High efficiency explains why Class D amplifiers can be compact. Understanding their progress in high-fidelity audio also means looking at error correction, loudspeaker loads, and performance across real operating conditions.
Start with the output stage
In a Class D amplifier, the power devices operate mainly as switches. Modulation controls the energy delivered to the load. In the high-power designs discussed here, an output filter suppresses the high-frequency switching components while passing the wanted audio. This reduces output-stage losses compared with linear operation, although switching losses, conduction losses, and auxiliary-circuit consumption remain. Analog Devices explains the operating principle and its trade-offs.
Efficiency describes how energy is used. Fidelity describes how closely the output follows the intended amplified input. Both matter, and neither is a substitute for the other.
Consider an illustrative power stage delivering 200 W. At 90% efficiency, its loss is about 22 W; at 95%, it is about 11 W. These figures come from input power minus output power and exclude power-supply and other circuit losses. Across several channels, the heat that the enclosure must dissipate becomes substantial.
Better efficiency makes compact, multichannel amplifiers practical. It does not remove the need for appropriate thermal contact, enclosure design, and ventilation.
An important approach: include the output filter in feedback
A loudspeaker is not a resistor with a constant impedance. Its impedance changes with frequency, and the amplifier's output filter can interact with it. If the control circuit observes only the signal before the filter, some changes occurring after that point are outside its correction path.
Post-filter feedback takes output information closer to the loudspeaker terminals and feeds the error back into the control circuit. UcD already used this approach; subsequent development also concerns how effectively feedback operates across a wider range of conditions.
Purifi's work on output-inductor distortion illustrates why the filter matters. The errors to be addressed include the inductor's own nonlinearity. Correction and stability must be designed together: a larger feedback number alone does not establish a better result. Purifi discusses the output filter, hysteresis, and loop stability here.
For the listener, the objective is straightforward: changes in loudspeaker impedance should have as little unwanted influence as possible on the amplifier's frequency balance.
There is also a distinction between having feedback and having effective correction at a particular frequency. Where an error enters, whether it lies inside the loop, and how much correction remains at that frequency all affect the outcome. Bruno Putzeys' article The F Word explains why feedback needs to be considered through its frequency-dependent behavior.
Progress across an operating range
Maximum power and the lowest distortion figure are easy numbers to compare. Music, however, continually changes in frequency, level, and dynamics. A good result at one measurement point does not describe every operating condition.
Hypex's NCOREx development continues the NCORE approach, with control-loop changes that improve noise and distortion. Purifi's second-generation Eigentakt module documentation emphasizes higher loop gain across the audio band. Both show that high-performance Class D development remains closely concerned with error control. Hypex NCx500 · Purifi 1ET6525SA datasheet
Read power, noise, and distortion with their conditions
An output-power specification needs to establish both how much voltage is available before clipping and how long that output can be sustained. Short musical peaks and continuous sine waves place different demands on the supply and cooling. A multichannel specification should also state how many channels are driven.
The NCx500 datasheet separates peak from continuous output and notes that continuous capability depends on the thermal implementation. Module capability therefore has to be supported by the finished amplifier's power supply and enclosure. Comparisons also need similar distortion limits; a heavily clipped result cannot be compared directly with low-distortion output. NCx500 datasheet, Electrical Specifications
Noise and distortion describe different effects. Noise can remain audible during quiet passages; distortion is a nonlinear alteration of the signal. THD+N combines harmonic distortion and noise, so the low-power part of a curve may be dominated by noise, while the high-power end may be dominated by clipping. The curve is more informative than its single lowest point.
Measurement bandwidth, weighting, input gain, and test frequency also matter. Intermodulation tests add another view by showing whether multiple input frequencies produce unwanted new components. None of these measurements translates directly into a numerical change in perceived soundstage or musical enjoyment.
What does an upgrade need to solve?
If a system already has sufficient headroom at normal listening levels, additional power may not be its most urgent need. More useful questions are whether it can handle low loudspeaker impedances, reproduce large peaks without early clipping, support several active channels, and remain quiet with sensitive speakers.
Maroon builds finished amplifiers around Hypex and Purifi modules, integrating analog input stages, power supplies, and thermal design. Understanding how those choices serve your speakers, room, and listening level makes an upgrade easier to assess. Component count, package size, and price do not replace evidence of performance.
The finished amplifier remains the reference
A capable module provides a foundation. The input stage, gain structure, power supply, cooling, and protection determine how that foundation is used in a complete product. Module specifications quoted in this series are manufacturer figures under their stated conditions, not measurements of a Maroon finished amplifier.
The meaningful progress in modern Class D is the combination of efficiency and compactness with accurate amplification over a wider operating range. That is more useful to a music system than an isolated maximum-wattage number.
Compare the finished stereo amplifiers
A module platform is one part of a finished amplifier. Compare the chassis, main power supply, published output references and available editions, then ask us about your system.
More in this series
How Much Amplifier Power Do You Really Need?
Class D Does Not Mean Digital: Analog Inputs and Preamp Matching
Understanding Hypex: From UcD to NCORE and NCOREx
Understanding Purifi: Why Eigentakt Focuses on Error Control
Bruno Putzeys: Bringing Class D to the Heart of High-End Audio
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