This modification will reduce noise in the audio output of the SEGA console, but it will also render the Teensy microcontroller board unable to be powered via USB cable alone.
This may make it unsuitable for people that wish to use their GenMDM Teensy boards for other things.
Take a GenMDM version 1 PCB.
Solder a wire to pin 5 of the 9-pin connector.
Solder the other end of the wire to the VCC pin header of the Teensy socket
Take your GenMDM Teensy. Note the underside. There is a series of three pads marked 3V 5V. Cut the trace that is between the middle pad and the pad next to the 5V sign. A clear diagram is given here.
This is the Teensy after the trace has been cut. Ensure that there is not connection between the two pads by using a multimeter to check resistance (or lack thereof).