Licensed Eurorack reissue of the Buchla 200-series 258 dual VCO. Two independent oscillators, 5Hz-20kHz with no range switching, voltage-controlled waveshape (OSC1 sine-to-saw, OSC2 sine-to-square) and a processing-input attenuverter per side.
Each oscillator covers 5Hz to 20kHz continuously with no octave-range switch. Allows a single knob turn to move from LFO-like sub-audio into full audio-range FM territory · useful for live frequency sweeps and gestural timbral moves.
OSC 1 morphs sine↔saw while OSC 2 morphs sine↔square. Patching the same CV to both waveshape inputs creates a spectrum that sweeps through complementary harmonic series — saw (odd+even) from OSC 1 against square (odd only) from OSC 2.
The per-oscillator Processing attenuverter removes the need for an external attenuverter or processor to scale, invert or compress incoming CV. Sequencer patched to Processing with the attenuverter at CCW inverts the melody; at 12 o'clock the input is muted; CW passes positive with adjustable depth.
Manual notes 'low sine wave harmonic content' · the two rear trimmers (SHAPE, VC WAVE SHAPE) are specifically for tuning the waveshaper to produce clean sines. Critical for West Coast-style FM where sine purity affects spectral cleanliness of the resulting modulation.
Manual highlights 'negligible settling error and high short and long-term stability, even with rapidly changing ambient temperatures.' Allows reliable V/oct tracking in gig environments and after rack open/close without constant retune.
Each oscillator has two OUT jacks — route one to audio path and one to modulation path (e.g., OSC 1 to filter audio and to OSC 2 FM) without using a buffered mult.
The dual layout is designed for classic Buchla two-oscillator West Coast voices: one oscillator modulates the other's frequency or waveshape, producing complex timbres that evolve as the modulator's pitch tracks. Use FM attenuverter at center for no modulation; set off-center for depth/polarity.
| OSC 1 / OSC 2 | FREQ (coarse) | Sets base frequency · spans 5Hz to 20kHz continuously · no range switch Original panel graphic '5cps 20kc' is approximate per manual |
| OSC 1 / OSC 2 | FINE | Fine-tune offset · small range around coarse setting for beating/detune between the two oscillators Use for subtle detune against the paired oscillator |
| OSC 1 / OSC 2 | FM attenuverter | Bipolar attenuator on FM input · CCW negative, center zero, CW positive Zero position silences FM input regardless of source level |
| OSC 1 / OSC 2 | Processing attenuverter | Scales/inverts processing input · lets sequencer or keyboard CV be compressed, expanded or inverted without an external processor Implements the classic Buchla 'processing' scaling in-module |
| OSC 1 | Waveshape (OSC 1 sine↔saw) | Morphs OSC 1 output from sine through asymmetric shapes to sawtooth · voltage-controllable via waveshape input Icons on panel show target shapes |
| OSC 2 | Waveshape (OSC 2 sine↔square) | Morphs OSC 2 output from sine to square · voltage-controllable via waveshape input Square end gives PWM-like timbres; sine end is clean |
| OSC 1 / OSC 2 | 1V/oct trimmer (rear) | Octave-tracking trim · factory-calibrated with precision instruments · rarely needs adjustment Access from back of module |
| OSC 1 / OSC 2 | SHAPE trimmer (rear) | Trims sine-wave purity by setting the core waveshaper · paired with VC WAVE SHAPE for clean sines Rear-access; adjust by ear or scope for lowest harmonic content |
| OSC 1 / OSC 2 | VC WAVE SHAPE trimmer (rear) | Sets waveshaper response to incoming CV on the waveshape input Paired with SHAPE trimmer to dial in sine purity under CV |
| OSC 1 / OSC 2 | VPP1 / VPP2 trimmers (rear, V1.2+) | Sets waveshape output peak-to-peak amplitude · added from firmware V1.2 Rear-access; used for output-level matching |