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What Is the A21+ and What Does It Do?
A power amplifier is the engine of your audio system. It takes the tiny audio signal from your preamp, streamer, or other source component and amplifies it with enough muscle to drive your speakers. The Parasound Halo A21+ is a two-channel (stereo) power amplifier that delivers 300 watts per channel into 8 ohms — and a substantial 500 watts per channel into 4 ohms. If you need even more power, it can be bridged into a single-channel monoblock delivering 1,000 watts into 8 ohms.
The A21+ is designed by John Curl, one of the most respected circuit designers in the history of high-end audio. Curl has been designing amplifiers since the 1970s, when he helped establish transistor amplifiers as serious competitors to tube designs while working with Mark Levinson. His work with Parasound’s Halo line has produced some of the most acclaimed amplifiers in the industry.
The A21+ operates in high-bias Class A/AB mode. In plain terms, the amplifier runs the first several watts of output in pure Class A — a topology prized by audiophiles for its smooth, natural sound. When the music calls for more power (a loud drum hit, a full orchestral crescendo), it seamlessly transitions to Class AB for the heavy lifting. This gives you the best of both worlds: Class A sweetness at normal listening levels, with hundreds of watts on tap when you need them.
Who Is This Amplifier Best For?
- ✅ You own (or plan to buy) demanding, power-hungry speakers that need serious amplification to reach their full potential — planar magnetics, electrostatics, or large tower speakers all thrive with the A21+.
- ✅ You want a dedicated two-channel power amp to pair with a separate preamp for serious stereo listening.
- ✅ You’re building a high-end home theater system and need a rock-solid amplifier for your front left/right channels, driven from your AV processor’s preamp outputs.
- ✅ You want the benefits of John Curl’s world-class circuit design at a price that’s a fraction of what you’d pay for comparable performance from other high-end brands.
- ✅ You need an amplifier that can be bridged to a 1,000-watt monoblock for single-channel applications.
How Does It Connect to Your System?
The A21+ offers both balanced (XLR) and unbalanced (RCA) inputs, so it will connect to virtually any preamp, DAC, or processor. The balanced inputs use discrete circuits for the cleanest possible signal path — use these when your source component offers balanced outputs.
Each channel has its own gain control on the rear panel, calibrated with clear markings from “Min” to “Max” (29dB unbalanced / 35dB balanced). This lets you fine-tune the volume level and match the amp’s sensitivity to your preamp or processor.
A single pair of heavy-duty 24K gold-plated five-way speaker binding posts per channel accepts banana plugs, spades, or bare wire. A 12V trigger input and audio-signal auto-on make it easy to integrate into automated home theater systems.
Keep in mind, this is a power amplifier only — it does not have a built-in preamp, volume control for direct source connection, or any digital inputs. You’ll need a separate preamp or a source with its own volume control (like many DACs offer). If you want a Parasound preamp to pair with it, the Halo P 6 is a natural companion. Give us a call and we’ll help you put together the right system.
Pairs Well With
Building your system? Here are some great companions for the A21+:
Preamps & DACs: The Parasound Halo P 6 is the natural partner — it includes a DAC, phono stage, and the connectivity to drive the A21+ via balanced XLR. Browse our Preamps & DACs.- Speakers: With 300–500 watts on tap, the A21+ is a dream match for demanding speakers. Explore our Tower Speakers and Bookshelf Speakers.
- Interconnect Cables: Get the most from the balanced inputs with quality XLR cables, or use our RCA interconnects. Browse Cables & Interconnects.
- Speaker Cables: The heavy-duty binding posts deserve quality cables to match. Check out our Speaker Cables from AudioQuest, Analysis Plus, and Cardas.
Frequently Asked Questions
What’s the difference between a power amplifier and an integrated amplifier?
A power amplifier like the A21+ does one thing: it amplifies the audio signal to drive your speakers. It does not include a preamp, volume control, source switching, or digital inputs. An integrated amplifier combines a preamp and power amp in one box. The advantage of a separate power amp is that it can devote all of its resources to clean amplification, and you can pair it with whatever preamp or processor best suits your needs.
Do I need a preamp to use the A21+?
Yes, in most setups. You’ll need a preamp, a DAC with a variable volume output, or an AV processor/receiver with preamp outputs to control volume and source selection. The Parasound Halo P 6 is the matching preamp in the Halo line and includes a built-in DAC and phono stage. If you’re using the A21+ for home theater, connect it to the front left/right preamp outputs on your AV receiver or processor.
How does the A21+ compare to the original A21?
The A21+ is a meaningful upgrade across the board. Power increased from 250W to 300W at 8 ohms (and proportionally at 4 ohms and bridged). The power supply gained a larger transformer and 20–30% more filter capacitance. Distortion was halved at full power. Channel separation improved, internal connections were upgraded to gold-on-gold, and the speaker terminals were upgraded to the flagship JC 5 models. The cosmetics were also refreshed with aluminum end caps and gold accents.
Can I use this for home theater?
The A21+ is an excellent home theater amplifier for your front left and right channels. Connect it to the preamp outputs of your AV processor or receiver, and use the 12V trigger input for automatic power-on when your system starts. For a complete Parasound home theater setup, you could add the Halo A 31 (three-channel) or A 52+ (five-channel) for your remaining channels.
How hot does it run? Where should I put it?
The A21+ runs warm, especially at idle (160 watts). The side-mounted heat sinks can get quite hot during extended listening. Give it plenty of ventilation — do not place it inside a closed cabinet or stack other components on top of it. An open rack or a well-ventilated shelf with several inches of clearance on all sides is ideal.
Can I bridge two A21+ amps into monoblocks?
Yes. A rear-panel switch lets you bridge the A21+ into a single-channel monoblock delivering 1,000 watts into 8 ohms. You’d need two A21+ amplifiers for a stereo monoblock setup. Note that bridged operation into 4 ohms is not recommended by Parasound.
What speakers pair well with the A21+?
Just about any speaker on the market. The A21+ has the power and current capacity to drive even the most demanding loads — large tower speakers, planar magnetic designs like Magnepan, electrostatic speakers, and inefficient studio monitors all pair beautifully. With 60 amps of peak current and stability down to 1.5 ohms, it won’t run out of gas. If you need a recommendation, call us at 800-942-0220.
Does it support bi-wiring?
The A21+ has a single pair of speaker terminals per channel, so it does not natively support bi-wiring from the amp side. If you want to bi-wire your speakers, you can split the cable at the speaker end, or look at the Parasound JC 5, which offers dual speaker terminals per channel.
Is it worth the upgrade from the original A21?
If you already own an A21 and it’s working well for you, the A21+ is an upgrade, not a revolution. According to the Positive Feedback review, the A21+ puts meaningful distance between itself and the original in terms of soundstage depth, focus, and texture. The power increase and lower distortion are measurable improvements. If you’re buying new, the A21+ is the clear choice.
What else do I need to get started?
At minimum: a preamp or DAC with volume control, interconnect cables (XLR balanced recommended), speaker cables, and speakers. If you’re building from scratch, give us a call at 800-942-0220 and we’ll help you put together a complete system.
Professional Reviews
What Are Reviewers Saying?
Stereophile has honored the A21+ as a Recommended Component every year since 2023, placing it in their prestigious Class A category. Reviewer Kalman Rubinson described his experience as satisfying from the very first note, praising the amplifier’s transparency and its effortless handling of orchestral dynamics. Technical Editor John Atkinson’s bench measurements confirmed the amp exceeded its power specs, delivering a full 400 watts per channel into 8 ohms and remaining stable into impedances as low as 2 ohms.
Rubinson described his time with the A21+ as satisfying from the very first note, praising its transparency and effortless handling of dynamic orchestral passages. Technical measurements by John Atkinson confirmed the amp delivered 400W per channel into 8 ohms — exceeding its rated specs — and remained stable into 2-ohm loads. Herb Reichert later adopted it as his reference solid-state amplifier.
Stereophile — Kalman Rubinson, March 2020 — Recommended Component, Class A (2023–2025)
At HomeTheaterHiFi.com (October 2023), the reviewer reported finding no fault at all with the A21+’s audible performance, noting particularly impressive bass control and seemingly limitless reserves of power and headroom.
The reviewer found nothing to criticize in the A21+’s audible performance, noting that it took firm control of his speakers and delivered a powerfully musical presentation. He praised the impressive bass response, flexible hookup options, and exceptional value for the dollar.
HomeTheaterHiFi.com — October 2023
Michael Zisserson at Positive Feedback (January 2019) praised the A21+ for advancing the original’s already excellent value proposition, noting meaningful improvements in soundstage depth, focus, and textural detail over its predecessor.
Zisserson praised the A21+ as proof that exceptional performance-per-dollar is still possible, highlighting meaningful improvements in soundstage depth, focus, and texture over the original A21. He noted that the amplifier delivered both explosive dynamics and delicate quiet passages with equal authority.
Positive Feedback — Michael Zisserson, January 2019
Dylan Seeger at Home Theater Review (February 2020) highlighted the smooth, natural, and organic sound quality that comes from the high-bias Class A/AB design, concluding that it would be hard to find speakers the A21+ couldn’t power with ease.
Seeger praised the high-quality chassis, thoughtful circuit design, and excellent sound quality, calling the A21+ an impressive value and recommending it to anyone shopping for a stereo amplifier in this price range.
Home Theater Review — Dylan Seeger, February 2020
The Future Audiophile review (2023) called it a benchmark for high-power amplification at this price point, noting that competitive amplifiers typically cost $7,000 to $10,000.
The review praised the A21+ as the benchmark for high-power amplification at this price level, noting that comparable amplifiers typically cost $7,000 to $10,000 and recommending it for anyone spending up to $5,000 on a dedicated stereo amplifier.
Future Audiophile — 2023 — Best Affordable Audiophile Power Amp
One practical note that reviewers consistently mention: this is a big, heavy amp (71 lbs) that runs warm, especially at idle. It needs good ventilation and should not be placed inside a closed cabinet. Multiple reviewers recommend having a second pair of hands for setup.
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