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Audio Files: Class D Amps

Tiny, super-affordable amplifiers are bringing jazz fans good sound at shockingly low prices

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Lepai LP-2020TI
Lepai LP-2020TI

Traditional stereo systems sound better than wireless all-in-one speakers like Sonos, but they’ve largely fallen out of favor—no surprise when you can get a good wireless speaker for less than $200. Audio enthusiasts craving higher fidelity are embracing an even more affordable option, though: recently developed amplifier technology that makes it easy to put together a nice stereo system for around $100.

The technology is called Class D amplification, sometimes referred to as “digital” amplification. It debuted about 20 years ago, and has become the norm in inexpensive audio gear. In a conventional amp, the transistors that power your speakers always run somewhere between on and off, and any energy they’re not using is converted to heat, which has to be removed by fans or large aluminum heat sinks. In a Class D amp, the audio is converted to radio frequencies, which allows the transistors to always run either fully on or fully off, so there’s no waste heat produced. At the output of the amp, a filter eliminates the radio frequencies and leaves the amplified audio signal.

A Class D amp consumes less power and produces almost no heat, so it can be much smaller. About 95 percent of the energy that goes into a Class D amp (from an AC power supply or batteries) makes it into your speakers; with a conventional Class AB amp, about 50 percent of the energy is wasted as heat. Because a Class D amp can use a smaller power supply, fewer transistors and no heat sink, it can shrink to the size of a paperback book.

Or even smaller. In the Bitches Brew era, a 50-watt-per-channel stereo amp would have been about the size of a large shoebox. The Class D amp currently powering my desktop system delivers comparable power, but is no larger than a box of saxophone reeds.

By pairing these mini-amps with inexpensive speakers from such companies as ELAC, Pioneer, and Polk, audio enthusiasts are creating stereo systems that cost about the same as all-in-one wireless speakers but sound much better. And by adding inexpensive accessories such as the Amazon Echo Flex, they can have all the convenience and extensive media access that smartspeakers deliver.

Topping MX3
Topping MX3

The Players

Mini-amps have a sort of underground vibe, in part because they carry relatively unfamiliar brand names such as Dayton Audio, Lepai, SMSL, and Topping. They’re not available at mainstream outlets like Best Buy—you’ll find them mainly on Amazon and the Parts Express website. The quality and features vary a lot, and the published power ratings can be misleading. Some have only an analog audio input, some add Bluetooth, and some have digital inputs so they also work as digital-to-analog converters.

In much the same way Coleman Hawkins turned people on to what could be done with a tenor sax, the Lepai LP-2020 hipped people to how good a cheap, tiny amp can be. The LP-2020 puts out a rated 20 watts per channel from a chassis measuring less than six inches wide. It has bass and treble controls with an analog input that’ll work with a computer or tablet, a smartphone that has a headphone jack, a Bluetooth receiver, or many Amazon Echo devices. The latest version is available from Parts Express as the LP-2020TI, and it costs about $25. It’s a fairly cheesy-looking component, and the actual amount of power you get will depend on the power supply you use with it, but it’s enough to power most speakers to reasonably loud levels.

Learn more about the Lepai LP-2020 at Amazon!

On the opposite end of the trend is the Topping MX3, which runs about $130 and looks like a miniature version of a high-end preamplifier. It’s just a little larger than the LP-2020TI but is rated at 40 watts per channel, and includes all of the LP-2020TI’s features plus Bluetooth, digital inputs, a headphone jack, and a subwoofer output.

Learn more about the Topping MX3 at Amazon!

The Facmogu F900—the amp I’m using with my desktop system—is the mini-est of mini-amps, measuring just three inches wide and costing about $32. It looks like a cigarette pack made from anodized aluminum and fitted with a volume knob and speaker connectors. The F900 has an analog input, but I mostly play music from my phone through its Bluetooth connection. I can’t say the F900 has the power, punch, or clarity of a high-quality conventional amp, but it gets the job done for casual listening even when I connect it to my ultra-revealing, $3,500-per-pair reference speakers.

Learn more about the Facmogu F900 at Amazon!

I doubt we’ll see these mini-amps replacing such storied high-end brands as McIntosh or Parasound. But as the basis of a desktop, bedroom, garage, or dorm room system paired with, say, Pioneer SP-BS22 or Dayton Audio B652 bookshelf speakers, they’re a great way to get real stereo sound into places where you might be tempted to settle for an all-in-one wireless speaker.

Facmogu F900
Facmogu F900

Brent Butterworth

Brent Butterworth has been a professional audio journalist since 1989, and has evaluated and measured thousands of audio products. He is currently a writer at Wirecutter and editor of the SoundStage Solo headphone site; served as an editor at such magazines as Sound & Vision and Home Theater; and worked as marketing director for Dolby Laboratories. He also plays double bass with several jazz groups in Los Angeles.