A look at the Oberheim Synthesizer Expander Module (1974) and Two Voice (1975), which were Oberheim's first two synthesizer products respectively.

0:00 Intro Jam
1:00 The Synthesizer Expander Module
2:04 Demo 1: State Sync
2:49 Emu Systems
3:32 Demo 2: Two Voice
4:38 Dennis P Colin
5:49 Demo 3: Pull Seq Wonk
6:56 Jim Cooper
7:46 Demo 4: Transistor Bass Workout
9:04 Tom Oberheim
10:09 Demo 5: August Nineteen SeventyFive
11:16 The Life Aquatic, Stranger Things and Drokk
13:50 Outro Jam

Two Voice Listening:

Life Aquatic Mark Mothersbaugh:
   • Ping Island/Lightning Strike Rescue Op  
   • We Call Them Pirates Out Here  
   • Zissou Society Blue Star Cadets/Ned's...  

Stranger Things Theme:
   • Stranger Things (Extended)  

Drokk Music Inspired by Mega City One:
   • Drokk: Music Inspired by MegaCity One  

Nerdy Details:

MiniSequencer
x2 two parallel sequences of 18 steps with CV set via the dualconcentric knobs.
Independent assignment of sequence 1 to SEM 1 and sequence 2 to SEM 2 as well as sample and hold or keyboard control for either.
Optional sequence transposition via keyboard.
Sample and hold range and lag.
Internal clock frequency, run and step control, plus clock frequency modulation from sequence 2 CV.

Each SEM:
VCOs: x2
Waves: Sawtooth or Pulse
Tuning: Fine/Course
Other: Phase sync
Modulation: Frequency, Pulse Width, PWM
Modulation Sources: Envelopes, LFO, Sample & Hold (EXT)
Mixer:
VCO waves
EXT #1 Rear connection, although SEM 2 is normalled to SEM if nothing is connected, allowing for use of the SEMs in series
EXT #2 White Noise from S&H circuit
Filter: 2pole multimode. Continuously variable low pass, notch, high pass, plus switched band pass.
Control: Cutoff, Resonance, Mode
Modulation: Bipolar cutoff modulation from envelope 2, S&H (EXT), LFO
VCA: Controlled from Envelope 1 or drone (ON/EXT)
Envelopes: x2 ADSD
LFO: Triangle with frequency control

Performance:
Voice assignment duophonic with left/right voice priority as well as unison.
Pervoice portamento
Master tuning and octave select.

Output mixer: SEM 1 and 2 and master level. Signal overdrives beyond about 60%.

Rear connections: These seem to vary from unit to unit and are usually modded. Furthermore, the original manual doesn't describe them, so I'm not actually sure what the "stock" rear connections are.

On my unit I have CV/gate for each SEM, external signal in, external sequencer clock in and line out (mono).