The circuit diagram of Pocket headphone amplifier has been given here. The core part of this circuit is the operational amplifier IC OPA 134 developed by BURR-BROWN Semiconductors. In addition to this the circuit contains some passive components also.
The IC OPA 134 is used in this circuit as a non-inverting amplifier. High input impedance for this IC is provided by the FET biased input stage and this also makes this IC suitable for audio applications. A switch S1 is used in this circuit to accomplish circuit ON/OFF. An indicator LED shows whether the circuit is powered or not. Resistor R2 (100K) and capacitor C1 (0.1 uF) connected to the non-inverting terminal (pin 3) of OPA 134 is a high-pass filter network having a corner frequency approximately 15 KHz. To reduce noise and distortion in output, a load resistance R5 (20 ohm) is used. This load resistance also stabilizes the virtual ground. The output of this circuit is DC coupled. The variable resistor port R1 (47K) is the volume controller of this amplifier circuit.
Split power supply of +/- 4.5 V is required for IC OPA 134. This obtained from a 9V PP3 battery using a network composed of resistors R6 (10K), R7 (4.7K), R8 (4.7K) and capacitors C2 (220 uF), C3 (220 uF).
- Use a good quality PCB to assemble components.
- Sound sources like MP3 players, I Pods, mobile phones etc can be plugged in this circuit.
- IC OPA 134 is specially designed for audio applications.