Headphone Amplifier

Input impedance - 15k Output impedance - 16,32,64ohms Output power - 100mW in 16ohms ; 50mW in 32ohms ; 25mW in 64ohms. If you want to increase power on the higher impedance loads just decrease the input resistor. I recommend adding a trimmer and adjusting it until you get the required power. Now normally 9V batteries have a limited capacity of around 200mah so the expected life of the battery on a 16ohm load should be 4hours. For 32ohms 6.25 hours are to be expected and for 64ohms - 9hours. Increasing the output power will inevitably cause higher current draw so the life expectancy of the battery counts only for the given ratings. I recommend building this not as a portable amplifier but instead using an lm7809 regulator and powering two sets of this amplifier in order to have a stereo effect. For the transistors I recommend bc550 for the first two and for the last two almost every high gain medium power transistor should do the job just fine. Now it shows sinewave power. Flip the switch and see it work in musical power mode. May last more with the battery connected this way (through the diode and the cap)

published 11 years ago