Note: Measurements performed by BHK Labs can be found through this link.
Parasound Products, based in San Francisco, has a reputation for building great-sounding consumer-audio equipment and selling it at reasonable prices. Many readers will be familiar with the connection between the company and John Curl, who since 1988 has designed many of the circuits used in Parasound components. Less well known is that Parasound’s equipment is in use in many professional film-sound and music-production applications. Professional sound design requires well-engineered, high-resolution gear that imposes on the sound as little as possible of its own sonic character. The combination of a talented circuit designer, great sound, and professional use often leads to high-priced consumer gear -- but not at Parasound in general, and specifically not in the case of their Halo A 23 two-channel power amplifier.
The Halo A 23 amplifier is reasonably priced ($995 USD), and has enough power to meet the needs of most audiophiles: 125Wpc into 8 ohms, 225Wpc into 4 ohms, or 400W into 8 ohms in bridged mono mode. Other important specifications include total harmonic distortion of less than 0.06% at full power, and a signal/noise ratio of 112dB. The well-written owner’s manual states that the A 23 operates in class-A/AB: Its input and driver stages run in pure class-A, while the output stage runs partially in class-A before rolling over to the more efficient class-AB at higher wattages than do “many amplifiers selling for two or three times its price.” Parasound indicates that the result is “less fatiguing, more natural sound.”
I didn’t read the A 23’s manual until I’d done most of my listening, and I completely agree. Parasound took the trouble to provide clear and thorough technical descriptions of the A 23’s circuitry and design concepts. I’ve rarely seen elsewhere the level of detailed technical analysis provided by Parasound in its manuals. In this one, John Curl states that “the circuits I design for Parasound are extremely sophisticated and are typical of products that are far more expensive. I can’t think of any other audio products that offer nearly as much bang for the buck.”
A quick glance inside the Halo A 23 shows densely packed circuits, with lots to be happy about for those who get excited about parts quality and technical stuff. Centrally located inside the case is a large, 1kVA toroidal transformer; Parasound says that its separate secondary windings for each channel will help reduce “inter-channel crosstalk, [which] can blur the sound and impair the correct sense of where instruments are positioned.” Metal-foil resistors of 1% tolerance are used because their resistance changes minimally at operating temperatures. Polypropylene and mica capacitors were selected for “superior linearity and low dielectric absorption,” and gold-plated input and speaker connectors ensure the best current transmission into and out of the A 23. JFET inputs are used in a differential layout, which means they’ll be less affected by the impedance and noise of the preamplifier’s output circuit; and Parasound says that the A 23’s MOSFET drivers will prevent “the harshness and brittle sound so often found in other amplifiers.” Finally, the three pairs of bipolar transistors per channel are claimed to be robust enough to safely provide the high current and voltages needed to drive a wide variety of speakers. Parasound indicates that these “lightning-fast (60MHz) transistors respond instantly to complex demands in the musical signal, virtually eliminating distortions that occur with slower transistors.” What I heard confirmed all of this.
The Halo A 23 looks almost identical to the Halo P 5 preamplifier, which I recently reviewed. Available in black with gold labeling, like the review sample, or in silver with black labeling, the A 23 measures 17 1/4”W x 4 1/8”H x 13 1/4”D and weighs a hefty 28 pounds. Its rectangular metal faceplate has rounded plastic end plates at left and right, a case of folded sheet metal, and most of its top plate is pierced by ventilation slots. Stamped into and running nearly the full width of the front of the top plate is “Parasound” in large capital letters. Along the bottom of the faceplate is a horizontal groove that contains the blue, backlit On/Off button, and blue LEDs to indicate channel power and high temperature. At the top center of the front panel is the Parasound logo, subtly backlit in red -- it glows brighter when the unit is running. Below that is the THX logo, indicating the A 23’s professional qualifications. The A 23 doesn’t make a strong aesthetic statement, and should complement the appearance of most equipment in its price range. The build quality seems very good for the price.
On the rear panel, between the two convenient carrying handles, are the usual ports and connectors and some handy set-and-forget features. On the left are 12V auto-turn-on trigger ports and loops, with a welcome addition: The input trigger also has an Audio setting, with a Gain dial that allows the A 23 to power up when it senses a signal at the input. This feature will be handy for those who like to keep all of their components except for the power amp turned on and warmed up at all times. When set to do so, the A 23 shuts off automatically after a period of time with no signal at the input.
Next up on the rear panel, in mirror pattern for the two channels, are: Gain controls that can be turned down to zero if needed, a Loop Out (RCA) for subwoofer connections, an unbalanced input (RCA), and a balanced input (XLR). Between these mirrored sets are three toggle switches, for Ground Lift, Inputs Balanced/Unbalanced, and Mono Bridge/Stereo. Below these are two pairs of speaker terminals that will work with most cable types, but will be slightly challenging for fat cables -- the terminals are close together. At the rear panel’s far right are an IEC mains connection and an AC voltage selector with settings of 115V/60Hz and 230V/50Hz, to allow the A 23 to be used overseas. Once I’d tried the various settings and connections, I left them alone with the Gain dial set at its maximum or THX Reference setting, and didn’t change them again.
My listening was done with my iMac optically feeding data to the appropriate input on the DACs used for this review -- primarily, the Parasound Halo P 5 and the Rotel RC-1570. The preamplifiers were then linked to the Halo A 23 with balanced interconnects.
Arcade Fire’s “Abraham’s Daughter,” from The Hunger Games: Songs from District 12 and Beyond (16-bit/44.1kHz AIFF, Republic), threw a broad soundstage that extended well past the side panels of my Bowers & Wilkins 801 Series 2 speakers, though the stage was shallow. It felt as if the opening, heavily distorted guitar was there in the room with me, and the snare drum that’s played almost throughout the track sounded clear and accurate, without any of the harsh flash that I’ve heard it produce through other systems.
It’s soundtrack day as I complete this review. I love tracks like “My Name Is Lincoln,” from the soundtrack to The Island (16/44.1 AIFF, Milan). The music, by Steve Jablonski, has the same futuristic feel as the film itself. What caught me while listening via the Parasound Halo combo of P 5 and A 23 was the precision of all sounds in this track. It begins quietly and slowly, with some nearly inaudible bass sounds. Gradually, other sounds are added, increasing the complexity, as well as a bass line that accelerates the pace. Eventually, a large chorus enters, to make a hugely complex but very catchy piece that is really moving along by the time it reaches its climax some three minutes in. Then, in a rapid decrescendo, instrument after instrument disappears until the track fades to silence. This track seemed made for the Parasounds. Deep bass was deep but not pushy or flatulent, and there was a precision to each sound, but without a tipped-up bottom end. You’ll find deeper bass elsewhere, but the modest power of the A 23 never left me wanting more -- its low-end precision sounded natural. I find that electronic soundtracks can often sound shrill or bright through higher-resolution amplifiers, but the Halo A 23 didn’t let that happen. At no point did electronic highs sound harsh.
Something a little less big sounding is the partially acoustic “Dreams,” from the Cranberries’ Everybody Else Is Doing It, So Why Can’t We? (16/44.1 AIFF, Island). Dolores O’Riordan’s Irish-accented voice sounded as if she could have been right there, a few feet behind the speakers, in a room strangely larger than mine. The acoustic percussion is spread out a bit unnaturally in this 1993 recording, but the fantastic thing about playing this track through the A 23 was the clarity of each sound. Everything was distinct, in a precise location, and didn’t move around, as I find in some recordings. The sound of the percussion instruments was natural -- a word I keep coming back to. Drums sounded like drums, not big, bloated cartoon versions of themselves without specific location. The percussive cacophony in the last few moments of “Dreams” was especially terrific through the A 23 -- each instrument and sound had a specific position in space.
James Horner’s soundtrack to the 1988 film Glory is a favorite of mine, and must be of Horner’s as well -- he’s used some of its themes in other films. “An Epitaph to War” is a wonderful piece for chorus that brought out the best traits of the A 23: Individual members and sections of the Boys’ Choir of Harlem were easy to place in space, and the soprano and alto sections were vividly distinct from each other. Basses and tenors, when they enter toward the end, took up their positions alongside or behind the higher sections. Through the A 23, I was able to hear that the choral sound was made up of individual voices. At the end of this track, a trumpeter soulfully plays a short theme that recurs throughout the film, without too bright or brassy a tone. The voices and trumpet sounded natural, without the high-pitched glare that often accompanies them on recordings.
I compared the Parasound Halo A 23 with the Rotel RB-1582 MkII amplifier ($1599), a sample of which I had on hand. The Rotel costs $604 more than the Parasound and puts out more power: 200Wpc into 8 ohms vs. the A 23’s 125Wpc. While the 75W disparity never surfaced as something that made a difference, positive or negative, replacing the Halo with the Rotel did make a noticeable change. The Rotel had a generally warmer sound that went well with my B&W 801s, reinforcing their own warmish nature. The A 23, by comparison, sounded more precise and accurate, and more natural than the Rotel, which was a bit too soft in some areas, with a narrower soundstage. The Halo A 23 let me easily locate specific instruments and sounds on the soundstage; the RB-1582 MkII softened the sounds and spread them around a bit more. Listening to the Parasound was like looking at a high-resolution photograph. Switching to the Rotel was like looking at the same image just slightly out of focus, or through a soft filter: Edges of things were less distinct, the entire image less sharp. Depending on your taste, you may find the softer image more interesting or artistic, and your taste in sound might be similar. Which do you prefer?
Here’s my answer to that last question. I prefer the accuracy and resolution provided by the Parasound Halo A 23 to softer, warmer options. The price of purchase of this quality of sound is unexpectedly modest. John Curl is not being arrogant when he says that he can’t think of components that give better bang for the buck than the ones he’s designed for Parasound. I can’t, either. I was surprised by the A 23’s clarity, soundstaging, and natural sound. I estimate that the combination of it and Parasound’s recently reviewed Halo P 5 preamplifier will result in sound that is unassailable in quality by any other combination of components that can be bought for a like amount. The A 23 sounded surprisingly good from the moment I first turned it on. Several months later, I hated to turn it off for the last time and send it back.
. . . Erich Wetzel
- Speakers -- Bowers & Wilkins 801 Series 2
- Preamplifiers -- Benchmark Media Systems DAC2 HGC, Hegel P20, Parasound Halo P 5, Rotel RC-1570
- Amplifiers -- Audio Research D300, Rotel RB-1582 MkII
- Source -- Apple iMac running iTunes
- Digital-to-analog converters -- Benchmark Media Systems DAC2 HGC, Parasound Halo P 5, Rotel RC-1570
- Speaker cables -- Transparent MusicWave Ultra
- Interconnects -- AudioQuest King Cobra XLR, Transparent MusicLink Super RCA, AudioQuest Ruby RCA, generic TosLink optical
Parasound Halo A 23 Stereo Amplifier
Price: $995 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