Although Parasound’s Halo amplifiers have remained essentially unchanged for over a decade, they are still considered to offer outstanding value, even by today’s standards: reference-quality sound for budget prices. Boasting classic circuit designs by renowned engineer John Curl and prices that range from just under $1000 to a few thousand dollars, Parasound’s Halo models have gained a fervent following among value-minded audiophiles.
A couple of years ago, Parasound introduced the Halo A 31 ($3295 USD), a three-channel version of their top-of-the-line stereo and multichannel amplifiers, and the subject of this review. It joins the two-channel Halo A 21 and the five-channel Halo A 51 -- only the Halo JC 1 monoblock costs more. Over the years, I’ve heard the Halo JC 1s driving myriad high-end speakers at many audio shows, and have always been impressed by their sound. With regard to the two-channel A 23, Parasound’s smallest, least expensive Halo amp, the SoundStage! Network’s Erich Wetzel estimated that an A 23 driven by a Halo P 5 preamp would “result in sound that is unassailable in quality by any other combination of components that can be bought for a like amount.”
Parasound says that the Halo A 31 was developed in response to the increasing demand for a high-performance, high-power, three-channel amplifier. I’m not sure how much demand there actually is for three-channel amps, but I do use one to drive the center and surround speakers of my home-theater system, so I can see the utility of the A 31. With a claimed power output of 250Wpc into 8 ohms, the A 31 should be able to drive the three front speakers of just about any home-theater system.
John Curl’s circuit design for the Halo A 31 features complementary matched pairs of JFETs for the input pre-driver stages, matched pairs of MOSFETs for the driver stages, and an impressive eight matched 15A, 60MHz bipolar output transistors for each channel. The massive, encapsulated toroidal transformer produces 1.5kVA, and has independent secondary windings for each channel and 98,400µF of power-supply filter capacitance. It’s claimed to provide pure class-A operation up to 7Wpc, high-bias class-A/B operation thereafter, and to deliver 250Wpc into 8 ohms or 400Wpc into 4 ohms, all three channels driven.
The A 31 comes properly packed in a large double box. Very solidly built, it weighs 65 pounds, and its large case, measuring 17.25"W x 7.6"H x 19.1"D, is the same one used for the Halo JC 1 monoblock, the A 21 stereo, and the A 51 five-channel amps. The many screws securing the top plate slightly protrude and are easily visible, but are not particularly distracting. The many fins of the large heatsinks that comprise the side panels, and the Parasound logo stamped into the top plate, are all covered in a high-quality, black-anodized finish that gives the A 31 a professional, refined appearance. All Halo products are available in black or silver finish.
The slightly curved and rounded front panel is a thing of beauty. The gold lettering is understated, and the red Parasound logo glows to indicate that the mains power is connected. A single button switches the amp from standby to on, and four tiny lights -- one for power, and one for each channel -- glow softly blue to indicate activity. The ends of the front panel seem made of plastic, but are well matched, and don’t detract from the A 31’s handsomeness, or the overall impression of outstanding build quality.
Around back, the Halo A 31 is equally impressive. It has XLR and RCA input jacks, toggle switches for selecting between them, and binding posts far enough apart to accept heavy-duty, audiophile-approved cables. The power-on options include Manual, 12V Trigger, and Auto, with an adjustable Turn On Threshold. The gain can also be adjusted by +/-6dB using the Gain Normal/THX knob. The A 31 is certified THX Ultra2, for those who care about such things. My only complaint about the massively built A 31 is that while its binding posts are claimed to be of high quality, they look a little cheap and out of place in relation to the otherwise impeccable appearance and build quality. There are also two large handles, a mains power switch, and an IEC receptacle for the provided power cord.
Three to get ready . . .
I set up the Parasound Halo A 31 to drive the three front channels of my reference multichannel system, primarily using an Anthem Statement D2 surround-sound processor to listen to multichannel audio recordings and movies as well as two-channel recordings. The front speakers were KEF’s R900 and R600C (center). My Definitive Technology BP-8080ST surround speakers were powered by an Axiom ADA-1000 or a Bel Canto eVo6. I also used a pair of Definitive Technology Mythos ST-Ls. The subwoofers were two Paradigm Reference Servo-15 v.2s.
Now, go cat, go
The Halo A 31 was exceptional with two-channel recordings. It had the excellent transparency and imaging, with plenty of grip, that you’d expect from a high-powered solid-state amp, but it also had a richness through the midrange, and a smooth treble that was easy to listen to while still being very revealing. Even at low volume levels, the A 31 took control of my speakers, providing a refined sound that was at once rich and inviting, as well as a precisely defined soundstage. And it had no trouble driving my speakers to any volume level I desired.
While the Halo A 31’s power and bass control were impressive, its midrange clarity and ability to vividly float voices between the speakers at exactly the right depth -- not too up-front or recessed -- rivaled that of much more expensive amps. On Cyndi Lauper’s The Body Acoustic (16-bit/44.1kHz FLAC, Sony BMG), the various stringed instruments -- including a particularly steely guitar -- and the singer’s raspy voice can sometimes be a bit jarring, but the A 31 struck the perfect balance between vividly realistic reproduction of the acoustic instruments and a deft addition of just a touch of warmth to the voice. The sound of Willie Nelson’s To All the Girls . . . (16/44.1 FLAC, Columbia/Legacy) is a little dry, but the A 31 reproduced Nelson’s world-weary voice with a bit of smoothness. There was a natural presence and richness to his voice, and to those of the many female guest singers. With every cut I played, there was great pace and musicality in these arrangements for acoustic instruments. For example, in “Always On My Mind,” the piano was placed slightly in the back right of the soundstage, accompanied by a lone snare drum that did an excellent job of keeping time.
When I played multichannel recordings, I heard the same precision and musicality, as well as impressive dynamics across all three front channels. Peter Gabriel’s Back to Front: Live in London (BD, Eagle Rock Entertainment), probably the best-sounding Peter Gabriel concert video available (I’ve watched a lot of them), is a great test for multichannel systems. Early in the film, the mostly acoustic version of “Come Talk to Me” was notable for its nicely differentiated mix of voice, piano, acoustic guitar, accordion, electric bass, and deep but taut kick drum. The sustained hissing of hi-hat cymbals is prominent here, as in many recordings, but with the A 31, I was struck by how different each tom-tom sounded as it was hit. As the drummer’s sticks moved across the toms, each stroke differed slightly from the next; the strokes were spaced evenly and precisely between the speakers, closely matching the onscreen placement of the drums.
The Halo A 31 was highly musical, but it also had the massive amounts of power required for playing hi-rez audio from movies on Blu-ray. Edge of Tomorrow is a surprisingly smart, exciting film with an electrifying soundtrack. Through the A 31, the sound across the front channels was flawless. Atmospheric scenes had dead-silent backgrounds when required, and dialogue was more than merely intelligible -- it was realistic, and perfectly integrated within the mix, heightening Emily Blunt’s deadpan delivery of some of the film’s most memorable lines. During the numerous battle scenes, the metallic clanking and grinding of robotic exoskeletons, alien mimics, and powerful blasts from automatic weapons were perfectly positioned, while Christophe Beck’s low, pulsing music score effectively filled every bit of the rest of the soundscape. Even at reference levels at which I could feel the jarring kick of weapons’ recoil among the frenetic action, there was no discernible distortion: the music and dialogue remained stable and coherent, allowing me to listen at these levels for extended periods without fatigue.
As accomplished as the A 31 was, it wasn’t the last word in transparency. My reference Anthem Statement M1 mono amplifiers ($3750 each) have a midrange that is slightly clearer, making voices more present, and small vocal inflections and nuances more discernible. For instance, it was easier to follow the gently rising and falling line of the lilting humming in “Latika’s Theme,” from the Slumdog Millionairesoundtrack (16/44.1 FLAC, Interscope). And with a claimed power rating of a whopping 1000Wpc, the M1s had more power in reserve for the up-tempo “Jai Ho,” with its intense Bollywood dance beat and soaring singing. But while the M1 is a fantastic-sounding and amazingly powerful and revealing amplifier, the Halo A 31, for less than a third as much per channel, wasn’t far behind. If I didn’t already own the Anthems, I’m not sure I’d choose them over the Parasound.
Operated in bridged mono, Bel Canto’s six-channel eVo6 ($4900, discontinued), which I usually use to drive my center and surround channels, is claimed to produce a powerful 350Wpc into 8 ohms, three channels driven -- and it has a transparent and musical sound. Even so, with Edge of Tomorrow it lacked some of the A 31’s weight and depth. The film’s soundscape wasn’t quite as expansive, and I couldn’t feel the forceful recoil of the automatic weapons as easily as I had with the A 31. While there was still plenty of detail, the explosive, metallic sounds of battle were a little forced and lacking in weight in comparison to the A 31’s smooth, effortless delivery. Although the Parasound has a lower power rating, it sounded more dynamic and visceral with sound effects, yet more refined with the film’s musical score.
The A 31 also got the better of the eVo6 with two-channel music. There was a richer, woodier character to the double bass in “Linus and Lucy,” from the Vince Guaraldi Trio’s A Charlie Brown Christmas (SACD/CD, Fantasy), and the difficult task of articulating the deepest notes of this instrument was accomplished more precisely. While the eVo6 didn’t sound thin in any way, there was a richness to the A 31, as evinced by the big but melodic, gentle notes of the piano in “Christmas Time Is Here.” Lorde’s voice on her Pure Heroine (24/48 FLAC, Lava Music/Republic) had a wonderful purity in the midrange with the Bel Canto, but the Parasound -- also very clean through the midrange -- had just a touch of warmth, and a bigger but better-defined image of the voice, that were more musically satisfying. And when this album’s deep, sustained bass kicked in, the Parasound packed more punch, with a tight concussive quality and extremely low sustained tones.
Parasound’s Halo A 31 might get overlooked because it’s a three-channel amplifier designed primarily for use in multichannel home-theater systems -- or because, at $3295, it costs more than a budget multichannel amplifier, if less than what many audiophiles would pay for a two-channel amp.
It should not be overlooked. The Halo A 31 has a clear, detailed sound that belies its price, combined with just a touch of warmth. This blend of qualities made it a joy to listen to. Add to that its prodigious power output and rock-solid build quality, and I can assure you: It’s the real deal.
But if a three-channel amp is really not what you’re looking for, Parasound still has you covered, with their A 21 two-channel and A 51 five-channel versions of the same basic Halo design. $3295 isn’t exactly a low price, but based on what I heard from the Halo A 31, I can’t think of a single reason for not considering it and/or one of the other Halo amps for powering any or all of the channels in a high-quality audio system and/or home theater. It’s a fantastic-sounding amp with power to spare. I consider the Halo A 31 to be one of today’s best values -- if not the best value -- in a power amplifier.
. . . Roger Kanno
- Speakers -- KEF R900 mains, KEF R600C center, Definitive Technology BP-8080ST surrounds, Paradigm Reference Servo-15 v.2 subwoofers (2); Definitive Technology Mythos ST-L
- Amplifiers -- Anthem Statement M1 (2 monoblocks), Axiom Audio ADA-1000, Bel Canto Design eVo6
- A/V processor -- Anthem Statement D2
- Sources -- Oppo BDP-105 universal Blu-ray player, Asus Aspire One 722 computer running Windows 7 and foobar2000, Bel Canto Design mLink USB converter
- Cables -- Analysis Plus Solo Crystal Oval interconnects and Black Oval 9 speaker cables, DH Labs Silver Sonic DV-75 digital interconnect, AudioQuest Carbon USB cable
- Power cords -- Essential Sound Products MusicCord-Pro ES
- Power conditioners -- Blue Circle Audio Peed Al Sea Thingee, Zero Surge 1MOD15WI
Parasound Halo A 31 Three-Channel Power Amplifier
Price: $3295 USD.
Warranty: Five years parts and labor.
Parasound Products, Inc.
2250 McKinnon Avenue
San Francisco, CA 94124
Phone: (415) 397-7100
Fax: (415) 397-0144
Parasound Halo A 31 Power Amplifier POWER AMPLIFIER SPECIFICATIONS
- Design: Solid State Multi-channel Power Amplifier
- Power Output: 250 watts RMS x 3 @ 8 ohms, 400 watts RMS x 3 @ 4 ohms
- 98,400 µF Power Supply Capacitance
- 1.5 kVA Toroidal Power Transformer
- Connectors: RCA and XLR Inputs, 12V Trigger Input and Output, 5-way Binding Posts
- Dimensions: 7.6″ H x 17.25″ W x 19.1″ D
- Weight: 65 Pounds
- Price: $2,999 USD
- SECRETS TAGS: Parasound, Amplifiers, Power Amplifiers, Multichannel Power Amplifiers
Design and Setup of the Parasound Halo A 31 Power Amplifier
Offering the same 250 WPC into 8 ohms and 400 WPC into 4 ohms that the A21 and A 51 do, the A 31 makes an ideal mate for your front three speakers without having to spend money on extra power for surround channels that may not need it. With the balanced inputs it also allows you to keep the amplifier close to the front channels, allowing for shorter, more convenient speaker cable runs and longer runs of the balanced interconnects that are less prone to picking up noise.
Looking at the specifications for the A 31, it is effectively a three-channel version of the Halo A51 amplifier that has been in their line for years. Each channel has the same number output transistors and filter capacitance, though there is a bit larger toroid power transformer in the A 31 on a per-channel basis. Using the same John Curl designed amplifier circuit that is in the A51 is a good thing, as the A51 has been thoroughly analyzed and tested over the years and always has performed well.
The silver front panel of my unit looked quite nice, with a single power button up front for controls, with lights to indicate power and channel status. The rear contains all of the inputs and outputs for the A 31, as well as a set of handles to help you move it into position. Each channel has XLR and RCA inputs, with a switch to change between the two, and an adjustable gain knob. By default it comes at the THX reference level of 28.28 V of output for 1 V of input, but you can adjust this by up to +6 dB per channel to level match amplifiers in your system that might run higher than the THX standard.
A 12V trigger input allows you to set the amplifier to turn on based off the trigger, or it can power on when it sees an input signal, or from the front power switch if you want the manual option. Both sides of the A 31 are covered by large heat sinks to dissipate all of the heat given off by the amplifier, and there is no fan to introduce noise while in operation. Rated for 250 WPC into 8 ohms, and 400 WPC into 4 ohms, the first 5 watts of the Halo A 31 are actually Class A before it crosses over into Class AB. With most listening actually taking place at 5 watts or less, this offers sonic benefits to the user with lower distortion and odd-order harmonics.
I used the unbalanced RCA inputs with my Marantz AV7005 processor, and the 12V trigger input for controlling power. The 12V trigger out was used for an Emotiva UPA-5 to power the surround channels.
The Parasound Halo A 31 Power Amplifier In Use
Ideally an amplifier should reach out and grab your speakers tight, exerting full control over them at all times. A well-designed amplifier should perform like the most ideal car, able to start and stop instantly, take a 90-degree turn without slowing down, and be able to keep the accelerator pressed to the floor without worrying about damaging the engine.
From the time I plugged it in until I wrote this review, the A 31 grabbed my speakers by their throat and never let go. Listening to all my favorite music cuts and films, the A 31 never hiccups or backs off, and even driven to the limits that I could provide the case was never hot to the touch. On the SACD version of Wish You Were Herethe front soundstage was huge and dynamic, with guitars coming across clear and natural, with smaller details remaining clear and not obscured. Bass notes were clear, fast, and tight, as the A 31 never lost control and allowed the bass to turn muddy and fat.
On Simon and Garfunkel’s iconic Bridge Over Troubled Water, the soundstage thrown by the A 31 was very wide and deep, more so than the Emotiva could manage. The location of the instruments and vocals were precise, and their vocal harmonies sound fantastic. Melodies were smooth and clear and the treble isn’t fatiguing at all, but a pleasure to listen to.
The Mobile Fidelity version of Sea Change from Beck continues to be my reference CD recording, with clarity and detail I find unsurpassed. Though the A 31 the heartache of his voice was palpable, with words lingering on his tongue and in the air. Accompanying instruments effortlessly floated in the air around his voice, which anchored between the speakers but well behind them. Delicate acoustical instruments sound crisp and clear, with each note distinct and clean. The power of the A 31 might be overkill for a laid back album like this, but it certainly hasn’t sounded much better. The A 31 amplified everything in the music: backgrounds were blacker, instruments had more space around them and notes were better defined. It took the quality I had and stepped it up another notch.
To make sure the A 31 could keep up with whatever I gave it, I went back to “One”, from Metallica’s …and Justice for All album. The rapid-fire drums in the middle of the track have always proven to be a challenge at loud volumes, demanding a continuous attack and release by the amplifier to keep up with the accompanying guitar. With both pairs of speakers I had on hand, I didn’t hear the bass get muddy, or had a timing disconnect develop between the bass and the guitars.
Films proved to be no challenge for the A 31 either. Dave Matthews and Tim Reynolds sounded wonderful on stage, while the mid-air crash in Fight Club attacked me from the front speakers with reckless abandon.Even Nine Inch Nails didn’t cause the A 31 to blink as the industrial riffs from Trent Reznor blared from the speakers. With all material I pulled out, the A 31 performed wonderfully and didn’t leave me missing anything. I refrain from
The Parasound Halo A 31 Power Amplifier On The Bench
When put onto the test bench, the A 31 performed up to its rated specifications on all the tests I could subject it to.
Rated at <0.2% THD+N, the A 31 outperformed that for both 4 ohm and 8 ohm loads. There was over 85dB of headroom on the tests, and no noticeable artifacts from any of the tests.
With 10 kHz there were artifacts at the odd and even fundamentals, though they were 75 or 85dB below the primary and outside of the audible spectrum. THD+N numbers were still well below the rated numbers from Parasound.
IM Distortion was specified at 0.04% but scored 0.03% or better on the testing. Looking to the sides of the 7 kHz tone you can’t see any artifacts and the noise floor is very low.
With 19 kHz and 20 kHz tones we see almost no artifacts on the 2V tests, but we do see some begin to develop on the 5V tests but they are still close to 90 dB below the main tones. There are small artifacts out in the non-audible spectrum as well, and a slow rise in the noise floor out to 95 kHz.
Looking at THD+N vs. Frequency, we see that THD+N stays right by 0.05% out until almost 50 kHz where it begins to rise.
From 10-22,000 Hz we see the frequency response is within 0.1dB all the way out.
Looking all the way out to 95 kHz we see there is a gradual roll-off in frequency response that accelerates around 60 kHz.
Overall the bench tests on the A 31 indicate very good objective performance, with no clearly visible flaws that would need to be addressed, and numbers that surpass their own specifications.
Conclusions about the Parasound Halo A 31 Power Amplifier
The A 31is a superb amplifier during my time with it. Impeccable in fit and finish, meeting all its specifications on our bench tests, and handling all the material I threw at it with no issue. The A 31 is powerful but refined, presenting a large, detailed soundstage and bringing out all the details in the recordings that I listened to. Movies that used the fronts and center had no issues pushing the speakers to reference level without losing control or leaving the bass muddled and slow.
Really this review was a challenge to write. Amplifiers don’t have an interface or user experience where I can complain about the interface, or a large number of controls that can be too complex to setup. When an amplifier works, it should become invisible to the user and just do its job without getting in the way. By staying out of the way and letting me enjoy the music, the A 31 made this review a challenge to find new ways to say that it sounded wonderful.
The only faults I found with the A 31 were the lack of a black finish finish, which has been remedied by a new finish that Parasound is releasing now, and the bright lights on the front of the unit. As many three-channel amps will be placed at the front of the theater, it is nice to be able to disable all the lights on them so they don’t distract from your movie experience, but with the Halo you have to cover them with tape to do so. Beyond these two cosmetic issues, I found nothing to complain about with the performance of the A 31. In fact, it performed so well I let Parasound know I’ll be paying for it and keeping it as my reference amp going forward.
The Halo A 31 is able to drive any speaker you are going to throw at it and not complain, as well as impeccably built and beautiful in appearance. The Halo A 31 is a wonderful amplifier and a product I imagine will remain in the Halo catalog for a long time to come.