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Portable Headphone Amplifier Circuit
Description
This amplifier can be directly connected to CD players, tuners and tape recorders. It is 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.
Circuit diagram
Parts:
- R1 = 10K
- R2 = 100K
- R3 = 68K
- R4 = 1.5K
- R5 = 3.3K
- R6 = 330R
- R7 = 4K7
- R8 = 2.2R
- C1 = 1µF-63V
- C2 = 100µF-25V
- C3 = 470µF-25V
- Q1 = BC239C
- Q2 = BC337
- Q3 = BC327
- J1,2 = Stereo 3mm. Jack socket
- SW1 = SPST Switch
- B1 = 3V Battery (two 1.5V AA or C cells in series, but see Notes)
Upgrade:
- 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.