Parasound Halo A21+ Stereo Amplifier - Black

Power & Performance

Massive Clean Power — 300 watts per channel into 8 ohms (both channels driven), 500 watts per channel into 4 ohms, and a staggering 1,000 watts bridged into 8 ohms. Stereophile’s bench tests confirmed the amp actually exceeds these specs. All power measurements are rated at 0.1% THD, continuous RMS power, full audio bandwidth (20Hz–20kHz).

High-Bias Class A/AB Operation — The first several watts per channel operate in pure Class A, a topology prized for smooth, natural sound. Class AB kicks in seamlessly for high-power demands. Parasound’s exclusive bias circuit lets the amp sound its best from the moment you turn it on — no warm-up wait required.

Vanishingly Low Distortion — Less than 0.1% THD at full power, less than 0.03% at normal listening levels. Intermodulation distortion is below 0.04%. Transient intermodulation distortion (TIM) is unmeasurable. In plain terms: distortion is so low it simply isn’t a factor.

60 Amps Peak Current Per Channel — This means the A21+ can deliver enormous bursts of power to handle sudden dynamic peaks in music without compressing or straining. It can drive speakers with impedance dips down to 1.5 ohms — making it compatible with virtually any speaker on the market.

Oversized Power Supply — A 1.3 kVA shielded toroidal transformer with independent windings for each channel, paired with 108,000 μF of filter capacitance, gives the A21+ the energy reserves to deliver clean, effortless power even during the most demanding musical passages.

Circuit Design

John Curl’s Legendary Topology — JFET input stage, complementary MOSFET driver stage, and 16 beta-matched 15-amp, 60 MHz bipolar output transistors. Each stage has its own independent power supply. The direct-coupled signal path uses no capacitors or inductors, so there’s nothing between you and the music.

DC Servo Protection — Sophisticated protection circuits (DC servo, relay protection, thermal monitoring) keep the amplifier running safely and reliably for years without interfering with the audio signal.

Connectivity

Balanced (XLR) and Unbalanced (RCA) Inputs — Connect to any preamp, DAC, or processor. The balanced inputs use discrete circuits for the lowest possible noise.

Dual-Mono Gain Controls — Independent level controls for each channel with clear calibrated markings, allowing precise gain staging to minimize system noise.

12V Trigger & Audio Auto-On — Turn the amp on automatically via trigger signal from your preamp or processor, or via audio signal detection. A rear-panel master AC switch provides a full “vacation” power-off option.

Bridgeable to Mono — A rear-panel switch lets you bridge two A21+ amplifiers into monoblocks for even greater power (1,000 watts into 8 ohms). Bridged operation into 4 ohms is not recommended.

Design & Build

Updated Cosmetics — Slim brushed-aluminum end caps (replacing the original plastic), gold metallic accent stripe, gold feet on black units, and an engraved metal Parasound badge. Tasteful blue LED indicators show power and channel status.

Upgraded Speaker Terminals — The same heavy-duty 24K gold-plated five-way binding posts from Parasound’s flagship JC 5, with butterfly grips that hand-tighten securely without tools. Accepts banana plugs, spades, or bare wire.

Ground Lift Switch — A rear-panel switch that can eliminate audible hum caused by ground loops in your system.

• Type: Two-channel stereo power amplifier (bridgeable to mono)
• Topology: High-bias Class A/AB
• Power (8Ω, stereo): 300W x 2, both channels driven
• Power (4Ω, stereo): 500W x 2, both channels driven
• Power (8Ω, bridged mono): 1,000W x 1
• Peak Current: 60 amps per channel
• THD: < 0.1% at full power; < 0.03% at typical listening levels
• IM Distortion: < 0.04%
• S/N Ratio: > 115dB (A-weighted); > 110dB (unweighted)
• Frequency Response: 5Hz – 100kHz (+0 / −3dB); 20Hz – 20kHz (+0 / −0.25dB)
• Damping Factor: > 1,100 at 20Hz
• Slew Rate: > 130 V/μs
• Crosstalk: > 80dB at 1kHz; > 70dB at 20kHz
• Total Gain: 29dB (unbalanced) / 35dB (balanced)
• Input Impedance: 33kΩ (unbalanced); 66kΩ (balanced)
• Inputs: 1 pair balanced XLR; 1 pair unbalanced RCA
• Speaker Outputs: 1 pair per channel, 24K gold-plated five-way binding posts
• Trigger: 3.5mm, 9–12V DC; audio signal auto-on
• Transformer: 1.3 kVA shielded toroidal, independent channel windings
• Filter Capacitance: 108,000 μF
• Power Consumption: Standby: 1W |
• Idle: 160W | Typical: 300W | Maximum: 1,400W
• Dimensions: (W x H x D) 17⅝″ x 7¾″ x 20″ (21½″ with cables)
• Weight: 71 lbs (32.2 kg)
• Finishs: Available: Black, Silver
• Warranty: 5 years parts & labor (2 years for remote controls, displays, moving parts)

What’s in the Box

• Parasound Halo A21+ stereo power amplifier
• Detachable AC power cord
• Owner’s manual

Note: Interconnect cables and speaker cables are sold separately. Verify contents with manufacturer for the most current packing list.