Margules U280SC User manual

Amplifier U280SC

Margules Audio
Amplifier U280SC
Congratulations!
The Margules U280-SC amplifier combines the superior
sound of vacuum tubes with innovative technology. The
result is exceptionally good sound and unusual
versatility.
You acquire a piece that is state of the art, we are
positive that will bring you long hours of listening
enjoyment.
Introduction:
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 gotten around this problem by
incorporating Active Servo bias (patent pending).
The bias actively tracks in input signal, permitting full
class-A output, but without overdriving the tubes.
Active Servo Bias also sets DC bias and AC drive levels
automatically, 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 a
time-consuming setup.
Active Servo Bias also makes it possible to use a variety of
output tubes. The 6550, KT88, KT99, or KT100 can be
interchanged, without modification.
Active Servo Bias is implemented with semiconductors
designed for the aerospace industry, assuring long, trouble-
free operation.
Regulated Power Supply
The input and driver stages incorporate classic, time-proven
circuitry used by many other manufacturers. The U280-SC’s
design differs because it includes tightly regulated high
voltage for these critical circuits. Good regulation reduces the
loss of signal integrity that occurs when the signal itself shifts
the amplifier’s operating point.
Each channel has separate regulators for improved imaging.
Zero Feedback
The U280-SC does not use overall negative feedback. This
would normally result in a low damping factor, which is not
desirable for most speakers. Margules has developed the
BEFS (Back Electromotive Force Sensor), which changes
the amplifier’s output impedance as the load requires.
BEFS permits the amplifier to drive difficult speaker loads
with exceptional dynamics and extended, controlled bass.
The U280-SC’s innovative design is complemented with
precision metal-film resistors and polypropylene capacitors.

Operation:
It is very important to set select the output impedance
correctly.
To use the amplifier in Stereo mode the range is the
following:
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 in the same
output impedance range.
The recommended settings are the following:
2 Ohms from .5 to 2 ohms load
4 Ohms from 2 to 4 ohms load
8 Ohms from 4 to up ohms load
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, 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.
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 unplug it from the
wall outlet if your 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. High voltage no 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.
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 35ma.
- 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 ground loops between equipment.
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 interconnect 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 interconnects, 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.
-Check for further advises in the operation section of
this manual.

Characteristics
Frequency response 10-45KHZ
Power
Ultralinear 60W/channel
Triode 30W/channel
Mono (Ultralinear). 120W.
Mono (triode). 60W.
Noise 1.2M.V.
Maximum total harmonic distortion 0.35%
Weight 32KG.
Power consumption
Standby 170W.
Max. output 600W.
For more information please contact us at:
MARGULES AUDIO
Uruapan #17-4
Col. Roma
Mexico D.F. 06700
Mexico.
Tel. [phone]
Toll free 1-888-538 8605
FAX [phone]
Email: [email protected]
Visit our home page in internet:
http://www.margules.com.mx