This circuit is the sound controls automatic circuit, by it will fix to don’t give popularity level in the sound doesn’t expire. When feed sound signal reaches in this circuit , as a result , will have a signal, will the power goes up to flow through LED shine to LDR. The connection and a resister have a side input ,make control popularity level in the sound that a side output get , when see the circuit has already. I uses important equipment , be the transistor number BC109 and other equipment a little again. By you can fix signal sound level can control with VR1 with try fine can decorate follow want.