AmplifierCircuits

With this indicator you can see how much power an amplifier delivers. The circuit uses a LM 3915, the logarithmic variation of the known LED VU meter IC LM 3914. The circuit is connected directly to the speaker output of the amplifier, and the power state of 0.2 watts to 100 watts. The sensitivity of the circuit can be varied with R1. The basic settings are shown in the table.   R1 = 10 k (see text) R2 = 10 k R3 = 390 Ω R4 = 2.7 K? C1 = 22 V μF/25 LED1-LED10 = LED (color of choice) IC1 = LM 3915

This indicator can be used, or to see if you can get the sound output. Damaged speakers with P1 lets you set the limit at which D1 LED lights. The potentiometer is 100k here, you can experiment. Themselves with other values ​​if you could turn a logical port on the LED or opto coupler would use, you can turn it so that the signal between the preamp and power amp would fall away. Or that the signal to the speakers with the aid of a relay would be turned OFF. R1 = 680 Ω R2 = 1.2 K? P1 = 100 k linearly B1 = 4 x B250C1000 or 1N4003 D1 = LED T1 = 2N3904