REVIEW – Parasound Halo A 21 Two Channel Power Amplifier

By on Apr 22, 2013 in Amplifiers, Reviews


The heart of any two channel or home theater system is the amplifier. It provides the life’s blood to your speakers, without which there would be no sound. But not all amplifiers are created equal nor or any two alike. Amplifiers come in all shapes, sizes, number of channels and power outputs. They also run the gamut in terms of price, which isn’t always comparable to the level of performance, power, etc. that they produce. This is no doubt why many contest the “value” of so-called high-end amplifiers, for how much better can one amplifier sound over another when seemingly the only difference between the two is price? I happen to believe there are differences between, say a $1,000 200-watt amplifier and a $10,000 amplifier with the same power rating. I also believe that justifying the differences rests not with the masses but rather the individual. I’m more attracted to products, specifically with relation to amplifiers, that fall somewhere in the middle. Not mid-fi mind you, but rather amplifiers that strike a balance between all the determining factors that go into what makes them good. This is why I chose to take a look at the Parasound Halo A 21 two channel amplifier; I wanted to see if it could pull off such a price-to-performance balancing act while striking an emotional chord with the listener.

The A 21 retails for $2,300, which in my opinion puts it in the category  of aspirational, yet still obtainable. While there are definitely less expensive options available to consumers, few high-end offerings manage to look as good as the A 21. The A 21 comes in your choice of silver or black (a new addition to the line) and in either finish the aluminum casework is striking. The front panel is the epitome of simplicity featuring a slightly sculpted front curve with round edges accented with a glowing Parasound logo and a pair of channel indicator lights and back-lit on/off button. Both sides of the A 21 are awash in rounded heat sink fins that lead the eye to the back panel, which is nearly as stylish as the amp’s front -despite being a bit more adorned with connectors and controls.

The back panel of the A 21 features two large handles to aid in rack mounting; the handles, while functional, also frame the amp’s input/output options. Each channel has both balanced (XLR) and unbalanced (RCA) inputs as well as an unbalanced loop out convenience option. Each channel is also equipped with a variable gain knobs, which I’ll discuss in more detail later in this review. Between the inputs are three small toggle switches; one for ground lift, input type (balanced, unbalanced) and amplifier mode, i.e. stereo or bridged mono. The right and left pair of five-way binding posts rest along the bottom of the rear panel, to the right of which (looking at the back panel) resides the AC power receptacle. In the upper left corner there are options and inputs for auto turn on, including 12-Volt triggers as well as an audio signal sensing auto turn on switch.

The amp itself is quite large, though its industrial design does go a long way in minimizing its overall girth -that is to say it is such a thing of beauty that you want to look at rather than hide it away. The amp itself measures 17 1/4 inches wide by nearly 8 inches tall and just over 19 inches deep. Remove the factory attached feet and the amp’s height drops to an even 7 inches. While solidly built, it weighs a “mere” 60 pounds without its sturdy shipping carton, which is a bit less than expected given its physical size.

While the A 21 does sport striking good looks, its beauty is more than skin deep. The A 21 itself was designed by legendary designer John Curl and features a fully complementary topology as well as a direct-coupled signal path, meaning there are no capacitors or inductors to impair audio quality. The A 21 also boasts THX Ultra2 certification. It also is a high bias Class A/AB design, meaning its first few watts of power -in this case 10 -are delivered via Class A, and power above this in Class AB. Lastly, the A 21 comes with Parasound’s full 5 year parts and labor warranty, which is extended to authorized purchases made in the US and Canada.


In terms of power output the A 21 churns out an impressive 250 Watts into 8 Ohms, which increases to a staggering 400 Watts into 4 Ohms. In its bridged mono configuration the A 21 is capable of producing 750 Watts into 8 Ohms.  Total harmonic distortion is listed at less than .2% at full power, with a reported signal to noise ratio of 112dB.


It’s no secret that Parasound does have a bit of a professional pedigree in that their products can be found in both professional mixing and mastering environments as well as in consumer two-channel and home theater systems. I only bring this up because upon installing the A 21 (and A 31) into my reference system I noticed a few functional similarities between the Parasound and my commercial Crown amplifiers -specifically their use of gain controls. Many consumer amplifiers lack this feature, and yet it’s present on the A 21. For me this is a good thing for it adds a level of flexibility to the A 21 that is essential when running a setup that includes both pro and consumer AV gear. Why I tend to respond favorably to gain controls is due in part to some of my speakers being of the pro or commercial variety whereas others are not. The A 21′s gain controls therefore allow me to level match the speakers at the amplifier for maximum performance without having to (over) compensate in my preamp or processor.

For example; my JBL Pro Cinema 3677s with the A 21′s gain control set to “THX Reference” churns out a staggering 90+ dB in my room when presented with a test tone from my Integra. Too “hot.” If I leave the A 21′s gain control on reference but dial back the “gain” in my Integra I soon run out of “bandwidth” as my Integra can only attenuate the signal plus or minus 15dB. With the JBLs set to -15dB in my processor the resulting test tone is still a lively 78dB. Level matching other, non commercial, speakers to the JBLs means I have to “juice” them plus or minus three to five dB. Most traditional consumer amps that lack gain controls fall within 3-5dB of 75dB when sent a test tone from an AV preamp or receiver, which is fine. However, they (consumer amps) would run into the same problem described above if used in a commercial or pro setup -only they wouldn’t have enough gain. The Parasound therefore bridges the gap and is able to work in both capacities, which is a HUGE plus for me as my reference theater is as much a personal retreat as it is a workspace. A workspace that sees its fair share of both professional and consumer gear. The A 21′s gain controls also come in handy if your loudspeakers are insanely efficient, as is the case with not only my JBL 3677s but also my Tekton Design Pendragon speakers. Gain controls also allow you to better level match the A 21 with other, non-Parasound branded amplifiers.

For the purposes of this review I used my Pendragon speakers in their complete theater configuration and as a result utilized the A 21′s gain controls to adjust the Pendragons’ output to 75dB with my Integra AV preamp’s internal levels set to 0. Doing things this way ensured both the A 21 and the Integra were performing at their peak potential without one having to compensate for the other. I used the A 21 to power my Pendragon towers, with Parasound’s A 31 supplying power to the center and surround channels. Side note: the A 31 which retails for $3,000 is the three channel equivalent of the A 21 amplifier.

I installed both the A 21 and A 31 in my Sanus equipment rack using their included rack ears, which is a huge plus for me as most companies charge extra for rack mount kits. Not so for Parasound’s 4 rack space amplifiers. Both amplifiers were connected to my Integra DHC 80.2 AV preamp via 1 meter balanced interconnects from Monoprice. My source component of choice was the Dune -HD Max media player, which I fed a steady diet of music and movies from my custom built NAS box. Again, all cabling coming by way of Monoprice.

The Tekton Theater speakers themselves resided in my reference room, with the front three living behind my 120-inch diagonal Elite Screen with AcousticPro 4K material. The surround channels were then situated to either side of my primary listening space and atop stands courtesy of Sanus. While the video portion of my system had no real impact on the A 21′s performance, the visuals in my theater were supplied via my SIM2 M.150 LED DLP projector.

Personal Impressions

I began my evaluation of the A 21 with some two channel music by way of Alanis Morissette’s “Not The Doctor” off her Jagged Little Pill Acoustic album (Maverick). Right off the bat what struck me most about the A 21′s performance was its presence, both “physically” as well as “emotionally”. First the physical; the A 21′s midrange possessed solid weight and focus that lent a sense of lifelike dimension to Morissette’s vocals. The A 21 resonated “emotionally” in that the tonality and natural inflection in Morissette’s voice sounded nothing if not organic and true to the singer herself. High frequencies via the A 21 were extended and airy, and I was quite impressed by the amp’s ability to resolve more of the leading and trailing edges of notes -specifically as they related to high frequency elements such as cymbals. Not to be outdone was the bass, which through the A 21 proved resolute, dynamic and controlled, though not in a sort of “look at me,” iron-fisted way. That isn’t to suggest the A 21′s bass was wooly, but rather that its bass performance fit within the larger frame of its overall sonic canvas versus standing out as an individual strength. Dynamics were on par with the best that I’ve encountered as was soundstage definition -though admittedly this track isn’t the best test for soundstage width and/or depth. Still, the performance on a whole sounding convincing and natural in its portrayal.

In order to flex the A 21′s muscles a bit I cued up Audioslaves’ “Show Me How To Live” off the band’s self titled album (Sony). With peaks easily resonating well over 100dB the A 21 proved to be nothing if not unflappable. More impressive was that even at the limits of my own personal comfort the sound stemming from the A 21/Pendragon combo was not fatiguing or harsh in anyway. Nor did the A 21 come off as sounding compressed or strained at high volume. The resulting sound was brash, bold and 100% rock and roll. The guitars were “crunchy” and the kick drum and snare hits bordered on violent. Again, these are not descriptors meant to be misconstrued as bad, but rather true to the source material as not all music is “polite.” The A 21′s impact and dynamics were impressive, possessing copious detail throughout the frequency range even at reference level volumes. The drummers’ rim shots specifically were positively startling, ringing true with lifelike scale and force. The resulting soundstage easily extended beyond my room’s physical boundaries and seemed to extend backwards in space several feet, with clear delineation between each performer despite the higher than thou SPL levels.

Content with the A 21′s musical prowess (not to mention its awe-inspiring power delivery) I pressed on to movies, beginning with Wolfgang Peterson’s Poseidon on Blu-ray disc (Warner Bros.). Obviously this disc packs a number of great action sequences that do a phenomenal job of showcasing why many of us love our home theaters so much. But what many probably don’t realize is that it’s also a great test of a product’s vocal prowess too. Peterson shoots a lot of the sequences in this film via some very long lenses. This in turn means that microphones can’t always be placed where optimal, resulting in actors being recorded via wireless devices or through mics on long range booms. Having such a wide range of sound capturing devices in one scene means the sound mixers have a hell of a job keeping everything sounding uniform. A good example of what I’m talking about can be heard in the ballroom scenes prior to the rogue wave’s arrival. It’s not uncommon for actors such as Richard Dreyfuss to sound a certain way in one take or angle and completely different in another.

Less resolute components mask this phenomenon whereas those that remain neutral and truer to the source will not. The A 21 falls into that latter category but does so in a way that doesn’t  take you out of the film, which is in line with the master. The differences in the vocals can’t be helped in this instance but they shouldn’t be jarring, either. More importantly, via the A 21, the resulting tone still rings true to the actors’ natural sound and inflection. Also the dialog was always intelligible, even in the face of unrelenting chaos.  I should note that for the purpose of this test I did use one of the A 21′s channels to power the center speaker. I did so in order to test the A 21′s abilities in this regard and not the A 31′s.

Moving the right channel back to the right speaker and allowing the A 31 to tackle the center and surround channel duties, the two amps proved to be a sonic match in that I couldn’t tell them apart. Again, as was the case with my music tests, the A 21 proved incredibly resolute and capable, regardless of where I chose to set the volume. Even at low volumes the A 21′s  level of engagement proved to be infectious. The A 21, again, was unflappable in its delivery and seemed to have no limit to its power in my room and system. In truth, I didn’t even feel as if I made the A 21 break a sweat -though admittedly my chosen speakers were on the more efficient side. Still, I’ve paired up the A 21 with average efficiency loudspeakers such as the EMP Tek E5Bi bookshelf speakers as well as the Paradigm Atom Monitors and neither seemed to cause the A 21 any trouble.

I could go on and on about the A 21′s strengths but I fear I would become repetitive, so I’ll just wrap it up by saying this; at its price of $2,300 the A 21 manages to sound every bit as composed, resolute and true to the source as amplifiers I’ve demoed costing much, much more. That isn’t to say that it’s better, it’s just that in my personal experience and hands on testing, the A 21 may represent the best example of what it means to possess true high performance but at a reasonable price.

What I Would Change

There isn’t much I didn’t like about the A 21′s performance, so any gripes are going to be a bit nitpicky. For one, I felt as if the binding post could have been better, or at least of a higher quality than what is given. Obviously some corners have to be cut or curbed in order to hit certain price points, but I cannot imagine a slightly more robust pair of binding posts to be that expensive. I’m not suggesting the binding posts themselves weren’t functional, they were, they just didn’t echo the rest of the amplifier’s attention to detail.

This last point isn’t so much something I can change but rather something you as a potential customer must be aware of and that is the A 21′s ability to generate heat -and lots of it. This heat is the inevitable consequence of the A 21’s generous amount of operation in Class A.  Proper ventilation to get rid of hot air is required for the A 21 to perform at its best, and if you’re planning on installing one in a confined space you may want to consider investing in a fan.

Comparable Products

There is no shortage of two channel amplifiers in the marketplace today. Like I said in my introduction, some two channel amps can be had for less than the A 21 while others can cost considerably more. While I’d put the A 21′s performance on par with the likes of Classe’s CA2300 and Mark Levinson’s No 532, it isn’t far from matching the performance benchmarks set by even Pass Labs’ X350.5 and Krell’s 302/402e.

Another viable option would be to “go pro” so to speak, in which case the Crown XLS DriveCore Series of amplifiers would be my go to. While the A 21 and XLS amps do share some functional similarities, I consider the A 21 to be the superior product as its sound is much more “mature” top to bottom and applicable for a wider range of loudspeakers. The Crown amp represent a phenomenal value and is in truth a great amp, one that I use as a point of reference, but I do consider the A 21 to be better.

That being said, I think the A 21 or the Halo lineup of amplifiers in general represent my personal cutoff point in terms of price and performance. You can definitely spend more, but I’m not sure the single digit differences are worth it –for me, at least.


What more is there left to say about the Parasound Halo A 21 that hasn’t already been said? The A 21 is a phenomenal amplifier, one that, in my opinion, represents a near perfect balance between price and performance. This is why I am hanging onto the A 21 (and A 31) amplifier for long term use and reference. I realize that there are some less expensive options available to consumers, just as there are more expensive ones, but in my travels I don’t think I’ve encountered an amp that toes the line between the two as brilliantly as the A 21. I love it, and I love that it is every bit a reference grade product as its costlier competition and yet is priced within the realm of reason for everyday folks.