The Halo A 21+ is a replacement of Parasound’s beloved Halo A 21 amplifier. A 21+ offers more impressive dynamics, a more accurate stereo image, wider stereo separation, andmore impressive control over speakers' drivers on a regular basis. The A 21+ has a high-bias Class A/AB circuit design, which is one of the amp's standout features. Class A operation often imparts a particularly sweet, smooth, and organic sound signature, and the A 21+ definitely qualifies for these sonic traits, with treble frequencies in particular rendered smoothly and grain-free. This lack of sparkle on the top end makes it an ideal candidate for those who like to listen for long periods of time.
- Upgraded toroidal transformer: The custom-made, shielded toroidal transformer has been pumped up from 1.2 to 1.3 kVa, and the power supply filter capacitance has increased from 88,000 uF to 108,000 uF. The upgrade of the power supply provides a roughly 20 percent increase in output power.
- Improved circuit design: The circuit design for A 21+ has been modified to improve performance and increase sound quality. The new design halves THD, which is now specified at 0.1 percent. Crosstalk and signal-to-noise ratio see improvements too, now rated at 70dB and 115dB, respectively.
- Long-term stability: The amp also features a new auto-turn-on circuit for in-rush surge protection and gold-on-gold internal connections to help with long-term stability.
- High-bias Class A/AB topology: Parasound classifies the amp's topology as high-bias Class A/AB. In practice, this means the amp is biased to output a little over six watts per channel of pure Class A power. From that point onward, the amp switches over to Class AB operation.
- 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
Dimensions and Warranty
- 17-5/8" W x 7-1/8" H x 20" D (without feet, cables)
- 17-5/8" W x 7-3/4" H x 21-1/2" D (with feet, cables)
- Weight: 71 lbs
- Warranty: 5 years
- Our 30-day money-back guarantee
- MFR #