Parasound Halo A21 Two Channel Amplifier


The Parasound Halo A21 two amplifier is a power amplifier that draws directly from the hefty lineage of the 5 channel A51 and also obviously the A31 additionally.

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The Parasound Halo A21 two amplifier is a power amplifier that draws directly from the hefty lineage of the 5 channel A51 and also obviously the A31 additionally. Like it’s bigger brothers – it’s also a THX Ultra 2 certified product, and it can be used in tandem with the A51 to bolster a 7 or 9 channel home cinema system, or be a stand-alone high end two channel amplifier also – or a combination of both. On this last point – the A21 can be used to stunning effect with the Parasound range of pre-amplifiers such as the JC3+, P5 or the larger and flexible P7. So the A21 is a real all rounder for want of a better phrase, but don’t let this deftness fool you in any way shape or form. As the A21 is based on exactly the same topology as the John Curl A51 and A31 design, as an the amplifier it can of be sublimely subtle when required, and unflinchingly ‘brutal’ (in a terribly good way!) when raw power is needed. Remember – again the A21 has the same high bias class A/AB operation of the A31 and A51, and also has the benefit of the directly coupled design  which means that there are no capacitors or inductors in signal path, which gives the utmost accuracy for the amplifier to work with. This balance of clarity and ‘clout’ means that the power output to draw upon (with both channels drive) is 250 watts @ 8 ohm’s and 400 watts @ 4 ohm’s, meaning that it has real dynamic headroom for the best depth of field and aural texture. It can of course be used effectively as a ‘mono-block’ in bridged mono mode as well meaning that you can drive up to 750 watts into an 8ohm load for those of you requiring huge power into larger more challenging loads, or for those of you whom are hard of hearing! As you would expect the build quality and components used in the A21 are pretty much second to none. The A21 features both balanced and unbalanced inputs (RCA’s are gold plated) with a designated ground lift switch, and these high quality inputs are matched with heavy-duty 24k gold-plated 5-way speaker terminals on the output stage. For those also wanting to tweak their THX certified installations the A21 features adjustable gain pots for up to +6db over THX Reference level. Despite it’s impeccable ‘HiFi’ credentials – the A21 also features included rack ears and has a choice of power activation (front panel, auto sensing and 12v) to ensure that for those wanting the best sound in the custom installation scenarios it is a mandatory option.


  • Continuous power output (all channels driven): 250 watts RMS x 2, 20 Hz – 20 kHz @ 8 Ω; 400 watts RMS x 2, 20 Hz – 20 kHz @ 4 Ω; 750 watts RMS x 1, 20 Hz – 20 kHz @ 8 Ω
  • 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/µsecondDynamic 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 Ω unbalanced; 66 k Ω balanced
  • S/N ratio: 112 dB, input shorted, IHF A-weighted
  • Damping factor: > 1100 at 20 Hz
  • Dimensions: Width: 17-1/2” (445 mm); Panel height: 7” (178 mm); Height with feet: 7-5/8” (194 mm); epth: 19-1/8” (485 mm)
  • Power Requirement: Standby: 25 Watts; Full Power into 4 Ω: 1500 Watts
  • Net Weight: 60 lb. (27.3 kg)

Additional information




Black, Silver


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