Power up your surround sound system

Parasound's Halo A 51 amplifier offers outstanding power for the front left/right/center speakers and a pair of surrounds in your home theater system. The amp delivers 250 watts per channel with all five channels driven, and it's stable at very low impedances, so it's compatible with a very wide range of speakers. With its sheer power — and thoughtful circuit design courtesy of Parasound's audio guru John Curl — this amplifier delivers impressive volume, clarity, and dynamics to your surround sound system.

Class A/AB operation for smoother sound

The A 51 uses a Class A/AB power circuit. You don't see an amplifier described that way 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.

The legacy of John Curl

The A 51 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 51 were chosen to offer high performance at a reasonable price.

Product highlights:

• 250 watts per channel into 8 ohms (20-20,000 Hz) at 0.2% THD with 5 channels driven

• 400 watts per channel into 4 ohms (20-20,000 Hz) with 5 channels driven

• designed by legendary audio engineer John Curl

• THX Ultra2 certified for reference home theater sound

• high-bias Class A/AB amplifier design

• large toroidal transformer

• frequency response: 5-100,000 Hz (-3dB)

• signal-to-noise ratio: 112 dB

• handles very low impedances for use with virtually any speakers

• five balanced XLR and five unbalanced RCA inputs

• heavy-duty gold-plated 5-way speaker terminals

• switchable turn-on options: manual, signal sensing, or 12-volt trigger

• detachable power cord

• rack mounting ears included