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 priceâ¦" "Its luxurious appearance is more than skin deep. Parasoundâs 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 Parasoundâs ability to resolve detail, while remaining composed and easy on the ear, proved the equal of my âreferenceâ 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 ÂµF 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 Allâ¦ 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.
Circuitry designed by legendary John Curl THX Ultra2 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 100,000 ÂµF power supply filter capacitance DC Servo and relay protection circuits AC present, channel status, high temperature indicators Heavy-duty 24k gold-plated 5-way speaker terminals Gold-plated RCA input jacks; ground lift switch Auto turn-on by 12v trigger or audio signal, 12v trigger out 4u Chassis, carry handles, rack mounting adapter included Parasound 5 year parts, 5 years labor warranty (For USA and Canada purchases only)
SoundReproduction.com, October 2005
"Out of the box the A 21 sounds wonderful. I sampled several Red Book CD's of different recording quality and musical genera's and quickly came to the realization that the A 21 was indeed a very special amplifier, and I could not wait to begin the serious evaluation after burn-in." - Shane Mattson
Audioholics, December 2004
Product of the Year Award 2004 - Two-Channel Power Amplifier
"For those who desire the power of a Mack truck with the finesse of a Mercedes Benz in a two-channel amplifier, look no further than Parasound." "With the assortment of unbalanced and balanced inputs, triggered output, and ground lift option no stones were left unturned with this well built, attractive design."
Audioholics, October 2004
"The A 21 and A 51 amplifiers are both loaded with usable features above and beyond most other amplifiers in today's market." "I cranked the volume way up and found myself free of that inhibiting audio alarm in my head that nags at me to turn it back down. Using the Parasound amp allowed my speakers to portray every aspect that I had come to expect without adding any noticeable sign of distortion or flaw." "The Parasound Halo A 21 and A 51 are top rate amplifiers at a great value. Parasound seems to have attended to every aspect of their design including the excellent build quality internally and externally matched with great looks." Overall Rating: 5/5 Stars - Ken Stein and Steve Dellasala
Luister (Netherlands), November 2003
Audiophile.no (Norway), July 2003
Continuous power output: 250 watts RMS x 2, 20 Hz - 20 kHz, 8 Î©, all channels driven 400 watts RMS x 2, 20 Hz - 20 kHz, 4 Î©, all channels driven 750 watts RMS x 1, 20 Hz - 20 kHz, 8 Î© 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: balanced 16 V rms < 0.04 % Slew rate: > 130 V/Âµsecond 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 Î© unbalanced; 66 k Î© balanced S/N ratio: 112 dB, input shorted, IHF A-weighted Damping factor: > 1100 at 20 Hz Voltage: 110V - 120V Dimensions: 17-1/4" w x 7-5/8" h x 19-1/8" d, 7 " h without feet Net weight: 60 lb.