A dual oscillator project

The 258D Dual Oscillator is designed to replicate the functionality of the Buchla 258C module using modern construction techniques and readily available parts. Like Mark Verbos’ 258V and Dustin Stroh’s 258J, the 258D uses the exponential converter and triangle core from the Electronotes VCO option 3, designed by Bernie Hutchins, with output waveshaping derived from Don Buchla’s original 258 Design.

Additionally, the 258D includes:

• A stable voltage reference to isolate the frequency controls from fluctuations and noise on the power supply rails.
• High frequency compensation for improved tracking.
• A scaled V/O CV input in place of the original scaling potentiometer.
• The option to select either saw or square waveshapes for each oscillator by setting a jumper on the rear of the module.
• A buffered copy of the triangle core replacing the rightmost output of each oscillator.

There are several build options to adjust the function of the module to a particular users requirements.

The repository contains:

• KiCad project files
• Schematic and build/calibration notes as PDF files
• Bill of Materials in ODS format
• Interactive webpage for matching BOM items to PCB locations