Sallen-Key subwoofer filter schematic as a 389 KB PDF, with a source tag in the file name. Sallen-Key is a common active filter topology using an op-amp with resistors and capacitors, here applied as a low-pass for a sub-woofer feed. No cutoff frequency or op-amp type is stated in the name. Builders use such a drawing to set the crossover point by changing component values and to diagnose a dead or distorted sub output. Check the power supply rails shown before wiring it into an amplifier.
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