Marshall JCM800 Bass 2001 (375W) - Channel A preset

Verified · 91/100 confidence. Complete schematic. All component values readable. Parameters derived directly from the circuit.

The JCM800 Model 2001 is a 375-watt all-valve bass head from 1981, among the most powerful valve bass amps Marshall built. Two footswitchable channels have their own volume and bass and treble; Channel A adds a six-position mid-frequency switch, and each has its own send/return. A FET compressor with Compression Depth follows the mix stage, and an ECC83 inverter drives eight 6550s, with a balanced 600-ohm DI with earth lift.

• Made in: UK
• Wattage: 375W
• Channels: 2
• Preamp tubes: 3× ECC83, 2× ECC81
• Power tubes: 8× 6550

Tags: british, bass, 6550, high-wattage, 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.