Parasound Halo A52+ 5-Channel Power Amplifier

Circuit Designed by John Curl

Parasound design consultant John Curl has been a legend among audiophiles and electronic engineers for decades. He pioneered measurements to correlate musical accuracy with the materials used in parts, worked with world-class touring companies, has designed highly coveted audio classics, including the original Mark Levinson JC-2, Denneson JC-80, Vendetta Phono Preamplifier, and CTC Blowtorch preamplifiers; master recorders for Wilson Audio and Mobile Fidelity; and the mixing consoles used in live concerts by The Grateful Dead and the Montreux Jazz Festival in Switzerland.

Carefully Selected Components

Every part within the A 51 is carefully chosen for its accuracy and reliability. Metal film resistors with 1% tolerance are selected for their precision and because their values don�t drift as they heat up during operation. Polypropylene and mica capacitors are used extensively for their superior linearity and low dielectric absorption. Semiconductors are selected for superior performance in their specific roles in the circuit. Gold has the best conductivity of any metal, so high-quality gold-plated input connectors and speaker terminals are used. The double-sided circuit boards are FR4 glass epoxy for long-term durability. The chassis is made of heavy gauge steel to safely house the internal circuitry. This attention to detail when selecting parts makes the difference between a very good amplifier and an outstanding amplifier.

Audio Circuit Path Topology

Parasound�s circuit topology is a hybrid of carefully chosen discrete transistors that result in superior performance at each stage. Parasound use JFETs (Junction Field Effect Transistors) for the input stage, MOSFETs (Metal Oxide Field Effect Transistors) for the driver stage, and bipolar transistors for the output stage. Discrete transistors are more sonically accurate than integrated circuits commonly used by other brands.

Class-A/AB Operation

Pure Class-A operation provides the purest sound. However, an amplifier operating entirely in Class-A operation would be enormous, highly inefficient, and generate too much heat. Class-A/AB combines some of the advantages of Class-A with the efficiency of Class-B operation. It is a compromise that reduces the heat generated in pure Class-A operation and the odd-order harmonic distortion created in Class-B. In Class-A/AB, the driver and output stages are always partially turned on, which provides a nominal amount of pure Class-A operation. At higher power levels, when the musical waveform swings from positive to negative and vice versa, each bank of transistors is allowed to rest momentarily. This resting, or quiescent time, makes it possible to deliver high amounts of power without overheating. It also makes it possible to use passive cooling and avoid fans, whose noise can be heard over the music. The A 51 input and driver stages employ pure Class-A while its output stage operates with higher pure Class-A power than many amplifiers selling for twice or three times its price. The result is less fatiguing, more natural sound.

Additional Features

• Direct coupled input circuits, no capacitors or inductors in signal path
• Beta-matched 15 amp, 60 MHz bipolar output transistors (3 pairs per channel)
• 1.5 kVA toroidal power transformer encased in an epoxy-filled steel canister for ultra-quiet performance
• Transformer wired with independent secondary windings for each channel
• 100,000 ?F power supply filter capacitance
• Employs advanced DC Servo and relay protection circuits to protect against current overload and interference
• AC present, channel status, and high-temperature indicators
• Adjustable audio trigger sensitivity for auto-on function
• 3U chassis is rack mountable with HRA3 kit (sold separately)

Parasound A52+ Specs

Channels	5.0
Power Output per Channel	5-Channel Driven: 180 W at 8 Ohms / 20 Hz to 20 kHz / 0.05% THD (RMS) 255 W at 4 Ohms / 20 Hz to 20 kHz (RMS) 2-Channel Driven: 225 W at 8 Ohms / 20 Hz to 20 kHz 350 W at 4 Ohms / 20 Hz to 20 kHz
Rear A/V Outputs	No
Speaker I/O	5x Gold-Plated 5-Way Binding Post Pairs
Wi-Fi	No
Bluetooth	No

Amplifier Type	Power Amplifier
Channels	5.0
Amplifier Class	Class-AB
Power Output per Channel	5-Channel Driven: 180 W at 8 Ohms / 20 Hz to 20 kHz / 0.05% THD (RMS) 255 W at 4 Ohms / 20 Hz to 20 kHz (RMS) 2-Channel Driven: 225 W at 8 Ohms / 20 Hz to 20 kHz 350 W at 4 Ohms / 20 Hz to 20 kHz
Frequency Response	5 Hz to 100 kHz +0/-3 dB (1 W) 20 Hz to 20 kHz +0/-0.3 dB
THD	< 0.05% (Full Power)
Speaker Impedance	4 to 8 Ohms
Tone Control	No
Damping Factor	> 1100 (20 Hz to 20 kHz)

Supported Sample Rates

No

Rear A/V Inputs	5x Mono XLR Balanced 5x RCA Unbalanced
Rear A/V Outputs	No
Front I/O	No
Other Rear I/O	1x 1/8" / 3.5 mm (12 V Trigger) Input 1x 1/8" / 3.5 mm (12 V Trigger) Output
Speaker I/O	5x Gold-Plated 5-Way Binding Post Pairs
Media Card Slot	No
A/B Speaker Selection	No
Bi-Amp Capability	No
Input Impedance	XLR: 94 Kilohms RCA: 47 Kilohms
Input Sensitivity	Balanced, Unbalanced: 1 V
Signal to Noise Ratio	> 112 dB (IHF-A / Input Shorted) > 102 dB (Input Shorted / Unweighted)
Crosstalk	78 dB (1 kHz) 63 dB (20 kHz)

Wi-Fi	No
Bluetooth	No

External Control Support	No
Mobile App Compatible	No

Input Power	115 VAC, 60 Hz
Power Consumption	Maximum: 1500 W No Sound: 125 W Standby: 1 W

Dimensions (W x H x D)	17.2 x 5.9 x 20.0" / 437.0 x 149.0 x 508.0 mm (with Feet) 17.2 x 5.2 x 20.0" / 437.0 x 133.0 x 508.0 mm (without Feet)
Weight	55.1 lb / 25 kg

Package Weight	64 lb
Box Dimensions (LxWxH)	28.25 x 26 x 12.5"