Bogen GA20 - Instrument preset

Verified · 84/100 confidence. Complete schematic. All component values readable. Parameters derived directly from the circuit.

The GA20 is Bogen's 20-watt tube instrument amplifier. Instrument inputs 1 and 2 share one 12AX7 triode and volume, Instrument 3 has the other triode and its own volume, and a microphone input runs through a 6SF5 with a third volume. All three mix into a single tone control and the second 12AX7, which works as gain stage and paraphase inverter for a cathode-biased push-pull pair of 6L6Gs with negative feedback, on a 5Y3GT rectifier.

Tags: american, vintage, 6l6, two-channel, mid-wattage.

Schematic-derived preset files for the Neural DSP Quad Cortex and 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.