Bogen CHA-20 Conversion (Carolina Blues Special) - Normal preset

Close · 78/100 confidence. Most values readable. Minor gaps filled by inference from similar circuits.

The Bogen CHA-20 Conversion refers to the practice of transforming surplus Bogen PA amplifier heads into guitar combo or head-and-cabinet configurations. Converters would add guitar-appropriate input impedances, revoice the tone stack, and install a suitable speaker. These conversions were DIY precursors to the boutique amp movement and remain sought after for their raw, uncompressed character.

• Years produced: 1960s–1980s (conversion era)
• Made in: USA
• Wattage: 20W
• Channels: 1
• Preamp tubes: 2x 12AX7
• Power tubes: 2x 6V6

Schematic-derived preset files for 16 Fractal and Line 6 modelers: Axe-Fx II/XL/XL+, Axe-Fx III, FM3, FM9, and the full Helix family (Floor, LT, Rack, HX Stomp, HX Stomp XL, Native).

Gridleak extracts amp parameters from original circuit schematics using AI vision — component values, gain staging, tone stack topology, tube types — then generates native preset files for every supported modeler. Every extraction is scored 0–100 and the score is published.