HALO A21+ Power Amp
Halo A21+ — Power You Can Feel, Control You’ll Love
The Parasound Halo A21+ delivers commanding power with effortless musicality. At 300 W per channel into 8 Ω (500 W into 4 Ω), and up to 1,000 W bridged, it drives any loudspeaker with authority while keeping the sound spacious, controlled, and fatigue-free.
Based on legendary John Curl’s circuit design, the A21+ refines Parasound’s most celebrated power amp for today’s systems—blending raw performance with elegant simplicity. Balanced XLR and RCA inputs, 2 Ω stability, and flexible bridging make it an ideal match for both stereo and home theater setups.
Praised by audiophiles and reviewers alike:
- “The soundstage just bloomed. Bass is crisp… mids and highs are singing.”
- “Ridiculously high damping… bass is tight and controlled at all volumes.”
- “Delightful and satisfying from the first note… impossible to fault.”
Winner of multiple awards and recommendations, including:
- Secrets of Home Theater & High Fidelity – Best Stereo Power Amplifier (2024)
- Stereophile – Recommended Component
- Future Audiophile – "Best Affordable Audiophile Power Amp"
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 recommended
Power 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
- 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
Future Audiophile Feb 2023 - Read why the A21+ was selected as the "Best Affordable Audiophile Power Amp of 2023"
Stereophile March 2020
"The new Parasound A 21+ was impossible to fault... remarkably powerful, transparent and quiet. Anyone in the market for a stereo power amp would be well advised to consider the Parasound A 21+, especially those who believe that they must spend more."
Home Theater Review Feb 2020
"With its high-quality chassis, thoughtful circuit design, and excellent sound quality, the A 21+ offers an impressive value proposition. Those shopping for a stereo amplifier in this price range should give the A 21+ serious consideration."
Positive Feedback January 2019
"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 provided an awe-striking feel."