headphone 2

Headphone Class A Amplifier [2]

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�� , �� , �� Linsley Hood �� 1984 �� Electronic Today International. �� 50�, �� 600�. �� 100mA, �� , �� 100mA �� . � �� 15V �� 7815/7915 � LM 317-337, �� . �� RV1 �� TR1 �� offset �� . �� , �� .

It is a very useful thing , to have a small headphone amplifier , capable of driving a couple of pairs phones. Fortunately, the headphone amp has a much easier job to do, in that neither the output power requirements nor the load characteristics are so severe, since headphones typically have a load, impedance , higher of 50 ohm, (typical 600 ohm), and only require 1-2V RMS. max, for normal output. Since only a low power output is required, a Class A stage, is perfectly feasible. For adequate Class A operation the output transistors Q5-6, should pass say 100mA each. With �15V supply this would mean 1.5Watts dissipation, so a smallish Heatsink, will be needed for each. With RV1 adjust input audio signal and Tr1 adjust the output DC Offset voltage for 0V (�30mV). For stereo application , you need two unit, of this amp. by L. Hood

Part List

R1-4= 1.2Kohm	R14=68Kohm	C9-11= 100nF 100V ceramic
R2-3= 3.9Kohm	RV1= 10Kohm Log. pot.	Q1-3= BC184
R5-10= 10Kohm	TR1= 10Kohm Trimmer	Q2-4= BC214
R6=100Kohm	C1= 4.7uF 63V MKT	Q5= BD136 or BD538
R7-9= 2.2Kohm	C2-7= 100uF 25V	Q6= BD135 or BD537
R8= 150 ohm	C3-5= 100nF 100V MKT
R11-13= 6R8 ohm	C4-6= 100uF 16V
R12= 4.7 ohm	C8-10= 470uF 25V	All resistors is 1/4W 1%