Bogen MXM 5-Channel Tube Mic Preamp/Mixer

Restoration and Modification to Include Direct Channel Outputs

[Note added July 2013: This is an early example of a channel breakout modification. While this example is quite useful, since I posted this in 2005, I have refined this type of modification both in concept and in technical execution. (For example, this modified MXM lacks mute switches and has unbalanced outputs.) Please see my channel breakout hub page.]

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:

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

Channel Breakout Modification Hub

Altec 1567A Extensive Modification Including Channel Breakout

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