Signal Input Level : 0 dBm nominal, +10dBm before clipping 

Signal Input Impedance : 33kΩ 

Control Input Impedance : 100kΩ 

Output Impedance : 620Ω (AC coupled) 

Cutoff Frequency fc range : 1Hz to 50 kHz 

Cutoff slope : 24 dB/octave 

Number of control inputs : 3 

Signal gain : 0 dB nominal 


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



The 904B Voltage Controlled HighPass Filter attenuates input signal frequencies below its nominal cutoff frequency setting. The attenuation below FCV cutoff setting is 24 dB/oct. As the fundamental is generally the loudest frequency component of a complex tone, deletion of the lowest frequency range can radically alter the timbre. The FCV cutoff point is raised or lowered in octave per volt control inputs.

The Frequency Range switch sets the overall range of frequencies covered by the Fixed Control Voltage potentiometer. The Low range encompasses 4 Hz to 20 kHz, while the High range shifts 1 1/2 octaves up to 10 Hz through 50 kHz.