A 21 Amplifier Owner’s Guide
THANK YOU! 1 Congratulations and Thank You for Choosing Parasound Your new Parasound Halo Series A 21 power amplifier presents the latest advancements in amplifier technology. The A 21 is built to the strict quality and performance standards set by Parasound. We’re proud to offer you this exceptional audio component that will bring you many years of enjoyment and dependability.
TABLE OF CONTENTS A 21 Amplifier 1 PLACEMENT GUIDELINES FOR YOUR A 21 _________________________________________________________________________________ 2 CONNECTING A STEREO PREAMPLIFIER OR A SURROUND CONTROLLER TO THE BALANCED INPUTS ON YOUR A 21 _________________________________________________________________________________ 3 CONNECTING A STEREO PREAMPLIFIER OR A SURROUND CONTROLLER TO THE UNBALANCED INPUTS ON YOUR A 21 _________________________________________________________________________________ 4
1 PLACEMENT GUIDELINES FOR YOUR A 21 Power amplifiers are usually heavier and generate more heat than other components. To avoid damage to the A 21 or other equipment and to reduce risk of fire, you must follow these guidelines: • Place the A 21 on a separate shelf that will adequately support its weight. • Keep it away from heat sources such as air ducts or radiators. • Avoid placing it on carpeting or another material that might obstruct airflow into the openings in the chassis bottom.
CONNECTING A STEREO PREAMPLIFIER OR A SURROUND CONTROLLER TO THE BALANCED INPUTS ON YOUR A 21 2 Left and Right Balanced Input Jacks Balanced connections will give you the best sound. If your preamplifier or surround controller has balanced XLR output jacks, we recommend that you connect them to these inputs. Refer to the Balanced and Unbalanced Lines in the Technically Speaking section for additional information about why we recommend using balanced lines.
3 CONNECTING A STEREO PREAMPLIFIER OR A SURROUND CONTROLLER TO THE UNBALANCED INPUTS ON YOUR A 21 Left and Right Unbalanced Inputs Use these inputs if your preamplifier or surround controller doesn’t have balanced output connectors or if you simply prefer to use unbalanced connections.
CONNECTING THE A 21 LOOP OUT JACKS TO ANOTHER POWER AMPLIFIER’S INPUTS 4 Loop Out Connector The Right and Left Loop Out jacks provide connections to route the same input signals from your preamplifier or surround controller to an additional power amplifier. In most instances, you won't use the loop out feature so you can skip this section.
5 CONNECTING SPEAKERS TO YOUR A 21 Speaker Terminals The five-way binding post speaker terminals on the A 21 accept most speaker wire terminations including single or dual banana plugs, 1/4” spade lugs, or bare wire. Refer to Bare Wire Speaker Termination in the Technically Speaking section for information about bare wire termination.
CONFIGURING THE A 21 FOR BRIDGED MONO OPERATION In certain applications, you may require your A 21 to power a single 8 Ω speaker by using its bridged mono feature. In most instances, you won’t use the A 21 this way and you can skip this section.
7 MANUAL AND AUTOMATIC TURN ON-OFF OPTIONS You can manually turn the A 21 on and off with its front panel On-Off button. It can also be triggered to turn on and off automatically when your preamplifier, surround controller, or system controller is turned on and off. Manual On-Off from the Front Panel If you want to manually turn on and off the A 21 at any time, you need to first select the Manual On-Off option by placing the Auto Turn On switch (on the rear panel) to its middle Man (Manual) position.
CONNECTING AN EXTERNAL DC SOURCE FOR A 21 AUTOMATIC TURN ON-OFF 8 If you want to automatically turn on and off the A 21 with an external DC voltage, choose the DC Triggering option by moving the Auto Turn On switch on the rear panel to its lower 12V position. What You’ll Need: • A cable with a 2.5 mm sub-mini plug on each end (provided) • A “control” component with +9Vdc to +12Vdc trigger voltage 2.5 mm sub-mini plug Before Connecting Remove Power to all the components in your audio system.
9 CONNECTING THE A 21 TO TRIGGER ANOTHER COMPONENT B Whenever the A 21 is turned on either manually or automatically, there is 12 Vdc present at its own DC Trigger Out jack so it can trigger additional amplifiers or other components on and off. What You’ll Need: • A cable with a 2.5 mm sub-mini plug on each end (in addition to the one provided with the A 21) • A component that can be triggered with an external +9 Vdc to +12 Vdc source. The A 21 DC Trigger output provides up to 150 mA of current 2.
UNDERSTANDING THE INDICATORS ON THE A 21 A&B B AC Present Indication When the A 21 is plugged into a live AC outlet, a soft blue halo glows behind its On-Off button and its red “P” Badge glows faintly. These indicate that the unit is plugged into a live AC outlet, even when it is turned off. On, Off and Fault/Protection Status Indicators Whenever the A 21 is turned on, the soft blue glow behind its On-Off button will change to red for about five seconds as its internal circuits stabilize.
11 CONNECTING THE A 21 AC POWER CORD AC Power Connections We recommend that you plug your A 21 into the same AC wall outlet or power strip that powers your other audio components, especially the preamplifier or system controller. Having all the audio components on the same power circuit helps prevent hum caused by possible ground loops. The A 21 requires AC power that is continuous rather than switched on and off.
MAINTAINING YOUR A 21 Your Parasound A 21 power amplifier requires no periodic maintenance and has no user-serviceable parts inside. To avoid the risk of electric shock, do not remove its top cover. The amplifier’s exterior can easily be cleaned with a soft cloth pre-moistened only with a few drops of water or glass cleaner. Main Power Fuse If this fuse blows, please contact Parasound Technical Service for further advice.
13 TROUBLESHOOTING GUIDE AC Voltage selector switch is in the wrong position REMEDY Connect power cord Check for correct position of the Auto Turn On switch Make sure the switch is in the correct position for your region AC fuse blown Replace with same value fuse Auto turn on doesn’t function with a trigger voltage DC trigger source wired in reverse or voltage too low Check polarity of DC source with a voltmeter Try connecting a 9 V battery to the 12V DC input Auto Turn On selector switch in wrong
SERVICING YOUR A 21 14 If All Else Fails –Call Us for Help Call your Parasound dealer or Parasound’s Technical Service Department toll free at 1-866-770-TECH (8324). We can often solve the problem with simple diagnostic tests you can perform yourself. If we determine that your A 21 will need further inspection or servicing, we will: a) Refer you to an authorized Parasound repair center near you, or b) Authorize return of the unit to us and advise you of the correct procedure.
15 TECHNICALLY SPEAKING Audio Trigger Sensitivity Adjustment The Audio Sensitivity Control sets the threshold of the audio trigger signal. You can adjust this level from a maximum sensitivity of 50 mV (fully counterclockwise) to a minimum sensitivity of 200 mV (fully clockwise). If you set this control to 50 mV, the A 21 might be falsely triggered on by non-musical or noisy signals that can appear in the system, such as when you switch preamp inputs at high volume levels.
TECHNICALLY SPEAKING continued Choosing Interconnect Cables and Speaker Wire We are often asked to recommend specific interconnect cables and speaker wire. It’s true that with some amplifiers, sound quality will vary greatly according to interconnect cables and speaker wires. However, Parasound amplifiers use robust circuitry that sounds superb regardless of interconnects and speaker wires. Therefore, we feel that choosing a brand of cable for Parasound amplifiers is purely a matter of personal taste.
17 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.
PARASOUND A 21 DESIGN OVERVIEW continued The Driver Stage The driver stage provides critical amplification for which we employ a complementary matched pair of MOSFETs selected for their tube-like sonic qualities. MOSFETs tend to generate less odd-order harmonic distortion than bipolar transistors. This is important because odd-order distortion sounds unnatural and fatiguing to the human ear, whereas even-order distortion is less offensive because it is consonant, rather than dissonant.
19 PARASOUND A 21 SPECIFICATIONS Power Output - Both Channels Driven 250 watts RMS x 2, continuous, 20 Hz - 20 kHz, 8 Ω 400 watts RMS x 2, continuous, 20 Hz - 20 kHz, 4 Ω Power Output - Mono 750 watts RMS, 20 Hz - 20 kHz, 8 Ω Current Capacity 60 amperes peak per channel Slew Rate > 130 volts per microsecond Frequency Response 5 Hz-100 kHz, +0/-3 dB at 1 watt Total Harmonic Distortion < 0.2 % at full power < 0.03 % at typical listening levels IM Distortion < 0.04 % TIM Unmeasureable Dynamic Headroom > 1.
Parasound Products, Inc. 950 Battery Street, San Francisco, CA 94111 415-397-7100 / Fax 415-397-0144 www.parasound.
