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
