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.

Correction: The COUPLER goes HIGH if the STEPPED OUT voltage is greater than SMOOTH OUT.  The catalog sheds no light on this but that's what my measurements say.

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=big 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.

First, some simple SSG applications:

1. Linear Glide
Patch the output of a sequencer or some other stepwise DC source into the Smooth input, then patch the Smooth output to an oscillator. 
See how turning the Rate control varies how fast the glide goes.  Technical note: in this application the glide has a linear slope so you will hear a constant gliding rate from the oscillator (for a given Rate setting the volts/second gliding thru will be constant, it won't be faster or slower at the beginning or the end of the glide).  In other words, perfectly nice and even.

2. Exponential Glide
Same patch as above, but now also run a short patch cord between Smooth out and its VC Rate jack.  Turn the VC rate knob clockwise so the control voltage is affecting the Rate to some degree.  Now the glide should speed up at the end, depending on the position of the VC rate knob.

3. VC LFO (triangle) or VCO
Run a short patch cord from IN to CYCLE.  You should see the LED go from dim to bright to dim in a nice smooth progression.
Patch SMOOTH OUT into a PCO or NTO and hear the pitch rise and fall.
Vary Rate to make it faster or slower. 
Use VC Rate jack & knob to make the frequency voltage controlled.
Patch SMOOTH OUT into your audio output path, whatever it is. 
You can use SMOOTH as a low-end audio VCO.  Note that tracking & stability are NOT as good as PCO, NTO or DSG in this application, but it does give you an extra audio oscillator in a pinch.  This is a triangle wave.

4. VC LFO (square) or CLOCK or VCO
Same basic patch as #3.  Instead of taking the signal from SMOOTH OUT, mult a banana plug into the patch cord connecting IN and CYCLE. 
This is a square wave that jumps from +10VDC to -10VDC approximately.  As in #3 you can use this as an LFO for control voltage applications or as an audio square wave.  Additionally it can be used to clock a sequencer or other module that needs a trigger or clock source. Note: if you use it as a trigger for the Stepped module it creates two triggers for every cycle.  I don't know why exactly but this is what I've observed.  As in #3 you can vary the frequency with a control voltage.

5. Lowpass Filter/Lowpass Gate
Same patch as #1.  Instead of patching a DC control voltage into the input, patch an audio source in, say, any PCO waveform. 
Send SMOOTH OUT to your audio output path.  Notice that the sound is more or less intact at 100% rotation of the Rate knob, and as you turn Rate counterclockwise the harmonics and harshness get filtered and Smoothed out.  Keep turning Rate counterclockwise, the sound will disappear altogether. 

So you can use this to filter harsh harmonics out of audio, or to create an unusual filtered effect.  Use the VC rate knob and jack to make this filtering effect voltage controllable. You can employ this effect to create an audio Gate. 

What's a Gate?  A gate is a general name for a device that lets you either permit or close off an audio signal.  That's usually what you use a VCA for, and VCA's are very high quality examples of gates.  You can use this patch, especially under Voltage Control, as an unusual substitute VCA:
First, set the Rate knob at around 10 o'clock to 12 o'clock, just so your audio is no longer audible at the output. 
Now send a note envelope from DSG, DTG, or Envelope Generator to the VC rate jack, with the VC rate knob turned sufficiently high.  You are creating low quality unusual envelopes where the harmonics are varying with amplitude.  Using harmonic rich input, you have an unusual effect.  Using purer input such as sine or triangle wave yields a more usual or typical result.

6. Sample and Hold
Now we'll use the Smooth section to create a sample and hold effect!
Send a varying signal from LFO or Random Source into Smooth In. 
Using a DSG or DTG create a rectangular clock pulse with a 99% duty cycle, that is, mostly 'on,' with a tiny 'off' part. 
Send that pulse into Smooth HOLD.  Turn Smooth Rate fully clockwise. 
Send Smooth Out to a VCO or some other module that needs a control voltage.  Play with the DSG rise/fall times and Smooth Rate. While HOLD is low the Smooth section takes a 'sample', when HOLD is high that sample is held. This should be enough to get you going for a while! More will follow later. John P.