Marshall 9004 Preamp - Boost preset

Verified · 92/100 confidence. Complete schematic. All component values readable. Parameters derived directly from the circuit.

The 9004 is a solid-state Marshall rack preamp from around 1990, built entirely from op-amps. A footswitchable Normal channel has Clean Volume with treble, middle and bass; the Boost channel has a gain stage clipping against LEDs, its own treble, middle and bass and a Boost Volume. A switchable -10/+4 dB send feeds stereo effects returns, blended by an FX Mix control, then Output Level into left/mono and right outputs and headphones.

• Made in: UK
• Channels: 2

Tags: british, preamp, crunch, two-channel.

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.