SequentialOB-6 6 Voice Analog Synthesizer

Serial Number: #557

Sequential OB-6

The OB-6 features two discrete voltage-controlled oscillators (plus sub-oscillator) per voice, with continuously variable waveshapes (sawtooth and variable-width pulse, with triangle on oscillator 2). There is a classic SEM-inspired state-variable filter (low-pass, high-pass, band-pass, and notch) per voice. Voltage-controlled amplifiers complete the all-analog signal path. “The classic, bold SEM sound is all there,” said Oberheim.

Present also is X-Mod, with filter envelope and oscillator 2 as modulation sources (with bi-polar control). Destinations include oscillator 1 frequency, oscillator 1 shape, oscillator 1 pulse width, filter cutoff, and filter mode.The knob-per-function front panel puts virtually all parameters at a user’s fingertips. Toggling on the Manual switch enables live panel mode, in which the OB-6 switches to the current settings of its knobs and switches. 

A dual effects section provides studio-quality reverbs, delays (including standard and BBD), chorus, and faithful recreations of Tom Oberheim’s acclaimed phase shifter and ring modulator. The effects are digital, with 24-bit, 48 kHz resolution, but a true bypass maintains a full analog signal path. Additionally, the OB-6 features a multimode arpeggiator and a polyphonic step sequencer with up to 64 steps (and up to 6 notes per step) plus rests. It allows polyphonic keyboard input and can sync to external MIDI clock. 

The full-size, four-octave, semi-weighted keyboard is velocity and aftertouch sensitive. Said Dave Smith, “As with the Prophet-6, we made size a primary concern on the OB-6. It’s the right mix of power and portability and it fits right in on-stage or in the studio.” Added Oberheim, “And of course, it’s got that unmistakable SEM sound that’s going to turn a lot of heads. ”

OB-6 Synthesizer Features

OSCILLATORS

• Two discrete VCOs per voice
• Continuously variable wave shape (sawtooth and variable-width pulse, plus triangle on oscillator 2) per oscillator
• Pulse width per oscillator
• Hard sync: oscillator 1 syncs to oscillator 2
• Square wave sub-octave generator (oscillator 1) per voice
• Low frequency mode (oscillator 2)
• Keyboard tracking on/off (oscillator 2)
• Oscillator detune amount for increased tuning instability, from subtle to extreme

MIXER

• Oscillator 1 amount
• Oscillator 1 sub-octave amount
• Oscillator 2 amount
• White noise amount

STATE-VARIABLE FILTER

• Two-pole, resonant, filter per voice with low-pass, high-pass, band-pass, and notch functionality inspired by the original Oberheim SEM filter
• Bi-polar filter envelope amount
• Velocity modulation of envelope amount
• Keyboard tracking: off, half, full

FILTER ENVELOPE

• Four-stage (ADSR) envelope generator
• Velocity modulation of envelope amount

AMPLIFIER ENVELOPE

• Four-stage (ADSR) envelope generator
• Velocity modulation of envelope amount

LOW FREQUENCY OSCILLATOR

• Five wave shapes: triangle, sawtooth, reverse sawtooth, square, and random (sample and hold)
• Clock sync (internal or external MIDI clock)
• Initial amount
• Mod destinations: oscillator 1 frequency, oscillator 2 frequency, oscillator 1 and 2 pulse width, filter cutoff, filter mode

X-MOD

• Sources: filter envelope (bi-polar) and oscillator 2 (bi-polar)
• Destinations: oscillator 1 frequency, oscillator 1 shape, oscillator 1 pulse width, filter cutoff, filter mode

AFTERTOUCH

• Source: channel (mono) aftertouch with bi-polar amount
• Destinations: oscillator 1 frequency, oscillator 2 frequency, LFO amount, amplifier envelope amount, filter envelope amount

CLOCK

• Master clock with tap tempo
• BPM control and display
• MIDI clock sync

ARPEGGIATOR

• Selectable note value: 16th note, 8th note triplet, 8th note, dotted 8th note, quarter note
• One, two, or three octave range
• Up, down, up/down, random, and assign modes

SEQUENCER

• Polyphonic step sequencer with up to 64 steps and rests

EFFECTS

• Stereo analog distortion
• Dual, 24-bit, 48 kHz digital effects, including: reverb (room, hall, plate, spring), delay (full bandwidth digital delay and emulated bucket brigade and tape delays), chorus, flanger, phase shifters, and ring modulator
• Delay sync
• True bypass maintains fully analog signal path when digital effects are off

PERFORMANCE CONTROLS

• Full-sized, semi-weighted, 4-octave keyboard with velocity and aftertouch
• Backlit pitch and mod wheels
• Spring-loaded pitch wheel with selectable range per program (1 to 12 semitones up and down)
• Transpose controls for an 8-octave range
• Hold switch latches held notes on
• Polyphonic portamento
• Unison (monophonic) mode with configurable voice count, from one to all six voices, chord memory, and key modes
• Manual switch: when off, the front panel is live; what you see is what you hear

PATCH MEMORY

• 500 user and 500 factory programs in 10 banks of 100 programs each
• Direct program access, including single-button access to the current set of 10 programs