If you want to enjoy CD music through headphones for under 30 yuan, I built a high-fidelity headphone amplifier with excellent sound quality. The NE5532 is commonly used as a preamplifier due to its great performance. But what happens if it's used as a low-power amplifier? After taking a quick look at the circuit diagram, it seems similar to a standard op-amp setup, but there are significant differences in resistor and capacitor values, leading to a different working state. Testing confirmed that the NE5532 performs well as a low-power amplifier. Beginners might find it worth trying.
During the trial phase, several key points should be carefully considered:
- The power filter capacitors C9 and C10 must be of sufficient size. Using too small a value can cause self-excitation. For preamplification, 100μF is enough, but for a power amplifier, they should be at least 470μF. These capacitors also play a major role in sound quality.
- The resistors R4 (R9) and R5 (R10) need careful adjustment. In a preamplifier setup, R4 is typically 1KΩ and R5 is 100KΩ, resulting in a gain of 100x. However, when used as a power amplifier, this can lead to instability. By changing R4 to 8.2K and R5 to 33K, the gain drops to about 4x, which prevents self-excitation and ensures a moderate negative feedback, resulting in smooth, clear, and transparent sound. If R5 is reduced further to 15K, the feedback becomes too deep, reducing volume and making the tone dull. Experimentation is encouraged to achieve the best result.
- C2 (C6) serves as the ground path for the input loop. In a preamplifier, 10μF is usually sufficient. However, when used as a power amplifier, the higher input impedance can block the signal, causing distortion or even self-excitation. Increasing C2 (C6) to 100μF significantly improves sound quality, expands the frequency range, gives a crisp treble, a clean midrange, and a rich, deep bass.
- This unit can operate on a voltage between 3V and 15V. It can be powered using two sets of batteries in either positive or negative polarity. While the volume remains similar at 12V, the sound quality is better. It’s recommended to use 9V to 12V for optimal performance.
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