Margules U280SC User manual

Amplifier
U280-SC
25th
anniversary

IMPORTANT SAFETY INSTRUCTIONS
CAUTION: To reduce the risk of electric shock, do not
remove the cover. There are no user-serviceable parts
inside; it is recommended that only qualified personnel
service this component.
1. OWNER’S MANUAL: Before powering up the
equipment, read all safety and operating instructions and
follow them as instructed. Retain the safety and operating
instructions for future reference.
2. ATTACHMENTS: Use only those attachments
recommended by the unit manufacturer, as others may
cause hazards.
3. ACCESSORIES: Do not place the unit on an unstable
cart, stand, tripod, bracket, or table. The unit may fall,
causing injury to a person or damage to the unit. Mount
the unit according to the manufacturer’s instructions with
the suggested mounting accessory.
4. WATER AND MOISTURE: Do not use the unit near
water (for example, near a swimming pool, bath tub,
wash bowl, kitchen sink, or laundry tub) or in a damp
environment (like a basement or outside in the rain).
5. WALL OR CEILING MOUNTING: Mount the unit to a
wall or ceiling only in the manner recommended by the
manufacturer.
6. OBJECT AND LIQUID ENTRY: Do not push objects of
any kind into the unit through openings as they could
touch dangerous voltage points and short-out parts,
possibly resulting in a fire or electric shock. Avoid spilling
liquid of any kind on the unit. If water or any metal object
(such as a paper clip, coin, or staple) accidentally falls
inside the unit, disconnect it from the AC power source
immediately and contact Margules Audio for further
instructions.
7. HEAT: Position the unit away from heat sources such
as radiators, heat registers, stoves, or other units
(including amplifiers) that produce heat.
8. VENTILATION: Slots and openings in the cabinet
create ventilation to protect the component from
overheating. Allow at least 6 inches (16cm) of clearance
above the unit and an opening behind the unit for airflow.
Do not place the unit on a bed, sofa, rug, built-in
bookcase, or rack without adequate ventilation.

9. GROUNDING OR POLARIZATION: As a safety
feature, the unit may be equipped with a polarized
alternating current line plug in which one blade is wider
than the other. This plug will fit into the power outlet only
one way. If you cannot insert the plug fully into the outlet,
try reversing the plug. If the plug still will not fit, contact a
licensed electrician to update your obsolete outlet. Do not
defeat the safety purpose of the polarized plug.
10. POWER SOURCES: Operate the unit only from the
power source indicated on the marking label. If you are
unsure of the type of power supplied to your home,
consult your unit dealer or local power company.
11. POWER CORD PROTECTION: Arrange power
supply cords so that they do not suffer from foot traffic or
pinching by items placed on or against them. Pay close
attention to cords where plug enter the AC outlet and
where they exit from the unit.
12. LIGHTNING: For added protection during a lightning
storm or when the component is idle for long periods of
time, unplug the unit from the wall outlet and disconnect
the antenna or cable system. This will help protect the
unit from lightning and power line surge damage.
13. POWER LINES: Do not locate an outside antenna
system in the vicinity of overhead power lines or other
electric light or power circuits. When installing an outside
antenna system, take extreme care to avoid touching the
power lines or circuits; contact with them could be fatal.
14. OVERLOADING: Do not overload wall outlets,
extension cords, or integral convenience receptacles as
this increases the risk of fire or electric shock
15. REPLACEMENT PARTS: When replacement parts
are required, be sure the service technician has used
replacement parts specified by the manufacturer or those
having the same characteristics as the original parts.
Unauthorized substitutions may result in fire, electric
shock or other hazards.
16. SAFETY CHECK: Upon completion of any service or
repairs to the unit, ask the service technician to perform
safety checks to ensure the unit is in proper operating
condition.
17. IMPORTANT SAFETY NOTE:
• Before connecting a new product such as the U280-SC
to your audio or home theater system, turn off all other
equipment (preferably unplugging them from the AC
power source). Many audio components feature
automatic turn-on circuits that may activate during an
installation, potentially causing damage to electronic
components and/or speakers. This type of damage is not

covered by product warranties, and Margules Audio
specifically disclaims responsibility for any such damage.
• Power Cord: The removable power cord provided with
your player was specifically designed for use with this
product, but other AC cords may be used. Consult your
dealer for advice on AC power cords and high quality wire
in your system.
• AC Fuse: The fuse is located inside the
chassis and is not user serviceable. If the
unit does not power up, contact an
authorized service representative
• Wiring: Cables running inside walls should have the
appropriate markings to indicate compliance and listing
by the UL, CSA or other standards required by the UL,
CSA, NEC or your local building code. Questions about
cables inside of walls should be referred to a qualified
custom installer, a licensed electrician, or low-voltage
contractor.
18. RECORDING COPYRIGHT: Recording of
copyrighted material for other than personal use is illegal
without permission of the copyright holder.
19. NOTE TO CATV SYSTEM INSTALLER: This
reminder is provided to call the CATV system installer's
attention to article 820-40 of the NEC, ANSI/NFPA 70,
which provides guidelines for proper grounding and, in
particular, specifies that the cable ground shall be
connected to the grounding system of the building as
close to the point of cable entry as practical.
20. FCC INFORMATION FOR USER:
• CAUTION: Any changes or
modifications not expressly approved
by Margules Audio could void the user's authority to
operate the equipment.
• These limits are designed to provide reasonable
protection against harmful interference in a residential
installation. This equipment generates and can radiate
radio frequency energy, and if not installed and used in
accordance with the instructions it may cause harmful
interference to radio communications. However, there is
no guarantee that interference will not occur in a
particular installation. If this equipment does cause
harmful interference to radio or television reception,
which can be determined by turning the equipment off
and on, the user is encouraged to try to correct the
interference by one or more of the following measures:
• Reorient or relocate the receiving antenna.

• Increase the separation between the equipment and
receiver.
• Connect the equipment into an outlet on a circuit
different from where the receiver is connected.
21. OUTDOOR ANTENNA INSTALLATION/SAFE
ANTENNA AND CABLE CONNECTION:
• If an outside antenna or cable system is connected to
the equipment, be sure the antenna or cable system is
grounded in order to provide protection against built-up
static charges and voltage surges. Article 810 of the
National Electrical Code, ANSI/NFPA 70 (in Canada, Part
1 of the Canadian Electrical Code) provides information
regarding proper grounding of the mast and supporting
structure, grounding of the lead-in wire to an antenna
discharge unit, size of grounding conductors, location of
antenna discharge unit, connection to grounding
electrodes and requirements for the grounding electrode.
• Outside antenna system should be located well away
from power lines, electric light or power circuits and
where it will never come into contact with these power
sources if it should happen to fall. When installing an
outside antenna, extreme care should be taken to avoid
touching power lines, circuits or other power sources as
this could be fatal. Because of the hazards involved,
antenna installation should be left to a professional.

Congratulations!
The Margules U280-SC 25th Anniversary Stereo Tube
Amplifier combines the superior sound of vacuum tubes
with new and innovative technology. The results are
clearly apparent in its quick detailed dynamics and ultra-
smooth transient response. Unusual versatility and
unprecedented reliability provide an exceptional
performance upgrade to an already remarkable amplifier.
Class-A Output Stage & Active-Servo Bias
Vacuum tube power amps with class-A outputs are rare.
Class-A operation causes the tubes to run quite hot, and
increases the chance of saturating the output
transformer.
Margules has resolved this problem by incorporating an
Active Servo Bias (patent pending). The bias actively
tracks the input signal, permitting full class-A output,
without overdriving the tubes.
Active Servo Bias also sets DC bias and AC drive levels,
assuring optimum electrical and sonic performance.
Throughout the useful life of the output tubes, no drive or
bias adjustments are ever needed. New tubes can be
installed without test equipment or time-consuming setup.
Active Servo Bias also makes it possible to use a variety
of output tubes. The 6550, KT88, KT99, KT100, KT 120,
KT150 can be interchanged without modification.
Active Servo Bias is implemented with semiconductors,
which are designed for the aerospace industry, assuring
long, trouble-free operation.
The New U280-SC 25th Anniversary Stereo Tube
Amplifier includes a new and improved differential output,
as well, further reducing the THD and transient distortion.
Ultralinear / Triode & Strapped Operation
Audiophiles have argued the merits of Ultralinear vs
Triode operation for 50 years. Triode operation provides
lower distortion, at the price of reduced power output.
The U280-SC resolves this predicament by providing
switchable Triode / Ultralinear operation. For those
listening sessions where you prefer a more soft sound,
you simply switch to Triode Mode. And when more
power, dynamics, detail and punch is needed, you simply
switch to Ultralinear Mode.
Unlike most vacuum tube amplifiers, the U280-SC's
outputs can be strapped, for twice the output. Start with a
single amp and then add a second U280-SC for
increased power—or to convert to triode operation at the
same power level.
Separate gain controls for each channel make precise
balancing easy. This simplifies the setup of bi-amped
systems, as well.
Regulated Shunt Power Supply
The input stages of the new U280-SC 25th anniversary
include a special SHUNT power supply for these critical
circuits. Shunt technology provides a dramatic
improvement in Q damping, the key factor in regulating
voltage for those stages.
Good regulation reduces the loss of signal integrity that
occurs when the signal itself shifts the amplifier’s
operating point. Each channel uses separate regulators

that further improve the U280-SC’s already excellent
imaging.
Damping is critical to overall performance including
smoother transient response and overall staging. Further
improvements in quickness, dynamics and the overall life-
like listening experience result.
Our new Power Supply is virtually indestructible due to
specially designed regulation technology that protects the
amp from major tube failures.
Zero Feedback
The U280-SC does not use negative feedback as do
most tube amplifiers. Negative feedback results in a loss
of detail and sound richness. Margules has developed the
BEFS (Back Electromotive Force Sensor), which changes
the amplifier's output impedance per the load
requirement. BEFS permits the amplifier to drive difficult
speaker loads with exceptional efficiency, dynamics and
extended controlled bass.
The U280-SC's innovative design is complemented with a
fine new finish, new silver coated epoxy pc boards,
military grade potentiometers, precision metal-film
resistors and audio grade interstage capacitors.
SETUP
IMPORTANT: The amplifier should be unplugged from
the wall outlet.
First, choose the proper output impedance accordingly to
your speaker; both channels should be the same (1).
2 ohms from 1 to 2 ohms load
4 ohms from 4 to 8 ohms load
8 ohms from 8 up ohms load
In Mono mode always use both channels of the amplifiers
in ultralinear or triode mode (2) in the same output
impedance range.
The recommended settings are the following:
2 Ohms should not be used
4 Ohms from 2 to 4 ohms load
8 Ohms from 4 to up ohms load
If used as Stereo or Mono mode (3) the Triode/Ultralinear
mode should be the same in both channels.
Next, connect the speakers to the output binding posts,
red to red and black to black (4); the input signal of the
amplifier to the output signal of the preamplifier (5), see
also figure 1 for more details.
If you are not using a preamplifier set the level controls to
minimum, otherwise full clockwise (6).
Check the power switch in the back of the amplifier to be
off (7). Then connect it to the AC outlet of the wall, check
that all connections are OK and flip the switch to on.
Wait until the meter reads 43 ma! (8)
The panel meter is the actual current passing through the
right front output tube. When overpasses the 100ma, you

are overdriving the tubes; around 120ma, coincides with
the maximum power.
It is not important if you overdrive the tube in short
periods, but if you do it continuously, it will shorten the life
expectancy of the tubes. To change the tubes just unplug
the A.C. power line cord, pull out the old ones, and insert
the new tubes; the active bias will balance them.
We recommend matched pair output tubes, but this is not
indispensable.
Do not substitute with other type the two 12AU7 tubes in
the back of the amplifier. You will unbalance the circuit
and will raise the distortion.
Figure 1. Interconnection diagram
Figure 2. Front and back of the U280

Break-in
The break in period is about 150 hours of music
reproduction.
Tube life expectancy
For optimal performance we recommend to change the
set off tubes every two years, although they should last a
much longer period.
Precaution and care
This product is intended to be plugged directly to the
power supply line of your house.
Although we have taken all the precautions to make your
equipment completely safe and to comply with the safety
standards, we recommend to unplugging it from the wall
outlet if you are not going to use it for an extended period
of time.
Keep the equipment in a well-ventilated area and far
away from materials that can be ignited.
Do not expose to rain or direct sunlight.
Do not open. There are high voltage serviceable parts
inside.
The voltage supply should be ± 15% of the line nominal
voltage specified in the product.
To clean, use a soft lightly humid cloth.
WARNING: Never take the tubes out while the amplifier is
plugged!
It is important to substitute the tubes with the correct
numbers.
Troubleshooting
Doesn’t turn on
Look for:
- Proper connection to the wall outlet.
-The rear switch to be in on position.
-The U280 SC has a 3-minute delay pre warm up time.
Wait until the current meter display reaches 43ma.
- The circuit breaker in the rear of the amplifier is
probably activated, if you see the button ejected push it
in.
One channel doesn’t sound
Look for:
-The gain controls to be in the correct position.
-The connections to be properly set.
- A protection fuse can be blown, check
them and if is the case, replace it.
WARNING: HIGH VOLTAGE inside.
Be certain to have the amplifier unplugged from the
power line.
If the fuse blows again one tube is in short or damage,
replace it.
The amplifier does not sound properly.
Look for:
-The proper voltages supply.
-The amplifier output impedance selector to be in the
proper position.
Check for further advises in the operation section of this
manual.

Noise in your system.
Check for ground loops in the system.
No more than one physical ground should have the
system.
Advises
Always mount your amplifier in a firm platform avoiding
external vibrations from loudspeakers.
You can change the tonal characteristics by placing your
amplifier in different type of supports like footer, spikes,
etc.
To minimize unwanted noise in the system:
-Avoid excessive length in the interconnection cables.
-Avoid having AC line cables and strong electromagnetic
fields near the signal ones.
Because you have a servo-controlled bias and the BEFS
always use the best interconnections cables, AC power
line and loudspeakers cables that you can get.
We recommend having the gain potentiometers at
maximum level. In our opinion you will achieve the best
sounding qualities.
WARNING
Electrical hazard! Misuse or
failure to follow instructions
properly may result in personal
injury or death!
CAUTION
No risk or personal injury;
however, misuse or failure to
follow instructions may result in
damage to equipment.
NOTE
No risk or personal injury or
equipment damage; however,
misuse or failure to follow
instructions may prevent proper
performance of the equipment.

Characteristics
Frequency response 20-55KHZ
Power
Ultralinear 75W/channel
Triode 40W/channel
Mono (Ultralinear). 130W.
Mono (triode). 70W.
Noise 1.2M.V.
Maximum total harmonic distortion 0.1%
Weight 30.5KG.
Power consumption
Standby 170W.
Max. output 585W.
LIMITED WARRANTY
What is Covered and What is Not Covered
Except as specified below, this warranty covers parts and
labor to correct all defects in materials and workmanship.
The following are not covered by the warranty:
1. Damage, deterioration, malfunction or failure to meet
performance specifications resulting from:
a. Accident, acts of nature, misuse, abuse, neglect
or unauthorized product modifications
b. Improper installation, removal or maintenance,
or failure to follow instructions supplied with the
product.
c. Repair or attempted repair by anyone not
authorized by Margules Audio to repair the
product.
d. Any shipment of the product (claims must be
presented to the carrier).
e. Any cause other than a product defect.
2. Cleaning, initial set-up, check-ups with no defects
found, or charges incurred for installation, removal or
reinstallation of the product.
3. Any product, on which the serial number has been
defaced, modified or removed.
4. Accessories, including but not limited to, batteries,
cables, mounting hardware and brackets, cleaning
accessories, antenna and detachable power cords.
5. Warranty is void if purchase was made from anyone
other than an authorized Margules Audio dealer.
Who May Enforce the Warranty?
This warranty extends to products purchased directly
from Margules Audio or an authorized Margules Audio
dealer. Purchasers should inquire of the dealer regarding
the nature and extent of the dealer’s warranty, if any.

What Will We Pay For?
We will pay for all labor and material expenses for items
covered by the warranty. Payment of shipping charges is
discussed in the next section of this warranty
How You Can Get Service?
In the event that the owner needs to return the unit to
Margules Audio for service or repair of a possible defect,
he must do the following:
Contact Margules Audio at [phone] in
Mexico or at 707-5811830 in USA and ask for
technical support.
Or visit Margules Audio at the address in the end
of this manual with your product. If you want to
send it the cost is on your account.
Limitation of Implied Warranties
All implied warranties, including warranties of
merchantability and fitness for particular purchase, are
limited in duration to the length of this warranty.
Exclusion of Damages
Margules Audio’s liability for any defective product is
limited to repair or replacement of the product at
Margules Audio’s option. Margules Audio shall not be
liable for damage to other products caused by any
defects in Margules Audio products, damages based
upon inconvenience or loss of use of the product, or any
other damages, whether incidental, consequential, or
otherwise.
How State Law Relates to the Warranty
Some states do not allow limitations on how long an
implied warranty lasts and/or do not allow the exclusion
or limitation of incidental or consequential damages, so
the above limitations or exclusions may not apply to you.
This warranty gives you specific legal rights, and you may
also have other rights which vary from state to state.

MARGULES AUDIO
Uruapan #17-4
Col. Roma
Mexico D.F. 06700
Mexico.
Tel. [phone]
Toll free 1-888-538 8605
FAX [phone]
Email: [e-mail]
MARGULES USA
820 Elm Drive/div. PetalumaCA, 94952
Phone number:
707-5811830
Collect USA & Canada:
1-888-538 8605
Fax number: 707-5811830
Visit our home page in internet:
http://www.margules.com