Marshall JTM45 PA Type 1963 - CH-4 preset

Verified · 82/100 confidence. Complete schematic. All component values readable. Parameters derived directly from the circuit.

The Marshall JTM45 PA is a four-channel public address variant of the original JTM45 head, sharing its KT66 power stage and basic circuit topology while adding additional input channels for microphone and instrument reinforcement. As with other Marshall PA heads of the period, it quickly found use as a guitar amplifier after players discovered that the JTM45's warm, responsive character translated beautifully to guitar at manageable stage volumes. Its multi-channel architecture allowed creative cross-patching between inputs, and surviving examples with their original KT66s represent the earliest chapter of the Marshall story.

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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.