We will use a class A headphone amplifier circuit that is very good quality sound. It consists of a low noise Op-Amp IC and two transistors as main. So there are very cheap and easy to build. It can increase all audio source such as CD players, AM-FM radios, and others.
Many people like this Hifi transistor headphone amplifier It has a good sound. Because of using pure transistors. But sometimes you may like this project because it is the modern circuit.
How does it work
Figure 1 is a complete class a headphone amplifier circuit. By showing only the left channel. For the parts lists at the right channel will start with the number 10. For example, R101, Q101, C101, etc.
Fist, the audio signal comes to the input through J1 and C1. The C1 is coupling capacitor to block DC voltage away.
Then, the audio signal is adjusted volume by VR1. So it causes an input impedance equal to VR1 is about 47K.
The IC1 is op-amp acts as the low signal amplifier. Which we set form circuit to become the non-inverting circuit.
The signal out of IC1 at pin 1. Both resistors R3 and R4 are set in the class A mode, to be the bias current to the base of transistors Q1, Q2.
Both resistors R5, R6 are the heart of this class A designing. As they set the feedback signal to the output section to be more stable better.
The feedback signal from the output will turn through resistor-R2 into inverting pin of IC1.
The gain of IC1 is determined by R1 and R2, with a value about 11 times.
From the complete circuit, we also add the power supply circuit. T1 is a transformer to reduces AC line voltage 220V to 6V (6V-CT-6V) to diode D1, D2, D3, and D4.
It is a dual power supply that there are capacitors C3 as a positive filter and C4 for negative. And LED1 is power on display of circuit.
How to builds
This Class A headphone amplifier circuit can be assembled on a perforated board.
You need to assemble carefully the priority to the positive-negative of electrolytic capacitors and diodes and transistors.
If you want the components layout of the perforated board please contact me by email.
This Headset amplifier with power wattage to about 120 mW, for headphone 8-32 ohms. Which it is a common size. This circuit has the frequency response of 2.5Hz to 100 kHz.
You can take the signals from the line-out of the tape player, tuners and more. To enter into the input of the circuit. Then, the well sound out of the headphones.
Recommendation: This project should be assembled onto steel or aluminum box to prevent noise.
The parts lists
Resistors ¼ W +-5%
R3, R103—180 ohms
R4, R104—910 ohms
R5, R105, R6, R106—10 ohms
LED1—LED red 5 mm.
IC1—TL072 Dual Low-Noise JFET-Input General-Purpose Operational Amplifier.
J1, J101—RCA Jack.
J2, J102—Stereo Headphone Jack
T1__transformer In 220V Out 6V-0V-6V 1A
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