Marshall JMP PA 50W 1985 - Channel 1 preset

Verified · 88/100 confidence. Complete schematic. All component values readable. Parameters derived directly from the circuit.

The Marshall JMP PA 1985 is a 50W PA amplifier head from the late JMP era, built on a clean-voiced multi-channel circuit intended for vocal reinforcement. Like other Marshall PA heads, it has been adopted by guitarists for its transparent, headroom-rich platform.

• Years produced: 1975–1981
• Made in: UK
• Wattage: 50W
• Channels: 4
• Preamp tubes: 4× ECC83
• Power tubes: 2× EL34

Tags: british, vintage, pa, jmp.

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.