A 21+ Stereo Power Amplifier OWNER’S GUIDE
Important Safety Instructions The lightning flash with the arrowhead symbol within an equilateral triangle is intended to alert the user to the presence of “dangerous voltage” inside the product that may constitute a risk of electric shock. The exclamation point within an equilateral triangle is intended to alert the user to the presence of important operating and maintenance instructions in the literature accompanying the product. TO REDUCE THE RISK OF ELECTRIC SHOCK, DO NOT REMOVE COVER.
Table of Contents Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Placement and Ventilation Guidelines AC Mains Voltage . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5 Front Panel Illustration . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
INTRODUCTION Thank You for Choosing Parasound Your new Parasound Halo A 21+ power amplifier has been designed with the most advanced, proven class A/AB amplifier technology. The A 21+ is built to extremely strict quality and performance standards for which Parasound is renowned. We’re proud to offer you this exceptional audio component that will bring you many years of enjoyment and dependability.
Unpacking Your A 21+ & Placement Guidelines Unpacking Your A 21+ Carefully remove your A 21+ from its shipping carton and locate the enclosed accessories: • AC power cord • A 12V trigger wire for auto turn on. It has a mono 3.5 mm mini plug at each end. • Rack mount ears While you are unpacking your A 21+, inspect it thoroughly for possible shipping damage and tell your Parasound dealer immediately if you find any evidence of shipping damage.
Rack Mounting Your Parasound A 21+ To mount the A 21+ into a 19" wide equipment rack, you must first attach its two “L” shaped rack mount brackets (included). With its four feet removed, the A 21+ chassis and front panel height occupies four rack spaces (7" or 176 mm). When mounting equipment below the A 21+, you will also need to allow about 1 8" below the unit for the bottom chassis screws. To attach the rack mount brackets: • Remove the three screws from each side of the A 21+.
Audio Input Connections Always disconnect the AC cord to your A 21+ before making or changing any input, output or trigger wire connections. Inserting or removing an input or output cable while the A 21+ is turned on can result in a blast of sound that can damage your loudspeakers. Balanced XLR Input Jacks In most systems balanced XLR connections will give you the best sound. If your stereo preamplifier has balanced XLR output jacks, we recommend that you connect them to the A 21+ XLR inputs.
Bi-Amping is Often Superior to Bridged Mode Bridging offers a massive power increase but It is often more power than your speakers need or can safely handle. Bi-amping is an alternative to bridging and many people report greater sonic improvements. Like bridging, bi-amping will require a A 21+ amplifier for each speaker. Note: Bi-amping in this context is technically “passive bi-amping” so an external electronic crossover is not required.
Turn On Options The setting of the rear panel Turn On Options switch determines how the amplifier turns on and off. Setting the Turn On Options switch to Audio or 12 V disables the A 21+’s front panel Power button. There are three positions for this switch: Manual: When the Turn On Options switch is set to Manual the A 21+ is turned on and off manually only by pressing the Power button on its front panel every time you want to listen to music.
Front Panel Operation On-Off Button Push once to turn on the A 21+. When the A 21+ is turned on the dim blue glow around the On-Off button will become brighter and the two blue channel indicators will illuminate. Push the button again to turn off the A 21+. The front panel On-Off button will be disabled when the Turn On Options switch is set to Audio or 12 V.
Technically Speaking Balanced and Unbalanced Lines Recording and broadcast studios use balanced connections exclusively because of their inherent ability to reject noise and hum, thus assuring the best sound. Certain high quality preamplifiers and surround controllers built for residential use utilize balanced connections with XLR jacks for the same reasons.
Parasound A 21+ Design Overview Circuit Designed by John Curl Parasound design consultant John Curl has been a legend among audiophiles and electronic engineers for decades.
Audio Circuit Path Topology Parasound’s circuit topology is a hybrid of carefully chosen discrete transistors that result in superior performance at each stage. We use JFETs (Junction Field Effect Transistors) for the input voltage amplifier stage; MOSFETs (Metal Oxide Field Effect Transistors) for the drivers of a second voltage amplifier stage and bipolar transistors for the current amplifier output stage.
Total Protection - DC Servos Even a miniscule amount of Direct Current (DC) will burn out speakers without any warning. Every power amplifier must have some way to insure that DC from its power supply never reaches its + or - speaker terminals. Most amplifiers simply use adjustable trim controls to reduce their DC offset or capacitors to block DC.
Problems and Remedies Unit will not turn on • Check the setting of the Turn On Options switch. (The front panel On-Off button will be disabled if this switch is set to Audio or 12 V) • If using Audio Turn on, try increasing the sensitivity of the audio trigger by turning the audio threshold knob to the “Quieter” position. • Check that the rear panel power switch is on and that the AC power is live. No sound from speakers • Check that input cables and speaker wires are secure at both ends.
Are You Having Difficulty? Repair or Service Call your Parasound dealer first. If the dealer can’t help you with your problem we encourage you to call Parasound’s Technical Service Department at 415-397-7100, Monday - Friday, 8am - 4pm Pacific Time. We can suggest other diagnostic tests you can easily perform.
Chassis Illustration and Dimensions 19
Specifications Power Output – Stereo Mode Total Gain 300 watts x 2, 8 Ω both channels driven 500 watts x 2, 4 Ω both channels driven 29 dB Input Sensitivity for 28.28 V Output into 8 Ω Power Output – Bridged Mode Unbalanced: 1 V Balanced: 1 V per leg 1000 watts x 1, 8 Ω Bridged 4 Ω operation is not recommended S/N Ratio Power measurement are at 120 VAC: 0.
