The Behringer 904B is an authentic Eurorack reproduction of the legendary "System 55" High Pass Filter circuitry from the 1970s. This module is a classic voltage-controlled resonant filter designed to remove low frequencies while allowing highs to pass through with vintage character. Its distinct, aggressive tonal profile is a staple for creating thin, cutting leads, evolving textures, and precise frequency carving in a modular setup.

• Vintage Circuitry: Faithful recreation of the 1970s "Modular 55" series, providing the organic, warm, and sometimes unpredictable analog response sought after by synth purists.

• Fixed Control Voltage: Large, tactile knob for manual adjustment of the cutoff frequency, allowing for smooth or stepped frequency sweeps.

• Frequency Range Switch: Features a 3-position switch (Low, Mid, High) that shifts the frequency bands, providing a total range from 10 Hz up to 50 kHz.

• Dual Signal Connectivity: Equipped with dedicated Signal Input and Output jacks for easy integration into any audio chain.

• CV Modulation: Includes three parallel CV inputs for external control of the cutoff frequency. This allows for complex modulation from LFOs, envelopes, or sequencers to create rhythmic or evolving filter movements.

• Active Filter Design: Uses a 24 dB/octave slope for a sharp, musical cutoff that retains clarity even at extreme settings.