Pass Labs Stereo Amplifier X3505 User Manual

passTM  
X350.5 Owner’s Manual  
May 17, 2006  
1
 
Previously these kinds of simple Class A circuits have been popular  
for their sound quality in low power amplifiers, but have not found  
application at high power levels due to excessive distortion and low  
efficiency. Supersymmetry™ overcomes this barrier, delivering the  
sweetness, staging, and detail of very simple circuitry up to kilowatt  
power levels and beyond.  
The X.5 Series amplifiers have the tremendous dynamic range (>140  
dB) to do justice to the high-resolution digital recordings of the 21st  
Century and the elegance to retrieve the micro dynamics offered by  
the most sensitive loudspeakers. The simple but powerful circuitry  
moves easily from total silence to explosive transient and back to  
silence without a trace and without information loss. Very unlike  
conventional high power amplifiers, they provide this level of power  
with a subtlety befitting some of the better tube amplifiers. This per-  
formance is consistence across the audio spectrum and the amplifiers  
are unconditionally stable into all speaker loads.  
So relax and enjoy your amplifier. Call us if you ever have a problem  
or question. You are welcome to ask questions or offer comments.  
Thank you for buying our product.  
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X350.5 Owners Manual  
 
Setup  
You can position this amplifier most anywhere you wish, but it re-  
quires adequate ventilation. We do not recommend placing 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. This amplifier idles at about 550  
watts, most of which dissipates as heat across the heatsinks. As a point  
of reference, these heatsinks should never become too hot to touch  
for several seconds.  
Let’s talk about AC power requirements. This amplifier draws about  
5 amps (continuous rms) at 120 volts out of the wall during normal  
operation, and this power draw reflects mostly the idle current that  
we run through the output stage. If you are driving a low impedance  
load, you will draw more power than this, but this will not be typical.  
The amplifier’s voltage and current rating are indicated on the rear  
panel. It will be 240 volts, 220 volts, 120 volts or 100 volts, all with  
an appropriate rear mounted resetable circuit breaker. The frequency  
rating of the AC line source in all instances will be 50 to 60 Hz. Please  
verify that the amplifiers indicated voltage requirements are consistent  
with the line voltage supplied at your location.  
The Pass Laboratories™ X350.5 is provided with a conventional IEC  
detachable AC line cord, which is rated at 15 amps. The safety ground  
is attached to the chassis in the conventional approved manner. The  
AC power input to the amplifier runs through a RF filter, which re-  
moves high frequency noise coming into and going out of the ampli-  
fier power supply.  
Under no circumstances should you defeat the ground connection of  
the power cord. For your safety, the chassis of the amplifier should be  
earth grounded. Signal ground is isolated from chassis, safety ground,  
to reduce the incidence of ground loop noise. The presence of a  
safety ground will not degrade the audio signal chain.  
You may substitute an aftermarket detachable IEC 320 style power  
cord of your choosing; provided it is rated for at least 15 amps and it  
meets all legal requirements and has been approved by the local testing  
authority for such things.  
Looking at the rear panel you will see the IEC 320 AC power cord  
receptacle, a thermal magnetic breaker switch, two pairs of output  
connectors, a pair of binding post connectors for remote turn-on, one  
RCA input connector and one XLR balanced input connector.  
Make sure that the breaker switch is off (down). Plug the AC cord  
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X350.5 Owners Manual  
 
into the back of the amplifier, and then into the wall. Then turn the  
breaker switch on (up). The lights in your house will blink when the  
power supply charges the capacitors; this is normal. This magnetic  
breaker switch is not to be used as a safety disconnect during servicing  
and is not a substitute for unplugging the power cord.  
On the front panel, the “Standby” LED indicator should be glowing  
blue, indicating that the power is on. The “Power” LED should not  
be on. If the “Power” LED is on, don’t get excited, just use the front  
panel stand-by button to go into stand-by mode, with the “Standby”  
LED on and the “Power “ LED off.  
OK, so the amplifier is sitting there in stand-by mode with just the  
single blue LED lit. No speaker connected, as yet. You can go ahead  
and connect the source and speakers. Some speaker cables are very  
difficult to work with due to physical size and construction, make sure  
the speaker connections do not short together. It is recommended  
that you connect the speaker ends of these cables first.  
Some powered subwoofers require an audio signal ground reference  
and their makers may suggest that a black speaker terminal is where  
this voltage reference might be found. On complementary designs,  
which would be typical of all power amps produced by Pass Laborato-  
ries™, this is an incorrect and unsafe assumption. On all Pass Labo-  
ratories™ power amplifiers a reference of 0 volts will be found only at  
pin 1 of the XLR input or at the shell of the RCA input.  
Reference connections for these devices require special consideration  
when used with our product. If you have such a device, and wish to  
use it with our product, please contact our Foresthill, California fac-  
tory for specific instructions.... you have been warned.  
The amplifier can be driven single-end or balanced, if driving the am-  
plifier single-ended, leave the supplied jumper in place (between pins  
1 & 3 on the XLR). Your amplifier will operate without the jumper  
in place, but performance will be significantly diminished. You must  
choose either XLR or RCA inputs it is not advised to try and run both  
concurrently.  
Now that the source component is connected, make sure there is no  
signal coming from it, probably by turning the volume all the way  
down.  
With the speakers connected, push the front panel button to activate  
the amplifier. The “Power” LED will come on.  
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X350.5 Owners Manual  
 
You are ready to play music  
Do everybody a favor and try not to have shorted output cables. It  
happens accidentally all the time, and the amplifier is designed to sur-  
vive, mostly.  
Of course it’s always possible that something could go wrong. If so,  
don’t get excited, just relax. It’s really aggravating when something like  
this doesn’t work, we understand, but it will get fixed. We go to a lot  
of trouble to make products reliable, and the failure rate of our ampli-  
fiers 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 often interested in how long it takes for these amplifiers  
to break in. Perhaps a more salient question is how long does it take  
them to reach their sonic best after turn on. It takes about an hour for  
them to fully warm up, and this is where we adjust them first. Then  
we adjust them again and again over a couple of days, keeping the bias  
and offset in the sweet spot. Our environment is about 23 degrees  
Centigrade and the heat sinks will rise approximately 25 degrees C.  
above that, for an average on heat sink temperature of 48 degrees C.  
Sonically they are at their best when the heatsinks are approximately  
50 degrees C.  
In your setup the temperature may vary a bit due to line voltage varia-  
tions and ventilation, but this is not a big deal. You should be able to  
put your hands on the heat sinks without discomfort for 10 seconds  
or so. It is normal for the heasink temperature to vary side-to-side and  
front to back.  
The amplifier has a thermal cutout that will disconnect AC power if  
the temperature exceeds 75 degrees Centigrade. This should never  
occur in real life.  
More things to know  
You can remotely operate the stand-by mode by applying 12 volts DC  
to the single pair of binding post connectors on the rear of the ampli-  
fier. The positive of the 12 volts DC goes to the red connector. This  
connection has an actual operating range of about 9 volts to 15 volts  
at a current draw of approximately 5.0mA. This switching will over-  
ride the front panel button, so if you want the front panel button to  
operate, leave the rear connection open.  
So much for the most essential information.  
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X350.5 Owners Manual  
 
Speaker Interface  
The Pass Laboratories™ X350.5 is optimized for loads nominally rated  
at 4 ohms and above. You can run the amplifiers into a lower nominal  
impedance without difficulty, and we are not aware of a speaker on the  
market that presents unusual difficulty with these amplifiers.  
The X.5 series amplifiers do not care particularly about the reactivity  
of the load. Reactive loads typically will have slightly less distortion  
at a given voltage/current level than resistive loads, but will make the  
amplifier run a little hotter. The X.5 circuit was designed to be quite  
happy driving electrostatic and other difficult speakers.  
When driving transformer-coupled loads directly, as in some elec-  
trostatic and ribbon designs, some attention must be paid to the DC  
character of the situation. If the transformer primary is being driven  
raw with no protection from DC and your source has DC voltage, or  
in cases where the small offset of the power amplifier is still too much,  
you may create distortion in the transformer and get less than optimal  
performance from it. Generally this is not the case with transformer-  
coupled loudspeakers, but it does occasionally surface. In these cases,  
take special care that the source does not contain a differential DC  
component, and confirm the differential DC offset of the pre-ampli-  
fier is sufficiently low. This differential voltage is easily adjusted by a  
qualified technician armed with the appropriate service documents.  
Interconnects and Speaker  
Cables  
We have a general recommendation about interconnects, which is that  
they should cost less than the amplifier, and be flexible enough to work  
with. We have tried a lot of products and most of them work well, but  
as a practical matter we cannot make blanket recommendations.  
The amplifier is not sensitive to source interconnects or ground loops.  
It is also not sensitive to radio frequency pickup, which allows some  
flexibility in choosing source interconnects without shields, though  
shields are always in good taste.  
We prefer speaker cables that are thick and short. Silver and copper  
are the preferred metals. If you find any cable made of gold, please  
gift us a couple hundred meters.  
Fortunately the amplifier is not sensitive to the capacitive/inductive  
character of some of the specialty speaker cables, so feel free to ex-  
periment.  
We have found that about 90 per cent of bad sounding cables are in  
reality bad sounding connections, and we recommend that special at-  
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X350.5 Owners Manual  
 
tention be paid to cleanliness of contact surfaces and proper fit.  
Speaker cables should be firmly tightened down at the speaker output  
terminals, but do not use a wrench. These connectors will not with-  
stand unrealistic foot-lbs of torque. Hand tightening without exces-  
sive force is plenty.  
Hardware Facts  
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  
20 years before needing replacement. Fortunately these components  
die gracefully; typically with years of warning and are easily replaced.  
After that, the longevity will depend on the number of operating ther-  
mal cycles, but we can attest to having had amplifiers operating in the  
field in excess of 20 years with no particular mortality except capaci-  
tors. We don’t have good information beyond that. More to the point,  
we would suggest that you not worry about it. This is a conservatively  
built industrial design, not a tweaky tube circuit run on the brink of  
failure. If it breaks, we will simply get it fixed, so sleep well.  
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X350.5 Owners Manual  
 
X350.5 Specifications  
All figures obtained after 1 hour warmup, with regulated 120 VAC  
power line. See manual notes about AC power line regulation.  
Gain  
30 dB  
Freq. Response  
Power Output  
-3 dB at 1Hz, -3 dB at 100 kHz  
350 watts maximum @ 1% THD,  
1 kHz, 8 ohms  
Maximum Output Voltage  
Maximum Output Current  
Input Impedance  
Damping factor  
plus, minus 90 volts  
plus, minus 20 amps  
22 kohm balanced  
250 ref 8 ohms nominal  
plus, minus 50 V/uS  
Slew rate  
Output Noise  
Balanced CMRR  
300 uV unweighted 20-20 kHz  
-60 dB @ 1 kHz (input common  
code rejection ratio)  
DC offset  
< 100 mv differential  
Power Consumption  
Temperature  
Dimensions  
550 watts idle, 1800 watts maximum  
25 degrees C. above ambient at idle  
19 “ W x 22” D x 11.5” H  
150 lbs.  
Shipping Weight  
For more information please contact:  
Pass Laboratories Inc.  
P.O. Box 219,  
24449 Foresthill Rd.,  
Foresthill, CA 95631  
Tel: 530.367.3690  
Fax: 530.369.2193  
www.passlabs.com  
© 2006 Pass Laboratories Inc.  
“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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X350.5 Owners Manual  
 
Please check with the factory-authorized distributor in the country you are  
purchasing this product for specific warranty information.  
Warranty Information  
All Pass Laboratories products purchased from an authorized Pass Labora-  
tories dealer in North America are covered by a transferable, limited 3-year  
warranty. This warrantee includes all parts and labor charges incurred at the  
repair facility in addition to return shipping to the domestic customer, exclu-  
sive of subsequent damages. Damage due to physical abuse is specifically  
not covered under this warranty.  
For this warranty to apply the customer is responsible for returning the  
product unmodified to the factory within the warranty period. The customer  
assumes all responsibility for shipping and insurance to the factory or a fac-  
tory specified repair facility. The conditions and stipulations of this Pass  
Laboratories warranty only applies to units sold new in North America.  
Non-North America customers should consult with their original Pass Labs  
dealer or distributor for warrantee 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  
warrantee service. Foreign distributors are only required to offer warranty  
service on Pass Laboratories product that they have imported.  
Please note: Conditions of warranty service and customer rights for product  
purchased outside the United States may vary depending upon the distribu-  
tor and local laws. Please check with your local distributor for specific rights  
and details.  
Any modifications to Pass Laboratories products that have not received  
written factory approval nullify all claims and void the warrantee. Should a  
modified product be returned to the factory for repair the owner will be re-  
quired to pay all necessary charges for the repair in addition to those charges  
required to return the product to it’s 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 inter-  
national markets either to authorized Pass Labs dealers or to third parties  
located in the United States or Canada.  
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X350.5 Owners Manual  
 
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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X350.5 Owners Manual  
 

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