Marshall Rackmount Preamp 9004 preset

Verified · 80/100 confidence. Complete schematic. All component values readable. Parameters derived directly from the circuit.

The Marshall 9004 is the four-channel successor to the 9001 rack preamp, expanding the programmable valve preamp concept with additional channels and enhanced MIDI control capabilities. With four independently EQ'd channels accessible via MIDI program changes, the 9004 offered a level of tonal versatility unprecedented in Marshall's history, making it popular with session players and touring professionals who needed instant access to multiple distinct sounds. Its five ECC83 valves provide genuine Marshall valve character throughout, and the extensive MIDI implementation made it compatible with virtually any MIDI switching system of the era.

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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.