Headphone amplifier made of NE5532

In order to listen to CD (VCD) with headphones, I spent only more than 30 yuan to install a high-fidelity headphone amplifier with beautiful sound quality. NE5532 is generally used as a preamplifier with excellent performance. Now it is used as a low-power amplifier, how is the effect? ​​A rough look at the circuit schematic is almost the same as the general op amp circuit, but the resistance and capacitance have changed greatly, and the working state is different from the op amp circuit. Experiments have proved that NE5532 has excellent performance as a low-power amplifier. Beginners may wish to give it a try.

The following points should be noted during the trial production process:

1. If the power supply filter capacitors C9 and C10 are too small, it will cause self-excitation. When used as a preamplifier, 100μF is enough for C9 and C10, but when used as a power amplifier, it must be increased to more than 470μF. At the same time, the filter capacitor is directly related to the sound quality.

2. The resistance values ​​of R4 (R9) and R5 (R10) in the circuit should be repeatedly adjusted. In the preamplifier circuit, R4 (R9) is generally 1KΩ, and R5 (R10) is 100KΩ, so its amplification factor can reach 100 times. But now as a power amplifier, self-excitation will occur, so R4 (R9) is changed to 8.2K, and R5 (R10) is reduced to 33K, and the amplification factor is only 4 times. The circuit will not self-excite, and the negative feedback is also appropriate, and the sound quality is soft, clear, and transparent. If R5 (R10) is further reduced to 15K, the negative feedback is too deep, not only the volume becomes lighter, but the tone is dull. Readers can repeatedly adjust it to achieve perfection.

3. C2 (C6) is the ground path of the input circuit. In the preamplifier circuit, it is only 10μF. When used as a power amplifier, the input impedance is too large, the signal is blocked, and distortion or even self-excitation is caused. Now C2 (C6) is increased to 100μF, and the sound quality is significantly improved, the range is widened, the treble is crisp and pleasant, the midrange is pure and bright, and the bass is deep and rich.
 
4. The power supply of this machine can be selected from 3V to 15V. Four batteries can be connected in series to form a two-way (positive and negative 3V). The volume is not much different from 12V, but the sound quality is not as good as 12V. It is recommended to use 9V to 12V.

In addition, R1 (R6) 51K is connected in series at the input end because the volume is too loud when listening with headphones. If R1 (R6) is removed, a small speaker of less than 5 inches can be connected, and the listening effect is also very good at the desk or bedside.