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"

Covered by Parasound's 5-Year Parts & Labor Warranty.

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

Download Manual

Spade Terminal Compatibility