Check the listing for details. CT Sounds Universal Bass Knob for Car Amplifier with Digital Volt Meter Display. Condition: New. Listed at 39.99 USD. There is nothing worse in car audio world than the magic blue smoke caused by voltage drop. It is real critical & at the same time; very very necessary to monitor your vehicles voltage to prevent damage to all your car audio equipment. Installing a separate voltmeter, separate power switch and a separate bass knob can prevent all those which can be of great hassle. Combining those three issues, CT Sounds represents the solution with its Universal Bass Knob with Digital Voltmeter (Pushable ON/OFF for Amp). This patent-pending technology offers remote gain control, a rotary pushable on-off switch and a digital volt meter display. Technical Specifications: Dash mount amplifier level control for volume adjustmentCan adjust the amplifier gain even while drivingIn-dash or Under-dash mountableCompatible with most head units/amplifiers combinationsRotary push turn ON/OFF knob for amplifierDigital volt-meter (10V ~ 15.9V)Blue LED display (high voltage / low voltage)