This power amplifier is a Power Boss!
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.
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.
Product highlights:
300 watts per channel into 8 ohms (20-20,000 Hz) at 0.1% THD with 2 channels driven
500 watts x 2 into 4 ohms
1,000 watts x 1 at 8 ohms in bridged mode
designed by legendary audio engineer John Curl
high-bias Class A/AB amplifier design
large custom toroidal transformer
frequency response: 5-100,000 Hz (-3dB)
signal-to-noise ratio: 115 dB
stable with speaker impedance dips down to 1.5 ohms
left and right balanced XLR and unbalanced RCA inputs
individual gain control for each channel
RCA loop outputs for each channel
let you daisy-chain additional amps
in bi-amp configuration, passes input signal from one channel to the other’s RCA input
custom 5-way binding post speaker connectors
in bridged mode, only the positive binding posts are used
switchable turn-on options: manual, signal sensing, or 12-volt trigger
detachable power cord
rack mounting ears included
Dimensions and warranty:
17-5/8″W x 7-3/4″H x 21-1/2″D (4U rack spaces)
weight: 71 lbs.
MFR # A 21+ BLACK
What’s in the box:
Stereo power amplifier
6′ AC power cord
6′ Mono-minijack cable
Rack-mount hardware
Owner’s Guide
