Smooth / Stepped Generator (SSG)

The Smooth Stepped Generator (SSG) is one of the most versatile function generators ever developed for modular synthesis. Rather than being designed for a single purpose, it combines two independent voltage processors that can work on their own or interact to create an enormous range of control voltages.

The Smooth section is a voltage-controlled slew processor. It can smooth changing control voltages for portamento, glide, lag processing, and low-frequency filtering. When its Cycle output is patched back into the input, it becomes a voltage-controlled triangle LFO with a wide frequency range. The Hold input freezes the current output voltage, allowing the Smooth section to function as a track-and-hold processor as well.

The Steppedsection operates as a precision sample-and-hold with an adjustable slew limit. Unlike a conventional sample-and-hold that immediately jumps to each newly sampled voltage, the Rate control limits how large each step may be. Large voltage changes can therefore be broken into a series of smaller steps, creating staircase waveforms and slowly evolving random voltages. When self-patched, the Stepped section becomes a unique staircase waveform generator unlike traditional sequencers or LFOs.

Connecting the two sections together is the Coupler, an internal comparator that continuously compares the Smooth and Stepped outputs. This interaction opens the door to many of the classic Serge patches including chaotic modulation, self-generating control voltages, and random voltage generation when used with an external noise source.

The result is a deceptively simple module that rewards experimentation. Whether you're creating smooth portamento, sample-and-hold effects, evolving modulation, complex LFOs, or self-patching feedback networks, the Smooth Stepped Generator remains one of the most powerful utility modules available in the Serge modular format.

Panel Functions

Smooth Section

• IN – Signal or control voltage input.

• VC RATE – Voltage control input for the slew rate. This is an attenuating input.

• RATE – Sets the slew speed. Fully clockwise gives the fastest response, while counter-clockwise increases the amount of lag.

• OUT – Smoothed output voltage.

• CYCLE – Oscillator output used for self-patching. Patch to IN for LFO operation.

• HOLD – Freezes the output voltage, allowing the Smooth section to function as a track-and-hold processor.

Stepped Section

• IN – Input signal to be sampled.

• SAMPLE – Trigger input that samples the input voltage.

• VC RATE – Voltage control over the maximum step size.

• RATE – Sets the maximum voltage change allowed for each sample.

• OUT – Stepped output voltage.

• CYCLE – Oscillator output used for generating staircase waveforms when patched back to the input.

Coupler

• HOT – High-voltage comparator output. (Rail to Rail!)

• COUPLER – Buffered comparator output generated by comparing the Smooth and Stepped outputs.

Features

• Classic Serge-inspired Smooth Stepped Generator

• Smooth slew processor with Track & Hold capability

• Precision Sample & Hold with adjustable slew limiting

• Self-cycling triangle LFO operation

• Internal comparator (Coupler) for complex patch interactions

• Excellent building block for random voltage generation when paired with an external noise source

• Wide range of modulation, control voltage, and feedback patch possibilities
  

Patch Ideas

Voltage Controlled Portamento

Patch a keyboard or sequencer CV into the Smooth IN and take the Smooth OUT to your oscillator. Use the Rate control to adjust the glide time, or apply modulation to the VC Rate input for dynamic portamento.

Triangle LFO

Patch Cycle to IN on the Smooth section. The module becomes a voltage-controlled triangle LFO with a wide frequency range. The VC Rate input allows external modulation of the LFO speed.

Track & Hold

Feed a control voltage into Smooth IN. When a gate is applied to the Hold input, the current output voltage is frozen until the gate is removed, creating a classic Track & Hold function.

Sample & Hold

Feed a control voltage or noise source into the Stepped IN. Apply trigger pulses to the Sample input. Each pulse captures the input voltage and holds it until the next sample.

Staircase Generator

Patch the Stepped Cycle output back into the Stepped IN. Trigger the Sample input from an external clock or from the Smooth section. Adjusting the Rate control changes the size of each step, producing evolving staircase waveforms.

Smooth Random Voltages

Feed a noise source into the Stepped IN and trigger the Sample input with a clock. Patch the Stepped OUT into the Smooth IN to create continuously changing random voltages.

Random Voltage Generator

Patch the module following the classic Serge configuration by combining an external noise source with the Smooth, Stepped, and Coupler sections. This reproduces the behavior of the dedicated Random Voltage Generator while leaving the patch completely configurable.

Chaotic Feedback

Patch the Coupler output back into either section to create self-modulating feedback networks. Small changes to the Rate controls often produce dramatically different modulation patterns.

From the original SMMS Catalog:
”The SMOOTH & STEPPED FUNCTION GENERATOR (SSG) is a complex multi-functional module to provide various slew and sample functions.

The Smooth section will place a positive and negative slew (glide) on a changing input voltage for lag effects, voltage controlled portamento, and non-linear, low frequency filtering. With the CYCLE jack patched to the input, the unit will oscillate yielding a voltage controlled triangle wave LFO. A high level into the HOLD input will hold the current output level, whether the unit is oscillating or processing an external control voltage. This is identical to a track-and-hold function. 

The Stepped function can be used as a sample-and-hold with voltage controlled slew rate limiting. Slew rate limiting limits the size of the step at the output. For example, with a random voltage input and the step size set to a small value, the output is a random voltage that varies only slightly from step to step, gradually covering the entire range of the input voltage. No large changes in the output will be allowed. With the Cycle jack patched to the input and a trigger applied to the Sample input, complex staircase waveforms are generated. 

The COUPLER is an internal comparator comparing the Smooth and the Stepped outputs. This is useful for generating complex control voltages and for patching a random voltage generator. In fact, the Random Voltage Generator module is a Smooth & Stepped Generator internally patched to function exclusively as such. If random voltages are often used, a Random Voltage Generator is a more space-efficient module; but if seldom used, the Smooth & Stepped Generator can be patched when needed (and can be used for other functions when not used as a random voltage generator). Note that a Noise Source is needed for use of the Smooth & Stepped Generator as a random voltage generator.”

”The SSG is of course the Smooth and Stepped Generator module. It consists of two sub-modules, the top being the Smooth section, the bottom is the Stepped section. The outputs are tied together with a comparator at the CUPL. jack - this gives a HIGH if the smooth output is greater and a LOW if it isn't. *** CAUTION *** HIGH at CUPL is ~ 10VDC, LOW is ~ -10VDC. This is fine for use as a trigger but be careful when using it as a control voltage.... you won't hurt the Serge but if you're using it to control a VCA for example you may destroy your speakers and bring plaster raining down on your head from shattered walls. The Smooth section is a VC lag processor with some interesting additions: 1. Hold input. When this goes high the output no longer tracks the input but is held at the same level that was present when Hold went high. 2. Cycle. This is similar to GATE on the DSG but not the same thing. It is normally not HIGH but LOW (-10V) The Rate knob determines the rate of lag. At zero rotation the *rate* is low, so that translates to a lot of lag. The Stepped section is a sample-and-hold, also with interesting additions: 1. A rate knob. This determines how big each step is at the Stepped output. Full rotation = bi steps, zero rotation = very tiny steps. 2. Cycle jack. This is also normally LOW (-10V). More on this in another installment. The stepped section can serve as an extremely high quality sample-and-hold --- MOTM's sample and hold claims a droop rate of about 1mv per second - in other words, if you do a single sample driving a VCO at 1 volt per octave, then hold it and just listen without resampling you should be able to hear a VCO's tone drop perceptibly, without any trouble. An informal test I did measured > 10mv droop in 400 seconds on the SSG. Other listening tests bear this out.” -John Papiewski (2001)

Calibration: From Serge kit instructions:

• For this module to work properly, a jumper must be installed between pad S and pad L. (This should have been installed during construction, although if you wish to test the two parts of the Stepped generator individually, it can be left disconnected until you have.)

Patch the CYCLE output of the Smooth Function into the IN jack. Monitor the OUTPUT while turning the RATE knob full clockwise. The pitch should be about 100 Hz, and should go to sub-audio rates (as seen from the LED'S) when the knob is turned down. Check that a control voltage into the VC IN jack will control the rate. Note that this is an attenuating input only, with no inverting processing.

A high level applied to the HOLD input (greater than about 4.5 volts) should stop the Smooth Function from cycling. With the Smooth Function patched to cycle, connect the CYCLE of the Smooth Function into the SAMPLE input of the Stepped Function. Patch the Stepped Function CYCLE to its IN jack. Using the STEPPED OUT to control the pitch of an oscillator, listen for the pitch change motion as the Stepped RATE is turned up. When fully clockwise, a triangular "staircase" waveform will be generated by the Stepped Function Generator. For best audible rate, the Smooth Function should be fairly slow. As the Stepped RATE knob is turned down, the staircase will slow down.

Note: It’s difficult to get a satisfactory result from the Stepped function using these procedures, instead simply adjusting the trimmer until it worked as expected.

** 4U Modular is a term used for the format most commonly known as “Serge Format” or “Loudest Warning Format”. Out of respect for the ever growing format, 4U Modular is the easiest way to refer to it. More Specifically it refers to the panel height and mounting hole style. 4U Modular will patch up just fine with other 4U "Serge" formats such as "Random Source", but it will not mount in RS boats or Buchla Boats (or power off Buchla power for that matter). An info page about this will be added to the website soon to make this a lot more easy to understand.

SDIY Build Documentation:

LGE092 V2 Main Board:
LGE092 V2 Main Board Bill of Materials (Contains both Main, I/O Boards)(V1.X pcbs have Thru-Hole coupling caps instead of SMD on the bottom on V2’s)

LGE092 V1.3 Main Board:
LGE092 V1.3 Main & I/O Board Mouser Cart (Does not include mechanical parts like knobs, pots, board to board headers, screws, etc)
LGE092 V1.3 Main Board Bill of Materials
LGE092 V1.3 Main Board Schematic
LGE092 V1.3 Main Board PCB Layout w/ Designators

LGE092C V1.1 I/O Board:
LGE092C V1.1 I/O Board Schematic (Wiring Diagram) (When using unipolar LED’s, install the Smooth and Stepped LEDS in backwards for them to work with more common positive voltages)
LGE092C V1.1 I/O Board PCB Layout w/ Designators
LGE092C V1.1 I/O Board Jumper Modification (The wiper of the Stepped Rate Potentiometer has a missed trace connection to Pin “O” on the I/O PCB. A simple jumper will fix this)

LGE092 Panel Art:
LGE092 V2.1 Panel Art (DIY Version)


Mechanical Parts BOM generally required for building Low-Gain Electronics Modules

Patch Ideas & Uses: (Compilation of Message Board Posts formatted by Guy D2)

Details:

• PCB Size: 6” x 2”

• Current Draw: TBD

  Assembled Modules are built to order, please be patient when ordering. Use the contact page if you have any questions or requirements!