Stetsom 4in1 Universal Bass Knob Gain Control + Voltmeter + On/Off Switch + High to RCA input converter, Blue LED Display, One Touch On/Off Display, Continuous Touch On/Off Amplifier 4in1 Product: 1) Bass Knob Gain Control, 2) Built-in Voltmeter, 3) On/Off Amplifier Switch, 4) High to RCA input converter The Stetsom Gain Control was developed with all the essential features you need to control your audio system right at your fingertips, very convenient. Stetsom precision Built-in Voltmeter. It comes with a blue LED display that you can turn on and off with just one click on the level knob whenever you feel necessary Very convenient feature On/Off Amplifier Switch, you will be able to connect the remote wires from your amplifier to the Stetsom Gain Control and conveniently turn your amplifier On and Off with a simple continuous hold click on the level knob As if that was not enough, Stetsom can offer you even more. Besides the bass knob, voltmeter, and remote on/off features, the Stetsom Gain Control can also be used as an audio input converter for car audio factory players that do not support RCA connections.