Complete Guide to Amplifier Classes

Understanding the differences between Class A, A/B, and D amplifiers

Choosing the right amplifier is essential for achieving optimal sound quality in your audio system. This comprehensive guide will help you understand the key differences between amplifier classes.

Detailed Comparison

A

Class A

Class A amplifiers represent the pinnacle of audio purity, operating with output devices conducting throughout the entire signal cycle. This continuous operation eliminates crossover distortion entirely.
Sound Characteristics
Exceptional warmth, linearity, and the lowest distortion levels. Renowned for natural, uncolored sound reproduction.
Technical Operation
Output transistors remain fully conducting at all times, drawing constant current regardless of signal level.
Ideal Applications
High-end audiophile systems, critical listening environments where sound quality is paramount.
Efficiency 20-30%
Distortion < 0.01% THD
Heat Output Very High
Price Range £2,000 - £20,000+
Advantages
  • Absolute lowest distortion and purest sound quality
  • No crossover distortion whatsoever
  • Exceptional detail retrieval and musicality
Considerations
  • Very low efficiency means high electricity costs
  • Generates substantial heat requiring ventilation
  • Premium pricing and typically large, heavy units
A/B

Class A/B

Class A/B amplifiers combine the best aspects of Class A and Class B designs, operating in Class A mode at low levels and switching to Class B for higher power demands.
Sound Characteristics
Excellent balance of clarity, warmth, and dynamics. Very close to Class A performance with improved efficiency.
Technical Operation
Operates in Class A at low power, transitioning to Class B for higher output, minimizing crossover distortion.
Ideal Applications
Home hi-fi systems and general high-quality audio reproduction.
Efficiency 50-70%
Distortion < 0.05% THD
Heat Output Moderate
Price Range £500 - £10,000
Advantages
  • Excellent sound quality approaching Class A
  • Much better efficiency than Class A
  • Industry standard with proven reliability
Considerations
  • Still generates noticeable heat during operation
  • Slight crossover distortion at transition point
  • Heavier and larger than Class D alternatives
D

Class D

Class D amplifiers use pulse-width modulation and switching technology to achieve exceptional efficiency. Modern designs have overcome early limitations to deliver impressive sound quality.
Sound Characteristics
Clean, accurate, and detailed. Premium Class D designs now rival traditional amplifiers in sonic performance.
Technical Operation
Switching amplification using PWM technology, operating transistors as switches rather than linear devices.
Ideal Applications
Active / Powered speakers, Active Subwoofers, compact systems, Modern Amplifiers and modern high-power applications.
Efficiency 85-95%
Distortion < 0.1% THD
Heat Output Very Low
Price Range £200 - £5,000
Advantages
  • Exceptional efficiency reduces power consumption
  • Compact, lightweight design ideal for modern systems
  • Minimal heat generation, no large heatsinks needed
Considerations
  • Some designs may exhibit high-frequency artifacts
  • Quality varies significantly between implementations
  • May require careful speaker cable selection

Side-by-Side Comparison

Feature Class A Class A/B Class D
Sound Quality
Efficiency 20-30% 50-70% 85-95%
Power Consumption Very High Moderate Low
Heat Generation Significant Moderate Minimal
Size & Weight Large & Heavy Medium Compact & Light
Typical Price Premium Mid to High Affordable to Mid
Crossover Distortion None Minimal None
Best Use Case Critical Listening General Hi-Fi Modern Systems

Expert Buying Tips

Match to Your Speakers
Consider your speaker's sensitivity and impedance. High-efficiency speakers pair well with lower-powered Class A amps, while demanding speakers may benefit from Class A/B or D.
Consider Your Room
Class A amplifiers generate significant heat. Ensure adequate ventilation and space. Smaller rooms may benefit from the cooler operation of Class D.
Listen Before Buying
Whenever possible, audition amplifiers with your own speakers and music. The differences between classes can be subtle but significant to your ears.
Budget Wisely
A well-designed Class A/B or Class D amplifier often outperforms a budget Class A. Focus on overall quality and implementation rather than class alone.