The 904C Filter Coupler is a connecting module which combines the functions of the 904A Lowpass and 904B Highpass Filters together. In the “off” position, the Highpass and Lowpass Filters are disconnected from the 904C and may be used independently. When switched to the “Brandpass” mode, Highpass and Lowpass Filters are coupled in parallel to process a central band of frequencies – deleting both bottom and top. The bandreject mode presents the inverse relationship, rejecting a central frequency band, and passing only the lowest and highest frequency components. Voltage controlled bandwidth and center frequency controls are included on the coupler. Bandwidth can be extended to three octaves with manual settings or control voltage. Center Frequency ranges from 5Hz to 20kHz, via manual or voltage controlled settings.


When using the 904C for Bandpass or Bandreject filtering, the following standard settings should be obeserved :

904A Fixed Control Voltage = +9

904A Frequency range = 2

904B Fixed Control Voltage = -1

904B Frequency range = Low


Passband settings = Bandwidth knob plus control voltage.
Notchwidth = Minus bandwidth knob minus control voltage.

Power supply requirements : +12V@50mA / -12@40mA