A 23 Amplifier
Owner’s Guide
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TABLE OF CONTENTS
A 23 Amplifier
PLACEMENT GUIDELINES FOR YOUR A 23
1
_________________________________________________________________________________
2
CONNECTING A PREAMPLIFIER OR SURROUND CONTROLLER
TO THE BALANCED INPUTS ON THE A 23
_________________________________________________________________________________
3
CONNECTING A PREAMPLIFIER OR SURROUND CONTROLLER
TO THE UNBALANCED INPUTS ON THE A 23
_________________________________________________________________________________
4
CONNECTING THE LOOP OUT JACKS ON THE A 23 TO ANOTHER
POWER AMPLIFIER’S INPUTS
_________________________________________________________________________________
5
CONNECTING SPEAKERS TO THE A 23
_________________________________________________________________________________
6
CONFIGURING THE A 23 FOR BRIDGED MONO OPERATION
_________________________________________________________________________________
7
MANUAL AND AUTOMATIC TURN ON-OFF OPTIONS
_________________________________________________________________________________
8
CONNECTING AN EXTERNAL DC SOURCE FOR AUTOMATIC ON-OFF
_________________________________________________________________________________
9
CONNECTING THE A 23 TO TRIGGER ANOTHER COMPONENT
_________________________________________________________________________________
10
UNDERSTANDING THE INDICATORS ON THE A 23
_________________________________________________________________________________
11
CONNECTING THE AC POWER CORD
_________________________________________________________________________________
12
MAINTAINING YOUR A 23
_________________________________________________________________________________
13
TROUBLESHOOTING GUIDE
_________________________________________________________________________________
14
SERVICING YOUR A 23
_________________________________________________________________________________
15
TECHNICALLY SPEAKING
_________________________________________________________________________________
17
PARASOUND A 23 DESIGN OVERVIEW
_________________________________________________________________________________
19
PARASOUND A 23 SPECIFICATIONS
_________________________________________________________________________________
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1
PLACEMENT GUIDELINES FOR YOUR A 23
Power amplifiers are usually heavier and generate more heat than other components. To avoid
damage to the A 23 or other equipment and to reduce risk of fire, you must follow these guidelines:
• Place the A 23 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.
• Leave at least 3” of space around both sides and the top. The bottom clearance can be a little
less. This helps facilitate heat dissipation.
• Do not block the front of the A 23 behind closed cabinet doors during use.
• Do not stack the A 23 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 23
If you plan to mount the A 23 into a standard 19” wide equipment rack, you will need to purchase
the optional Parasound HRA 2 Rack Mount Adapter. With its four feet removed, the A 23 chassis
and front panel height occupies two rack spaces (3-1/2” or 88mm). Please call your Parasound
dealer or Parasound Technical Services if you need additional advice about rack mounting the A 23.
A standard single rack space allows 1- 3/4 vertical inches in a 19-inch 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 fit in a uniform space.
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CONNECTING A PREAMPLIFIER OR SURROUND CONTROLLER
TO THE BALANCED INPUTS ON THE A 23
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.
What You’ll Need:
Male
• One pair of balanced interconnect cables with XLR connectors
• A preamplifier or surround controller with
Female
balanced connectors.
XLR Connectors
Before Connecting
Leave the A 23’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 Balanced - Unbalanced switch on the rear of the A 23 is in its Balanced
(up) position.
To Connect
1
Plug the male end of the balanced interconnect cable into the Balanced Right Channel
input jack on the A 23.
2
Plug the female end of the cable into the balanced right channel output jack on
your preamplifier (or a channel from your surround controller).
Repeat steps 1 and 2 above to connect the left channel.
3&4
1
3
CAUTION
2
4
COMPONENTS
SURROUND
SOUND
CONTROLLER
Right
Left
or
PREAMP
OUTPUTS
YOU SHOULD KNOW
Balanced XLR Jacks and Their Pin Configuration
The balanced inputs of the A 23 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 23 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.
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 23
so you’ll always hear the channels in their intended position.
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CONNECTING A PREAMPLIFIER OR SURROUND CONTROLLER
TO THE UNBALANCED INPUTS ON THE A 23
3
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:
Left
• One standard pair of shielded interconnect cables with
Right
RCA plugs
• A source component with RCA output jacks
RCA Plugs
Before Connecting
Leave the AC cord on the A 23 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 Balanced-Unbalanced switch on the A 23 is in its Unbalanced (down) position.
To Connect
Plug one end of the cable into the Unbalanced Right Channel Input jack on the A 23.
1
2
Plug the other end of this cable into the unbalanced right channel output jack on your
preamplifier (or a channel from your surround controller).
3&4
Repeat steps 1 and 2 for the left channel.
3
1
CAUTION
2
4
COMPONENTS
SURROUND
SOUND
CONTROLLER
Right
Left
or
PREAMP
OUTPUTS
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CONNECTING THE LOOP OUT JACKS ON THE A 23 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.
What You’ll Need:
Left
• One standard pair of shielded interconnect cables with
Right
RCA plugs
• An additional amplifier
RCA Plugs
Before Connecting
Leave the AC cord on the A 23 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
1
Plug one end of the cable to the right channel Loop Out jack on the A 23.
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.
2
3&4
3
1
CAUTION
2
4
COMPONENTS
Right
Left
INPUTS
POWER AMP
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 23 and another amplifier. The A 23 Loop Out 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.
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5
CONNECTING SPEAKERS TO THE A 23
Speaker Terminals
The five-way binding post speaker terminals on the A 23 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.
Common Speaker Connectors
What You’ll Need:
The GND notch
signifies ground
or speaker left
Red ususally
designates right
• Two lengths of speaker wire
AWG 16 or thicker with banana
plugs, spade lugs, or bare wire
• Loudspeakers or a speaker
selector box
Dual
Banana Plug
Single
Banana Plug
Spade Lug
Stripped
AWG wire
Before Connecting
Remove power to all the components in your audio system.
To Connect
1
Insert one wire with the ridge or other marking into the red Right + (positive) speaker
terminal on the A 23. Insert the wire without the ridge or other marking into the black
Right - (negative) speaker terminal on the A 23.
2
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.
3&4
Repeat steps 1 and 2 for the left channel
CAUTION
3
1
2
4
Speakers
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.
• Keep wire lengths for both channels as close to equal as possible.
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6
CONFIGURING THE A 23 FOR BRIDGED MONO OPERATION
In certain applications, you may require your A 23 to power a single 8 Ω speaker by using
its bridged mono feature. In most instances, you won’t use the A 23 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 23 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 23 Stereo - Mono Switch to its Mono (up) position.
To Connect: From the Source
1
2
3
Plug one end of the interconnect cable into the Balanced or Unbalanced Right
Channel & Mono Input jack on the A 23
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 23.
To Connect: To the Speaker
4
Insert the wire with the ridge or other marking into the red Right + (positive) speaker
terminal on the A 23. (This is the positive speaker terminal in bridged mono.)
5
Insert the wire without the ridge or other marking into the Left + (positive) speaker
terminal on the A 23. (This is the negative speaker terminal in bridged mono.)
6
7
Insert the wire with the ridge or other marking into the red + (positive) terminal on the speaker.
Insert the wire without the ridge or
6
7
other marking into the black --
(negative) terminal on the speaker.
Speaker
8
Do not make connections to either
of the A 23's black speaker terminals.
4
5
3
1
C A U T I O N
8
Common speaker connectors
Components
The GND notch
signifies ground
or speaker left
Red ususally
designates right
Surround
2
Sound
Controller
OUTPUTS
Preamp
Dual
Banana Plug
Single
Banana Plug
Spade Lug Stripped
AWG wire
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 23 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.
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7
MANUAL AND AUTOMATIC TURN ON-OFF OPTIONS
You can manually turn the A 23 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 23 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 23 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 active audio source connected to the left or right Input jack on the A 23
Before Connecting
Remove power to all the components in your audio system.
Make sure the Auto Turn On switch on the A 23 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).
Switch in up position
Start Sensitivity at 12 o'clock
CAUT IO N
YOU SHOULD KNOW
Turn Off Delay in the Audio Mode
When the music (audio signal) stops, the A 23 will remain turned on for about five minutes. This
delay prevents unwanted turn-off during silent passages in music or pauses between tracks.
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CONNECTING AN EXTERNAL DC SOURCE FOR
AUTOMATIC ON-OFF
8
If you want to automatically turn on and off the A 23 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.
Make sure the AutoTurn On switch on the a 23 rear panel is in it 12V (down) position.
To Connect
1
2
Plug one end of the trigger wire into the 12V Input jack on the A 23.
Plug the other end of this wire into the external DC source
1
CA UT IO N
CONTROL
2
COMPONENT
Output
YOU SHOULD KNOW
If the device you want to use to control your A 23 doesn’t have a 2.5 mm trigger output
connector, you can cut one plug off the cable and terminate the end as required. The lead with
the red stripe is positive and the lead without the stripe is negative.
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9
CONNECTING THE A 23 TO TRIGGER ANOTHER COMPONENT
Whenever the A 23 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 23)
• A component that can be triggered with an external
2.5 mm sub-mini plug
+9 Vdc to +12 Vdc source. The A 23 DC Trigger output
provides up to 150 mA of current
Before Connecting
Remove power to all the components in your audio system.
To Connect
1
2
Plug one end of the trigger wire into the 12V Out jack on the A 23.
Plug the other end of this wire into the component that you want the A 23 to trigger.
1
CA UTI ON
CONTROL
2
COMPONENT
Input
YOU SHOULD KNOW
If the device you want to use to control your A 23 doesn’t have a 2.5 mm trigger output
connector, you can cut one plug off the cable and terminate the end as required. The lead with
the red stripe is positive and the lead without the white stripe is negative.
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10
UNDERSTANDING THE INDICATORS ON THE A 23
A
AC Present Indication
When the A 23 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.
B
C
On and Off Indications for Both Manual and Automatic Modes
When the A 23 is first turned on, the soft blue glow behind the On-Off button turns red for about
five seconds and then becomes a brighter blue.
Channel Status Indicators
These are two small round indicators in the center of the recess in the front panel. The indicator
on the left displays the status of the left channel and the indicator on the right displays the status
of the right channel.
D
E
No Illumination:
When the A 23 is turned off, these indicators are off.
Blue Illumination of Channel Status Indicator:
When both channels are operating normally, these both glow blue.
F
No Illumination of Channel Status Indicators:
A blue channel indicator will stop glowing if there is a fault in its corresponding amplifier
channel. If this occurs for either channel, the halo glow behind the On-Off button will also
change from blue to red.
G
H
High-Temp Indicator
This indicator is near the right side of the panel recess. It will glow red if either channel overheats.
Level Controls
We recommend that you rotate the Left and Right Level controls to their maximum clockwise
positions, marked THX Reference. Refer to Level Controls in Technically Speaking for more
information about setting level controls.
I
Ground Switch
The Ground switch can assist in reducing audible hum caused by ground loops in your system.
Leave this switch in its Normal (down) position unless you hear hum through your speakers (you’ll
only be able to hear this hum after your entire system is installed and operating). You can try the
Lift (up) position to eliminate it. Please refer to the Technically Speaking section for detailed
technical information about the causes of ground loops and what you can do about them.
A
B
G
C
D
E
F
H
I
H
50
3
C A U T I O N
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11
CONNECTING THE AC POWER CORD
AC Power Connections
We recommend that you plug your A 23 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 23 requires AC power that is continuous,
rather than switched on and off.
What You’ll Need:
An IEC 65 AC Cord (provided)
An AC outlet or high quality AC power strip within reach of the AC cord
Before Connecting
Remove power to all the components in your audio system.
To Connect
1
2
Plug the female end of the AC cord to the AC receptacle on the rear of the A 23.
Plug the male end of the AC cord to an AC outlet or power strip.
AC Voltage Selection Switch
The A 23 can operate on either 110-120 Vac or 220-240 Vac operation. When you
purchased your A 23, its rear panel Voltage Selector switch was already set for the
proper voltage in your area. Nevertheless, it’s wise to double-check it before plugging
into an AC outlet.
If you move to a location with a different line voltage, you can easily convert the A 23.
For 110-120 Vac Operation: Remove the lock-out bracket with a phillips screwdriver.
Next, slide the switch sideways toward the left until the indent on the switch lines up
with the 115/60Hz label on the rear panel. The main fuse value should be 6.3 A for
110-120 Vac operation
For 220-240 Vac Operation: Remove the lock-out bracket with a phillips screwdriver.
Next, slide the switch sideways toward the left until the indent on the switch lines up
with the 230V/50Hz label on the rear panel. The main fuse value should be 3.15 A for
220-240 Vac operation
If you’re unsure about the correct setting for your region, please consult your Parasound
dealer or a qualified service technician.
1
2
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12
MAINTAINING YOUR A 23
Your Parasound A 23 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.
Notes:
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13
TROUBLESHOOTING GUIDE
PROBABLE CAUSE
REMEDY
TROUBLE
Power cord is disconnected
Connect power cord
No power
Auto On selector switch is in wrong
position
Check for correct position of the Auto On switch
Make sure the switch is in the
correct position for your region
AC Voltage selector switch is in the
wrong position
Replace with same value fuse
AC fuse blown
DC trigger source wired in reverse
or voltage too low
A 23 will not turn on
with DC voltage
Check polarity of DC source with a voltmeter
Try connecting a 9 V battery to the 12V DC input
Auto On selector switch in wrong
Make sure Auto On selector switch
position
is in its 12V position
Make sure Auto On selector switch
is in its Audio position
Auto On selector switch in wrong
position
A 23 will not turn on with
audio source
Sensitivity incorrectly adjusted
Turn the Audio trigger Sensitivity
knob counterclockwise
A 23 will not turn off when Sensitivity level too high
audio signal is removed
Turn Sensitivity knob clockwise toward 200mV
Level controls turned too low
Power on, but no sound
Turn level controls clockwise
Bad connection from preamplifier or Check input connections or try a
different set of cables
controller
Over-current protection circuitry has
been activated- one or both blue
channel LEDs not illuminated
Check speaker load impedance. Check speaker
wires and connections
A 23 has overheated - red Hi Temp
indicator is on
Allow A 23 to cool. Check that there is adequate
ventilation around the A 23. Be sure the load
impedance of each channel is no less than 4 Ω
Distorted sound
Damaged speaker
Connect each speaker to the opposite channel
on the A 23. If the same speaker remains distorted,
the speaker or its wire is damaged. If the other
speaker distorts, the problem may be with the
A 23, the preamp, or a source component
Problem with preamplifier or source Switch the left and right input cables. If
distortion moves to the other channel, the
problem is with a component other than the A 23
component
Move to the correct position for the
jack in use
Balanced-Unbalanced switch is in
the incorrect position
Mono Bridge switch is in the Mono Move switch to its Stereo position
bridged position
Hum and / or buzz
through speakers
Move the Ground Lift switch to its Lift position
Ground loop between preamplifier
and A 23 or at the equipment rack
Install nylon shoulder washers on both sides of
the panels of all equipment to insulate metal
from touching the rack
Move the Ground Lift switch to its Lift position.
Install cable isolation device such as the
Xantech 634 Ground Breaker
Ground loop from cable TV
Other ground loop
Contact Parasound Technical Service
Load impedance at speaker terminals Make sure the speaker or speaker
is too low
A 23 is overheating
selector load is 4 ohms or higher
Not enough ventilation
Make sure the A 23 has adequate ventilation
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14
SERVICING YOUR A 23
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 23 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.
Procedure for Returning Your A 23 to Parasound for Service
If Parasound determines that you should send your A 23 to Parasound, you will be given a Return
Authorization (RA) number. This RA number must be clearly marked on the outer carton only.
IMPORTANT: Enclose a copy of your original purchase receipt. A unit is eligible for warranty repair
ONLY when the purchase receipt shows that the unit was purchased from an Authorized
Parasound Dealer. A unit obtained through unauthorized channels is not eligible for warranty
repair. Parasound is not responsible for any sellers’ misrepresentations about our warranties or
other service policies.
We do not accept any of the following:
Units with collect shipping charges
Units without a valid RA number
Units without a suitable shipping carton
Units for which we see or hear evidence of improper packing
For a non-warranty repair, contact us for an estimate of the repair charges before you ship the unit
to us. The same packing and Return Authorization number procedures apply.
Important Notice - Shipping the A 23
Before shipping the unit to Parasound, you MUST re-pack the unit into its fitted molded foam
insert sandwich and its original carton. If you do not have the original packing cartons and foam
inserts, call us for new packing materials that we can provide to you for a nominal charge. Use of
any other carton and packing materials will probably result in shipping damage, and refusal of the
unit. Common carriers such as UPS seldom pay claims for damage incurred during shipment
when a product is surrounded only with Styrofoam "peanuts" or otherwise improperly packed.
We cannot stress enough the importance of properly packing your A 23. Shipping damage
resulting from inadequate packing can cost you a lot of money and significantly increase the time
required for repair.
Ship the unit with adequate insurance. After repair under warranty, the unit will be returned to you
via prepaid UPS within the continental United States.
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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 23
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. If
you set this control to 200 mV, the A 23 might not turn
on during quiet musical passages. The detented
position (click stop) at 12 o’clock corresponds to 100
mV. It’s a good starting point and will be suitable for
most systems.
balanced line is common to both its positive and
negative conductors with respect to ground.
Therefore, it is canceled or rejected by the differential
input circuit.
This phenomenon of rejecting noise signals common
to both positive and negative conductors is called
common mode rejection. Differential inputs are
specified according to how well they reject signals
common to both conductors. This is measured in dB
and is called the common mode rejection ratio or CMRR.
Bare Speaker Wire Ends
If you plan to use connections with bare wire ends,
use a wire stripper to remove just enough insulation
to expose a 1/2” (13mm) length of bare wire. You can
insert the stripped wire into the hole that goes
sideways through the terminal's metal post. Before
inserting the wire, twist its bare strands to prevent
any of the strands from making contact across the
two speaker terminals. If you have a soldering iron,
you can “tin” (apply a small amount of molten solder)
to each stripped bare wire to prevent it from
unraveling, fraying and oxidizing.
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. All Parasound Halo series power amplifiers
have balanced inputs with XLR jacks so you can take
full advantage of their inherent noise reduction
capability and superior sound quality.
Bridged Mono Operation
Unbalanced connections with RCA jacks are found on
all home audio equipment. RCA jacks and two-
conductor wires are less costly than the additional
circuitry, higher priced XLR connectors and three-
conductor wiring required for balanced connections.
In normal operation, the left and right amplifier
channels each amplify both the positive and negative
halves of the musical signal. In bridged mono
operation, the A 23’s entire left channel drives only
the positive half of the musical signal and its entire
right channel drives only the negative half of the
musical signal. This doubles its voltage swing.
In an unbalanced line, the positive audio signal
appears at the center pin of the RCA jack and the
negative signal on the outer shield wire, which also
functions as the ground connection. Unbalanced
interconnect cables are vulnerable to hum from an AC
line, or other noise, such as RF (Radio Frequency),
which can be reproduced through your loudspeakers.
Since the unbalanced line’s ground also carries the
audio signal, there is no way for the connected
amplifier or preamplifier to distinguish between the
audio signals you want and unwanted noise
emanating from external sources.
This doubled voltage swing enables the A 23 to
deliver double its 150 watts per channel 4 Ω power, or
300 watts, into a single 8 Ω speaker.
The audible benefit of this higher power is increased
dynamic range, or headroom, so that musical peaks
can be reproduced with less distortion. Considering
that musical peaks and crescendos require 10-100
times as much power as average listening levels, this
added headroom is a substantial advantage for
unrestrained, undistorted listening, even if your
average listening level is moderate.
Balanced lines are superior because they utilize
separate conductors for audio and ground: two inner
conductors carry the positive and negative audio
signal, and a third outer wire connects the grounds
and also shields the two signal conductors. When the
positive and negative signals appear at the
component receiving the signal they are equal, but
180 degrees out of phase with each other with respect
to ground. To send and receive balanced signals
requires special differential circuitry.
Bridging allows an amplifier to deliver more power into
a single speaker because in this mode, the load appears
to the amplifier as only half of its rated impedance.
Thus, the single 8 Ω speaker appears as a 4 Ω load and
a 4 Ω speaker appears as only a 2 Ω load.
The A 23 is not capable of driving 2 Ω for extended
periods because it will draw more current and
generate more heat than it can dissipate. We strongly
recommend against using speakers rated at less than
8 Ω when bridging.
A
differential input circuit amplifies only the
difference between the positive and negative signals.
For example, when a 1 Volt signal arrives at a
balanced input stage, the differential input “sees” a
positive 1 Volt minus a negative 1 Volt, or 2 Volts total.
External hum and noise that somehow gets into a
Remember that mono bridging requires a separate A 23
for each speaker. You can’t simultaneously drive two
speakers in stereo and one speaker mono bridged.
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16
TECHNICALLY SPEAKING continued
Choosing Brands of Interconnect Cables and Loop Out Jacks
Speaker Wire
The Right and Left Loop Out jacks are convenient
connections to route the same input signals from
your preamplifier or surround controller to an
additional power amplifier. These jacks eliminate the
need for “Y” connectors to split the source signal
between your A 23 and another amplifier. The Loop
Out jacks work with either the Balanced or the
Unbalanced Input jacks. Here are some examples of
where you could use the Loop Out jacks:
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.
1. When multiple speakers and amplifiers are to be
played simultaneously, you can route the output of your
preamplifier or controller to the first A 23 then connect
Eliminating Hum and Buzz - Ground Loops and the
A 23 Ground Lift Switch
Audible hum and buzzing noises in a system are
usually related to issues with the component its Loop Out jacks to a second A 23 (or other amplifier)
grounds. Ground (sometimes called common) is a
point of reference for voltages in virtually all audio
and video components. Ground is supposed to
remain at zero volts while the audio signal swings
positive (voltage above ground) and negative (voltage
below ground). If ground isn’t at zero, there can be an
audible 60 Hz hum (or 50 Hz hum in regions with 50
Hz AC). The harmonics of these frequencies (120 Hz,
240 Hz, 480 Hz or 100 Hz, 200 Hz, 400 Hz) may add
buzz in addition to the hum.
to power additional speakers for the same channel.
2. Some high-end speaker manufacturers recommend
bi-amplifying or “bi-amping” without using an
electronic crossover. When bi-amping this way, one A 23
drives only the woofers and another A 23 drives only
the tweeters. For example, you could connect the left
and right channel outputs of the preamplifier to the
inputs of the first A 23 to power the woofers, and then
connect its Loop Out jacks to the second A 23 to
power the tweeters.
The ideal of zero voltage ground for all the
components in a system is practically impossible,
because some resistance between the ground points
of different components is inevitable. By keeping
components close together with their power cords
plugged into a common AC outlet or power strip,
you’ll avoid the problems created by resistance in the
house’s wiring.
Level Controls
When the Level knobs are turned fully clockwise, the
actual level controls are essentially out of the circuit.
The left and right channels are perfectly matched, and
your A 23 can reach its fullest sonic potential.
In some cases, you’ll need to reduce the level
settings. For example, if you find it difficult to make
precise volume adjustments at low listening levels,
your preamplifier or surround controller probably has
a very high output (or gain) that you can match by
reducing the A 23’s level. Conversely, if you need to
advance your preamplifier or surround controller’s
volume to nearly the top of its range for average
listening levels, you should increase the level settings
on the A 23. The A 23 Level adjustment that optimizes
the range of motion on the preamplifier’s volume
control is sometimes called “gain staging”.
Hum and buzz is also caused when unwanted voltage
flows through multiple component ground points
called ground loops. Here are three tips to avoid
ground loops:
1. Use balanced input lines with your Parasound A 23.
(See Balanced and Unbalanced Lines in this section).
2. When rack mounting, always use insulated
“shoulder” washers. These break the ground loops
caused by metal-to-metal contact between the rack,
the units, and their rack-mount bolts. Washers are
included in Parasound rack mount kits. Extras are
available from rack manufacturer Middle Atlantic
3. Use the Ground Lift switch on the A 23 to eliminate
most ground loops. This separates the A 23’s signal
input ground from its chassis ground to isolate
unwanted voltage in the ground shields of the
unbalanced (RCA) interconnect cables. Be sure your
system installation is finished before you try moving the
Ground Lift switch from its "Normal" to its "Lift" position.
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17
PARASOUND A 23 DESIGN OVERVIEW
Circuit designed by John Curl
Parasound design consultant John Curl has been a To create the +/- 55 Vdc B+ and B- supply rails for each
legend among audiophiles and electronic engineers channel, we use high-speed rectifier diodes and four
for decades. He pioneered measurements to correlate enormous 12,000 uF Elna electrolytic filter capacitors,
musical accuracy with the materials used in parts, chosen for their low Equivalent Series Resistance
worked with world-class touring companies, has (ESR) and dielectric absorption. In addition, these
designed highly coveted audio classics, including the filter capacitors are bypassed with smaller
original Mark Levinson JC-2, Denneson JC-80, polypropylene capacitors to reduce AC ripple in the
Vendetta Phono Preamplifier, and CTC Blowtorch DC supply and to further eliminate noise and
preamplifiers; master recorders for Wilson Audio and interference that is generated in AC power lines from
Mobile Fidelity; and the mixing consoles used in live computers and other appliances in the home.
concerts by The Grateful Dead and the Montreux Jazz
Festival in Switzerland.
Audio Circuit Path Topology
Parasound’s circuit topology is a hybrid of carefully
As our featured amplifier designer since 1990, he has chosen discrete transistors that result in superior
created many products that have earned Parasound performance at each stage. We use JFETs (Junction
worldwide acclaim. John is particularly proud of what Field Effect Transistors) for the input stage; MOSFETs
he and Parasound have accomplished together: “The (Metal Oxide Field Effect Transistors) for the driver
circuits I design for Parasound are extremely stage and bipolar transistors for the output stage.
sophisticated and are typical of products that are far Discrete transistors are more sonically accurate than
more expensive. I can’t think of any other audio integrated circuits commonly used by other brands.
products that offer nearly as much bang for the buck.”
Complementary Configuration
Each stage of amplification has transistors fed by the
Parts Selection
Every part within the A 23 is carefully chosen for its positive DC power supply and complementary
accuracy and reliability. Metal film resistors with 1% transistors fed by the negative DC power supply.
tolerance are selected for their precision and because Thus, half of the devices amplify the positive half of
their values don’t drift as they heat up during the musical waveform while the other half of the
operation. Polypropylene and mica capacitors are devices
amplify
the
negative
half.
This
used extensively for their superior linearity and low complementary topology is inherently linear, which
dielectric absorption. Semiconductors are selected for reduces distortion and improves sonic accuracy.
superior performance in their specific roles in the
circuit. Gold has the best conductivity of any metal, so The Input Stage
we use high quality gold-plated input connectors and The A 23’s input stage uses matched pairs of discrete
speaker terminals. The double-sided circuit boards JFETs arranged in a differential configuration. JFETs
are FR4 glass epoxy for long-term durability. The are ideal for the input stage because their inherently
chassis is made of heavy gauge steel to safely house high impedance is unaffected by the impedance of
the internal circuitry. This attention to detail when selecting source components. Differential configuration
parts makes the difference between a very good amplifier provides superior noise reduction. These precision
and an outstanding amplifier.
input JFETs are also cascoded to produce the current
necessary to drive the MOSFET drivers in the
following stage.
The Power Supply
The heart of the power supply is a 1 kVA toroidal
power transformer, chosen for its efficiency, low hum The Driver Stage
field, and high power rating. Encapsulating this The driver stage provides critical amplification for
massive power transformer in an epoxy-filled steel which we employ a complementary matched pair of
canister assures ultra-quiet performance.
MOSFETs selected for their tube-like sonic qualities.
MOSFETs tend to generate less odd-order harmonic
The A 23 power transformer employs multiple distortion than bipolar transistors. This is important
independent secondary windings so that each because odd-order distortion sounds unnatural and
amplifier channel has its own power supply, assuring fatiguing to the human ear, whereas even-order
more than ample DC voltage at all times and under all distortion is less offensive because it is consonant,
conditions. It also reduces inter-channel crosstalk that rather than dissonant. Our MOSFET driver stage
can blur the sound and impair the correct sense of prevents the harshness and brittle sound so often
where instruments are positioned.
found in other amplifiers.
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18
PARASOUND A 23 DESIGN OVERVIEW continued
The Output Stage
Parasound power amplifiers incorporate ingenious
The amplifier’s sonic characteristics are established
by its input and driver stages. Now, the sole job of its
output stage is to deliver the enormous current and
voltage from its power supply to the speakers. Bipolar
output transistors are better than MOSFETS in the
output stage because of their higher safe operating
area (SOA) and inherent ruggedness. Each channel’s
output stage employs three pairs of high current (15-
ampere) bipolar transistors to insure long-term
reliability, even with continuous high power operation
and challenging speaker loads. Lightning-fast (60
MHz) transistors respond instantly to complex
demands in the musical signal, virtually eliminating
distortions that occur with slower transistors. Slew
rate limiting and Transient Intermodulation Distortion
(TIM) are simply not an issue in the A 23.
and fast-acting DC servo circuits, completely
eliminating the need for coupling and blocking
capacitors. The A 23 is direct-coupled from its input
jacks to its speaker terminals. This advanced circuitry
never needs adjustment or maintenance. It operates
outside the audio signal path to keep the DC offset at
the output of the A 23 at a constant 0.00 Vdc. The
results are startling clarity, freedom from listening
fatigue, and formidable bass response.
Relay Protection
Each channel of the A 23 has a high-quality protection
relay with gold-plated contacts for long-term
reliability. These relays function to protect either the
amplifier, the speakers, or both. When the A 23 is first
powered on, these relays remain open for three
seconds as the positive and negative power supplies
stabilize and reach equilibrium. This prevents
annoying popping or other transient noises. Relay
protection also prevents damage to your speakers in
case of a catastrophic amplifier failure. Any amplifier
that doesn’t use relay protection for its speaker
outputs compromises the safety of the amplifier and
your speakers.
Class A-A/B 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/B 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 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 23 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.
Over-Current Protection
Specialized current-sensing transistors are connected
to the output stages of the A 23 to constantly monitor
the current flow through the output transistors. If the
current drawn by this stage exceeds a predetermined
safe level due to a load impedance below 1 ohm or a
short circuit at the speaker terminals, the output relay
will open immediately to prevent any of the output
transistors or other parts from failing.
Fuse Protection
Each channel of the amplifier has a separate fuse for
its positive and negative DC voltage rails. These fuses
provide backup protection in case the over-current
protection does not work in time, or if an internal part
fails. In the event of a part failure, these fuses halt
operation to minimize damage to additional parts.
Total Protection
DC Servo
Direct Current (DC) burns out speakers. 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 trim controls to
reduce their DC offset or capacitors to block DC.
Unfortunately, trim controls can allow DC offset to
increase over time, and even the most expensive
capacitors in the audio signal path will “veil” sonic
clarity and attenuate bass response.
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19
PARASOUND A 23 SPECIFICATIONS
Continuous Power Output - Stereo
125 watts RMS x 2, 20 Hz-20 kHz, 8 Ω,
both channels driven
Loop Output Level
Same as input level
200 watts RMS x 2, 20 Hz-20 kHz, 4 Ω,
both channels driven
S/N Ratio
> 112 dB, input shorted, IHF A-weighted
Continuous Power Output - Mono
Damping Factor
400 watts RMS, 20 Hz-20 kHz, 8 Ω
> 800 at 20 Hz
Current Capacity
DC Trigger Requirements
45 amperes peak per channel
+9 Vdc to +12 Vdc, 2 mA
Slew Rate
Audio Trigger Requirements
> 130 volts per microsecond
50 mV AC - 200 mV AC
Frequency Response
DC Trigger Output Capacity Requirements
5 Hz-100 kHz, +0/-3 dB at 1 watt
+12 Vdc, 150 mA
Total Harmonic Distortion
Dimensions
< 0.06 % at full power
Width: 17-1/2” (437 mm)
< 0.03 % at typical listening levels
Panel Height: 3-1/2” (88 mm)
Total Height with feet: 4-1/8” (105 mm)
Total Height with rack adapter attached: 3-5/8”
Depth: 13-3/4” (350 mm)
IM Distortion
< 0.04 %
TIM
Power Requirement
Unmeasureable
Standby: 25 Watts
Full Power into 4 Ω: 700 Watts
Dynamic Headroom
> 1.5 dB
Net Weight
28 lb.(12.7 kg)
Interchannel Crosstalk
> 80 dB at 1 kHz
> 63 dB at 20 kHz
Shipping Weight
35 lb.(15.9 kg)
Input Impedance
33 k Ω
Input Sensitivity
Balanced-1 V for 28.28 V output into 8 Ω
Unbalanced-1 V per leg for 28.28 V output
into 8 Ω
Features and specifications subject to
change without notice.
© Parasound Products, Inc. 2002. V 1.0
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