Halo A 21 User manual

A 21 Amplifier
Owner’s Guide

1
THANK YOU!
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.
Here at Parasound, we design our products to perform at a higher level of flexibility
and sonic performance than you may have expected. We encourage you to read
this entire manual to learn all the features and capabilities of your new Halo Series
A 21 Amplifier.
If you’re eager to get up and running right away, simply follow the basic step-by-step
instructions to connect and operate the A 21. If you want to learn about some of the
technical and design aspects of your A 21, refer to the Technically Speaking and
Parasound A 21 Design Overview sections in the back of the manual. If you run into
difficulties, the Troubleshooting Guide should help you quickly remedy the problem.
We appreciate you taking the time to read these instructions and thank you for
selecting Parasound for your listening pleasure.
The Parasound Staff
Unpacking Your A 21
Unpack your A 21 from the shipping carton, remove the enclosed rack mounts, AC
power cord, and the control wire with 2.5 mm sub-mini plugs on each end. (This is
the trigger connection wire). While you are unpacking your new amplifier, inspect
it thoroughly for possible shipping damage. If you see any, contact your Parasound
dealer right away. Be sure to save and store both the inner and outer cartons and the
packing inserts for possible future transport. To save room for storage, you can cut the
seams on the bottom of the cartons and flatten them.
Keeping Records for Future Reference
Record the serial number located on the bottom of your A 21 in the space below. Also
note your Parasound Dealer’s name and phone number. We recommend that you keep
your purchase receipt with this manual and store them both in a safe place. You may
need to refer to this information sometime in the future.
Parasound A 21 Amplifier Serial #: ____________________
Parasound Dealer: ____________________________________
Phone Number:_______________________________________
Date of Purchase: _____________________________________
YOU SHOULD KNOW
There is no Parasound warranty for this unit if it was not purchased from an Authorized
Parasound Dealer. Investigate any warranty claims made by unauthorized dealers very
carefully as you will need to depend entirely upon the dealer, and NOT upon Parasound.
Unauthorized dealers may lack the capability to arrange repairs of Parasound equipment.
Authorized Parasound Dealers are listed at www.parasound.com or you can call 415-397-7100
between 8:30 am and 4:30 pm Pacific time.
A missing or tampered serial number could indicate that this unit was stolen or sold by an
unauthorized dealer. If this unit is missing its serial number, you should return it to your
dealer immediately for a full refund.

PLACEMENT GUIDELINES FOR YOUR A 21
_________________________________________________________________________________
CONNECTING A STEREO PREAMPLIFIER OR A SURROUND
CONTROLLER TO THE BALANCED INPUTS ON YOUR A 21
_________________________________________________________________________________
CONNECTING A STEREO PREAMPLIFIER OR A SURROUND
CONTROLLER TO THE UNBALANCED INPUTS ON YOUR A 21
_________________________________________________________________________________
CONNECTING THE A 21 LOOP OUT JACKS
TO ANOTHER POWER AMPLIFIER’S INPUTS
_________________________________________________________________________________
CONNECTING SPEAKERS TO YOUR A 21
_________________________________________________________________________________
CONFIGURING THE A 21 FOR BRIDGED MONO OPERATION
_________________________________________________________________________________
MANUAL AND AUTOMATIC TURN ON-OFF OPTIONS
_________________________________________________________________________________
CONNECTING AN EXTERNAL DC SOURCE FOR A 21 AUTOMATIC TURN ON-OFF
_________________________________________________________________________________
CONNECTING THE A 21 TO TRIGGER ANOTHER COMPONENT
_________________________________________________________________________________
UNDERSTANDING THE INDICATORS ON THE A 21
_________________________________________________________________________________
CONNECTING THE A 21 AC POWER CORD
_________________________________________________________________________________
MAINTAINING YOUR A 21
_________________________________________________________________________________
TROUBLESHOOTING GUIDE
_________________________________________________________________________________
SERVICING YOUR A 21
_________________________________________________________________________________
TECHNICALLY SPEAKING
_________________________________________________________________________________
PARASOUND A 21 DESIGN OVERVIEW
_________________________________________________________________________________
PARASOUND A 21 SPECIFICATIONS
_________________________________________________________________________________
1
TABLE OF CONTENTS
A 21 Amplifier
19
17
13
12
15
14
11
10
9
8
7
5
4
2
1
3
6

PLACEMENT GUIDELINES FOR YOUR A 21
Power ampliers 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 re, 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 airow into the openings
in the chassis bottom.
• Leave at least 3” of space around both sides and 6” of space above the top. The bottom
clearance can be a little less.
• Do not block the front of the A 21 behind closed cabinet doors during use.
• Do not stack the A 21 with other components inside a cabinet unless you use a fan to circulate
and exhaust the warm air that builds up between them.
Rack Mounting Your Parasound A 21
To mount the A 21 into a 19” wide equipment rack, you must rst attach its rack mount brackets
(provided). 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. A single standard rack space allows
1-3/4” vertical height in a 19" wide equipment rack. This measurement standard was developed
by the EIA (Electronic Industries Association) so manufacturers of electronic components and
equipment racks could build products in standardized heights that would t in a uniform space.
Please call your Parasound dealer or Parasound Technical Services if you need additional advice
about rack mounting the A 21.
To attach the rack mount brackets:
• Remove the three screws from each side of the A 21. These are arranged vertically, behind its
front panel and in front of its rst heatsink n.
• Line up the three holes on each bracket with the three holes on the A 21 and reinsert
the screws.
• Make sure the screws are tight because they will support the entire weight of the A 21 in the
equipment rack
1
HRA-4 Rack Adapter Mounted on JC 1
Rack Mount Brackets Attached to A 21

XLR Connectors
Male
Female
YOU SHOULD KNOW
Balanced XLR Jacks and Their Pin Configuration
The balanced inputs of the A 21 use XLR jacks that conform to the industry standard of:
Pin 1: Ground, Pin 2: Positive (+), Pin 3: Negative (--). The balanced outputs on some
components use terminals with 3 screws instead of XLR jacks. These are compatible with
the A 21 as long as you match the bare wires to the corresponding pins on the XLR plug: +
to pin 2, - to pin 3, and Ground to pin 1.
CONNECTING A STEREO PREAMPLIFIER OR A SURROUND
CONTROLLER TO THE BALANCED INPUTS ON YOUR A 21
1
2
3&4
2
3
Left
Right
COMPONENTS
SURROUND
SOUND
CONTROLLER
PREAMP
OUTPUTS
or
1 2
3
1 2
3
42
1
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.
What You’ll Need:
• One pair of balanced interconnect cables with XLR connectors
• A preamplifier or surround controller with balanced outputs
Before Connecting
Leave the A 21’s AC cord disconnected until you have made all other connections to
prevent any surprise burst of sound.
Make sure that all your cables are long enough so they are not strained or stretched
once they are connected.
Make sure the Inputs switch on the rear of the A 21 is in its Balanced (up) position and
the Ground switch is in its Normal (down) position.
To Connect
Plug the male end of the balanced interconnect cable into the Balanced Right Channel
input jack on the A 21.
Plug the female end of this cable into the balanced right channel output jack on
your preamplifier (or a channel on your surround controller).
Repeat steps 1 and 2 above to connect the left channel.

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.
What You’ll Need:
• A pair of shielded interconnect cables with RCA plugs
• A source component with RCA output jacks
Before Connecting
Leave the AC cord on the A 21 disconnected until you have made all other connections
to prevent any surprise burst of sound.
Make sure that all your cables are long enough so they are not strained or stretched
once they are connected.
Make sure the Inputs switch on the A 21 is in its Unbalanced (down) position and the
Ground switch is in its Normal (down) position.
To Connect
Plug one end of the cable into the Unbalanced Right Channel Input jack on the A 21.
Plug the other end of this cable into the unbalanced right channel output jack on your
preamplifier (or a channel on your surround controller).
Repeat steps 1 and 2 for the left channel.
CONNECTING A STEREO PREAMPLIFIER OR A SURROUND
CONTROLLER TO THE UNBALANCED INPUTS ON YOUR A 21
3
3
COMPONENTS
SURROUND
SOUND
CONTROLLER
PREAMP
OUTPUTS
or
4
2
1
Right Left
2
RCA Plugs
Right
Left
3&4
1
YOU SHOULD KNOW
Interconnect Cables and Their Color Codes
Common color codes for input and output jacks are red for right and white for left. Match
the colors at the outputs from your preamplifier or surround controller to the inputs on your
A 21 so you’ll always hear the channels in their intended position.

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.
What You’ll Need:
• One pair of shielded interconnect cables with RCA plugs
• An additional amplifier
Before Connecting
Leave the AC cord on the A 21 disconnected from the wall until you have made all of
the connections in the system to prevent any surprise burst of sound.
Make sure that your interconnect cables are long enough so they are not strained or
stretched once they are connected.
To Connect
Plug one end of the cable to the right channel Loop Out jack on the A 21.
Plug the other end of this cable to the right channel input jack on the other power amplifier.
Repeat steps 1 and 2 for the left channel.
RCA Plugs
Right
Left
CONNECTING THE A 21 LOOP OUT JACKS
TO ANOTHER POWER AMPLIFIER’S INPUTS 4
YOU SHOULD KNOW
These jacks eliminate the need for two “Y” connector cables to split the outputs from the
two source channels between your A 21 and another amplifier. The A 21 Loop Out Jacks
jacks provide the same signals that are received at either the balanced or the unbalanced
inputs. Refer to Loop Out Jacks in the Technically Speaking section for more information
about when to use the Loop Out Jacks.
3
COMPONENTS
1
24
POWER AMP
Right Left
INPUTS
2
1
3&4

Stripped
AWG wire
Dual
Banana Plug
Common Speaker Connectors
Single
Banana Plug
Spade Lug
Red usually
designates right
The GND notch
signifies ground
or speaker left
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.
What You’ll Need:
• Two lengths of speaker wire
AWG 16 or thicker with banana
plugs, spade lugs, or bare wire
• Loudspeakers or a speaker
selector box
Before Connecting
Remove power to all the components in your audio system.
To Connect
Insert one wire with the ridge or other marking into the red Right + (positive) speaker
terminal on the A 21. Insert the wire without the ridge or other marking into the black
Right - (negative) speaker terminal on the A 21.
Insert the other end of the wire with the ridge or other marking into the red right +
(positive) terminal on the speaker. Insert the wire without the ridge or other marking
into the black right - (negative) terminal on the speaker.
Repeat steps 1 and 2 for the left channel.
YOU SHOULD KNOW
Correct Speaker Polarity is Important
Polarity refers to + and – connections. Speaker wires are coded with printing or a ridge on
the insulation on one of the leads so you know which lead was connected to the + and –
terminals at the other end. This coding will help you keep the + and - polarity consistent
for both channels.
Speaker Wire Length and Gauge (thickness)
When selecting speaker wire, follow these guidelines:
• Keep the length of your speaker wire as short as possible
• Use the thickest wire practical. For lengths greater than 50 feet, use speaker wire with an AWG
(gauge) of 14 or lower. The smaller the AWG, the thicker the wire.
• Do not use speaker wire that is thinner than 16 AWG.
CONNECTING SPEAKERS TO YOUR A 21
5
1
2
3&4
2 4
1 3
Speakers

CONFIGURING THE A 21 FOR BRIDGED MONO OPERATION 6
YOU SHOULD KNOW
IMPORTANT! - Before Trying Bridged Mono
You should not connect a speaker with an impedance of less than 8 Ω to the A 21 when it is
configured for bridged mono operation. Refer to Bridged Mono Operation in the Technically
Speaking section for additional information about. Use the right channel Gain control to
adjust level in the bridged mode.
1
2
3
6
4
5
7
8
Speaker
7
6
4 5
88
2
3
8
1
RightLeft
Components
Surround
Sound
Controller
Preamp
OUTPUTS
In certain applications, you may require your A 21 to power a single 8 Ω sp eaker by
using its bridged mono feature. In most instances, you won’t use the A 21 this way and
you can skip this section.
What You’ll Need:
• One length of speaker wire with banana plugs, spade lugs, or bare wires
• One shielded balanced or unbalanced interconnect cable for each A 21 used
in bridged mono
• One loudspeaker with an impedance of 8
Ω or higher
Before Connecting
Remove power to all the components in your audio system.
Set the A 21 Stereo - Mono Bridge Switch to its Mono (up) position.
To Connect: From the Source
Plug one end of the interconnect cable into the Balanced or Unbalanced Right
Channel & Mono Input jack on the A 21
Plug the other end of this cable into the desired output channel on the preamplifier
or surround controller.
Do not make any connection to either Left Channel Input jack on the A 21.
To Connect: To the Speaker
Insert the wire with the ridge or other marking into the red Right + (positive) speaker
terminal on the A 21. (This is the positive speaker terminal in bridged mono.)
Insert the wire without the ridge or other marking into the Left + (positive) speaker
terminal on the A 21. (This is the negative speaker terminal in bridged mono.)
Insert the wire with the ridge or other marking into the red + (positive) terminal on the speaker.
Insert the wire without the ridge or other marking into the black -- (negative) terminal
on the speaker.
Do not make connections to either of the
A 21's black speaker terminals.

MANUAL AND AUTOMATIC TURN ON-OFF OPTIONS
7
YOU SHOULD KNOW
Turn Off Delay in the Audio Mode
When the music (audio signal) stops, the A 21 will remain turned on for about five minutes.
This delay prevents unwanted turn-off during silent passages in music or pauses between
1Switch in up position
Start Sensitivity at 12 o'clock
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 Active Audio Source for Automatic On-Off
If you want to automatically turn on the A 21 whenever music is playing (an audio
signal is present), choose the audio triggering option by moving the Auto Turn On
switch to its upper Audio position.
What You’ll Need:
• An audio source that's playing
Before Connecting
Remove power to all the components in your audio system.
Make sure the Auto Turn On switch on the A 21 is in its Audio (up) position.
Set the Audio triggering Sensitivity adjustment knob on the rear panel to the desired
level. Start with the 12 o’clock position.
To Connect
Connect an active audio source to either the Left or Right Balanced or Unbalanced
Input jacks. (Refer to to pages 2 and 3).