This is a 35mm VU meters with drive boards Work for Phone ,Computer,Pre-amp, Mp3;Can't Connect to Amplifier Output;DC internal resistance: 650 ohm + -15%;Calibration position: +5; Accuracy: Level 5;DC current; 500uA +-15%;Backlight: LED*3; Working temperature: -22%-55 degrees Celsius;VU Meter Backlight voltage: AC6V-12V ; L, G, R: This is the two-channel input terminal for low-level signal of the driver board, which is used to connect the audio of mobile phones, computer sound card pre-stage, and other audio source devices (the signal is the signal that the earphone can hear). L, GND, and R correspond to the left, ground, and right channels respectively AC12V is the power supply. (It is recommended to use an independent power transformer or independent winding power supply!)Note: Can't connect to the power amplifier output Can not connect to the output of the power amplifier. Can not connect to the output of the power amplifier. Including car CD player cannot be used Level meter debugging Find a signal generator to adjust the output frequency of 1KHz, the effective value of the signal is 0.775V, and then connect the signal input of the drive board, and the pointer of the meter head points to the 0DB of the instrument panel. (If you don't have a signal generator, you can download an APP signal generator with your mobile phone, and you can adjust it according to the previous method) The debugging of the VU meter, the adjustment of the VU meter is much simpler, the driver board is connected to the audio signal, and the driver board can be adjusted. Adjust the resistance to synchronize the loudness and rhythm of the ear to the sound with the pointer, so that the pointer swings moderately so that the pointer points to the 100% position of the sign or the maximum value of the sign when the sound is maximum. Color: Yellow Material: plastic Package Contents: 2*level meters, 1*driver board with wiring