes. It isn't actually a calibrated and temperature compensated volt-per-octave, but it's certainly exponential, so the VCO-style function of the module will behave more musically with a voltage source

Knobs

1. the shape knobs change how the slope will respond. 12 o'clock will be a linear slope, good for a nice well-behaved triangle wave, at least if you have both rate knobs set to the same level. Counterclockwise is an exponential slope, clockwise is a logarithmic slope. The circuit is tweaked to get more extreme shapes than the original circuit this module is based upon.
2. the rate knobs change how fast the slopes rise or fall. Counterclockwise is (counterintuitively) a quicker rise or fall, clockwise is slower.
3. the lights under the two rate knobs indicate how much voltage is being passed to the part of the circuit that controls the rate. Higher voltage means brighter LEDs, and slower rise/fall times
4. the bottom "attenuverter" knob adjusts the amplitude and polarity of the signal available at the higher "out" jack or whatever signal you plug into the "attenuvert in" jack. At noon, the amplitude of the signal is zero, clockwise it's a copy of the incoming signal, counterclockwise, it's an inverted copy of the incoming signal. The LED under it shows what voltage is available at the "attenuvert out" jack. The bipolar LED will be a cool green or a red color if you used the LEDs I provided

Outputs

1. already mentioned the top "out" and "fall" jacks. That's where you'll get an end-of-cycle trigger or a falling-voltage gate. In VCO mode, this output will be a narrow-spike signal, or a PWM-square wave (voltage-controlled by the "fall" CV input)
2. the output jack with a drawing of a triangle wave crossing zero volts is the signal but slewed negative so the average output (depending on slope shapes) is near zero volts
3. the "out" jack is the output of the slope generator. There is a jumper on the back of the module that sets this output to buffered or nonbuffered. If unbuffered, this output is connected to a part of the circuit that can be affected by a low-impedance signal, which means you can force this to behave as an input. If the jumper is set to "buffered", you won't be able to affect the circuit no matter what you plug in there. This output is normalled down to the attenuverter

Okay I guess that's about it. I'll once again mention the buffered/nonbuffered jumper on the back. The original slope generator circuits had the output extracted from a part of the circuit that could be affected by a low-impedance voltage source, so like a CV or audio signal. Usually you don't want that to happen -- good modular synth design says no output should behave this way, BUT there are patches for other slope generators that use this output as an input. If you want to do those patches, leave the jumper set to nonbuffered. If you want to be able to patch any way you want without changing what the slopes are doing, set the jumper to buffered.

Okay I guess that's really it! Remember that the world of slope generators gets better and better the more you have. I crosspatched five of these in one of my racks just for fun, and yeah, it was a LOT of fun. Plenty of surprises and delights, twisting this knob or that, crosspatching at random, creating a squeaking hooting spaghetti monster.