C1237HA speaker protection circuit board delay boot, the operating voltage 18-24VAC 5ASize installed after the: length 71mm * 40mm * high 29mm wide selection of high quality plate 1.6mm double-sided fiberglass board, double-sided alignment, for LM1875 LM3886 TAD7294 so these low-power amplifier.BOM:PCB circuit board: 1pcsG2R-2 Relay 1pcsC1237 IC 1pcsMetal film 1 / 4W resistor 6pcsLED indicator