NE5532 making headphone amplifier circuit diagram

Single chip microcomputer STM32L151CCU6

Filter 18.432M

When I wanted to enjoy CD music through headphones for more than 30 yuan, I decided to build a high-fidelity headphone amplifier with excellent sound quality. The NE5532 is commonly used as a preamplifier and has great performance. But what happens when it's used as a low-power amplifier? After reviewing the circuit diagram, it looked very similar to a standard op-amp setup, but there were significant differences in resistor and capacitor values, leading to a different working state. Testing proved that the NE5532 can indeed function as an efficient low-power amplifier. Beginners might find it worth trying.

During the trial production, several key points should be carefully considered:

1. The power filter capacitors C9 and C10 are crucial. If they are too small, self-excitation may occur. For preamplification, 100μF is sufficient, but for a power amplifier, they should be at least 470μF. These capacitors also play a major role in sound quality.
2. The resistors R4 (R9) and R5 (R10) need to be adjusted repeatedly. In a preamplifier circuit, R4 is usually 1KΩ and R5 is 100KΩ, giving a gain of 100 times. However, when used as a power amplifier, this configuration can cause oscillation. By changing R4 to 8.2K and R5 to 33K, the gain drops to 4 times, which reduces the risk of self-excitation while maintaining moderate negative feedback. This results in a soft, clear, and transparent sound. Further reducing R5 to 15K will make the feedback too deep, resulting in lower volume and a dull tone. Experimenting with these values can help achieve the best sound.
3. C2 (C6) serves as the grounding path for the input loop. In a preamplifier, it’s typically 10μF. When used as a power amplifier, the high input impedance can block the signal, causing distortion or even oscillation. Increasing C2 and C6 to 100μF significantly improves sound quality, expands the frequency range, enhances treble clarity, makes the midrange pure and bright, and gives the bass a deeper, richer feel.
4. The power supply for this unit can range from 3V to 15V. It can be connected in both positive and negative directions using four batteries. While the volume remains similar at 12V, the sound quality is better at that voltage. It is recommended to use 9V to 12V for optimal performance.

Overall, this project offers a cost-effective way to build a high-quality headphone amplifier. With careful adjustments and attention to component values, you can achieve excellent audio results. Whether you're a beginner or an experienced hobbyist, experimenting with the NE5532 in this configuration is a rewarding experience.