Class AB Amplifiers

Why Class AB Is Still the SQ Default

Class AB runs two output stages that hand off between the positive and negative halves of the waveform, with a bias current holding both partially conducting at all times. That bias is the whole point: it removes the crossover distortion a pure Class B design produces at the handoff, without paying Class A's price of conducting continuously whether there is signal or not.

What it costs is efficiency. Class AB runs at roughly 50% to 65%, so a third to a half of what it draws leaves as heat. That means a bigger chassis, real ventilation, and more current from the alternator than a Class D amp of the same rated power. What it buys is the linearity that sound-quality builders keep coming back to on a front stage.

Class AB or Class D

This is not a good-versus-bad question, and anyone telling you Class D is a compromise has not listened to a modern one. They are different trades.

Plenty of good systems run both: Class AB on the front stage, Class D on the sub. See Class D amplifiers, the reference tier in Class A amplifiers, or the full amplifier lineup.

When Class AB Is the Right Call

Reference builds where Class A is impractical. Class A conducts continuously, which is why it measures the cleanest and why it needs a high-output alternator, battery capacity and dedicated cooling to live in a car. Class AB gets you linear amplification without redesigning the electrical system around it. The Audio Wave Aspire Pro USA and CR 401 Dual Mono sit at that ceiling.

Matched topology across a multi-amp system. Running one topology from front stage to sub keeps the character consistent end to end. Tru Technology is the line that makes this easy: Tungsten and Tungsten Grande both come as monoblock, 2-channel and 4-channel, so the whole rack can match.

Full-range speaker duty. A subwoofer works a narrow band. A front stage works 80Hz to 20kHz, through the midrange and treble where the ear is least forgiving. That is where topology choice actually shows up, and it is why the common SQ layout is Class AB on the components and Class D on the sub.

Competition. We judge IASCA and MECA and we compete in our own truck. The front stages that score at the top run Class AB or Class A.

Catalog by Tier

Entry Tier, $159 to $399

US Acoustics Lisa, 4-channel at 4 x 50W ($159.99). The accessible way into 4-channel Class AB, and the right answer for putting proper power on factory speakers. Wendy, 2-channel at 2 x 75W ($159.99), does the same job for a dedicated front stage. Andrea, 2-channel at 2 x 150W ($289.99), steps the per-channel power up for higher-output components. Barbara Ann, 4-channel at 4 x 100W ($399.99), handles most aftermarket component sets cleanly. See the full US Acoustics lineup.

SQ Mid-Tier, $499 to $799

Crescendo Revolution 3A4, 4-channel ($499.00) and 5A4, 4-channel ($779.99). US Acoustics Lanna, 6-channel at 6 x 150W ($695.00), is the practical entry to an active three-way, which normally costs a lot more to get into. Crescendo Revolution 5A1 ($749.99) is the odd one and the interesting one: a Class AB full-range monoblock holding 450W at 4, 2 or 1 ohm, where nearly every other monoblock on the market is Class D. See Crescendo amplifiers and 6-channel amps.

Audiophile Mid-Tier, $1,399 to $2,399

Tru Technology Tungsten in 2-channel and 4-channel (both $1,399.99), then Tungsten Grande as monoblock ($1,999.99), 4-channel ($2,399.99) and 2-channel ($2,399.99). US-built, and the reason to buy into the line is that it covers every channel count at one topology. Crescendo Revolution 7A4, 4-channel ($1,699.99), is the SQ pick of the Revolution line. See Tru Technology.

Audio Wave Reference Tier, $2,499 and Up

Active 250, full-range monoblock ($2,499.99). Excel, 2-channel ($2,600), and Excel Monoblock, full-range ($3,099.99). Aspire Pro USA, 2-channel ($7,999.99, marked down from $8,999.99), and the Aspire Pro USA Monoblock ($8,999.99) for a matched pair. The Aspire Pro 6 Channel is a previous demo at $21,999.99 against $29,999.99, and it is the last one. At the top, the CR 401 Dual Mono ($39,999.99). See Audio Wave amplifiers.

If you are running an active front stage, the DSP lineup does the crossover work these amps would otherwise be guessing at. And whatever you buy, gain is what protects it: how we set amplifier gain.