Note: Measurements can be found through this link.
Parasound Products was founded in 1981, in San Francisco, by Richard Schram, whose mission was to provide value for the money to his customers. As Parasound defines it, value begins to decline when additional cost provides only marginal and diminishing returns, and increases when a product is reliably functional over decades. Parasound serves both the consumer and professional markets; their products have been used by multiple Oscar-winning sound designers, from such studios as Lucasfilm, Pixar, Sony Pictures, 20th Century Fox, Universal Pictures, and Warner Bros.
Parasound currently makes preamplifiers and phono preamplifiers; mono, stereo, and multichannel power amplifiers; and integrated amplifiers; in the past they’ve offered AM/FM tuners, loudspeakers, preamplifier-processors, CD players, and DACs. Their four current product lines are: ZoneMaster, for stable power amplification into impedances of 2 ohms, and outboard crossovers for multi-speaker custom installations; the Z models, half-rack-space components also intended for the custom market; NewClassic, their budget line; and the Halo line, which comprises their most extensive, expensive, and highest-performing models. (Rack-mounting kits are available for all models in all lines.) Parasound emphasizes that their products are supported from their San Francisco headquarters, and at dozens of authorized service centers across the US.
The Halo A 23+ stereo power amplifier ($1495 USD) measures 17.25”W x 4.2”H x 15.25”D and weighs 27 pounds. Its case is available in silver or the black of my review sample, which looked very elegant. The only control on the faceplate, an On/Off button in the lower-left corner, is set into a flute, or rounded groove, that runs the entire width of the thick faceplate -- when the A 23+ is turned on, this button is illuminated in a soft blue that makes it seem to float above the groove, and nicely complements the two vertical pinstripes of gold at far left and right. There are other lights -- tiny LEDs that glow blue to indicate that each channel is functioning properly, red to warn of overheating. During my time with the Halo A 23+, these never reddened.
On the Halo A 23+’s rear panel are balanced (XLR) and unbalanced (RCA) inputs; each channel has a toggle switch for choosing between them, as well as its own loop output (RCA) for additional amplification (e.g., a subwoofer), and a Gain knob. The A 23+ can be switched between its Stereo and Bridged Mono modes with a single toggle switch between the sets of left- and right-channel inputs -- in bridged mode, the Halo A 23+ delivers an astounding 500W into 8 ohms throughout the entire audioband (20Hz-20kHz). The two binding posts support speaker cables up to 10AWG.
At far left are some interesting alternatives to turning on the amp with its front-panel On/Off button. You can connect a 3.5mm 12V trigger cable from a preamplifier, which in turn can pass a trigger signal to another device; or you can tell the A 23+ to detect an audio signal by setting its little Turn On Threshold knob somewhere in its range of Quieter to Louder (selecting either of these options disables the front-panel On/Off button). Then, after ten minutes of receiving no signal, the Halo A 23+ will shut itself off.
At far right are the fuse bay, the main power switch, and a three-pronged IEC power inlet. The power cord provided was, appropriately, quite a bit heavier than that provided with a typical component.
The Halo A 23+ was designed by engineer John Curl, who’s well known in audio circles, and since the 1990s has designed many amplifiers for Parasound. The Halo A 23+ includes a number of upgrades from its predecessor, the Halo A 23: The power output in mono has increased from 400W to 500W; in stereo, the increase is from 125 to 160Wpc into 8 ohms, and from 225 to 240Wpc into 4 ohms; the filter capacitors have been upgraded, from 40,000 to 54,400µF; the large, shielded toroidal transformer, formerly 1.0kVA, is now 1.1kVA; the crosstalk has improved, from 63 to 70dB; and the speaker terminals are now the “heavy-duty” ones used in the Halo HINT 6 integrated amplifier.
The A 23+ offers 45A peak current per channel, and has gold-plated terminals and sockets, discrete Junction Field Effect Transistors (JFETs) for inherently high-impedance input, and Metal Oxide Semiconductor Field Effect Transistors (MOSFETs) to reduce odd-order harmonic distortion in the driver stages. There are independent power supplies for its input, driver, and output stages. The output-stage transistors support high current levels and are extremely fast (60MHz), to tame transient intermodulation distortion. Parasound uses several protective measures to deal with so much power: DC servos to maintain the DC offset at 0VDC; relays to protect speakers from pops and transients; current-overload monitoring; and separate fuses for the input and output voltage rails. It’s an impressive set of features.
System and setup
I connected the Halo A 23+’s 12V trigger using the mono interconnect included with Parasound’s NewClassic 200 Pre preamplifier, also in for review, and set the A 23+ to turn itself on when the 200 Pre sent a trigger signal. As the amp was placed atop the preamp, this configuration made sense, and the Halo’s auto-sensing worked reliably. Via unbalanced (RCA) interconnects, I fed the A 23+ audio signals from my primary sources, a Music Hall MMF CD-25 CD player and a Cambridge Audio CXN (V2) network player. The Halo A 23+ drove my Sonus Faber Principia 3 minimonitors.
I found that the Halo A 23+, given enough breathing space on top, ran cooler than my NAD C 356BEE integrated amplifier.
When my source was Cambridge’s CXN (V2) network player, what most impressed me about the Halo A 23+ was its clarity in the delicate introductory solo of Saint-Saëns’s Introduction and Rondo Capriccioso for Violin and Orchestra, performed by soloist Leila Josefowicz with Sir Neville Marriner conducting the Academy of St Martin-in-the-Fields, on their Bohemian Rhapsodies (16-bit/44.1kHz FLAC, Philips). The reproduction of this recording takes a light but deliberate touch, and the A 23+ delivered it with well-managed dynamics in the solo violin, orchestral strings, and rumbling timpani. The punctuated call-and-response phrasing later in the work was also quite clear. The Parasound really came into its own at higher volume levels, sufficient juice for which it had no trouble providing to my Sonus Fabers. At lower levels, Josefowicz’s E-string glissandi had a slight tendency to get lost against the orchestral backdrop in Sarasate’s showpiece Zigeunerweisen.
With small-combo jazz, the Halo A 23+ offered detail, precision, accuracy, and well-balanced tonality. In “Venture Within” from Interplay, a duo album by Kenny Barron and Mark Sherman (24/192 AIFF, Chesky), Sherman’s vibraphone strokes were definitive and reverberant. These attributes of the Parasound’s sound were much more pronounced with well-recorded, high-resolution recordings than with run-of-the-mill CDs. A vibraphone comprises an array of tuned aluminum bars that are struck with cord-wrapped rubber mallets. As Sherman traversed his instrument’s range, I could follow the movements of his mallets across the soundstage with the A 23+. (In this intimate recording, the vibes and Barron’s piano together occupy a big share of the soundstage.)
The rambunctious second movement of Bruckner’s large-scale Symphony No.9 delivers deliberate punch in energetically throbbing unison ostinato in the recording with Gustavo Dudamel leading the Gothenburg Symphony Orchestra (24/48 AIFF, Deutsche Grammophon/HDtracks), and the Parasound delivered room-filling sound, the timpani extending deep into the low bass without congestion. It had a dramatic punch, but also expressed delicate flute motifs, and even silence when needed. Rapid changes in the ranges of frequency and dynamics, and spatially across the soundstage, were effortlessly accomplished. The power was clean and clear. I found that the Parasound didn’t suffer from power-line inconsistencies, as my NAD C 356BEE integrated amp ($900) does when plugged directly into the wall -- which is why I plug the NAD into an APC Line-R LE1200 power conditioner. The Parasound managed just fine without it.
My NAD integrated has two preamp-level outputs, one of them tied with a coupler to the main input to allow the NAD to be used as a preamp or power amp, which made it easy to compare the NAD’s power-amp section with the Halo A 23+. Although the two amps share some specifications, in terms of sound the Parasound consistently bested the NAD. With the recording of Bruckner’s Symphony No.9, for example, the Halo sounded generally cleaner and more refined -- a definite step up in sound quality. The Parasound reproduced the extremes of low-frequency percussive punch and finessed the emotive flutes, excelling at highlighting microdynamics and timbral characteristics; the NAD provided less in the way of such contrasts. While I’d never thought the NAD lacked for power, the Parasound offered much more, and was able to deliver it with greater control across the audioband. The low end felt precise, controlled, and natural, as evidenced in this symphony’s many passages for timpani. This was also particularly true of its reproduction of recordings of double bass. In “Lester Leaps In,” from Bucky Pizzarelli’s Swing Live (24/96 FLAC, Chesky/HDtracks), Michael Moore’s bass was more intense and driving through the Parasound. Through the NAD, it had less energy and verve. The aural images of the instruments on this intimate recording of an acoustic jazz quintet were also more defined through the Halo.
In much the same way, “Shattering Sea,” from Tori Amos’s Night of Hunters (24/88.2 FLAC, Deutsche Grammophon/HDtracks), an acoustic tone poem presented as pop music, lost much of its urgency with the NAD. The Parasound elevated this recording -- its introduction builds a gradual crescendo with layers of instruments that then suddenly cut out, leaving only Amos’s voice and acoustic piano. The strata of instruments -- piano, strings, woodwinds -- remained distinct, producing an exciting feel. This is pop music as film soundtrack -- the Parasound delivered the roller-coaster with impressively expressive dynamics on a soundstage populated by detailed aural images.
Parasound provides great value in the Halo A 23+ power amplifier. While their focus was clearly on sound and build quality rather than a long list of features, they’ve nonetheless provided enough flexibility to satisfy a variety of users. Some audio products impose their own signature on the sound of any recording played through them, but the Halo A 23+ consistently let the music itself shine through, reproducing it with a sound that was always detailed, accurate, and balanced. I was impressed by its quietness, the amount of power it could swiftly deliver, and its tremendous dynamic range.
In the extensive write-up provided in the Owner’s Guide, Parasound design consultant John Curl says: “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.” After spending several months with the Halo A 23+, I have to agree: I haven’t heard better sound or seen a higher quality of build at this price. In the Halo A 23+, Parasound has delivered an impressive power amplifier.
. . . Sathyan Sundaram
- Speakers -- Sonus Faber Principia 3
- Headphones -- Grado Labs SR80, HiFiMan HE-500
- Subscription service -- Google Play Music
- Digital sources -- Music Hall MMF CD-25 CD player; Cambridge Audio CXN (V2) network player; Google Chromecast Audio; Monoprice HDX-401TA; Raspberry Pi2 running Volumio 2.2389
- Analog sources -- Goldring GR1 turntable and Elektra cartridge, Rega Research RB100 tonearm
- Phono preamplifier -- Cambridge Audio 540P
- Preamplifier -- Parasound NewClassic 200 Pre
- Integrated amplifier -- NAD C 356BEE with MDC DAC 2.0 module
- Power conditioner -- APC Line-R LE1200
Parasound Halo A 23+ Stereo/Mono Amplifier
Price: $1495 USD.
Warranty: Five years parts and labor.
Parasound Products, Inc.
2250 McKinnon Avenue
San Francisco, CA 94124
Phone: (414) 397-7100