|Parasound - Halo A21 Two-Channel Amplifier
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"Editors' Choice Award" 2012 - The Absolute Sound Magazine
The Absolute Sound "Best Solid-State Amplifier" 2008/2009
250-Watt THX Ultra II Amp Hits a 'Home Run'
Parasound's Halo A21 two-channel power amplifier has the brute force you need for ultra-realistic musical reproduction and hair-raising movie soundtracks. Its raw power is matched by elegant circuit design from audio guru John Curl in collaboration with CTC Builders.
"Highly Suitable for Driving Anything"
The Absolute Sound magazine rated the Halo A21 as the "Best Solid-State Amplifier" in the Winter 08 / Spring 09 issue, praising it as "highly suitable for driving anything from power-hungry planars like Maggies to low-sensitivity acoustic suspension cones."
The A21 is the two-channel version of Parasound's benchmark A51 five-channel amp, which the May 2003 issue of DVD Etc. magazine said hit the "proverbial home run." Matched JFET inputs, MOSFET drivers, and high-current bipolar outputs contribute to its exceptional performance.
"Close Enough to the Very Best"
The Absolute Sound magazine awarded the Halo A21 its "Editors' Choice" recommendation for 2012. "Though not the last word in solid-state amplification, the A21 comes close enough to the very best, at such an affordable price…"
"Its luxurious appearance is more than skin deep. Parasound’s A21 dispensed truly sumptuous sound," notes England's Hi-Fi News magazine for November 2011. "Demonstrating the control and grip of the Bryston and Anthem but with the velvety midband richness of the ATC, the Parasound’s ability to resolve detail, while remaining composed and easy on the ear, proved the equal of my ‘reference’ Levinson amplifier."
Balanced Inputs and Discrete Circuits
The A21 boasts balanced inputs with discrete circuits and XLR connectors. Beautifully implemented high-bias Class A / AB operation makes the most of an impressive 250-watt-per-channel power output at 8 ohms and 400-watts-per-channel at 4 ohms. The 1.2 kVA encapsulated toroidal power transformer with independent secondary windings for each channel and 100,000 µF power supply filter capacitance delivers an impressive current capacity of 60 amps per channel. The direct-coupled design uses no capacitors or inductors in signal path. The complementary MOSFET driver stage relies on the firepower of 16 beta-matched 15 amp, 60 MHz bipolar output transistors and works in combination with a JFET input stage.
'Instant Warm-up' Feature
Like all the other amps in the Halo product series, the A21 has Parasound's exclusive bias circuit, which permits the amplifier to sound perfect from the instant it's turned on, rather than having to wait for bias to gradually build up as the amp warms up over time. Very high bias allows greater Class operating range than others. Even Halo's implementation of its automatic turn-on feature is exceptional. Special relays bypass the AC "soft start" circuitry after it's done its job for the purest AC and the purest sound.
And That's Not All…
AC present, channel status, and high temperature indicators team up with DC Servo and relay protection circuits to keep this powerhouse running safely at peak performance for years of reliable service. Auto turn-on by 12-volt trigger or audio signal simplifies home theater and multi-room operation. Other features include heavy-duty 24k gold-plated five-way speaker terminals, gold-plated RCA input jacks, and a rear-panel ground lift switch.
Owner’s Manual (3mb PDF)
- Circuitry designed by legendary John Curl
- THX Ultra 2 certified
- High bias Class A/AB operation
- Balanced inputs with discrete circuits and XLR connectors
- Direct Coupled - no capacitors or inductors in signal path
- Complementary MOSFET driver stage and JFET input stage
- 16 beta-matched 15 amp, 60 MHz bipolar output transistors
- 1.2 kVA encapsulated toroid power transformer with
independent secondary windings for each channel
- DC Servo and relay protection circuits
- AC present, channel status, high temperature indicators
- Gold-plated RCA input jacks, loop output jacks
- Heavy-duty 24k gold-plated 5-way speaker binding posts
- Auto turn-on by 12v trigger or audio signal, 12v trigger out
- Rear panel gain controls; ground lift switch
- 4u Chassis; carry handles; rack mounting adapter included
- Continuous power output (20 Hz - 20 kHz):
250 watts RMS x 2 at 8 ohms, 400 watts RMS x 2 at 4 ohms,
750 watts RMS x 1 (bridged mono mode) at 8 ohms
- Current capacity: 60 amperes peak per channel
- Power bandwidth: 5 Hz - 100 kHz, +0/-3 dB at 1 watt
- Total harmonic distortion: < 0.2 % at full power
- IM distortion: < 0.04 %
- Slew rate: >130 V / µsecond
- Dynamic headroom: > 1.5 dB
- Interchannel crosstalk: > 80 dB at 1 kHz; > 63 dB at 20 kHz
- Input sensitivity: 1 V for 28.28 V, THX Reference Level
- Input impedance: 33 k ohm unbalanced; 66 k ohm balanced
- S/N ratio: > 112 dB, input shorted, IHF A-weighted
- Damping factor: > 1100 at 20 Hz
- Voltage: 110V – 120V
- Dimensions: 17.25" wide, 7.625" high (7" without feet), 19.12" deep
- Net weight: 60 lbs.
- Manufacturer's limited warranty: 5 years parts, 5 years labor
"Editors' Choice Award" 2012 - The Absolute Sound Magazine
"Though not the last word in solid-state amplification, the A21 comes close enough to the very best, at such an affordable price."
"Its luxurious appearance is more than skin deep. Parasound’s A21 dispensed truly sumptuous sound from Maxwell’s ‘Everwanting…’ with oodles of bass grunt and tight precision. The singer’s soulful multi-tracked vocal lines were depicted exquisitely within the track’s myriad percussion details. Demonstrating the control and grip of the Bryston and Anthem but with the velvety midband richness of the ATC, the Parasound’s ability to resolve detail, while remaining composed and easy on the ear, proved the equal of my ‘reference’ Levinson amplifier."
- Hi-Fi News magazine, November 2011
||Obvious power, authority, control, speed, punch, slam, and refinement
My wife and I listened to the Parasound A21 power amplifier along with the Parasound JC-2 preamplifier with the Usher Be-10s last weekend March 7th, 2009 with MIT speaker cables and interconnects. Sadly, the system only had a Rotel CD player for its source, so it was limited by that. However, this amplifier made it instantly clear that it has massive power to tap into at any moment and for long periods of time. It sounds as easy on the ears at very soft listening levels as it does when cranked up and then some. The abundant authority, control, punch, slam, speed, timing, pace, and drive were just downright visceral and intense. The bass tightness and impact were outstanding as well as offering terrific pitch definition and tracking of a bass line with the percussion without cluttering them together. The midbass was strong and tight too, yet musical and not overbearing one bit; just as the bass can be described. The midrange and treble were fluid, flowed like good red wine at an Italian dinner, and lavished our ears with sensuous saxophones, open and sonorous strings of plucked guitars, the epitome of intimate allure as the jazz singers wove their spells of song as if slinking around right in front of us with every breath and gasp for the next one rendered so realistically it was beguiling. The presence of the component was an asset to this system and listening experience as it allowed, and made, the speakers come to life with a palpable bloom and airiness that let our song by John Denver warm our hearts like never before due to how lifelike it sounded. This amplifier offers depth of soundstage and solidity to the foundation of bass that is exemplary and easily equal to other components many times its modest cost. We were thoroughly impressed and would gladly invest in one, or two, of these without any doubt at all. Richard Schram of Parasound told me in an Email from last summer that the A21 will offer about 15 to 20 wpc in full, legitimate class A mode when bridged mono. The class A high biasing comes through in stereo mode, as we listened to it, for about 7.5 wpc, and makes this amplifier very smooth and easy to listen to with no harshness or listener fatigue at all. It is extremely neutral and does not muffle, veil, dull, or slow down the sound at all. It breathes performance into your system so that you can enjoy your favorite music so easily. This system, with this Parasound A21 in it, is one of the most emotionally engaging systems that I, and now we, have ever heard; be it solid state, tube, or both, and regardless of cost or brands included. That says a lot for those who really know about and have heard what is out there to audition. I have auditioned 130 brands and sold 78 brands in addition to those, so I have a pretty good idea of this stuff, along with doing it since I was 16 and am now age 40, so theres two dozen years of experience to hopefully lend credibility to this personal review. The amplifier is also very visually appealing in general appearance, fit and finish first rate, and my WAF Wife Acceptance Factor is 100% positive. There are no perceivable flaws or shortcomings of any kind. You would have to, and I do mean have to, invest much more money to get noticeably better sound. We are planning on getting two of them and running them in a vertically bi-amplified manner at first or bridging them and having fun with that sheer power. Keep in mind that Mr. John Curl, formerly of Mark Levinson, is the designer of this product. That in itself says a great deal about the technical competency that this amplifier was conceived with. Bravo for a job very well done !!
Tom & Erin
near Allentown, PA.|
|- Tom F, PA|