Class D Amplifier Sound Quality Is Not Worse Than Class A
Class D amplifiers sound worse than Class A. That belief dates to the 1980s and 90s. In modern circuits, switching distortion sits at least 20 dB below a Class A stage’s own thermal noise, so at normal listening levels above 5 watts into a 4-ohm speaker, the audible gap has effectively closed.
- The claim is a fossil. The audible switching-noise penalty that made early Class D designs sound rough no longer exists in circuits built since the early 2000s.
- Topology is not quality. At realistic wattage and speaker impedance, a well-chosen Class D amplifier and a Class A amplifier deliver output that sits below the threshold of most listeners’ hearing.
- One narrow case survives. Very low-power Class D stages driving sub-4-ohm subwoofers can show crossover-interaction artifacts that a Class A amplifier avoids.
- Carry this forward. Judge an amplifier by its measured distortion at your actual listening level, not by the letter on its label.
What People Repeat
“Class D amplifiers produce inferior audio compared to Class A.” You hear that line in forums, in sales-floor conversations, and in well-meaning advice from friends who built their first listening system in the late 1990s. Two common variants ride along with it. One says, “Class A is warmer and more musical, while Class D sounds harsh or digital.” The other adds, “The switching noise makes it audible if you listen carefully.” All three versions point to the same idea: the circuit topology itself imposes a ceiling on sound quality that modern design cannot fix. You will also hear a softer version, “Class D is fine for computer speakers and car audio, but not for real hi-fi,” which quietly assumes the technology froze at its early, rougher form.
Where The Claim Came From
The belief has a real origin. In the 1980s and early 90s, the first practical Class D amplifier circuits used switching frequencies low enough that some of the switching energy bled into the audible band. Output filters were bulky and crude. Bandwidth was limited. Early designs genuinely showed in-band distortion that a Class A stage would not produce. Listeners could hear a slight harshness on cymbals and hi-hats, a thin, edgy character that made classical recordings feel scratchy. That was a real effect, not a rumor.
But the surrounding parts were the weak link, not the topology itself. The analog-to-digital converters, the feedback loops, and the output filter inductors were all immature. Filter components had high core-loss in their magnetic cores, which meant they smudged the very high frequency edges of the pulse train. As those components caught up over the next two decades, the switching noise got pushed further and further above the 20 kHz range where the ear can no longer follow it. By the mid-2000s, mainstream Class D designs were already pushing switching rates past 500 kHz, far outside any hearing range. The original constraint was real, but people froze the belief at the moment the constraint existed. The cause it implied (the letter D means worse sound) was not.
The Mechanism, Examined
Think of a bicycle brake. You squeeze the lever, and the cable pulls a pad against the wheel rim. The brake works. You do not care whether the cable is steel or carbon fiber, as long as it transmits your hand force to the pad cleanly. The material of the cable does not change the stopping power. It changes the weight and the feel.
A switching amplifier works like that cable. It chops the input signal into tiny on-off pulses at a very high rate, then a filter smooths those pulses back into a clean waveform. Switching frequency is how fast those on-off pulses repeat. In a modern Class D stage, that rate sits far above what your ear can track. Thermal noise is the faint hiss that any electronic stage produces just from electrons jiggling through resistors. It is the quietest floor the amplifier can reach, the sound you would hear if every other source of error were removed.
Here is the step where the claim breaks. In the 1980s, the switching rate was low enough that some pulse edges landed inside the 20 Hz to 20 kHz window your ears respond to. You heard the chop. In a modern design, the switching rate is high enough that those edges land well above 20 kHz, where the ear has no usable sensitivity. The residual switching distortion now sits at least 20 dB below the Class A stage’s own thermal noise floor. That means the Class A amplifier is, in practice, noisier in the audible band than the Class D amplifier next to it. The topology label no longer predicts what you hear.
[Input signal] ➔ [Pulse-width modulator] ➔ [Switching output stage] ➔ [Output filter] ➔ [Loudspeaker]
The output filter is the part that turned a rough early design into a transparent modern one. As filter inductors got smaller, cheaper, and more accurate in their magnetic core material, the smoothing job became so clean that the switching signature left the audible range entirely. A well-designed filter now passes the music and blocks the chopping in the same way a window screen lets air move while stopping insects. The screen does not change the air; it just removes the unwanted stuff that would otherwise ride along.
Where It Almost Holds
The claim is not a total fabrication. In one narrow setup it still has teeth. If you run a very low-power Class D amplifier (think 10 watts or less) into a sub-4-ohm subwoofer load, the interaction between the amplifier’s crossover network and the speaker’s impedance curve can produce measurable artifacts that a Class A stage, with its low output impedance, dampens away. The subwoofer’s moving magnet pulls current in and out, and a low-impedance Class A output acts like a dead weight on that motion. A Class D output with higher loop gain at those low frequencies cannot suppress the same ripple as firmly. The cone overshoots slightly on fast bass notes, adding a faint blooming to the attack.
This case matters mostly to subwoofer designers and to people running multi-way crossovers by hand in a dedicated low-frequency setup. For a main-channel amplifier driving a 4-ohm or 8-ohm bookshelf or full-range speaker at 5 watts or more of real power, the effect is below threshold. You would need a calibrated listening room and a reference pair to hear the difference, and even then the gap is small and sits near the edge of what most ears can resolve.
What To Believe Instead
Stop believing this: the letter on the amplifier’s topology label tells you what the music will sound like. Class D does not mean harsh. Class A does not mean warm. The letter describes how the output transistor handles current, not what your ears receive. A Class A output transistor carries current through the whole cycle, which is a valid design choice, but it does not make the sound inherently softer or more pleasant.
Carry this instead: at realistic listening wattage (5 watts and up into a 4-ohm or 8-ohm loudspeaker), a well-designed Class D amplifier produces output whose distortion sits at or below the noise floor of a comparable Class A stage. The audible differences that defined the 1980s and 90s have closed. If you hear a difference between two amplifiers in your system, the cause is usually the speaker, the room, the source, or the listening level, not the topology letter. Before you blame the amp, swap the source or move the speaker half a meter and listen again.
Why It Keeps Spreading
Three forces keep the claim alive. First, repetition. The idea was stated in every hi-fi magazine from 1992 to 2005, and forum posts recycle old threads without checking whether the hardware changed. A post from 2003 still gets linked in 2024 as though the circuit is the same. Second, plausible-sounding numbers. People say, “Class D has more switching harmonics,” which is technically true, but they stop before the next sentence: those harmonics sit above 100 kHz in a modern design and your ear cannot follow them. The number is real; the implication is not. Third, a real historical basis. The 1980s designs did sound rough. For anyone who owned one, the memory is honest and vivid. The belief simply lost its “as of 1994” timestamp and became a timeless rule that no longer fits the shelf.
More Claims, Checked
Is A Class A Amplifier Cooler-Running Than A Class D One?
No, the opposite is typically true. A Class A output transistor conducts current through the entire waveform cycle, so it dissipates heat even when the signal is quiet. A Class D transistor is either fully on or fully off, and it wastes very little energy as heat at the same output power. You will feel a Class A amp running warm to the touch at low volumes; a Class D unit of similar wattage stays noticeably cooler because most of the energy goes to the speaker, not to the chassis.
Does A Higher Wattage Rating Mean More Distortion?
No. Wattage tells you how much power the amplifier can push before it clips. Distortion is a separate measurement that describes how faithfully the amplifier reproduces the signal at a given level. A 50-watt unit and a 100-watt unit can both sit at 0.001 percent total harmonic distortion at 1 watt. The bigger number means more headroom for loud passages, not a noisier signal at normal listening levels.
Does Damping Factor Matter More For Class D Than For Class A?
Not in most modern designs. Damping factor is the amplifier’s ability to control the loudspeaker cone after the signal stops. Both topologies can reach very high values (100 or more) with modern feedback loops. Where damping factor does tip the balance is the narrow sub-4-ohm subwoofer case mentioned earlier, where a low-impedance Class A output holds the cone more firmly. For main-channel work at 4 to 8 ohms, the gap between the two is small enough that it sits below most listening thresholds.
Does “Digital” In A Class D Amp Mean It Sounds Like A Computer File?
No. The word “digital” here means the amplifier compares the input to a high-speed reference and decides on-off in steps. It does not mean the signal is quantized into 16-bit or 24-bit PCM the way a CD player is. The output filter turns those on-off steps back into a smooth analog waveform before the speaker ever sees it. Your ears receive a continuous signal, not a staircase. The “digital” part is a design trick inside the amp; it does not leak into the sound you hear.
(Debuted on hifireport.com. Unauthorized reproduction or scraping is prohibited.)