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JTM45 Master Volume mod (PPIMV)

Master Volume Mod it can be done on JTM45, JTM50, 1987 Lead, JCM800 2204A(50W), JCM800 2203A(100W), TW Express, & 5E3 amplifiers.

WARNING! – Please Read this Information Carefully:
The project described utilizes POTENTIALLY FATAL HIGH VOLTAGES. If you are in any way unfamiliar with high voltage circuits or are uncomfortable working around high voltages, PLEASE DO NOT RISK YOUR LIFE BY BUILDING THEM. Seek help from a competent technician before building any unfamiliar electronics circuit. While efforts are made to ensure accuracy of these circuits, no guarantee is provided, of any kind!

USE AT YOUR OWN RISK: THE WEBMASTER, PROJECT COORDINATOR, PROJECT CONTRIBUTORS AND WEB SPACE PROVIDER EXPRESSLY DISCLAIM ALL LIABILITY FOR INJURY OR PROPERTY DAMAGE RESULTING FROM THIS INFORMATION! ALL INFORMATION IS PROVIDED ‘AS-IS’ AND WITHOUT WARRANTY OF ANY KIND.

Master Volume Mod it can be done on JTM45, JTM50, 1987 Lead, JCM800 2204A(50W), JCM800 2203A(100W), TW Express, & 5E3.

PPIMV (Post-Phase-Inverter-Master-Volume) is by far the most transparent MV that can be added to an amplifier, due to it’s location in the circuit being after the preamp gain stages and phase inverter. When it is turned to max, it is essentially taken out of the circuit (similar to Matchless type MV).

Original amp (not modified yet)

Green and orange lines only shows, where are wires connected to the board.

DSC_0025

 

Modification

I replaced output jack with 250K Audio/Log dual pot. This pot replaces two 220Ohm resistors which we removed from the board. The pots must have “safety” 2.2M resistors.

Unsolder green and orange wires from the board, and connect them to the pot. Wires must be twisted to prevent hum.

 

The last step is to connect the pot to the turret board. Three wires goes from pot to the turrets where I disconnected green and orange wire.

DSC_0026

 

PPIMV (Master Volume Layout)

 


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