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Modular Linkwitz–Riley Active Crossover for DIY Audio Compact 4th-order active crossover for stereo speakers with optional mono subwoofer summing. Based on NE5532 (OPA2134 upgrade possible), with plug-in resistor daughterboards for fast cutoff-frequency changes. Single-sided, DIY-friendly PCB using 1% 1206/1210 SMD parts. Full build cost: ~€35–70 depending on configuration.

Modular Linkwitz–Riley Active Crossover for DIY Loudspeaker Systems

This project presents a compact, low-cost active Linkwitz–Riley crossover designed for a stereo loudspeaker pair combined with a mono subwoofer. The two main speakers (full range) are driven by a stereo amplifier, while the subwoofer is powered by a dedicated mono amplifier.

The design is based on dual op-amps (NE5532 as standard, with optional upgrades such as OPA2134) and provides 4th-order high-pass and low-pass outputs for both left and right channels. A configurable jumper allows summing L+R for mono subwoofer operation, enabling a 3-output configuration and reducing component count if desired.

A key feature is its modular cutoff-frequency system: the main PCB hosts fixed capacitors, while small plug-in daughterboards—each populated with ten matched 1% precision resistors—define the crossover frequency. This allows rapid experimentation and optimization without redesigning the core board.

The circuit is intentionally designed for DIY fabrication: single-sided PCB, 1206/1210 1% SMD components (hand-solderable with a standard iron), SOIC op-amps, and EasyEDA files for low-cost manufacturing. The complete build—including transformer, symmetrical PSU, enclosure, and connectors—ranges from approximately €35 to €70 depending on IC choice and configuration.

There is also available space inside the enclosure for implementing a Linkwitz Transform stage for extended low-frequency response (under evaluation).

This project targets DIY audio enthusiasts seeking a flexible, technically sound, and affordable active crossover platform.