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A Class D amplifier operates on a fundamentally different principle than Class A or Class AB designs. Rather than using output transistors that remain partially or fully on throughout the audio signal cycle, a Class D amplifier switches its output transistors rapidly between fully on and fully off states — typically at frequencies between 300kHz and 600kHz, well above the audible range. The audio signal is encoded in the width of these switching pulses (pulse-width modulation), then reconstructed by a low-pass output filter that strips the high-frequency switching carrier and recovers the audio signal for delivery to the speaker.
The efficiency advantage comes from the switching behavior itself. A transistor that's fully on or fully off dissipates almost no power — power dissipation in a transistor occurs primarily when it's in a partially conducting state, which is exactly where Class A and Class AB output stages operate. By eliminating that partially conducting state, Class D designs achieve efficiencies that Class AB designs can't approach, regardless of how well they're engineered.
The practical result for car audio is an amplifier that produces its rated output power while drawing significantly less current from the vehicle's electrical system and generating significantly less heat than a Class AB design at equivalent output. A well-engineered 500W RMS Class D monoblock draws roughly 50 amps at full output. An equivalent Class AB design would draw 80-100 amps and require a much larger heatsink to manage the thermal load.
Modern Class D amplifier designs from quality manufacturers have closed the sonic gap with Class AB to the point where the difference is either inaudible or irrelevant in any real-world car audio context. Output filter designs have improved dramatically. Switching frequencies have increased to push artifacts further above the audible range. Feedback topologies have been refined to reduce distortion figures to levels that compete directly with Class AB designs.
The Wavtech Link series and Crescendo Revolution line are both Class D designs that measure and sound at a level that would have required Class AB technology a generation ago. For subwoofer amplification specifically, Class D is universally the right choice. For full-range speaker amplification, modern Class D from a quality manufacturer is entirely appropriate for demanding builds.
Where Class AB retains a genuine advantage is at the absolute reference level of sound quality competition. For that application, Tru Technology's Tungsten series and Audio Wave remain in our collection as Class AB alternatives. For the vast majority of builds, Class D is the correct choice.
Class D amplifier specifications are among the most abused in the consumer electronics industry. Power ratings are frequently inflated, measured at impedances that don't reflect real-world use, or derived under test conditions that don't translate to sustained output.
When evaluating a Class D amplifier's output power, focus on RMS power at the impedance your system will present. A monoblock rated at 1000W RMS at 1 ohm may only produce 500W RMS at 2 ohms — which matters if your subwoofer wiring configuration presents a 2 ohm load. Every amplifier in this collection is rated honestly at usable impedances and tested for sustained output, not burst performance.
Minimum stable impedance is equally important. Class D amplifiers that are rated stable at 1 ohm can handle low-impedance subwoofer wiring configurations that 2 ohm-stable designs can't. If you're running a dual voice coil subwoofer wired in parallel, confirm the amplifier's minimum stable impedance before purchasing. Running a 2 ohm-stable amplifier into a 1 ohm load will either engage protection circuitry or damage the output stage.
The efficiency of Class D amplifiers doesn't eliminate electrical system planning for high-powered builds — it reduces the scale of the problem. A 2000W RMS Class D monoblock at 90% efficiency still draws roughly 185 amps at full output, which exceeds the capacity of virtually every factory alternator.
For builds over 1000W RMS total system power, Big 3 wiring upgrades are the baseline — replacing the factory ground cables and alternator positive cable with heavier gauge wire to reduce resistance and voltage drop under load. For serious builds over 2000W, a high-output alternator and supplemental battery capacity become necessary to maintain stable voltage under sustained high-output operation.
Voltage drop is the enemy of Class D performance. Most Class D amplifiers regulate their output power relative to supply voltage — at 12V supply, output is rated power; at 11V due to voltage drop under load, output drops proportionally and the amplifier may engage protection. Building the electrical system correctly isn't optional for high-powered Class D builds — it's what allows the amplifier to deliver its rated performance reliably.
Wavtech designs compact, high-efficiency Class D monoblocks with a strong track record in both daily and competition use. The Link series covers output tiers from 500W to 1500W RMS in a footprint that installs almost anywhere. Crescendo's Revolution series delivers Class D output power with distortion figures and frequency response measurements that compete with amplifiers at significantly higher price points. US Acoustics builds high-output Class D monoblocks with an emphasis on real-world power delivery — their ratings reflect sustained output, not marketing figures. Goldhorn rounds out the collection at the mid-tier with solid performance for buyers who want reliable Class D power without competition-grade pricing. Image Dynamics brings their SQ-focused engineering philosophy to their amplifier line, producing Class D designs built for listeners who want clean, accurate output above all else.
Class D Amplifiers
