Ampeg B-3158a (preamp board) - Main preset

Close · 73/100 confidence. Most values readable. Minor gaps filled by inference from similar circuits.

The B-3158a preamp board schematic documents the tone-shaping and gain control section of Ampeg's solid-state bass combo. The preamp provides Ampeg's characteristic bass EQ voicing feeding the solid-state power section. Used alongside the B-3158 power amp schematic for complete circuit coverage.

• Years produced: 1988–1993
• Made in: USA
• Wattage: 150W
• Channels: 1

Tags: bass, american, modern, mid-wattage, solid-state.

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.