Parasound Halo A21+ 2 Channel Power Amplifier
$5,500.00
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The A 21+ represents a new unparalleled value in amplifier performance. Details like soundstage depth, focus, and texture is where the A 21+ puts real distance from the A 21. The A 21+ is exceptional and provides an awe-striking feel.
Parasound’s 71-pound Halo A 21+ delivers a whopping 300 watts per channel, and it’s stable enough to drive just about any speakers you might care to hook up. This amp is an improvement upon the company’s original Halo A21, which was a popular choice among audiophiles during its own 15-year run. This newer “plus” version has a refined new look, and offers more power and improved specs almost across the board.
The large toroidal transformer inside Parasound’s Halo A 21+ amplifier delivers a mighty 300 watts per channel of clean power.
In bridged mode, the A21+ really turns on the firehose, putting out an amazing 1,000 watts into a single channel. All that power comes from a beefy toroidal transformer and a high-bias Class A/AB amplifier design that help your system reproduce music with stunning clarity and accuracy.
Class A/AB operation for smoother sound
You don’t see a Class A/AB amplifier every day, so let’s break down the benefits.
Engineers and audiophiles generally agree that Class A designs offer the purest sound, but they tend to run hot and take up a lot of space. As a result, home audio amplifiers often use a compromise known as Class AB, which hands off part of the audio signal to a different set of output transistors at high power levels. AB can sacrifice a bit of signal purity, but it lets the amp run cooler and more efficiently.
So this Class A/AB amp operates in pure Class A mode up to a higher power level than most other amplifiers in its price category, before the second set of transistors kick in. The result is a sound that’s smoother, less fatiguing, and more natural.
Convenient connections
On the back panel are balanced XLR and unbalanced RCA inputs for each channel, and each has its own individual gain control knob and loop output. There are also binding posts for connecting a pair of speakers. The amp can be rack mounted using the included ears.
The legacy of John Curl
The A 21+ features circuitry designed by John Curl, a legend in audio engineering. He started his career in the 1970s, designing tape and video recorders at Ampex, and he had a hand in building the Grateful Dead’s famous Wall of Sound. Curl has worked with Parasound since 1989, designing all of their high-power amplifiers and more. The power supply, transistors, capacitors and other parts in the A 21+ were chosen to offer high performance at a reasonable price.
Features & Specifications
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Changes from the original A 21→A 21+
- 250 → 300 Watts (8Ω)
- 400 → 500 Watts (4Ω)
- 750 → 1000 Watts (bridged)
- Filter cap: 88,000 uF → 108,000 uF
- S/N: 112dB → 115 dB
- THD (at full power): 0.2% → 0.1%
- Crosstalk (20kHz): 63dB → 70dB
- Transformer size: 1.2 kVA → 1.3 kVA
- Weight: 60 LB → 71 LB
- Refined Halo cosmetic with aluminum end caps & gold highlights
- Updated rear panel with heavy duty speaker terminals from JC 5
- Upgraded internal gold on gold audio connections
- Updated auto turn on circuit
All Features
- 300 watts x 2 @ 8 Ω RMS, both channels driven
- 500 watts x 2 @ 4 Ω RMS, both channels driven
- 1000 watts x 1 @ 8 Ω, in bridged mode
- Circuitry designed by legendary John Curl
- High bias Class A/AB operation
- 60 amperes peak current per channel
- Stable with speaker impedance dips to 1.5 Ω
- Balanced inputs with discrete circuits
- CHK Infinium, custom 5-way speaker binding posts
- Gold-plated RCA input & loop output jacks
- Direct-coupled signal path, no capacitors or inductors
- DC Servo and relay protection circuits
- AC turn-on inrush surge protection with relay bypass
- JFET input stage, MOSFET driver stage
- 16 beta-matched 15 ampere, 60 MHz bipolar output transistors
- 1.3 kVA shielded toroid transformer w/ independent windings for each channel
- Independent power supplies for input stage, driver stage and output stage
- 108,000 µF filter capacitors for output stages
- Full power is rated all the way down to 5Hz for unrestricted low-end bass
- Harris hyper-fast soft-recovery bridge diode rectifiers
- Automatic turn-on by 12 V trigger or audio sensing
- 4 rack space chassis with rear carry handles
- Rack mount hardware is included
- Available in silver or black
- Power Output – Stereo Mode (0.1% THD)
300 watts x 2, 8 Ω both channels driven
500 watts x 2, 4 Ω both channels driven - Power Output – Bridged Mode (0.1% THD)
1000 watts x 1, 8 Ω
Bridged 4 Ω operation is not recommendedPower measurement are at 120 VAC:
0.1% THD, RMS continuous power,
full audio band (20 Hz – 20 kHz) - Current Capacity
60 amps peak, per channel - Slew Rate
> 130 volts per microsecond - Frequency Response
5 Hz – 100 kHz, +0/-3 dB
20 Hz – 20 kHz, +0/-0.25 dB - Total Harmonic Distortion (THD)
< 0.1 % at full power
< 0.03 % at typical listening levels - IM Distortion
< 0.04 % - TIM
Unmeasurable - Inter-channel Crosstalk
> 80 dB at 1 kHz
> 70 dB at 20 kHz - Input Impedance
Unbalanced: 33 kΩ
Balanced: 66 kΩ,(33 kΩ per leg) - Total Gain
29 dB - Input Sensitivity for 28.28 V Output into 8 Ω
Unbalanced: 1 V
Balanced: 1 V per leg - S/N Ratio
> 115 dB, input shorted, IHF A-weighted
> 110 dB, input shorted, unweighted - Damping Factor
> 1100 at 20 Hz - DC Trigger Requirements
+9 Vdc to +12 Vdc, 5 mA - Audio Trigger Requirements
2 mV – 10 mV - XLR Pin Identification
1 = Ground (Shield)
2 = Positive
3 = Negative (Return) - Dimensions
Width: 17-5/8″ (448 mm)
Height without feet: 7-1/8″ (181 mm)
Height with feet: 7-3/4″ ” (197 mm)
Depth: 20″ (508 mm)
Depth with cables: 21-1/2″ (546 mm) - Net Weight
71 lb. (32.2 kg) - Shipping Weight
88 lb. (39.9 kg) - Power Requirement
Standby: 1 Watt
Idle (no music playing): 160 Watts
Typical Listening levels: 300 Watts
Maximum: 1400 Watts
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