Portable Headphone Amplifier using BC327
Notes:
* Can be directly connected to CD players, tuners and tape recorders.
* Tested with several headphone models of different impedance: 32, 100, 245, 300, 600 & 2000 Ohm.
* Schematic shows left channel only.
* B1, SW1, J1 & C3 are common to both channels.
* R3 value was calculated for headphone impedance up to 300 Ohm. Using 600 Ohm loads or higher, change R3 value to 100K.
* An interesting upgrade for this circuit was suggested by Mike Baum, NY USA. This involves the use of a Lithium-Ion Prismatic Rechargeable 340948 Battery, featuring a nominal voltage of 3.7V and a current rating of 1200mAH. These weight 38 grams and are 34.2mm x 8.5mm x 48mm. Correct value of R3 when using a 3.7V supply and 32 Ohm impedance headphones will be 100K: under these conditions, the amplifier will deliver about 3V peak-to-peak undistorted output. This means that the output power on 32 Ohm load will be almost doubled in respect to 3V supply. Current drawing will raise to 40mA. When powering a stereo version of this amplifier, the battery will last about 15 hours.
