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Putting a 500-watt subwoofer into a cabinet forces one specification decision before anything else: which amplifier class will drive the output stage. That single choice determines heat sink mass, power supply weight, enclosure volume, and how much headroom remains before distortion becomes audible. The practical conclusion for system builders: Class D dominates new professional audio module designs because it converts 85-95 percent of supply power into signal. Class AB remains the analog reference for transparent sound and predictable servicing. Class G and Class H deliver a middle path for high-power linear stages that need less heat. Class A and Class B matter mainly as concepts today, but their conduction-angle behavior explains every class that followed. What Defines an Amplifier Class? Every amplifier class is defined by the conduction angle of its output devices - the portion of each input cycle during which the transistors pass current. A device that conducts for 360 degrees stays on continuously; a device that conducts for 180 degrees handles only half of the waveform. The conduction angle sets a theoretical efficiency ceiling, because a conducting device that is not contributing signal still dissipates power. It also predicts the distortion signature of the stage. The classes below cover everything an audio system designer will encounter. Class C appears for reference only: operating below 180 degrees raises efficiency above 70 percent, but flattens the output so badly that it is restricted to radio-frequency transmitters rather than audio. Efficiency values are practical ranges cited in established electronics references and module datasheets; exact numbers depend on supply voltage, load, and operating level. Amplifier class conduction angle and practical efficiency in audio designs. Class Conduction angle Typical efficiency (audio) Main trade-off Class A 360 degrees 20-30 percent Lowest distortion, highest heat Class B 180 degrees 55-65 percent Crossover distortion without bias Class AB 180 to 360 degrees 50-65 percent Balance of linearity and heat Class C Under 180 degrees Above 70 percent (RF) Not usable for audio quality Class D PWM switching 85-95 percent Filter and EMC design needed Class G Switched supply rails 65-80 percent Multi-rail supply complexity Class H Modulated supply rail 65-80 percent Tracking supply cost Class A up to ~30% Class B ~60% Class AB 50-65% Class D 85-95% Class G ~72% Class H 65-75% 0% 25% 50% 75% 100% Class D delivers roughly three times the efficiency of the linear classes, which changes heat sink and power supply choices completely. Class A: Linearity at a High Operating Cost Class A output stages conduct for the full 360 degrees. A single device, or a pair running in single-ended mode, stays in its active region even when no input signal is present. That makes Class A the most linear topology of the analog families: there is no handoff between devices, so crossover distortion is absent by definition. The price is enormous idle dissipation. Practical single-ended Class A efficiency sits between 20 and 30 percent, so a 100-watt amplifier discards 200 to 300 watts as heat. Heat sinks grow, transformers grow, and running costs become permanent. In professional audio modules, full Class A output stages exist only at preamp level; within power amplifiers, Class A survives as the small-signal bias region of a Class AB input stage. Class B: The Push-Pull Origin Class B splits the waveform into two halves: one transistor pushes the positive half-cycle and the other pulls the negative half-cycle, so each device conducts for exactly 180 degrees. Theoretical efficiency rises to 78.5 percent, but the transition at the zero crossing introduces crossover distortion when neither device is fully in control. No serious audio output stage runs in pure Class B because the discontinuity is audible at low signal levels. Designers add a small bias current so both devices stay slightly on at the zero crossing, and that adjustment is what defines Class AB. Class AB: The Analog Workhorse Class AB adds controlled quiescent bias to the push-pull structure. Both output devices conduct a little at the zero crossing, eliminating the crossover notch, then step back toward cutoff as the signal grows. Efficiency settles between 50 and 65 percent in practical audio designs. A 600-watt Class AB module still throws off 200 to 300 watts when driven hard, so heat sinks with deep fins and sometimes forced air remain part of the design. Engineers choose Class AB when tonal behavior is the priority and enclosure size is permissive. The relationship between bias current, distortion, and thermal load is so delicate that manufacturers calibrate it over years of production refinement. That is also why engineers spend as much time on the output stage as on the drivers, because the amplifier module's contribution to sound quality is easier to hear than to measure. Class D: Switching for Efficiency Class D abandons the conduction-angle model completely. The output transistors alternate between full saturation and full cutoff at a carrier frequency well above the audio band, usually 400 kHz to 1 MHz, and the audio signal rides on the duty cycle of the resulting pulse-width-modulated waveform. An LC filter reconstructs the audio band at the output. Because a saturated switch drops almost no voltage and a cutoff switch passes almost no current, theoretical efficiency approaches 100 percent; real modules deliver 85 to 95 percent. The consequences for loudspeaker design are immediate. A 500-watt Class D stage keeps heat sinks small enough for a die-cast chassis, while an equivalent Class AB stage needs a heavy extruded profile and a larger transformer. Modern post-filter feedback corrects the distortion mechanisms of early switching designs, and well-implemented Class D modules pass blind listening comparisons against good analog amplifiers. The real engineering effort sits in the output filter, the EMI behavior, and the dead-time management of the switching stage. Suppliers who specialize in this area typically pair the switching core with a resonant or power-factor-corrected front end instead of treating the filter as an afterthought. EON522SUB Active Subwoofer Amplifier Module with LLC Resonant SupplyThis 500W Class D subwoofer module pairs an LLC resonant 800W supply with overload, short-circuit, and thermal protection, making it a practical fit for high-efficiency bass applications discussed in the surrounding text.View Product → Class G and Class H: Smarter Supply Rails Class G and Class H keep the linear output stage of an AB amplifier but feed it with a supply rail that adapts to the signal. Class G maintains two or more fixed rails, switching to the higher one only when signal peaks require it. Class H modulates the rail voltage continuously, tracking the signal envelope with a few volts of headroom. Output devices remain linear in both cases, so the distortion profile resembles Class AB, but the average voltage across the devices is lower. That reduces waste heat and pushes efficiency into the 65-80 percent range. The cost moves into the power supply: multi-rail transformers with switch-over logic for Class G, or fast tracking regulators for Class H. These classes suit subwoofer and line-array modules, where music with a high crest factor means the higher rail is active only for short peaks. The H-class approach is a common choice for bi-amplified enclosures with a linear transformer supply, which is why module suppliers list this combination as a standard configuration. Comparing Amplifier Classes in Real Modules The class decision is never made in isolation; it interacts with the power supply, the enclosure, and the duty cycle of the music program. The chart below shows why Class D is so attractive in portable and compact systems. 0% 25% 50% 75% 100% 0% 25% 50% 75% 100% Class D Class AB Efficiency versus output level for Class AB and Class D modules. Class D holds high efficiency far deeper into the operating range. Class D maintains high efficiency over most of its output range, while Class AB efficiency collapses at low listening levels. A 50-watt average output from a 500-watt Class AB module may sit at about 25-30 percent efficiency; the same condition keeps a Class D module above 75 percent. Over a touring season, that difference shows up in electricity cost, rack heat, and how often thermal protection triggers. Class recommendation matrix for common powered loudspeaker applications. Application Preferred class Reason Battery-powered portable speaker D Efficiency extends runtime and shrinks heat sink Mid-power PA monitor AB Predictable analog tone and simple supply Multi-channel line array D Low heat and compact PFC/LLC front end Subwoofer with heavy bass program D or H D for power density, H for linear feel Fixed installation AB, H, or D Depends on service familiarity and rail cost Understanding what an active power amplifier module contains helps buyers apply this matrix correctly. The class letter describes only the power stage; the supply design, feedback topology, and protection circuits determine real-world reliability. A subwoofer module, for example, combines a high-voltage rail with output limiting to survive continuous bass program, so the class choice and the protective features must be evaluated as one system. EON180S+2092 BTL Subwoofer Amplifier Module for Professional AudioFeaturing a 650W Class D BTL output and 800W switching supply, this subwoofer module includes protective circuits suited for continuous bass duty, aligning with the amplifier-class considerations described above.View Product → Anatomy of a Power Amplifier Module The cross-section of a modern module shows how the class interacts with everything around it. The input stage accepts balanced or DSP-processed signals, the driver stage shapes the switching or linear control, the output stage follows the chosen class, and the power supply sets the efficiency ceiling. The isometric diagram below shows the typical arrangement of these blocks in a self-contained module. Input / DSP Output filter Heatsink Power stage Typical block arrangement of a professional power amplifier module: input/DSP processing, switching or linear power stage, output filter, and heat sink. Frequently Asked Questions about Amplifier Classes Which amplifier class is best for professional audio? Class D offers the best balance of efficiency, weight, and heat for most pro audio modules. Class AB remains the analog-first choice, and Class H fits high-power linear stages. What is the difference between Class AB and Class D amplifiers? Class AB runs output transistors in the linear region, producing low distortion but wasting 30-50 percent of power as heat. Class D switches the transistors fully on and off, reaching 85-95 percent efficiency with an output filter. Are Class D amplifiers good for live sound? Yes. Modern Class D modules with LLC or PFC power supplies are widely used in line arrays and subwoofers; they handle high crest-factor program, stay cool, and reduce cabinet weight. Which amplifier class is the most efficient? Class D is the most efficient class used in audio, delivering 85-95 percent of input power to the load. Class C reaches even higher efficiency but is not usable for audio. Do Class D amplifiers sound as good as Class AB amplifiers? A well-implemented Class D module can sound very close to a well-implemented Class AB module. Output filter design, feedback loop, and power supply quality matter more than the class letter. What does amplifier class mean for speaker design? The class sets the conduction angle and efficiency of the output stage. It predicts heat generation, power supply demands, distortion behavior, and the physical size of the finished module. .article-section table{display:table!important;} .article-section thead{display:table-header-group!important;} .article-section tbody{display:table-row-group!important;} .article-section tr{display:table-row!important;} .article-section th{display:table-cell!important;} .article-section td{display:table-cell!important;} .article-section caption{caption-side:bottom;font-size:16px;margin-bottom:12px;font-style:italic;color:#808080;} .article-section th{font-weight:bold;border:1px solid #cccccc;padding:8px;} .article-section td{border:1px solid #cccccc;padding:8px;} .article-section ol{margin-bottom:12px;list-style-type:decimal;list-style-position:inside;padding-left:0;} .article-section ul{margin-bottom:12px;list-style-type:disc;list-style-position:inside;} .article-section li{list-style:inherit;font-size:16px;margin-bottom:6px;} .article-section h2{font-size:22px;font-weight:bold;text-align:left;margin-bottom:12px!important;} .article-section h3{font-size:16px;font-weight:bold;text-align:left;margin-bottom:12px;} .article-section p{font-size:16px!important;margin-bottom:12px;} .chart-wrap{width:440px;margin:24px auto;text-align:center;} .chart-wrap figcaption{font-size:14px;color:#666666;margin-top:8px;font-style:italic;} .faq-grid{display:grid;grid-template-columns:1fr 1fr;gap:14px;margin-top:18px;} .faq-item{background:#f2f6fa;border-left:5px solid #4c86a8;padding:14px 18px;border-radius:0 10px 10px 0;} .faq-item h3{margin-bottom:6px;color:#244b66;} .faq-item p{margin-bottom:0;} @media(max-width:640px){ .chart-wrap{width:100%;} .chart-wrap svg{width:100%;height:auto;} .faq-grid{grid-template-columns:1fr;} } .product-card{display:block;margin:20px 0;border:1px solid #e5e7eb;border-radius:10px;overflow:hidden;font-style:normal;background:#fff} .pc-inner{display:flex;text-decoration:none;color:inherit;align-items:center;min-height:120px} .pc-img{width:160px;min-width:160px;aspect-ratio:4/3;height:auto;min-height:120px;object-fit:cover;flex-shrink:0;display:block;align-self:stretch} .pc-body{padding:12px 16px;flex:1;min-width:0;display:flex;flex-direction:column;align-self:stretch;justify-content:center} .pc-title{display:block;font-size:15px;font-weight:600;color:#111;margin:0 0 6px;line-height:1.4} .pc-desc{display:-webkit-box;font-size:13px;color:#6b7280;margin:0 0 8px;line-height:1.5;overflow:hidden;-webkit-line-clamp:2;line-clamp:2;-webkit-box-orient:vertical} .pc-cta{display:block;font-size:13px;font-weight:600;color:#11700F;margin-top:auto} .pc-inner:hover .pc-title{text-decoration:underline} .article-section a:not(.pc-inner),article a:not(.pc-inner){color:#11700F}.pc-cta{color:#11700F!important}
You've saved up for a decent car audio upgrade, and the choice has come down to two four-channel amplifiers with nearly identical power ratings. One is a compact Class D unit. The other is a heavier Class AB design with a slightly lower price and a reputation for smooth, natural sound. Which one actually belongs in your trunk? This is one of the most common debates in car audio. Class AB amplifiers powered aftermarket systems for decades, but Class D has taken over most retail shelves in recent years. The engineering difference is real, and so are the trade-offs. This guide explains what the class label means in practical terms, what bench tests reveal about quality, and how to decide based on your speakers, your electrical system, and your listening habits. What Does "Class AB" Actually Mean in a Car Amplifier? Amplifier classes describe how the output transistors are biased and switched. In a pure Class A circuit, output devices conduct current all the time, which produces extremely linear sound but wastes most of the energy as heat. In Class B, each half of the audio waveform is handled by a separate transistor, which improves efficiency but creates crossover distortion where the two halves meet. Class AB is the middle path that became the car audio standard. A small idle bias keeps both output transistors slightly on around the zero-crossing point, so music at low and moderate levels is reproduced in a nearly Class A fashion. Vocals sound present, cymbals stay clean, and the transition between waveform halves does not add an audible notch. This is the technical reason behind the "warmth" so often attributed to Class AB. Power Supply Signal Input Bias & Driver Class AB Output To Speaker In a typical automotive Class AB amplifier, the signal path runs through an input buffer, a voltage amplifier, and a biased output stage before reaching the speaker. The power supply must keep the rail voltages clean under dynamic load, which is why good Class AB designs use either a generously sized linear transformer or a well-regulated switching supply. Class AB vs. Class D: Reading the Trade-Offs Correctly Class D amplifiers switch their output transistors on and off at frequencies above 100 kHz, then filter the result to recover the audio signal. The switching approach cuts power loss dramatically, which is why Class D amps are smaller, cooler, and easier on the alternator. The catch is that sound quality depends heavily on the quality of the filter, the feedback loop, and the power supply. A cheap Class D amp can sound harsh; a well-designed one can be nearly transparent. The numbers are typical values from manufacturer specifications and independent bench measurements. Actual performance varies with supply voltage and load impedance. Parameter Class AB Class D Typical efficiency 50–65% 75–90% Idle current draw Higher, continuous bias Much lower Heat output High Low Sound character Warm, natural midrange Transparent if well filtered Size and weight Larger, heavier Compact, lightweight Best use Component speakers, full range Subwoofers, tight installs The table is a starting point, not a verdict. A premium Class D amplifier with a clean output filter and robust power supply can measure better than a budget Class AB in distortion and noise. What Class AB gives you is a predictable, musically linear output stage that is hard to get badly wrong. What Bench Tests Reveal About Sound Quality An independent bench comparison published by BestCarAudio showed the efficiency gap in practice. The entry-level Class AB amp in that test drew just over 105 amperes and produced 793 watts during the dynamic power run. The premium Class D amplifier it was paired against produced about 80% more power with the same current draw, because it converted far less input energy into heat. Typical Efficiency at Moderate Output 0 25% 50% 75% 100% Class A ~25% Class AB ~55% Class D ~80% Representative values, not measurements of a particular model. The efficiency difference is not just a laboratory curiosity. The heat generated by a Class AB amp has to go somewhere: into the heatsink, the air behind a dashboard, or the interior of a sealed enclosure. This is what installers mean when they call Class AB "current hungry." Sound quality benefits are real, but they carry an electrical and thermal price. Total harmonic distortion (THD) and signal-to-noise ratio (SNR) also matter when you compare amplifiers. A well-executed Class AB amp commonly measures below 0.05% THD at moderate output. Budget Class D units sometimes show higher distortion at low levels because of switching noise. Take a familiar music track to your local shop and listen before you buy. Installation Realities: Heat, Fuses, and Wire Gauge Sizing the electrical path is part of any Class AB installation. At full output, a 400W RMS amp draws roughly 53A from a 13.8V system (about 400W divided by 13.8V and the 0.55–0.65 efficiency range). Under heavy bass, that load is sustained, not momentary. Use wiring and fuses rated for continuous operation. Recommendations assume a 13.8V electrical system and premium copper cable. Use the next heavier gauge if the cable run exceeds 5 meters. System RMS Power Class AB Current Draw Fuse Rating Wire Gauge 200W ≈27A 30A 8 AWG 400W ≈53A 60A 4 AWG 800W ≈105A 110A 2 AWG Treat the table as a floor, not a ceiling. In hot climates or enclosed trunks, a 12V cooling fan is an inexpensive upgrade for anything above 400W. The heatsink fin area of a Class AB amp should always be mounted with open airflow; never trap it against carpet or trim. Module-Level Options for Builders, Repair Shops, and OEM Integrators Custom fabrication shops, OEM audio brands, and technicians who rebuild factory sound systems often start with amplifier modules instead of finished chassis amps. A module provides a tested circuit layout, a mechanical footprint, and a documented power rating so you can design an enclosure around it. This shortens development time and reduces component-level debugging. For example, the amp300h-7294 module uses a Bi-Class H output stage and a linear transformer power supply. Its bias behavior resembles a Class AB amplifier, while the switched rail keeps heat production below a conventional AB design. That makes it a practical starting point when you need roughly 300W of low-frequency plus 50W of high-frequency output. When the build demands more headroom, a 400W plus 100W module with a U-shaped aluminum heat sink demonstrates how thermal design is solved at the board level. The radiator on the amp400h-7294 is already sized for sustained operation, so you do not have to guess at heatsink volume or airflow. AMP400H+7294 Class H Power Amplifier Module with U-shaped Aluminum RadiatorThis module combines a 400W Class H bass section with a 100W Class AB high-frequency stage, featuring a U-shaped heatsink and built-in protections for reliable, sustained car audio performance.View Product → Module-level sourcing is common because it shortens the path to production. Car audio builds that emphasize deep bass often combine a full-range module for the mid and treble channels with a dedicated subwoofer amplifier stage, which reduces development work and keeps the final assembly compact. Class AB Car Amplifier FAQ Is a Class AB amplifier good for car audio? Yes, especially for full-range speakers. The linear bias keeps vocals and instruments natural, and the midrange often feels more present than on an equal-cost Class D design. Just budget for the extra current draw and heat dissipation. What is the difference between Class AB and Class D car amplifiers? Class AB uses a biased linear output stage, which sounds smooth but generates heat. Class D switches its output transistors on and off and filters the result, which is more efficient and compact. Sound quality in both depends heavily on build quality and the power supply. Do Class AB amplifiers sound better than Class D? Most listeners find entry-level and mid-priced Class AB amplifiers sound warmer and less fatiguing than budget Class D designs. At the premium end, the gap narrows sharply, and many people cannot consistently tell them apart in blind listening tests. Can you use a Class AB amplifier for a subwoofer? Yes. Class AB bass tends to be tight and well controlled, and many subwoofer amplifiers still use a Class AB output stage. For custom builds, a dedicated subwoofer amplifier module is a good option when space is flexible. How many watts RMS do I need for a Class AB car amplifier? For component speakers, 50 to 100 watts RMS per channel is common. For subwoofers, plan on 300 to 600 watts RMS if your alternator can sustain it. Use RMS power at 4 ohms as the reference, because max power numbers are largely meaningless. Do Class AB amplifiers draw more current at idle? Yes. The bias current runs whenever the amp is on, typically 1 to 3 amperes depending on the design. Class D amplifiers idle at a fraction of that. If you leave the stereo playing with the engine off, battery drain will be noticeable. .article-section table{display:table!important;border-collapse:collapse;margin:0 auto 20px;} .article-section thead{display:table-header-group!important;} .article-section tbody{display:table-row-group!important;} .article-section tr{display:table-row!important;} .article-section th{display:table-cell!important;font-weight:bold;border:1px solid #cccccc;padding:8px;} .article-section td{display:table-cell!important;border:1px solid #cccccc;padding:8px;} .article-section table caption{caption-side:bottom;font-size:16px;margin-bottom:12px;font-style:italic;color:#808080;padding-top:8px;} .article-section ol{margin-bottom:12px;list-style-type:decimal;list-style-position:inside;padding-left:0;} .article-section ul{margin-bottom:12px;list-style-type:disc;list-style-position:inside;} .article-section li{list-style:inherit;font-size:16px;margin-bottom:6px;} .article-section h2{font-size:22px;font-weight:bold;text-align:left;margin-bottom:12px!important;} .article-section h3{font-size:16px;font-weight:bold;text-align:left;margin-bottom:12px;} .article-section p{font-size:16px!important;margin-bottom:12px;} .chart-container{width:440px;margin:24px auto;text-align:center;} .chart-container svg{width:440px;height:auto;display:block;margin:0 auto;} @media(max-width:640px){.chart-container{width:100%;}.chart-container svg{width:100%;height:auto;}} .faq-grid{display:grid;grid-template-columns:1fr 1fr;gap:16px;margin:20px 0 12px;} .faq-item{background:#f4f8fd;border-left:4px solid #2b6cb0;border-radius:0 8px 8px 0;padding:14px 18px;} .faq-item h3{color:#1a4a7a;margin-bottom:8px;} .faq-item p{font-size:15px!important;margin-bottom:0;} @media(max-width:640px){.faq-grid{grid-template-columns:1fr;}} .article-section a[data-product-card="true"]{display:inline-block;margin:14px 0;padding:10px 16px;background:#eef4fb;border-left:4px solid #2b6cb0;border-radius:0 6px 6px 0;font-size:15px;font-weight:600;color:#1a4a7a;text-decoration:none;} .article-section a[data-product-card="true"]::after{content:"View module details →";font-size:14px;font-weight:400;} .product-card{display:block;margin:20px 0;border:1px solid #e5e7eb;border-radius:10px;overflow:hidden;font-style:normal;background:#fff} .pc-inner{display:flex;text-decoration:none;color:inherit;align-items:center;min-height:120px} .pc-img{width:160px;min-width:160px;aspect-ratio:4/3;height:auto;min-height:120px;object-fit:cover;flex-shrink:0;display:block;align-self:stretch} .pc-body{padding:12px 16px;flex:1;min-width:0;display:flex;flex-direction:column;align-self:stretch;justify-content:center} .pc-title{display:block;font-size:15px;font-weight:600;color:#111;margin:0 0 6px;line-height:1.4} .pc-desc{display:-webkit-box;font-size:13px;color:#6b7280;margin:0 0 8px;line-height:1.5;overflow:hidden;-webkit-line-clamp:2;line-clamp:2;-webkit-box-orient:vertical} .pc-cta{display:block;font-size:13px;font-weight:600;color:#11700F;margin-top:auto} .pc-inner:hover .pc-title{text-decoration:underline} .article-section a:not(.pc-inner),article a:not(.pc-inner){color:#11700F}.pc-cta{color:#11700F!important}
When a powered speaker manufacturer evaluates amplifier platforms, every option carries a trade-off. Class AB is proven but runs hot, Class D is efficient but introduces switching artifacts, and Class H tends to sit between the two. Its engineering logic is simple: make the power supply follow the audio signal, so the output stage never wastes large amounts of voltage as heat. Class H amplifiers deliver analog sound quality with higher efficiency, and they remain a well-established option in professional audio module catalogs. This guide explains how Class H works, what efficiency you can expect, and how to evaluate Class H amplifier modules for OEM speaker and subwoofer designs. What Is a Class H Amplifier? A Class H amplifier is an analog power amplifier with a modulated power supply rail. In a conventional Class AB amplifier, the supply voltage stays fixed while the audio signal fluctuates, so the output transistors continuously dissipate the excess voltage as heat. In a Class H amplifier, a tracking circuit raises and lowers the supply rail so that it stays just above the level of the audio signal. This technique is commonly called rail tracking. When the music is quiet, the rail voltage drops; when a transient or kick drum hit arrives, the rail voltage rises to give the output stage enough headroom. The result is lower heat generation and better overall efficiency than fixed-rail analog designs. Design discussions among audio engineers often cite current savings of roughly 20-30% at typical music levels compared with a fixed-rail Class AB amplifier. According to the widely cited Wikipedia article on power amplifier classes, Class H differs from Class G in that the supply rail varies continuously rather than in discrete steps in response to the input. For a manufacturer, this same architecture is available as a building block: an active power amplifier module integrates the preamp, tracking controller, and output stage on one board, so you can adopt Class H performance without designing a tracking supply from scratch. A module such as the Amp300H-7294, for example, delivers 300 W low-frequency plus 50 W high-frequency output from a linear transformer supply for bi-amped speaker systems. Efficiency at a Glance: How Class H Compares Efficiency figures depend on load, signal content, and circuit design. Audio engineering references typically cite the following ranges at continuous high-level output: Class A ~25% Class AB ~55% Class H ~75% Class D ~88% Typical efficiency (percent) Class A dissipates the most energy because its output devices always conduct fully. Class AB improves on that but still burns significant heat at idle and at partial output. Class H reduces this dissipation by following the signal envelope, while Class D reaches the highest efficiency by switching its output stage at high frequency. General characteristics of the main amplifier classes relevant to professional audio design. Class Typical efficiency Supply rail Output stage Heat management Class A 20-30% Fixed Linear, always conducting Large heat sinks required Class AB 50-65% Fixed Linear Moderate heat sinks Class H 70-80% Tracking Linear Small-to-moderate heat sinks Class D 85-90% Switched Switching Minimal, but output filtering required How the Tracking Supply Rail Works The diagram below illustrates the key behavior. The central signal is a sine wave; the dashed lines above and below are the positive and negative supply rails. The positive rail rises only during the positive half of the signal, and the negative rail deepens only during the negative half. headroom Output signal Tracking +V rail Tracking -V rail Class H rails stay close to the signal, so the output stage dissipates little excess heat. 0V The tracking controller performs this modulation continuously. It monitors the input signal, predicts the required headroom, and drives an active regulation stage that feeds the output transistors. In practical module designs with a linear transformer power supply, the controller adjusts the rail so that the output stage always sees the minimum sufficient supply voltage. The input preamp conditions the audio signal and sends it to the tracking controller. The controller compares the instantaneous output envelope with the current rail voltage. The supply regulation stage raises or lowers the rail within microseconds, keeping a small margin above the signal peak. The output transistors amplify the signal using a rail that is just high enough, converting far less excess power into heat. Strengths and Trade-Offs of Class H What Class H does well Higher efficiency than Class AB at music duty cycles, with less heat sink burden Clean analog output with no switching noise or high-frequency artifacts Lower idle power consumption benefits thermally constrained or battery-powered products Peak headroom remains available for transients because the rail can rise quickly Where Class H makes you pay More complex power supply stage increases module cost relative to Class AB Tracking controller must be stabilized carefully to avoid distortion on fast transients Efficiency still falls short of Class D at sustained full power Linear transformer supplies add weight compared with compact switching supplies Design discussions among audio engineers note that Class H never became the dominant topology in consumer hi-fi, largely because the added cost and complexity of rail tracking were hard to justify for low-power, single-voltage applications. In professional speaker products, however, the efficiency and heat benefits matter much more, and module-based Class H designs sidestep much of the complexity concern. What to Check When Choosing a Class H Power Amplifier Module Not every Class H module behaves the same way. These points separate a rugged professional module from a board that will create problems in the field: Rated power and impedance: confirm the LP and HP power ratings and the nominal load impedance, such as 400 W and 100 W into 8 ohms. Supply topology: linear transformer supplies provide robust transient current and low noise, while switching supplies reduce weight and cost. Heat sink design: a large U-shaped aluminum radiator improves long-term reliability at high output levels. Protection circuits: look for overload, short-circuit, and over-temperature protection built into the module. Customization: if you are an OEM, check whether the manufacturer will adjust EQ presets, input sensitivity, or connector layouts. Manufacturing quality: SMT assembly, automated testing, and consistent component sourcing are essential for repeatable module performance. Linear transformer U-shaped aluminum heat sink Rail tracking control board Base PCB with output stage Isometric view: major building blocks of a compact Class H amplifier module. An example in this category is the Amp400H-7294, which delivers 400 W low-frequency plus 100 W high-frequency output with a U-shaped aluminum radiator and a linear transformer power supply. It is designed for OEMs who need dependable headroom in a compact module footprint. AMP400H+7294 Class H Amplifier Module with 400W LF and 100W HF OutputThis compact Class H module offers 400W low-frequency and 100W high-frequency power with a linear transformer supply and U-shaped aluminum radiator, making it a reliable choice for powered speakers requiring headroom.View Product → Where Class H Fits in Professional Audio Class H modules are most useful in powered speakers that play material with a high crest factor: short peaks above a relatively modest average level. This includes PA monitors, column speakers, line-array cabinets, and especially subwoofers. Subwoofers: bass transients demand sudden current, and the tracking rail supplies exactly the headroom needed without idling at the full supply voltage. Line arrays: amplifier modules are installed inside sealed cabinets where heat is difficult to remove; Class H reduces the thermal load compared with Class AB. Column speakers: compact form factors make efficient heat sink use essential, and the tracking supply helps keep the enclosure temperature manageable. For subwoofer duty, the Amp600S-FP delivers 600 W through a professional linear transformer power supply, making it a direct example of how Class H suits high-power low-frequency output. The same reasoning that makes it useful in subwoofer designs applies broadly when you evaluate how audio amplifier modules enhance sound quality in speaker systems: the amplifier must deliver clean power without overheating the cabinet. Frequently Asked Questions Is a Class H amplifier better than Class AB? Class H is more efficient than Class AB because the supply rail tracks the signal, which reduces heat at typical music levels while keeping an analog output character. Class AB remains simpler and less expensive for low-power, fixed-level applications. What is the efficiency of a Class H amplifier? Typical efficiency is around 70-80% at high output levels, depending on design and load. That is higher than Class AB at 50-65% but lower than Class D at 85-90%. Is a Class H amplifier good for speakers? Yes. Class H works well in powered speakers, column speakers, and subwoofers because it reduces heat and idle power loss while producing clean analog output without switching artifacts. What is the difference between Class D and Class H amplifier? Class D switches the output stage on and off for very high efficiency and needs output filtering. Class H keeps a linear output stage but modulates its supply voltage; it uses more current than Class D but is easier to integrate for clean analog performance. Does a Class H amplifier sound good? Class H can sound very good in practice. The output stage is linear, and the tracking supply preserves transient headroom, so the sonic character is close to a well-designed Class AB amp without the heat burden. Why use a Class H amplifier in a subwoofer? Bass content has a high crest factor: short peaks above a modest average level. Class H delivers the headroom when the peaks arrive and lowers the rail in between, which minimizes heat and power loss exactly where it matters most. .article-section{line-height:1.6!important;} .article-section table{display:table!important;border-collapse:collapse;} .article-section thead{display:table-header-group!important;} .article-section tbody{display:table-row-group!important;} .article-section tr{display:table-row!important;} .article-section th{display:table-cell!important;} .article-section td{display:table-cell!important;} .article-section table{caption-side:bottom;font-size:16px;margin-bottom:12px;font-style:italic;color:#808080;} .article-section th{font-weight:bold;border:1px solid #cccccc;padding:8px;} .article-section td{border:1px solid #cccccc;padding:8px;} .article-section ol{margin-bottom:12px;list-style-type:decimal;list-style-position:inside;padding-left:0;} .article-section ul{margin-bottom:12px;list-style-type:disc;list-style-position:inside;} .article-section li{list-style:inherit;font-size:16px;margin-bottom:6px;} .article-section h2{font-size:22px;font-weight:bold;text-align:left;margin-bottom:12px!important;} .article-section h3{font-size:16px;font-weight:bold;text-align:left;margin-bottom:12px;} .article-section p{font-size:16px!important;margin-bottom:12px;} .article-section svg{width:440px;height:auto;display:block;margin:16px auto;} .article-section .chart-caption{text-align:center;font-size:14px!important;color:#888;font-style:italic;margin-top:-8px;} .article-section .intro-block{background:#f7fafd;border-left:5px solid #2980b9;padding:22px 24px;border-radius:6px;} .article-section .efficiency-block{background:#fafbfc;padding:22px;border-radius:8px;border:1px solid #eee;} .article-section .sc-columns{display:flex;gap:20px;margin:14px 0;} .article-section .sc-col{flex:1;background:#f4faf4;border:1px solid #cfe8cf;border-radius:8px;padding:14px 16px;} .article-section .sc-col:last-child{background:#fdf3f3;border-color:#eec9c9;} .article-section .faq-grid{display:grid;grid-template-columns:1fr 1fr;gap:16px;margin:16px 0;} .article-section .faq-card{background:#f0f7ff;border:1px solid #cfe2f3;border-left:5px solid #2e86c1;border-radius:10px;padding:14px 16px;} .article-section .faq-card h3{color:#1a5276;} .article-section .faq-card p{margin-bottom:0;color:#2c3e50;} @media(max-width:640px){ .article-section svg{width:100%;} .article-section .sc-columns{flex-direction:column;} .article-section .faq-grid{grid-template-columns:1fr;} } .product-card{display:block;margin:20px 0;border:1px solid #e5e7eb;border-radius:10px;overflow:hidden;font-style:normal;background:#fff} .pc-inner{display:flex;text-decoration:none;color:inherit;align-items:center;min-height:120px} .pc-img{width:160px;min-width:160px;aspect-ratio:4/3;height:auto;min-height:120px;object-fit:cover;flex-shrink:0;display:block;align-self:stretch} .pc-body{padding:12px 16px;flex:1;min-width:0;display:flex;flex-direction:column;align-self:stretch;justify-content:center} .pc-title{display:block;font-size:15px;font-weight:600;color:#111;margin:0 0 6px;line-height:1.4} .pc-desc{display:-webkit-box;font-size:13px;color:#6b7280;margin:0 0 8px;line-height:1.5;overflow:hidden;-webkit-line-clamp:2;line-clamp:2;-webkit-box-orient:vertical} .pc-cta{display:block;font-size:13px;font-weight:600;color:#11700F;margin-top:auto} .pc-inner:hover .pc-title{text-decoration:underline} .article-section a:not(.pc-inner),article a:not(.pc-inner){color:#11700F}.pc-cta{color:#11700F!important}
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