Stereo headphone amplifier module


Portable and small unit, Can be built on a veroboard

Firstly, I’d like to stress that the intended use of this circuit is
only one of many possible applications. Apart from the obvious usage as
a headphone amplifier, the circuit can be used for a range of
applications where a wide bandwidth low power amplifier is needed. The
circuit is based on an opamp, with its output current boosted by a pair
of transistors.

The bias diodes should be 1N914 or similar – power diodes are not
recommended, as their forward voltage is too low. This may result in
distortion around the crossover region, where one transistor turns off
and the other on. Credit for this circuit goes to SiliconChip.

Picture of the circuit:

Main View Of Stereo Headphone Amplifier Circuit

Main View Of Stereo Headphone Amplifier Circuit Diagram

Parts layout:

Parts Layout Of Stereo Headphone Amplifier Circuit

Parts Layout Of Stereo Headphone Amplifier Circuit Diagram

PCB layout:

PCB Layout Of Stereo Headphone Amplifier Circuit

PCB Layout Of Stereo Headphone Amplifier Circuit Diagram

Circuit diagram:

Stereo Headphone Amplifier Circuit

Stereo Headphone Amplifier Circuit Diagram

Parts

Resistors
P1 = 50K
R1 = 56K
R2 = 22K
R3 = 330K
R4 = 10K
R5 = 10K
R6 = 33R
R7 = 33R
R8 = 68R

Capacitors
C1 = 0.27uF
C2 = 10uF-35V
C3 = 5pF
C4 = 100nF-63V
C5 = 100nF-63V

Semiconductors
D1 = 1N914
D2 = 1N914
Q1 = BC338
Q2 = BC328
IC1 = TL072

Misc.
J1 = Audio Input Socket
J2 = Stereo Headphone Socket

Performance of Prototype:

Output level 90mR (max) into 8W headphones
Input sensitivity 0.83V RMS for full power
Frequency response 0.5dB down at 30Hz and 20kHz
Signal-to-noise ratio -95dB unweighted (20Hz to 20kHz) with respect to 500mV input signal
Separation between channels = = -50dB between 20Hz and 10kHz


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