Pass Labs Stereo Amplifier XA2005 User Manual

pass®  
XA200.5 Owner’s Manual  
October, 2007  
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We start with simple FET circuits already having low distortion and  
noise, and arrange them in two symmetrical halves. The two halves  
of the amplifier channel are closely matched, eliminating a large  
portion of distortion and noise without feedback. A small amount  
of feedback is also applied, not so much for the purpose of reducing  
distortion but to make the distortion as identical as possible on both  
polarities of the balanced output.  
It is easier to make distortions more identical than to remove them  
with feedback, and this is the operating principle of X amplifiers.  
Since the X1000, Pass Labs products have continuously evolved  
toward higher performance. The Class AB “X” series was joined  
by the Class A “XAamplifiers. Subsequent improvements to the  
Class AB “X” amplifiers resulted in the “X.5” products, and their  
phenomenal success has led to the Class A “XA.5” series.  
As always the goal has been the best musical and objective  
performance possible with minimal parts in the signal path and  
minimal feedback. This process is not completely understood, and  
many of the improvements are the result of trial and error and  
extensive listening.  
Measurement of performance is important to us, and we feel that  
well-designed product sounds good and measures good. Apparently  
it is possible to make an amplifier which measures well but which  
does not please the ears, and so we let our ears be the final judge.  
X.5 and XA.5 amplifiers utilize the same basic circuit topology  
and gain devices. They differ in the sizes of the power supplies,  
the chassis and heat sinks, and the number of output devices. The  
output stages of the X.5 series are operated in heavily biased Class  
AB, with an idling dissipation similar to the rated output. The XA  
amplifiers operate pure Class A with idling dissipation more than  
twice the rated output.  
Within any given chassis size, the X and XA amplifiers are designed  
to dissipate about the same power, and it is not surprising that this  
leads to two channel amplifiers with half the output power per  
channel of comparable mono amplifiers, and Class A amplifiers with  
half the output of Class AB amplifiers.  
The X amplifiers deliver more output power per dollar, and the XA  
amplifiers have a better subjective performance. All of the amplifiers  
drive known loudspeaker loads without misbehaving, and all are  
unconditionally stable into low impedance and reactive loads.  
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All the usual performance metrics - power, distortion, noise, input  
impedance, damping factor and bandwidth have all been improved  
in this latest generation. The power supplies are larger, with fast  
rectifiers gating to larger capacitor banks. The increases in AC line  
noise worldwide have been addressed with heavier EMI filtering  
and dramatically quieter power transformers. In addition, through  
improved biasing regulation, the circuits give much more consistent  
performance under varying AC line voltages and over a variety of  
ambient temperatures.  
All this is very nice, but only if it improves your listening experience.  
We listen very carefully and critically to our amplifiers with a wide  
variety of associated equipment and we take our time with it.  
Musical performance is most important, and is the basis of our  
success over the years.  
It’s true that we also value the other things. The design and  
manufacturing decisions have to balance subjective performance  
against reliability, cost, specs, and ego (in approximately that order).  
That is why we make more than one amplifier, but all are built with  
the same commitment to quality.  
If you have purchased this amplifier, we thank you for your  
confidence, and hope that you enjoy it for many years. If you have  
any questions or comments, or if we can help you with your audio  
system, pelase don’t hesitate to contact us.  
Tel (530) 367 3690  
Fax (530) 367 2193  
Pass Labs,  
PO Box 219  
24449 Foresthill Rd,  
Foresthill CA 95631  
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SET UP  
X amplifiers run at about the same power as their output rating, and  
XA amplifier run more than twice that. The heat sinks on the side  
of the amplifier run hot to the touch – about 25 to 30 degrees C.  
above ambient, so you can expect 50 to 55 degrees C. temperatures  
on the heat sinks. It is very important to the long life of the  
amplifier that they get good ventilation.  
You can put this amplifier anywhere you want, but it must have good  
ventilation. Do not place it in enclosed cabinets or small closets  
without means for air to circulate freely. Stacking these power  
amplifiers directly upon each other is not recommended for the same  
reason. You should have a minimum of about 6 inches clearance to  
the top and sides for adequate air circulation.  
When not actually intending to play music the amplifier should be  
left in standby mode, where it draws only a few watts of bias on  
the output stage. If you wish to reduce the power draw to 0, you  
can shut the amplifier off via the rear panel switch, however we  
recommend that for minimum noise this switch should be toggled in  
stand-by mode.  
We have provided a standard IEC power cord that fits into the  
standard 15 amp IEC receptacle at the rear of the amplifier chassis.  
With the exception of the largest of the X and XA series, there is no  
difficulty running two amplifiers on a single 15-amp circuit. Given  
the high current draw, we generally do not recommend active line  
conditioners, although they are unlikely to damage the amplifier.  
This amplifier is equipped for operation with an earth ground  
provided by the users AC outlet. Never defeat this ground  
connection. The signal ground of this amplifier is connected to  
earth through a power thermistor, which provides a safety ground  
but provides isolation from system ground loops.  
For maximum safety we suggest that the power cord should be the  
last cable installed on your power-amplifier. You may, if you wish,  
substitute a 15-amp aftermarket power cord for the one we have  
supplied. Only use power cords, which meet all local safety standards  
and carry acceptance marks from the local regulatory authority. The  
power cord should be attached to the amplifier prior to plugging  
into house power. Place the rear mounted switch in the off (down)  
position before plugging in this amplifier.  
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The amplifier’s voltage and current rating are indicated on the  
rear panel. It will be either 240 volts, 230 volts, 220 volts, 120  
volts or 100 volts. The larger amplifiers have a circuit breaker of  
the appropriate capacity. The smaller power amplifiers use a slow-  
blow 3AG type fuse. The frequency rating of the AC line source  
is 50 to 60 Hz. Please verify that the amplifiers indicated voltage  
requirements are consistent with the supplied voltage and current at  
your location.  
On the rear panel you will find both RCA and XLR type input  
connections for single-ended or balanced inputs. If you use the RCA  
input, be certain that the XLR connector has a gold shorting plug  
between pins 1 and 3, which connects the “minus” input to ground,  
otherwise the amplifier will not operate properly. If you lose this  
plug, just contact the factory – we give them away all the time.  
The question comes up all the time – are balanced inputs (XLR)  
better than single-ended (RCA)? The answer is that balanced lines  
generally give lower noise and slightly less distortion. They are  
recommended unless your favorite source component has only RCA  
outputs.  
Also on the rear panel are the output connections for the  
loudspeakers. On stereo amplifiers there is one pair per channel, and  
on mono amplifiers we provide two pairs wired in parallel to facilitate  
“bi-wiring” a loudspeaker. As you are probably familiar, the red one  
is positive polarity, and the black one is negative.  
Please note that, being a balanced output, both of these terminals  
are electrically live – neither is grounded and should not be treated  
as ground. This is particularly important if you are using the  
output of the amp to also drive a subwoofer amplifier or other  
active component. If there is any question, please contact the  
manufacturers of the products involved – both they and we will be  
happy to advise you.  
If you happen to need a clean signal ground connection for any  
reason, we provide a dedicated 5 way binding post just for that on  
the rear of the amplifier.  
On the rear panel you will also find a pair of 5 way binding posts  
for external turn-on control. Applying 5 to 12 volts DC at this  
connection will override the front panel stand-by switch and turn the  
amplifier on.  
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So the amplifier is sitting there unconnected.  
Make sure that the rear panel power switch/breaker is off (down).  
Plug the AC cord into the back of the amplifier, and then into the  
wall. Then turn the power switch/breaker on (up). The lights in  
your house will dim for a moment as the power supply charges the  
capacitors.  
If your amplifier uses a circuit breaker and not a fuse, please note  
that this circuit breaker is not a “safety device” or “emergency  
disconnect” for this product. It will provide current limiting which  
will protect the amplifier, but it does not provide personal shock  
protection in the manner of a ground-fault interrupter. One more  
reason why it is important not to defeat the Earth connection of  
your power cord.  
On the front panel, the “Standby” LED indicator should be glowing  
blue, indicating that AC power is available and the capacitor banks  
are charged. If the “Power” LEDs are lighting the meter, use the  
front panel stand-by button to go to stand-by mode.  
Now turn off the rear power switch and unplug the AC power cord  
from the wall while you connect the speakers and inputs.  
Check to make certain that the loudspeaker cables aren’t shorted at  
the loudspeaker end, connect speaker cables to the output binding  
posts on the amplifiers, observing correct polarity. The output  
binding posts will accept either bare wire or spades. (Regulatory  
agencies in many countries have banned binding posts that will  
accept a banana plug, forcing us to abandon this option.) Make sure  
that your speaker wires only attach to the outputs of the amplifier,  
not to each other and never to the amplifier case.  
Remember the warning about treating the output connections as  
ground, particularly if you are using a powered subwoofer with this  
amplifier. If you need a ground, use the one provided specifically on  
the rear panel of the amplifier.  
The amplifier may be driven single-end or balanced, your choice.  
Single-ended input will always occur through the RCA connector and  
balanced input will always occur through the XLR connector.  
Again, if you drive the amplifier single-ended then leave the supplied  
jumpers in place between pins 1 & 3 on the input XLR.  
On the XLR connector pin 1 is ground, pin two is positive input and  
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pin 3 is inverted (negative) input. Pin numbers are marked on the  
XLR. If you re-install the jumper incorrectly or leave it lying about,  
the amplifier will not work properly, and you will be able to tell.  
Choose either XLR or RCA inputs. If you run both at once from  
different components, the sound is not likely to be optimal, but it  
shouldn’t cause damage anywhere.  
Now that the source component is connected, turn the volume all  
the way down. Plug the power cord back into the wall, and turn on  
the rear power switch.  
Push the front panel button to activate the amplifier. The lights will  
come on.  
You are ready to play music  
With any luck, you can now enter that blissful state, and we won’t  
expect you back for a while.  
It’s always possible that something may go wrong. If so, don’t get  
excited. We know It’s really aggravating when a product doesn’t  
work, but it will get fixed, and often it’s something really simple.  
We go to a lot of trouble to make products reliable, and the failure  
rate of our amplifiers is very low. This is small comfort to the few,  
but take it easy and give us a call if you have problems.  
People are interested in how long it takes for these amplifiers to  
break in. Depending on the resolution of the rest of your audio  
chain, you may or may not notice any break in of the amplifier  
beyond the first few hours of operation. You will very likely notice  
the difference in sonic character between cold and normal operating  
temperature over the first hour, so we recommend letting these  
amplifiers warm up before any serious listening.  
This generation of amplifiers warms up faster and is more bias-stable  
during warm up than previous versions, but we still recommend an  
hour for critical listening. At the factory we adjust the bias and offset  
values initially and then after warm-up and then again after 48 hours,  
If necessary. The “sweet spot” is a sink temperature between 50 and  
55 degrees C., but this is not critical, and will vary with your room  
temperature. You should be able to put your hands on the heat sinks  
without undue discomfort for 5 seconds or so.  
The amplifier has a thermal cutout that will disconnect AC power if  
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the temperature exceeds 75 degrees Centigrade. This thermal cutout  
should never occur in real life. This is a very rare occurrence, and  
would indicate a serious problem.  
Interconnects and Speaker Cables  
We have a general recommendation about interconnects, and  
speaker cables: They should cost less than the amplifier, and contain  
at least some conductive material. We have tried a lot of products  
and most work well, but as a practical matter we cannot make blanket  
recommendations.  
The amplifier is not sensitive to source interconnects. It is also not  
sensitive to radio frequency pickup, which allows some flexibility in  
choosing source interconnects without shields, though shields are  
usually a very good idea. For long runs balanced cables are highly  
recommended for their inherent rejection of noise.  
We prefer speaker cables that are short and stout. Oxygen-free  
copper and silver are the suggested materials. If you find any really  
exceptional cable made of gold, please gift us a couple hundred feet.  
Fortunately this amplifier is not sensitive to the capacitive/inductive  
character of some of the specialty speaker cables, so feel free to  
experiment.  
We have found that about 90 per cent of bad sounding cables are  
really bad sounding connections, and we recommend that attention  
be paid to cleanliness of electrical contact surfaces and proper  
connector fit.  
Speaker cables should be firmly tightened down at the speaker  
output terminals, but not with a wrench. Output terminals will not  
withstand the levels of torque that may be easily applied by wrench.  
Hand tightening without excessive force is plenty. Cleaning contact  
surfaces with one of the commercially available electronic contact  
cleaners should be part of your annual system maintenance.  
Product Life  
So how long will this hardware last? It is our experience that, barring  
abuse or the odd failure of a component, the first things to go will be  
the power supply capacitors, and from experience, they will last 15 to  
30 years. Fortunately they die gracefully and are easily replaced by a  
good technician.  
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After that, the longevity will depend upon the number of operating  
thermal cycles, but we can say that we have had amplifiers operating  
in the field in excess of 20 years with no particular mortality, and we  
don’t have good information beyond that.  
More to the point, you should not worry about it. This is a  
conservatively built industrial design, not a frail tube circuit run on  
the brink of catastrophic failure. If it breaks, we will simply get it  
fixed, so sleep well.  
Pass Laboratories  
PO Box 219  
24449 Foresthill Rd  
Foresthill, CA 95631 USA  
www.passlabs.com  
tel:  
fax:  
(530) 367 3690  
(530) 367 2193  
pass”, “Pass”, “Pass Labs”, “Pass Laboratories”,  
“Supersymmetery”, Aleph”, and “Zen” and are all registered  
trademarks of Pass Laboratories, Inc., and all rights thereto are  
protected by law.  
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Warranty Information  
All Pass Laboratories products purchased new from an authorized  
Pass Laboratories dealer in North America are covered by a  
transferable, limited 3-year warranty.  
This warranty includes parts and labor charges incurred at the repair  
facility. Consequential damages are specifically not covered and  
damage due to modification or physical abuse is also not covered.  
The customer assumes responsibility for shipping and insurance to  
and from the factory, or a factory specified repair facility.  
Non-North American customers should consult with their original  
Pass Labs dealer or distributor for warranty repair instruction prior  
to contacting the factory or shipping product for repair. Non-  
North American product must be returned to the country of origin  
for warranty service. Foreign distributors are only required to  
offer warranty service on Pass Laboratories product that they have  
imported.  
Conditions of warranty service and customer rights for product  
purchased outside the United States may vary depending upon the  
distributor and local laws. Please check with your local distributor  
for specific information.  
Any modifications to Pass Laboratories products that have not  
received written factory approval nullify all claims and void the  
warranty. Should a modified product be returned to the factory for  
repair the owner will be required to pay all necessary charges for the  
repair in addition to those charges required to return the product to  
its original configuration.  
In the case of safety issues, no product shall be returned to the  
customer without those safety issues being corrected to the most  
recent accepted standards.  
Removal or alteration of original Pass Labs serial numbers voids the  
factory warranty. Product with altered or missing serial numbers  
will be suspected as counterfeit product. Pass Laboratories will not  
repair or in any way indemnify any counterfeit or cloned product.  
Pass Laboratories does not offer products in voltages intended for  
international markets either to authorized Pass Labs dealers or to  
third parties located in the United States or Canada.  
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For your protection please  
read the following:  
Water and moisture: Electrical devices should not be used near  
water ( as per example, near a bathtub, washbasin, kitchen sink,  
laundry tub, wet basement or swimming pool ). Care should be  
taken such that objects do not have the opportunity to fall, and that  
liquid is never spilled onto or into the device enclosure through  
openings.  
Power Sources: An electrical device must be connected to a mains  
power source in strict accordance with the supplied product owner’s  
manual. Please verify that the AC mains voltage specified in the  
product manual matches those requirements indicated on the unit  
and the AC voltage provided to your location by the power company.  
Grounding: Adequate precautions should be taken so that the  
grounding provisions built into an electrical product are never  
defeated.  
Power Cords: Pass Laboratories provides a power supply cord that  
meets all legislated requirements for the market in which the product  
was originally sold. If you choose to substitute an after-market  
product we urge you to choose one that is fully safety rated by the  
necessary local authority.  
Power Cord Protection: Power supply cords should be routed so  
that they are not likely to be walked on, abraded, or pinched by items  
placed on or against them, paying particular attention to cords where  
they enter plugs or exit from a device. Never under any circumstance  
insert a cut or damaged power cord into a mains power socket.  
Power and Signal: Cables should never be connected /  
disconnected with equipment powered up. Failure to heed this  
warning may damage or destroy equipment.  
Ventilation: Power-amplifiers run hot, but you should be able to  
place your hands on them without discomfort. You must allow for  
this heat in installation, by providing for free air circulation around  
the product. Electronics should not be subjected to sources of  
excessive radiant heat. Excessive heat can shorten the life of the  
product and may cause the electronics to self-protect and shut down.  
Servicing: To reduce the risk of fire, electrical shock or other  
injuries, the user should not attempt to service the device beyond  
that which is described in the operating instructions. All other  
servicing must be referred to qualified service personnel.  
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