Class G Amplifiers

What Is a Class G Amplifier?

Class G amplifiers were developed to improve the efficiency of traditional Class AB designs without sacrificing their sound quality. Instead of operating from a single fixed power supply voltage, Class G amplifiers use multiple power supply rails.​
At low listening levels, the amplifier runs from a lower voltage supply, reducing wasted energy. When the music demands more power, it automatically switches to higher voltage rails.​
This approach significantly reduces heat while preserving the linear operation of the output stage.​

How Class G Works
A conventional Class AB amplifier always operates from its maximum supply voltage, even during quiet passages. Most of this energy is converted into heat.​
A Class G amplifier monitors the output signal continuously.​
• Low-level signals use the low-voltage rails.​
• Loud musical peaks activate higher-voltage rails.​
• Switching occurs automatically within microseconds.​
The listener experiences the same musical performance while the amplifier operates far more efficiently.​

Advantages
• Higher efficiency than Class AB​
• Lower operating temperature​
• Reduced electricity consumption​
• Excellent sound quality​
• Ideal for powerful integrated amplifiers​

Disadvantages
• More complex circuitry​
• Higher manufacturing cost​
• Sophisticated power supply required​

Typical Applications
Class G amplifiers are commonly found in:​
• Premium Hi-Fi amplifiers​
• High-power integrated amplifiers​
• Home theatre receivers​
• Professional monitoring systems​

Examples of Class G Amplifiers
• Arcam A49​
• Arcam FMJ A39​
• Arcam AVR550​
• Arcam AVR850​
• NAD M22​
• Cambridge Audio Edge W (hybrid implementation)​

Class H Amplifiers
What Is a Class H Amplifier?
Class H is closely related to Class G but goes one step further.​
Instead of switching between several fixed voltage rails, the power supply continuously adjusts its output voltage to match the incoming audio signal.​
The amplifier receives only the voltage it actually needs at any given moment.​

How Class H Works
A tracking power supply follows the music signal in real time.​
As the output voltage rises, the power supply increases accordingly.​
As the signal decreases, the supply voltage drops.​
This dramatically reduces wasted energy while maintaining the excellent linearity of the output stage.​

Advantages
• Excellent efficiency​
• Lower heat generation​
• High output power​
• Reduced weight​
• Reliable operation​

Disadvantages
• Complex power supply​
• Higher design cost​
• Mainly used in larger amplifiers​

Typical Applications
Class H amplifiers are widely used in:​
• Concert amplifiers​
• Touring sound systems​
• Installed PA systems​
• Cinema amplifiers​
• High-power subwoofer amplifiers​

Examples
• Crown XLS Series​
• QSC GX Series​
• Behringer NX Series​
• Lab Gruppen FP Series​
• Peavey IPR Series​

Class T Amplifiers
What Is a Class T Amplifier?
Class T is a proprietary amplifier technology originally developed by Tripath Technology.​
Although often presented as a separate amplifier class, it is essentially an advanced form of Class D with sophisticated digital control algorithms that improve switching accuracy and reduce distortion.​
Tripath amplifiers gained a loyal following because they delivered impressive sound quality from remarkably small and affordable products.​

Advantages
• High efficiency​
• Compact size​
• Excellent value​
• Surprisingly refined sound​

Disadvantages
• Proprietary technology​
• Limited availability​
• Tripath ceased operations, reducing long-term support​

Famous Examples
• Sonic Impact T-Amp​
• Trends Audio TA-10​
• KingRex T20​
• Audioengine N22 (early versions)​

Class I Amplifiers
What Is a Class I Amplifier?
Class I amplifiers are designed primarily for professional audio applications.​
The output stage uses complementary switching techniques to achieve very high efficiency while maintaining low distortion at high power levels.​
These amplifiers are commonly found in touring systems and large venue installations.​

Advantages
• Very high efficiency​
• High output power​
• Excellent reliability​
• Low operating temperatures​

Applications
• Stadium sound systems​
• Concert touring​
• Permanent installations​
• Professional cinema​

Examples
• Lab Gruppen PLM Series​
• Lab Gruppen IPD Series​
• Selected professional ICEpower-based amplifiers​

Modern Class D Technologies
The latest generation of Class D amplifiers has evolved far beyond early switching designs. Several innovative technologies now dominate the high-performance audio market.​

Hypex UcD
Developed in the Netherlands, Universal Class D (UcD) introduced self-oscillating feedback, providing excellent stability and low distortion.​
Advantages
• Low distortion​
• Excellent damping factor​
• Smooth frequency response​
• Outstanding reliability​
Popular manufacturers using UcD modules include:​
• NAD​
• DIY builders​
• Boutique Hi-Fi manufacturers​

Hypex NCore
NCore represents a significant evolution of the UcD concept.​
It offers:​
• Extremely low distortion​
• Outstanding signal-to-noise ratio​
• Exceptional linearity​
• Excellent loudspeaker control​
Examples include:​
• NAD C298​
• Apollon Audio amplifiers​
• Nord Acoustics amplifiers​
• ATI power amplifiers​

Purifi Eigentakt
Purifi Eigentakt is widely regarded as one of the most advanced Class D technologies available today.​
Designed by Bruno Putzeys and his engineering team, Eigentakt dramatically reduces distortion across the entire frequency range while maintaining remarkable efficiency.​
Key Features
• Ultra-low THD​
• Extremely low IMD​
• Excellent load independence​
• Exceptional transient response​
• Near-perfect measurements​
Examples include:​
• NAD M23​
• NAD M33​
• March Audio P452​
• Apollon Purifi Series​
• Audiophonics Purifi amplifiers​
Many reviewers consider Purifi Eigentakt among the finest amplifier technologies currently available.​

ICEpower
Originally developed by Bang & Olufsen, ICEpower modules have become one of the most widely used switching amplifier platforms in the industry.​
They combine:​
• High efficiency​
• Compact design​
• Proven reliability​
• Good sound quality​
Manufacturers using ICEpower include:​
• Bang & Olufsen​
• Jeff Rowland​
• Bel Canto​
• Wyred 4 Sound​

Pascal Audio
Pascal Audio develops high-performance Class D amplifier modules primarily for professional and premium consumer applications.​
Their amplifiers are known for:​
• Exceptional dynamic capability​
• High current delivery​
• Low distortion​
• Excellent reliability​
These modules are used by several high-end loudspeaker manufacturers and professional audio brands.​

Gallium Nitride (GaN) Amplifiers
One of the biggest recent advances in amplifier technology is the adoption of Gallium Nitride (GaN) FET transistors.​
Compared with traditional silicon MOSFETs, GaN devices switch much faster and with lower losses.​
Benefits include:​
• Reduced switching distortion​
• Improved efficiency​
• Lower heat​
• Better transient response​
• Cleaner high-frequency reproduction​
Examples include:​
• Orchard Audio Starkrimson​
• AGD Productions Tempo​
• AGD Productions Audion​
• Peachtree GaN1​
• Peachtree GaN400​
Many engineers believe GaN technology represents the next major step in the evolution of high-performance Class D amplifiers.​



Why These Technologies Matter
Today's amplifier landscape is no longer defined solely by traditional amplifier classes. Advanced switching architectures, innovative feedback systems, and next-generation semiconductor materials have enabled Class D amplifiers to achieve performance levels once associated only with the finest Class A and Class AB designs.​
As a result, many of the world's leading Hi-Fi manufacturers now rely on advanced Class D platforms for flagship products, combining exceptional sound quality with outstanding efficiency, compact size, and long-term reliability.