Parasound Halo A 21+ Stereo Amplifier Reviewed

Published On: February 19, 2020
Last Updated on: October 31, 2020
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Parasound Halo A 21+ Stereo Amplifier Reviewed

After 15 years of devoted service, Parasound has retired its beloved Halo A 21 amplifier. Its replacement, the Halo A 21+, is priced a little higher at $2,995. But what, exactly, do you get for that extra coin? As the...

Parasound Halo A 21+ Stereo Amplifier Reviewed

By Author: Dylan Seeger

Dylan is an expert in audio and  video reproduction with a emphasis on home theater projection.

After 15 years of devoted service, Parasound has retired its beloved Halo A 21 amplifier. Its replacement, the Halo A 21+, is priced a little higher at $2,995. But what, exactly, do you get for that extra coin?

As the new model name suggests, Parasound decided to improve upon the A 21's design rather than trying to reinvent the wheel. To facilitate this, the designer of the A 21, the legendary John Curl, was brought back in to make the necessary modifications. However, if judging the A 21+ on its outward appearance alone, it would seem not much has changed.

a21plus_inside_300.jpgInternally, though, the custom-made, shielded toroidal transformer has been pumped up from 1.2 to 1.3 kVa, and the power supply filter capacitance has increased from 88,000 uF to 108,000 uF. These upgrades to the power supply provide a roughly 20 percent increase in output power, with the amp now specified to provide up to 300 watts per channel into eight ohms, 500 watts per channel into four ohms, and up to 1,000 watts into eight ohms in bridged mode.

Curl also took a hard look at the A 21's circuit design and made several modifications, all aimed at improving performance and increasing sound quality. The new design halves THD, which is now specified at 0.1 percent. Crosstalk and signal-to-noise ratio see improvements too, now rated at 70dB and 115dB, respectively. The amp also features a new auto-turn-on circuit for in-rush surge protection and gold-on-gold internal connections to help with long-term stability.

The amp is still offered in both black and silver finish options, and although at first glance the chassis appears unchanged, a few upgrades have occurred there as well. One of the biggest gripes owners had with the A 21's chassis was the plastic end caps found on the faceplate. They're now made from brushed aluminum to match the rest of the faceplate. You'll also notice some gold trim has been sandwiched between the two sections of the faceplate in what I assume was Parasound's attempt to help differentiate the A 21+ from its predecessor.

Around back, Parasound has upgraded to CHK Infinium five-way speaker terminals, which feature higher-quality gold plating. In fact, these are the same speaker terminals found on the company's more expensive JC 5 amplifier, though only a single pair of terminals is included per channel, so those looking to bi-wire their speakers will need to consider a different amp. Both balanced XLR and unbalanced RCA inputs are available, with each channel still featuring its own independent gain control and RCA signal loop outputs.


Parasound classifies the amp's topology as high-bias Class A/AB. In practice, this means the amp is biased to output a little over six watts per channel of pure Class A power. From that point onward, the amp switches over to Class AB operation. While six watts may not seem like much, that's enough power to drive all but the most inefficient speakers to reasonably high SPLs for the majority of music or movies you'll likely listen to. So, depending on the power needs of your speakers and how hard you drive them, much of you listening will be done in pure Class A, with Class AB power provided only in particularly dynamic moments.

The A 21+ utilizes JFETs for the input stage, a MOSFET driver stage, and uses 16 beta-matched bipolar transistors for its output stage. Each of these stages features its own independent power supply and, in John Curl fashion, a strong emphasis on reducing higher-order harmonics has been made in the amp's circuit design, which Curl deems as the most detrimental type of distortion for sound quality an amplifier can have.


Unboxing and setting up the A 21+ may prove to be a difficult task for some. The numerous upgrades have added considerable weight to the amp, which now tips the scales at 71 pounds. It's also bulky in size, measuring in at 17.6 inches by 7.75 inches by 20 inches. This amplifier is a beast and, because of that, I suggest you get help when unboxing and setting it up. Due to its design, the amp is always drawing power when turned on and needs to dissipate a lot of it as heat, so I suggest you place the amp in a well-ventilated area. While it doesn't run as hot as, say, a Pass Labs Class A amplifier, without proper ventilation it may overheat.

I'm sure a lot of people reading this review are wondering if the A 21+ sounds a lot like the original A 21. These thoughts are perfectly appropriate when nothing but a plus sign has been added to the model name. As a previous long-time owner of the original A 21, I feel confident in saying the A 21+ does in fact sound similar. However, I also feel confident in saying the sound is not a carbon copy.

In a sense, you're getting an A 21, but with more of everything. Specifically, the A 21+ offers more impressive dynamics, a more accurate stereo image, wider stereo separation, and I heard more impressive control over my speakers' drivers on a regular basis. Like its predecessor, the A 21+ still punches well above its price point in overall performance and is still an amplifier that does most things right.

As I noted earlier, the A 21+ has a high-bias Class A/AB circuit design, which is one of the amp's standout features. Class A operation often imparts a particularly sweet, smooth, and organic sound signature, and the A 21+ definitely qualifies for these sonic traits, with treble frequencies in particular rendered smoothly and grain-free. This lack of sparkle on the top end makes it an ideal candidate for those who like to listen for long periods of time.

With that said, I found the most impressive part about the A 21+ was how it handled the bottom end. Bass performance from the A 21+ is as good as I've heard from any amplifier near its price point and even competes with many amps costing far more. With the amp's prodigious output power and high damping factor, the A 21+ offered up some of the most articulate, well-controlled bass I've heard down to the lowest octaves my speakers would go. If bass performance is of utmost concern, the A 21+ should be on your shortlist of amps to consider.

High Points

  • Build quality of the Parasound A 21+ is mighty impressive and handsome enough to fit into most décors.
  • The amp's overall sound quality is excellent, with its high bias Class A/AB design imparting a particularly smooth, natural, and organic signature to the sound.
  • It's unlikely you'll find a pair of speakers the A 21+ struggles to power. All of its high-power output is rated to be stable with speaker impedance dips down to 1.5 ohms.
  • When you consider all that's included in the price, the A 21+ continues the high value proposition of its predecessor.

Low Points

  • The amp's size, weight, and heat output could pose potential installation problems, especially for those looking to place it in a cabinet or enclosure.
  • The LED notification lights cannot be dimmed or turned off when the amp is operating.

Competition and Comparisons
If you're considering the A 21+, you're more than likely looking for an amp that is also Class A/AB. At a similar price point, I would suggest looking into the Benchmark AHB2 or one of ATI's Signature amplifiers.

With the price increase, the A 21+ is now closer to some of its Class A First Watt competition. While the A 21+ was here, I was able to compare it to my First Watt J2. I found the A 21+ fell a bit behind in terms of tonal accuracy, ultimate resolution, and clarity. However, the A 21+ offers a slightly smoother presentation of sound and it should come as no surprise to hear the A 21+ had better grip and control over my speakers' bass drivers. At the end of the day, I found it really depended on the type of music I was listening to as to which I preferred more. Both are excellent amplifiers in their own right.

The A 21+ builds upon its predecessor's design, offering upgrades that elevate an already stellar amplifier to a new level. While the upgrades do come with a slightly higher asking price, I found, in practice, these changes make a meaningful enough difference to justify the new cost.

With its high-quality chassis, thoughtful circuit design, and excellent sound quality, the A 21+ offers an impressive value proposition. Those shopping for a stereo amplifier in this price range should give the A 21+ serious consideration.

Additional Resources
Visit the Parsound website for additional information.
Parasound Halo P 5 2.1-Channel Preamplifier Reviewed at
Parasound Announces HINT 6 Integrated Amplifier at

  • Anonymous
    2023-08-05 21:17:02

    Did you perform a self psychiatric analysis to hold yourself accountable for your question? Did you do it blindfolded?

  • Anonymous
    2022-03-23 20:49:36

    Did you perform bench tests to hold yourself accountable for your conclusions? How about blind listening comparisons?

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