DUAL OSCILLATOR - MODEL 258t
Text from the Buchla 200 series catalogue from the 70's. Slight adjustments were made.
Two independent voltage-controlled oscillators. Each has one processing input, a frequency modulation input and a 1V/oct input. Waveshapes, as well as frequency, can be voltage controlled. Model 258 oscillators feature low sine wave harmonic content, negligible settling error, and high short and long-term stability, even with rapidly changing ambient temperatures.
TRIMMERS: There are three trimmers for each oscillator on the back of the module:
1V/oct is the octave tracking trimmer and is set at the factory using high precision instruments. SHAPE is the trimmer that set the sine wave, for the lower harmonic content of the sine wave. VC WAVE SHAPE sets the response of the waveshaper to the incoming control voltage. Both SHAPE and VC WAVE SHAPE trimmers are used to adjust the sine wave purity.
The processing control attenuverter input permits control of pitch scaling/inversion/expansion without the need for a separate external processor.
Frequency modulation control:
For adjusting vibrato depth or creating clangorous or bell-like tones, rich in non-harmonic upper partials.
Used to set desired range of incoming control voltage for expansion, compression and inversion.
Control Voltage input for 1V/oct note tracking.
Waveshape control input:
Waveshapes can be varied from sine to saw (OSC 1) and sine to square (OSC 2). Voltage control of waveshape enables powerful dynamic control of timbre.
Oscillator frequency control:
Spans the audio spectrum of 5 Hz to 20 kHz with no range switching.