Marshall JTM45 preset

Verified · 94/100 confidence. Complete schematic. All component values readable. Parameters derived directly from the circuit.

The JTM45 is Marshall's first amplifier, a Bassman-derived design with Normal and Bright channels sharing a Treble/Middle/Bass stack and presence control. Early units ran 5881s before KT66s became standard; with a GZ34 valve rectifier they give a warm, compressed breakup. The same circuit in a 2×12 combo is the sound of the 1966 Bluesbreakers album.

• Years produced: 1962–1966
• Made in: UK
• Wattage: 45W
• Channels: 2
• Preamp tubes: 3× ECC83
• Power tubes: 2× KT66

Known for: Eric Clapton, Peter Green.

Heard on: Hideaway — John Mayall & the Bluesbreakers with Eric Clapton (1966); All Your Love — John Mayall & the Bluesbreakers with Eric Clapton (1966).

Tags: british, vintage, crunch, breakup, kt66, mid-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.