OTA Low Pass VCF

OTA Low Pass VCF - PCB and Front Panel for Eurorack

• Formant: Eurorack
• Size: 8HP
• Skill Level: Intermediate

Inspired by the classic MS20 low-pass filter, our OTA VCF delivers a warm and juicy sound, perfect for adding analog character to your Eurorack system.

This 2-pole, 12dB/octave voltage-controlled filter is built around the reliable LM13700 Operational Transconductance Amplifier, allowing for rich, resonant sweeps.

Key Features:

• Classic Analog Sound: Experience the coveted warmth and juicy character reminiscent of vintage filters.
• 2-Pole, 12dB/Octave Slope: Provides a versatile filtering response suitable for a wide range of applications.
• LM13700 Based: Utilizes a well-regarded OTA for reliable and musical performance.

Important Build Notes & Calibration:

For optimal performance and to achieve that signature warm sound, careful calibration is essential.

• Component Correction: Please note that C3 will be 1uF and R32 will be 22K.
• Input Level Calibration:
1. Turn the Frequency knob fully clockwise and the Resonance knob fully counter-clockwise.
2. Adjust the In-Level trimmer so that the output signal is slightly less than the input signal. This provides necessary headroom, as increasing the resonance will add volume. Start the trimmer at its lowest setting and slowly increase it.
3. Please be aware: Feeding too hot an input signal can lead to circuit instability and unwanted screeching.

• Frequency Resolution Trimmer Adjustment:

1. The Frequency Resolution trimmer fine-tunes the resolution of your filter potentiometer.
2. Adjust it to achieve minimal sound (or heavy filtering) when the pot is fully down and no filtering when it's all the way up.

Video Demo