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V-TWIN RACKMOUNT PREAMP

 

The MESA BOOGIE© V-TWIN PREAMPLIFIER was available in a Rack-Version and Pedal-Version. (I have both types, but, here is the info on the Rack-mount unit...)

The Rack-mount version has 2-Channels with 6-Modes… any of those channels/ modes are available and selectable separately via front-panel toggle switches or via six ¼” phone plug tip-to-ground contact closure connectors on the rear-panel. Those rear-panel connectors also allow you to mix Channel 1 modes with Channel 2 modes to get different sounds using an external control switcher and activating two of the Tip-to-ground contact closure connectors.

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External Control Switching Panel

This rear-panel Tip-to-ground connector panel was an option from MESA©, my second-hand preamp did not have the connector panel, just a blank cover plate, meaning that all channel switching had to be done manually from the front panel or with the included 2 button footswitch.

ftsw

I fabricated a custom printed circuit board (PCB) for the six ¼” phone plugs and a 5 pin midi connector for installation on the blank panel. I had the stock blank cover plate Laser engraved by AD Engraving and drilled it for installation of the custom PCB 1/4" connectors. I purchased an 8 inch 0.100” 8-pin header cable for connection of the custom switching panel to the V-TWIN circuit board. All of the components for the switching circuitry were installed on the PCB from the factory, so, no PCB mods or component additions were required.

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Overheating of Current Limiting Resistors

After inspecting the V-Twin circuit board, I noticed some burn marks on the PCB around some 3 Watt resistors near the power supply. To increase the reliability, I removed those 3 Watt resistors, cleaned the PCB and replaced all of the power-resistors with 5 Watt Versions. I didn't want to further load the existing V-Twin transformer/ power supply with the new MIDI Control Board, so, I installed a separate circuit board with a torroidal transformer, rectifier & regulator to power the MIDI control Circuitry separetely.

Those power resistors still got hot so I ventilated the chassis by cutting vertical slots in the chassis and added a small 5 VDC brushless fan to blow cool air over the resistors... much cooler now.

ventfan

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MIDI Control Board

MIDI capability was added to the V-TWIN preamp to allow any single mode selection or a mixed mode selection of any 2 modes from the 2 channels.This was facilitated by the installation of a Highly Liquid© MSA-R MIDI Control Board and connection to a rear-panel MIDI connector and Internal 9VDC Power Supply.

 

midi