Parasound Stereo Amplifier A 31 User Manual

A 31  
Three Channel Amplifier  
OWNER’S GUIDE  
 
Table of Contents  
Introduction  
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4
5
Placement and Ventilation Guidelines.  
AC Mains Voltage  
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5
Rack Mounting  
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6
Audio Input and Output Connections  
7
Gain Control Settings  
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9
Turn On Options  
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10  
12  
13  
14  
17  
18  
19  
Front Panel Operation  
Technically Speaking  
Design Overview  
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Problems and Remedies  
If You Require Assistance or Warranty Repair  
Specifications  
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3
 
INTRODUCTION  
Thank You for Choosing Parasound  
Your new Parasound Halo A 31 power amplifier has been designed with the most advanced,  
proven class A/AB amplifier technology. The A 31 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. We  
designed your new Halo Series A 31 Amplifier to perform at a higher level of sonic performance  
than you may have expected and we encourage you to read this entire manual to maximize your  
enjoyment. We wish you many years of listening enjoyment.  
-The Parasound Staff  
Keeping Records for Future Reference  
Record the serial number located on the back panel or bottom of your A 31 in the space below.  
Also note your Parasound Dealer’s name and telephone number. Your purchase receipt/bill of  
sale is required to determine if your A 31 is eligible for Parasound warranty service. We  
recommend that you make an extra copy of your original purchase receipt/bill of sale and store it  
inside the A 31’s carton.  
Parasound A 31 Amplifier Serial #: ______________ (5 digit number below the bar code)  
Parasound Dealer: ___________________________________________________  
Parasound Dealer Phone Number: ___________________  
Date of Purchase: ______________________  
Important Warranty information  
There is no Parasound warranty for this unit if it was not purchased from an Authorized  
Parasound Dealer. Investigate warranty coverage statements made by an unauthorized dealer  
very carefully, as you will need to depend entirely upon your dealer, and NOT upon Parasound.  
Unauthorized dealers lack the capability to make repairs or arrange for repairs of Parasound  
equipment. A list of Authorized Parasound Dealers and detailed warranty information is available  
at www.parasound.com or you can call 415-397-7100 between 8:30 am and 4 pm Pacific time.  
A missing or altered serial number could indicate that this unit was re-sold by an unauthorized  
dealer or is stolen merchandise. If this unit is missing its serial number or the serial number has  
been altered, you should return it to your dealer immediately for a full refund.  
4
 
Unpacking Your A 31 & Placement Guidelines  
Unpacking Your A 31  
Carefully remove your A 31 from its shipping carton and locate the enclosed accessories:  
• AC power cord  
• Two trigger wires, one with 3.5 mm mini plugs, one with a 2.5mm and a 3.5mm mini plug  
While you are unpacking your A 31, inspect it thoroughly for possible shipping damage and tell  
your Parasound dealer immediately if you find any evidence of shipping damage.  
This would be a good time to make a copy of your sales receipt to store with the A 31’s original  
packing.  
Note: Please save and store both the inner and outer cartons and, most especially, the foam  
packing inserts to protect the A 31 if you have to move it or ship it. You may wish to flatten the  
cardboard cartons to save room in storage after cutting the taped seams on the bottom flaps.  
Placement Guidelines  
The A 31 will be easier to use and will last longer if you follow these simple guidelines:  
• Place the A 31 on a surface that will adequately support its substantial weight.  
• Use input and output cables that are long enough to leave some slack; that will enable you to  
pull the A 31 out of a cabinet to check or to change connections without inadvertently  
disconnecting cables.  
• The A 31 should never be placed in a completely enclosed cabinet  
• Place your A 31 where you can route input and output signal cables as far as possible from  
any AC cords.  
• Where signal cables must cross AC cords they should do so only at a 90° right angle.  
Ventilation Requirements  
• Always position the A 31 horizontally.  
The A 31 should never be stacked above another power amplifier.  
• Do not install the A 31 in an unventilated equipment cabinet or compartment. Pockets of  
stagnant hot air can build up even in a cabinet with an open front and back. A ventilation fan  
such as the Parasound Zbreeze is highly recommended to prevent “hot spots” in confined  
spaces.  
AC Mains Voltage  
NOTE: Before you plug this amplifier into an AC mains outlet:  
If you live in a region with 220V-230V AC mains:  
Plugging this amplifier into a 220V-240V AC mains outlet when the unit is wired internally for  
115V and its main fuse rated for 115V operation will severely damage it and could put you at risk  
of personal injury. If you are unsure of the internal voltage setting for this amplifier you should  
have a qualified electronics technician inspect it and change it as required.  
AC Voltage Rewiring Technical Information  
Parasound will provide technical information which pertains to the interior of this amplifier only to  
a qualified electronics technician. This restriction is for your safety as well as the correct  
functioning of your amplifier.  
AC Voltage Warranty Exclusion  
Amplifiers set for 115V which are damaged by 220V-240V are not covered under the Parasound  
Limited Warranty.  
Before Making Any Audio Connections  
Always turn off your A 31 and disconnect the AC cord before making or changing any input,  
output or trigger wire connections. Inserting or removing an input or output cable while the A 31  
and your preamp are turned on can result in a blast of sound that can damage your  
loudspeakers.  
5
 
Rack Mounting Your Parasound A 31  
To mount the A 31 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 31 chassis and front panel height  
occupies four rack spaces (7" or 176 mm). When mounting equipment below the A 31, you will  
also need to allow about 18" below the unit for the bottom chassis screws.  
To attach the rack mount brackets:  
• Remove the three screws from each side of the A 31. These are arranged vertically, behind its  
front panel and in front of its first heatsink fin.  
• Line up the three holes on each bracket with the three holes on the A 31 and reinsert the  
screws.  
• Make sure the screws are tight because they will support the entire weight of the A 31 in the  
equipment rack.  
Note: Tighten each bolt just enough to keep the unit secure in the rack to avoid deforming the  
shoulder washers. Eliminating metal-to-metal contact reduces the likelihood of creating a ground  
loop that might introduce hum into your system.  
A single standard rack space is 1-34" (44mm) high 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 fit in a uniform space. Please call your Parasound dealer or  
Parasound Technical Services if you need additional advice about rack mounting the A 31.  
6
 
Audio Connections  
Always disconnect the AC cord to your A 31 before making or changing any input,  
output or trigger wire connections. Inserting or removing an input or output cable while the  
A 31 is turned on can result in a blast of sound that can damage your loudspeakers. Make  
sure there is no strain or tension on any cables that could cause them to pull loose.  
Audio Input Connections  
Balanced XLR Input Jacks  
Balanced connections will give you the best sound. If your surround sound preamplifier 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.  
Unbalanced RCA Input Jacks  
Use these inputs if your surround sound preamplifier doesn’t have balanced output  
connections or if you simply prefer to use unbalanced connections.  
Balanced/Unbalanced Selector Switches  
Place the switch in the position for the input type you will be using.  
Note: The Balanced/Unbalanced switches are not input selectors. Their  
function is to optimize the s/n ratio for each type of input. You should  
not connect both the Balanced and Unbalanced jacks at the same time  
with the expectation of switching between to different signals.  
Balanced XLR Pin Configuration  
The balanced inputs of the A 31 use XLR jacks that conform to the  
industry standard of:  
Pin 1: Ground Pin 2: Positive (+) Pin 3: Negative (–).  
7
 
Speaker Connections  
Speaker Terminals  
The A 31 speaker terminals accept speaker wires with banana plugs, spade connectors or  
bare wire. Refer to “Bare Wire Speaker Ends” in the Technically Speaking section for  
information about bare wire termination.  
Correct Speaker Polarity is Important  
Polarity refers to + and – connections. Speaker wires are coded with color, 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  
all channels. If some of the speakers are wired with incorrect polarity you will significantly  
affect sound quality.  
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 number, 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.  
8
 
Gain Control Settings  
The Gain control knobs should be left at the 12 o’clock Normal/THX setting for most  
applications. When a Gain control knob is set to Normal the gain for that channel is 29. This is  
the THX Ultra2 Reference Level where 1V input = 28.28V output. (28.28V driving an 8  
speaker equals 100 watts.) If you are unsure where to set the Gain control knobs it is best to  
start with them in the Normal position and only change them if needed, as described below.  
When to Set the Gain Control Knobs Above or Below Normal  
You can increase loudness by turning the Gain control knobs clockwise if your system will not  
play loud enough with the Gain control knobs set at Normal. This could be the case if your  
A 31 is driven from the pre-out jacks of an AV receiver (as opposed to an AV processor). We  
recommend advancing the gain as little as possible past Normal. As you increase gain  
settings you increase the chance of hearing a “hiss” sound from your speakers. You also run  
the risk of damaging your speakers (not to mention your hearing) if the volume level is too  
high.  
The primary reason to reduce the gain below Normal would be if your speakers’ efficiency is  
extremely high and your listening position is close to your speakers. Reducing the gain would  
reduce audible “hiss” from your speakers.  
Don’t worry about setting the A 31 Gain control to exactly the same levels for all channels  
because you can always balance the channel volume using the speaker level calibration in  
your home theater AV receiver or AV processor’s setup menu.  
Note: We recommend re-calibrating your AV receiver or processor’s speaker levels  
after adjusting the A 31 gain controls.  
9
 
Turn On Options  
For convenience, there are three ways the A 31 can be turned on and off:  
Manually, by pressing the On-Off (Power) button on the front panel.  
Automatically, when an audio signal is present at any of the audio Input jacks.  
Automatically, when a suitable trigger voltage is applied to the 12V input jack.  
Note: When either automatic turn on option is selected the front panel  
On-Off button is disabled so that power on/off is determined solely by  
the triggering preamp, receiver or active audio signal.  
Manual Position  
When the Turn On Options switch is in its Manual position, the Turn On  
Options function is disabled and the A 31 must be turned on and off manually  
by pressing the On-Off button on its front panel every time you wish to use  
your audio system.  
Audio Position (Automatic on/off)  
When the Turn On Options switch is set to its Audio position, the A 31 will be turned on only  
when an audio signal is present at any of the Input jacks. After the audio signals cease the  
A 31 will remain on for about 8 minutes before shutting off. This prevents unintended turn-off  
during pauses in your music or movies.  
Note: The Audio position of the Turn On Options switch disables the  
front panel On-Off button.  
Turn On Threshold  
This knob sets the audio signal level required for the A 31 to automatically turn on when  
the Turn On switch is set to the Audio position. Fully counter-clockwise is the most  
sensitive setting and therefore is labeled “Quieter.” Fully clockwise will require a higher  
audio signal voltage and is therefore labeled “Louder.” In most systems the best results  
will be with the Turn On Threshold knob set towards the Quieter position. In some  
systems the A 31 might turn on if there is transient noise in the AC line, even when an  
audio signal is not present. Similarly, the A 31 might never shut off even after waiting  
more than 10 minutes. In this case, try setting the knob towards the Louder position.  
Note: When the Turn On Options switch is set to Audio the A 31 will turn itself on  
immediately when you connect its AC cord, even without any audio signal  
present. This is normal.  
Note: If the A 31 is driving only the sub(s), surround, center, or rear channels you will  
achieve more consistent automatic turn on by using the 12V DC trigger. At the  
beginning of most films the sub, center and surround levels are lower than the  
minimum level required by the Audio sensing circuit.  
12V Position (Automatic on/off)  
When the Turn On Options switch is set to its 12V position, the A 31 is turned on and off only  
with an external +9 V to + 12 V voltage from your preamp or AV Receiver. When the external  
voltage ceases the A 31 will turn off immediately. The 12V switch position disables the front  
panel On-Off button.  
10  
 
12 Volt Jacks  
12V In Jack  
The A 31 12V input uses a 3.5mm jack (mono). To use the 12V trigger, insert the trigger wire  
plug into this jack and the plug at the wire’s other end into the AV receiver or preamp’s 12V  
output jack. We have included a 3.5mm to 3.5mm trigger wire as well as a 3.5mm to 2.5mm  
trigger wire.  
Note: If the controller’s trigger output is a + and – terminal, you can cut the 3.5mm plug  
off one end of the included trigger wire and attach the bare wires to these terminals. The  
lead with the white stripe on it corresponds to the plug’s tip and the unmarked lead  
corresponds to the sleeve of the plug. The trigger plug tip is + (positive) and its sleeve –  
(negative).  
Note: The A 31 trigger circuit draws a negligible 15 mA. The total load on your preamp’s  
trigger output(s) is the sum of the trigger current drawn by each of the components  
you’ve looped together. Check the maximum capacity of your AV receiver, processor or  
home controller’s trigger outputs so you do not overload them by connecting too many  
power amplifiers. Typical ratings are 50mA to 100mA.  
12V Loop Out Jack  
The Trigger Out jack lets you loop or “daisy-chain” the incoming trigger voltage to an  
additional A 31 or another component(s).  
3.5mm vs. 2.5mm jacks  
Some other Parasound power amplifiers and preamplifiers might use 2.5mm “sub-mini”  
trigger jacks. To use the A 31 with products that use a 2.5mm jack we have included a  
trigger wire with a 3.5mm plug at one end and a 2.5mm plug at the other end.  
AC Power Cord  
The IEC standard AC cord supplied with your A 31 is an audiophile-grade component.  
Please connect it directly to an AC wall outlet or power conditioner that is always “live.” If  
possible, plug your A 31 into the same AC outlet that your preamplifier is plugged into. If  
different AC outlets are used for the A 31 and the preamplifier the ground potential may be  
higher or lower between the outlets, resulting in audible hum.  
11  
 
Front Panel Operation  
On-Off Button  
Push once to turn on the A 31. When the A 31 is turned on the blue glow around the On-Off  
button will be brighter, the red P badge will glow brighter and then the 3 channel indicators  
will illuminate blue. Push again to turn off the A 31. The front panel On-Off button will be  
disabled when the Turn On Options switch is set to Audio or 12V.  
Whenever the A 31 is turned on, the soft blue glow behind its On-Off button will change  
to red for a few seconds as its internal circuits stabilize. Then the red glow is replaced  
by a brighter blue glow to indicate normal operation. If the glow remains red after turn on  
or while the amp is playing, it indicates activation of the A 31’s protection circuits and no  
sound will be heard from the speaker.  
The A 31 protects itself from external conditions such as excessive heat, load impedance  
that is too low, or a short-circuited speaker connection or wire. After you correct the fault,  
the A 31 will resume operation. If the A 31 remains “in protection” after it has cooled down  
and you’ve confirmed there are no external faults, it could indicate an internal problem.  
Please contact Parasound’s Technical Service Department.  
Channel Indicators  
When all three blue channel indicators are lit, the A 31 is operating normally. If one or more  
of the indicators do not light even though the amp is turned on there is a fault in your system.  
In the case of a fault first check that there is no short circuit with your speaker wire or  
speakers.  
Hi Temp Indicator  
This indicator is near the right side of the panel recess. It will glow red if any channel  
overheats. The On-Off button will also glow red if the A 31 overheats. If such a condition  
occurs you must provide for better ventilation around the amplifier or check speakers for  
faulty operation that is causing the A 31 to over heat.  
12  
 
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. 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.  
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 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.  
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.  
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 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.  
Ground Loops - Eliminating Hum and Buzz  
Audible hum and buzzing noises in a system are usually related to issues with the  
component 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.  
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.  
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:  
13  
 
1. Your Cable TV or Satellite receiver box might require a Cable TV ground isolator.  
2. Use balanced input lines with your Parasound A 31. (See Balanced and Unbalanced  
Lines in this section).  
3. When rack mounting, always use the insulated “shoulder” washers. These break the  
ground loops caused by metal-to-metal contact between the rack, the components, and their  
rack-mount bolts. Extra washers are available from rack manufacturer Middle Atlantic  
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 12" (13 mm) 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.  
Parasound A 31 Design Overview  
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.  
As our featured amplifier designer since 1990, he has created many products that have  
earned Parasound worldwide acclaim. John is particularly proud of what he and Parasound  
have accomplished together: “The circuits I design for Parasound are extremely sophisticated  
and are typical of products that are far more expensive. I can’t think of any other audio  
products that offer nearly as much bang for the buck.”  
Parts Selection  
Every part within the A 31 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 we use high quality gold-plated input connectors and speaker  
terminals. 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.  
The Power Supply  
The heart of the power supply is a 1.5 kVA toroid power transformer, chosen for its  
efficiency, low hum field, and high power rating. Encapsulating this massive power  
transformer in an epoxy-filled steel canister assures ultra-quiet performance.  
The A 31 power transformer employs multiple independent secondary windings so that  
each amplifier channel has its own power supply, assuring more than ample DC voltage at all  
14  
 
times and under all conditions. It also reduces inter-channel crosstalk that can blur the sound  
and impair the correct sense of where instruments, dialogue and effect are positioned.  
Each channel’s +/- 80 Vdc B+ and B- supply rails use high-speed rectifier diodes and  
four enormous 8,200 uF electrolytic filter capacitors, chosen for their low Equivalent Series  
Resistance (ESR) and dielectric absorption. In addition, these filter capacitors are bypassed  
with smaller polypropylene capacitors to reduce AC ripple in the DC supply and to further  
eliminate noise and interference that is generated in AC power lines from computers and  
other appliances in the home.  
Relay-Bypassed Soft Start Circuit  
When the A 31 is first turned on, there is a significant amount of in-rush current  
required to charge the enormous power supply capacitors. In order to suppress this in-rush  
current and to prevent nuisance tripping of circuit breakers, we employ NTC (negative  
temperature coefficient) resistors. These resistors cut the in-rush current by approximately  
50%. Once they heat up, they essentially become a jumper with zero ohms resistance.  
However, the A 31 goes one step further for this circuit. After the NTC resistors have done  
their job of suppressing in-rush current a gold contact relay automatically is activated to jump  
across the NTC resistors to completely bypass them. This extra step insures that the  
resistors do not restrict any current whatsoever to the power supply once the A 31 is in full  
operation.  
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 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.  
Complementary Configuration  
Each stage of amplification has transistors fed by the positive DC power supply and  
complementary transistors fed by the negative DC power supply. Thus, half of the devices  
amplify the positive half of the musical waveform while the other half of the devices amplify  
the negative half. This complementary topology is inherently linear, which reduces distortion  
and improves sonic accuracy.  
The Input Stage  
The A 31’s input stage uses matched pairs of discrete JFETs arranged in a differential  
configuration. JFETs are ideal for the input stage because their inherently high impedance is  
unaffected by the impedance of source components. Differential configuration provides  
superior noise reduction. These precision input JFETs are also cascaded to produce the  
current necessary to drive the MOSFET drivers in the following stage.  
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. Our  
MOSFET driver stage prevents the harshness and brittle sound so often found in other solid  
state amplifiers.  
15  
 
The Output Stage  
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 four 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 31.  
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 31 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.  
Total Protection - DC Servos  
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.  
Parasound power amplifiers incorporate ingenious and fast-acting DC servo circuits,  
completely eliminating the need for coupling and blocking capacitors. The A 31 is direct (DC)  
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 31 at a constant 0.00 Vdc. The results are startling clarity, freedom from  
listening fatigue, and formidable bass response.  
Total Protection - Relays  
Each channel of the A 31 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 31 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.  
16  
 
Total Protection - Current Overload  
Specialized current-sensing transistors are connected to the output stages of the A 31  
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.  
Total Protection - Fuses  
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.  
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 the switch is set to Audio or 12V)  
• 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 AC power is live.  
No sound from speakers  
• Check that input cables and speaker wires are secure at both ends.  
• Make sure the surround preamp is switched to the correct input.  
• Is the Hi-Temp light illuminated? All three blue channel indicators should be  
illuminated. Check for excessive temperature, short-circuited speaker wires,  
low impedance speaker load, and inadequate ventilation.  
Background Hum or Hiss  
• Move audio cables and AC cords away from each other.  
• Try different routes for the audio cables and AC cords.  
• Make sure insulating shoulder washers are used if unit is rack mounted.  
• If you have cable or satellite TV, try disconnecting the incoming TV or satellite  
cable; if hum is eliminated you will need a Cable TV Ground Isolator or contact  
your TV service provider for assistance.  
• Try turning down the input gain controls  
Overheating  
• Remove any nearby external sources of heat such other audio equipment or  
heaters.  
• Increase ventilation around the A 31.  
• Check speakers for faults  
17  
 
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.  
If we determine that your A 31 should be returned to Parasound or an Authorized Parasound  
Warranty Center for inspection and possible servicing, we will provide the location of a  
warranty center near you or shipping instructions for the unit’s return to Parasound.  
Before You Return Any Unit to Parasound for Service  
Before you send your unit to Parasound, you will need to obtain a specific Return  
Authorization (RA) number and shipping instructions from Parasound’s Technical  
Department. The RA number must be clearly marked on the outer carton. Use the original  
factory packing materials and arrange adequate insurance to cover its value. You must  
include a copy of your purchase receipt, since this document establishes the validity of this  
unit’s warranty. Warranty repairs are only performed by Parasound or Parasound Authorized  
warranty centers when your purchase receipt is from a Parasound Authorized Dealer or  
Parasound Authorized Reseller.  
Shipments Will Be Refused by Parasound Under the Following Conditions:  
1. Unit was sent without the Parasound-assigned RA number marked on the carton.  
2. Unit was sent in an unsuitable shipping carton and packing inserts and is likely to have  
been damaged in transit.  
3. Unit has inadequate packing materials and is likely to have been damaged in transit.  
Wrapping the A 31 with bubble wrap will not protect it during shipment.  
4. Unit was shipped collect for shipping charges. We do not accept collect shipments.  
5. Unit was shipped via the US Postal Service.  
6. Unit was sent to an address other than the address instructed by our Technical  
Department.  
Warranty Repair  
Please read your accompanying Parasound Limited Warranty carefully to understand the  
applicable rights and limitations. This section provides instructions for obtaining repairs, both for  
units covered under the Parasound Limited Warranty and for units or situations which are  
Unit is not eligible for repair under the terms of the Parasound warranty if:  
1. Unit was not purchased from a Parasound Authorized Dealer.  
2. You do not have the original bill of sale or sales receipt from a Parasound Authorized  
Dealer.  
3. You are not the original owner. The Parasound warranty is not transferable.  
4. Unit’s serial number was removed, modified, or defaced.  
5. Unit shows evidence of abuse and/or misuse.  
6. Unit was modified in any way.  
7. A prior repair was attempted by an unauthorized repair station.  
18  
 
Specifications  
Power Output - All Channels Driven  
250 watts RMS x 3, continuous,  
(20 Hz - 20 kHz, 8)  
Input Sensitivity for 28.28 V Output into 8  
Unbalanced: 1 V  
Balanced: 1 V per leg  
(Gain controls set to Normal / THX)  
400 watts RMS x 3, continuous,  
(20 Hz - 20 kHz, 4)  
S/N Ratio  
Current Capacity:  
> 112 dB, input shorted, IHF A-weighted  
> 102 dB, input shorted, unweigh  
60 amperes peak per channel  
Slew Rate  
Damping Factor  
> 130 volts per microsecond  
> 1100 at 20 Hz  
Frequency Response  
DC Trigger Requirements  
5 Hz - 100 kHz, +0/-3 dB at 1 watt  
+9 Vdc to +12 Vdc, 2 mA  
Total Harmonic Distortion  
< 0.2 % at full power  
Audio Trigger Requirements  
2 mV AC - 10 mV AC  
< 0.03 % at typical listening levels  
XLR Pin Identification  
1 = Ground (Shield)  
2 = Positive  
IM Distortion  
< 0.04 %  
3 = Negative (Return)  
TIM  
Unmeasurable  
Dimensions  
Width: 1712" (445 mm)  
Panel height: 7" (178 mm)  
Height with feet: 7 58" (194 mm)  
Depth: 19 1/8" (485 mm)  
Dynamic Headroom  
> 1.5 dB  
Interchannel Crosstalk  
> 78 dB at 1 kHz  
Net Weight  
> 63 dB at 20 kHz  
65 lb. (29.5 kg)  
Input Impedance  
Unbalanced: 47k Ω  
Balanced: 94k per leg  
Shipping Weight  
79 lb. (35.9 kg)  
Power Requirement  
Standby: 1 Watt  
Maximum: 1800 Watts  
Specifications and features subject to change or improvement without notice.  
Copyright Parasound Product Inc., 2012  
Rev. 1.0  
19  
 
Parasound Products, Inc. 2250 McKinnon Ave, San Francisco, CA 94124  
415-397-7100 / Fax 415-397-0144 www.parasound.com  
20  
 

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