The important role of ripple size in switching power supplies in audio equipment
For audio equipment, the ripple of a switching power supply is essentially a form of "noise pollution" injected into the system. Its magnitude directly determines the signal-to-noise ratio and noise floor purity of the audio equipment, and is one of the key factors affecting the final sound quality. Excessive ripple will directly lead to sound quality degradation.
I. What is the Ripple of a Switching Power Supply?
First, we need to clarify the concepts. Switching power supplies efficiently convert voltage through high-frequency switching (typically tens to hundreds of kHz). Their output is not pure DC, but contains two main noise components:
Ripple: Caused by the high-frequency switching action of the switching transistors, it is a periodic fluctuation synchronized with the switching frequency. Its frequency is usually at the switching frequency and its harmonics.
Noise: Caused by the spike pulses generated by the switching transistors at the moment of turn-on/turn-off, it is a high-frequency random glitch with a very rich frequency composition, reaching the MHz level.
In engineering and everyday discussions, these two are usually collectively referred to as "ripple noise" or simply "ripple." The "ripple" we refer to below refers to this broad concept.
II. How Does Ripple Affect Audio Equipment? The signal path of audio equipment is highly sensitive, especially analog amplifier circuits. Ripple can intrude into the signal chain through various pathways, with the following specific effects:
1. Degrading the signal-to-noise ratio and creating audible "floor noise"
Mechanism: Power supply ripple couples directly to the power supply pins of the audio amplifier through the power lines. If the power supply rejection ratio is insufficient, this ripple is amplified and superimposed on the audio signal.
Audiographic manifestations:
High-frequency hiss: If the ripple frequency is in the audible range (below 20kHz) or its harmonics are in the audible range, you may hear a high-frequency hissing or squeaking sound when muted or at low volumes.
Low-frequency hum: If the ripple frequency is low (e.g., 100Hz/120Hz, from mains rectification), you may hear a low-pitched "humming" sound.
2. Inducing intermodulation distortion and polluting the mid-range timbre
Mechanism: This is the most severe and easily overlooked effect. When a strong audio signal (such as a bass drum sound) and power supply ripple are present simultaneously in an amplifier, intermodulation distortion occurs.
Sound Effect: Intermodulation distortion introduces new frequency components not present in the original audio signal. These new frequencies fall in the mid-frequency range, which is sensitive to the human ear, causing the sound to become muddy, blurry, lack detail, and have inaccurate soundstage positioning. Even if you don't hear a noticeable hissing noise, this degradation in sound quality still exists.
3. Interference with Sensitive Digital Circuits, Causing Clock Jitter
Mechanism: Modern audio devices (such as DACs, digital players, and DSPs) use mixed-signal circuits. The digital sections (such as crystal oscillators, PLLs, and digital interfaces) have extremely high requirements for power supply purity. Ripple interferes with the reference voltage of the digital circuits, causing clock jitter.
Sound Effect: Clock jitter directly affects the accuracy of digital-to-analog conversion, resulting in a dry, harsh, heavily digital sound lacking vitality. Even if the analog section is well-made, a "dirty" power supply can ruin the digital section's performance.
4. Impact on Dynamic Range and Transient Response
Mechanism: During high-dynamic-range musical passages (such as the climax of a symphony) or instantaneous high-power output (such as deep bass), the amplifier draws a huge current from the power supply. If the power supply ripple increases sharply under heavy load, it will cause the output voltage to collapse momentarily, failing to provide sufficient and clean energy to the amplifier.
Sound Performance: The sound sounds weak and powerless, with a strong sense of compression, lacking impact and punch.
III. Why is Ripple Particularly Important for Audio Equipment?
Compared to traditional linear power supplies, switching power supplies are more efficient, smaller, and generate less heat, making them the preferred choice for modern portable and high-performance audio equipment. However, their inherent high-frequency switching characteristics make their ripple problems more prominent.
Linear Power Supplies: Low ripple frequency (typically 100/120Hz), relatively easy to filter out with simple filtering circuits, but inefficient and bulky.
Switching Power Supplies: High ripple frequency, although also easy to filter, their high-frequency components are easily coupled to sensitive circuits through parasitic capacitance and radiation, requiring extremely high precision in design and layout.
Therefore, a well-designed switching power supply with extremely low ripple is fundamental for high-end audio equipment to realize its performance potential.
IV. How to Measure and Select?
For audio equipment users and designers, pay attention to the following:
Check the technical specifications: Excellent audio equipment usually specifies its power supply ripple noise level, such as < 10mVpp (millivolt peak-to-peak). The lower the value, the better. High-end products can achieve levels of < 1mVpp.
Design considerations:
Excellent filtering circuitry: Employ multi-stage LC filtering, and use high-performance solid polymer capacitors and ferrite beads.
Good PCB layout: Minimize the switching loop area and physically isolate sensitive analog circuitry from switching noise sources.
Use LDO regulators: Add LDOs to the analog and digital critical sections after the switching power supply stage, utilizing their extremely high power supply rejection ratio to further filter ripple.
Shielding: Metal shield the switching power supply module to prevent noise radiation.
Summary: The ripple size of the switching power supply plays a crucial role in determining the "background cleanliness" of audio equipment. While it doesn't directly contribute to "good sound," excessive ripple acts as a continuous source of interference, systematically and comprehensively degrading sound quality by raising the noise floor, introducing intermodulation distortion, and increasing clock jitter, making the sound impure, dull, and dynamically limited.
Therefore, whether purchasing audio equipment or selecting an external power supply, a low-ripple, high-purity power supply is a necessary but not sufficient condition for ensuring the equipment performs at its expected sound quality level. In the high-end audio field, the importance of "power supply mastery" lies, in one of the core aspects of combating ripple noise.
