Class-D amplifier
Class-D is a switching amplifier topology that turns transistors fully on and off at very high frequency, rather than partially conducting like Class-A or A/B. Result: 90%+ efficiency, cool running, small size, and (in modern designs) audiophile-grade sound quality.
Class-D refers to the amplifier topology, not a quality grade. The “D” is just the next letter after Class A, B, C. In Class-D, transistors switch fully on and off at very high frequency (typically 400+ kHz) rather than partially conducting. The output is then filtered back into a smooth analog waveform.
Advantages
- Efficiency 90%+ — vs. ~50% for Class-AB and ~25% for Class-A. Less heat, smaller heatsinks, smaller chassis.
- Cool running — you can put a Class-D amp in a small enclosed space without worrying about thermal shutdown.
- Powerful for size — 150W per channel from a shoebox-sized chassis.
Historical reputation
Early Class-D (2000s-early 2010s) had audible distortion at high frequencies and load-dependent behavior. This gave Class-D a “harsh, digital” reputation among audiophiles. That reputation is now obsolete. Modern chips like the TPA3255 with proper PFFB implementation measure and sound as clean as any Class-AB design at reasonable listening levels.
When Class-D might not be ideal
For extremely low-impedance loads (below 2Ω) or ultra-loud listening on very inefficient speakers (Magnepan, some electrostatic panels), traditional Class-AB or Class-A designs can still have an edge. For 95% of budget audiophile use cases, Class-D is the smart choice.
Common myths & realities
Class-D sounds harsh and digital
The 2010 stereotype. Modern TPA3255 + PFFB designs measure and sound clean.
Class-D is only for cheap amps
High-end brands (Purifi, Hypex NCore, ICEpower) use Class-D at the reference tier.
Ready to see this in action?
Browse honest, hands-on reviews of budget hi-fi gear that puts these concepts to the test.
