Bogen MXM 5-Channel Tube Mic Preamp/Mixer

Restoration and Modification to Include Direct Channel Outputs

By adding solid-state direct output buffers to a Bogen MXM preamp/mixer, I made five independent tube mic preamps available on this old unit (among other modifications). Here's how I did it:

• Introduction
• Condition of the MXM Upon Arrival
• Overview of MXM Modifications
• Mechanical Alterations and Power Supply Modifications
• Changes to the MXM's Audio Signal Path
• Considerations for the Direct Output Buffers
• Implementation of Direct Output Buffers
• Suggested Further MXM Modifications

All images are listed below and also linked in the text. You'll need to use the "back" button on your browser after viewing each image.

1. Before/After Block Diagrams
2. Before/After Front/Rear Photos
3. Before/During/After Photos Beneath Chassis
4. Before/After Interior Photos
5. Schematic Before Modification
6. Schematic of Power Supply After Modification
7. Schematic of Input Channels After Modification
8. Schematic of Other Circuits after Modification
9. Bogen MXM Gain by Stage
10. Schematics of Direct Output Buffers
11. Gain Diagram of Modified MXM

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