The OD-21M monitors up to five main power amplifiers which will be switched automatically to the spare amplifier should any one fail. With five independent channels, it can also be operated manually for power amplifier upgrades and maintenance. Each channel has a volume control, manual switch, and status indicator.

Specifications
* Input : 6 audio source channels; 5 main amplifier channels
* Output : 5 speaker channels
* Check Cycle : Input 50mV 20mS; Output : 100mV 20mS
* Channel Switching Cap : 150V/20A, audio signal
* Controls : 1 power switch, 1 reset button, 1 alarm tone control 5, volume controls, 1 address setting dip

 The OD-21M monitors up to five main power amplifiers which will be switched automatically to the spare amplifier should any one fail. With five independent channels, it can also be operated manually for power amplifier upgrades and maintenance. Each channel has a volume control, manual switch, and status indicator.

Specifications
* Input : 6 audio source channels; 5 main amplifier channels
* Output : 5 speaker channels
* Check Cycle : Input 50mV 20mS; Output : 100mV 20mS
* Channel Switching Cap : 150V/20A, audio signal
* Controls : 1 power switch, 1 reset button, 1 alarm tone control 5, volume controls, 1 address setting dip