Class D Amplifiers Explained: Efficiency, Sound Quality and How to Choose

Class D amplifiers have quietly taken over audio. Walk the floor of IFA Berlin 2026 and you will see desktop Class D everywhere; open any modern all-in-one streamer or soundbar and there is a switching stage inside. Yet confusion about them persists: Are they “digital”? Are they really more efficient? Do they sound as good as a Class AB amp? This guide explains how Class D works, where the genuine trade-offs are, and how to choose one — using the TRASAM M7 desktop amplifiers as measured, real-world examples.

What is a Class D amplifier?

Despite the name, a Class D amplifier is not a “digital” amplifier in the signal sense. Its output transistors are used as switches that turn fully on and fully off many hundreds of thousands of times per second, producing a high-frequency pulse-width-modulated (PWM) square wave. An output low-pass filter (inductor + capacitor) then reconstructs the smooth analog audio signal before it reaches the speakers.

Because the transistors dissipate almost no power in the on/off states, efficiency is radically higher than linear designs — that single fact explains most of Class D’s conquest of compact and desktop audio.

Efficiency and heat: why Class D owns the desktop

Concretely: the TRASAM M7BT and M7PLUS deliver 115W×2 (8Ω rated, 150W×2 peak) from a 48V DC supply inside a roughly 136mm-wide chassis with no fan at all. A Class AB amp of similar power would need a large toroidal transformer and a chassis several times bigger. If your listening space is a desk, a shelf or a bedroom, Class D is not a compromise — it is the only sane way to get real power there.

“Old” Class D vs “modern” Class D: what actually changed

Early switching amplifiers deserved their bad reputation: the output filter interacted with the speaker’s impedance and caused the frequency response to rise in the high treble, distortion climbed at high frequencies, and performance sagged as the supply voltage drooped under load. Modern designs fix those specific problems rather than “magically” sounding warmer.

So “modern Class D” is really a different product category from the cheap switching amps of two decades ago. What you should look for on a spec sheet is not just watts, but: post-filter feedback (PFFB), regulated supply stages, flat frequency response, noise floor and damping factor.

Sound quality: Class D vs Class AB

One thing Class D will never do is fake headroom with huge idle power. If your room is large, your speakers are big floorstanders, and you listen loud from several meters away, a full-size Class AB (or a very powerful Class D) with genuine current reserves is the honest recommendation.

How to choose: who should buy Class D

Worked example: the TRASAM M7 series

The M7 series shows how far desktop Class D has come. Both models use the TI TPA3255 with second-generation PFFB and regulated linear power stages, and share the same 48V power platform: 115W×2 (8Ω rated), 150W×2 peak. (A 36V version delivers ~55W×2 — fine for nearfield, but 48V is where the headroom lives.)

Rule of thumb for the pair: if you already own a DAC or player and want to grow an analog system (or add a subwoofer later), M7BT with its LINE OUT is the one. If your sources are digital — PC, TV, console — and you also want headphones at night, M7PLUS is the single-box answer.

2026 market context

Class D is now the default engine of consumer audio, not an experiment. At IFA Berlin (4–8 September 2026) the desktop wave was impossible to miss — Fosi ZH1 (ES9039Q2M, 2000 mW balanced, US$149.99), SMSL D100 (US$139) and Topping DX1 II (£119) all cram serious measured performance into pocket-size enclosures, while Yamaha’s compact WXA-70A uses an ICEpower Class D stage and Onkyo’s 80th-anniversary MUSE Y-50 puts out 250W of Class D in a lifestyle chassis. The trend is the same everywhere: heat-constrained, space-constrained products need switching amplification. Class D won efficiency; the remaining contest — flat response, low noise, good damping — is decided by engineering, which is exactly where modern designs like the M7 series spend their effort.

Frequently asked questions

Bottom line

Class D won on efficiency and size; modern engineering has closed most of the sound-quality gap, and in the desktop category Class D is simply the right tool. Buy on measured evidence — flat response, low noise floor, good damping, clean power — and choose the input/feature set that matches your sources. The TRASAM M7BT (analog, LINE OUT expansion) and M7PLUS (digital inputs, DAC, headphone out) are two concrete examples of what a well-executed 2026 desktop Class D amplifier looks like.