Here is a very sensitive sound activated LED circuit that can activate many LEDs from a distance sound or slow sound. It can also be used to flash LEDs on music. The circuit is using 9 LEDs of 25mA, you can also increase the number of LEDs in the circuit and add three to six more LEDs of 25mA in the
same manner as we have connected in the circuit. For further increasing the number of LEDs you can use a higher output current transistor like BD135 as Q3, it can handle upto 40 LEDs of 25mA. For further increasing the number of LEDs you can use a TIP31 or similar transistors. The sensitivity of the circuit can be adjusted with 100K variable resistor.
Working of the circuit
The electret microphone detects the sound signals and change them in to electrical audio signals these signals are amplified by the transistor Q1 and further amplified by Q2. The amplified signal at the collector of Q2 goes into the diodes D1 and D2 through the 10uF filter capacitor. The Diode D1 and D2 rectify the amplified audio signal and convert it in to DC signal. This DC signal is fed to the transistor Q3 base making it switch on and activates the LEDs.
The operating voltage of the circuit is 12 volt DC but you can also operate it with 9 volts. If you want to operate the circuit with 9 volts remove one LED from the 3 LEDs in each line and use 180 ohms resistor in the place of 68 ohms as shown in figure 2.