For the 2.1 amplifier project, I prepared a 4558 opamp preamplifier subwoofer filter circuit. The circuit is based on 2 4558 opamps, with the main audio input and bass output volume adjustment. Power supply symmetrical + -15VDC The PCB... Electronics Projects, 2.1 Preamp Bass Filter Circuit 4558 Opamp "audio control circuits, " Date 2019/12/08