Conrad-Johnson LP125sa User manual

Conrad-Johnson Owner’s Manual:
LP125sa Vacuum-Tube Stereo Amplifier
conrad-johnson It just sounds right.

LP125sa Owner’s Manual
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Thank you for selecting the LP125sa amplifier to power your audio
system. The LP125sa draws on three decades of research at
conrad-johnson into the reproduction of recorded music. The result
is a power amplifier with a remarkable ability to recreate the
dynamics, textures, tonalities, and ambience of live musical
performances. With the LP125sa, we believe that you will
experience the excitement of discovery in hearing more from your
favorite recordings than ever before.
At conrad-johnson, we expect our products to be a source of
satisfaction and of pride to their owners for many years to come.
Accordingly, circuit designs, parts and materials for all conrad-
johnson products are selected with a view to maintaining optimal
performance over the years. Our reputation for producing among
the industry's most reliable components is a natural consequence
of this engineering approach.
Although operation of the LP125sa amplifier is quite
straightforward, please take a few minutes to read this manual for
useful information on its installation and operation.
In closing, we’d like to welcome you to the family of conrad-
johnson owners. We want you to enjoy your conrad-johnson
product to the fullest. To this end, our staff stands ready to answer
any questions you may have about the function and application of
your LP125sa, and to provide any needed service both during, and
after the warranty period. Our goal is to heighten your enjoyment of
recorded music.

LP125sa Owner’s Manual
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imited Warranty For Conrad-Johnson Components
Conrad-Johnson Design, Inc. will provide service under warranty to
the original owner on products sold new in the United States for the
lesser period of three years from the date of purchase by the
original purchaser, or five years from the date of shipment to the
authorized conrad-johnson dealer. During the warranty period,
conrad-johnson will repair defective units without charge for labor
or parts (with the exception of vacuum tubes and batteries).
Exclusions. The following are not covered under this warranty:
a) Units that have been damaged by misuse, abuse, or
accident.
b) Units that have been modified, altered, or improperly
repaired by anyone not specifically authorized by conrad-
johnson design, inc.
c) Units not purchased from an authorized conrad-johnson
dealer in the United States for use in the United States.
d) Normal wear
e) Incidental or consequential damages are not covered under
this warranty. Some states do not allow the exclusion of
incidental or consequential damages, so this exclusion may not
apply to you.
Obtaining Warranty Service: To obtain warranty service, the unit
must be shipped, along with evidence of purchase, in factory
packing to conrad-johnson design (or designated service center)
with freight and insurance prepaid by the owner. After repair, the
unit will be returned with freight and insurance prepaid by conrad-
johnson design to any destination in the United States.
All implied warranties, including merchantability and fitness for a
particular purpose are limited in duration to the duration of this
express warranty. Some states do not allow limitations on the
duration of implied warranties so the above limitations may not
apply to you.
This warranty gives you specific legal rights and you may also
have other rights that vary from state to state.
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LP125sa Owner’s Manual
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Conrad-Johnson products purchased outside the United States are
covered by warranty terms of the importing distributor in the
country in which the product was originally purchased, which may
differ from the terms set out herein. Importing distributors are not
obligated to provide warranty service for products originally
purchased outside their country. Conrad-Johnson will provide
warranty service for products outside the United States, but in
these cases, the customer must pay all shipping, handling and
customs costs both to and from our Service Department.
Questions about this warranty should be addressed to:
Service Department
conrad-johnson design, inc.
2800K Dorr Avenue
Fairfax, VA 22031
The conrad-johnson service department can also be reached by e-
mail at [email protected], by phone at 703-698-8581,
or by fax at 703-560-5360.
Service
If your conrad-johnson audio component requires service, repack it
using the original box and packing material and ship to the Service
Department address above. Boxes and packing materials can be
purchased through our service department if you no longer have
yours. Include with the unit a note describing the problem you are
having in as much detail as possible. It is especially important for
our technician to know if the problem is intermittent. If you want an
estimate of cost for out of warranty service, be sure to request it in
this note. Be aware that requesting an estimate will delay service
to your unit, as we will have to contact you for approval before
commencing service.
Registering The Warranty
Please return the enclosed card to the factory within 30 days of
purchase to register the warranty

LP125sa Owner’s Manual
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nstallation
As is the case with any vacuum-tube power amplifier, the LP125sa
amplifier dissipates a significant amount of heat. Provision must be
made for adequate ventilation. Mount the unit on a flat, hard
surface, taking care that the ventilation holes in the bottom are
unobstructed. Maintain at least four inches of clearance above the
unit, and at least three inches on the sides. The cabinet or shelf
should be open at both front and back. For more restricted
installations, cooling fans are essential.
All LP125sa amplifiers sold in the United States are configured for
operation on a 60Hz ac power line producing between 108 and 126
volts. Export versions of the LP125sa will have the correct
operating voltage and frequency clearly marked on the back panel
of the unit, near the ac power cord. In all cases, the actual line
voltage should be within + 5/- 10% of the nominal rated voltage.
Electromagnetic Interference (EMI)
Considerable care has been taken in the design of the LP125sa to
minimize its susceptibility to radio frequency interference and other
forms of EMI. Choice of materials, physical layout, grounding
practice, and power supply design have all been specified with a
view to reducing the impact of electromagnetic fields on the
performance of this unit. At the same time, however, our primary
goal is the accurate reproduction of recorded music in the normal
home environment, and we have elected not to compromise this
objective by the application of heavy-handed RFI filters, or by using
grounding practices that reduce RFI at the expense of degraded
audio performance. We find that the approach we have taken has
worked extremely well, resulting in only rare instances of EMI
problems which could be treated locally as needed, rather than
compromising the performance of our product in the 99.9% of
installations where EMI is not a problem.
Care in installation can often avoid EMI induced problems. The
following practices should generally be observed in any
application, and will be especially important where EMI may be a
problem.
Interconnect cables should be kept as short as possible (3 meters
or less), and shielded cable should be used (cable which has two
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LP125sa Owner’s Manual
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center conductors, and a separate external shield connected at
only one end).
Physical location and cable “dress” can be an important factor in
minimizing hum pickup. The installation should situate the
preamplifier well away from the power amplifier, and power (ac
mains) cords should be dressed to remain at least 4" (100mm)
away from input/output cables.

LP125sa Owner’s Manual
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onnection
INPUT: Connect the preamplifier to your LP125sa amplifier at the
RCA type connectors located on the back of the amplifier.
OUTPUT: Five-way binding posts are provided for connection of
your loudspeakers, with correct spacing to accept a standard
"double banana" plug. They will also accept spade lugs, bare wire,
or pin connectors.
The two channels should be connected in correct "relative phase".
This means that when the same signal is applied to both channels,
the right and left channels speaker diaphragms will move
synchronously - in and out together. Terminals on speakers are
usually coded - one designated "C", "ground", "-" or black, the
other designated "+" or red. "In phase" connection of the speakers
can normally be achieved by taking care to connect the wire from
the "+" amplifier terminal to the red or "+" coded terminal on each
speaker, and connecting the "-" terminal to the black or "-" coded
terminal on each speaker. In phase connection of the speakers can
be readily ascertained by ear. Listen to a recording of a solo
vocalist (use a mono recording if available). With the speakers in
phase the voice should be clearly focused between the two
speakers. With the speakers connected out of phase, the voice will
be diffused, with no identifiable source. Relative phase may be
reversed by switching the "+" and "-" leads at one speaker only.
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LP125sa Owner’s Manual
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acuum Tube Replacement
The LP125sa uses eleven vacuum tubes of three different types:
one type 6189 (V1), two type 6N30P (V2 and V3), and eight type
KT120 (V4-V11). The brands of tubes we supply have been
chosen by first selecting those brands which are known to be most
reliable, then by extensive auditioning of these acceptable brands
with the final choices being made solely on the basis of sonic
performance. We know of no vacuum tubes available which will
improve the sonic performance of your LP125sa. We highly
recommend that you purchase replacement tube sets from conrad-
johnson design.
We anticipate tube life to accommodate two to three years of
operation without degradation in normal use - if the amplifier is
switched off when not in use. If it is left on at all times, tube life can
be exhausted in a matter of a few months.
The LP125sa has been designed to make tube replacement as
simple as possible. Because the output tubes are individually
biased, replacement tubes need not be matched pairs. No a-c
balance adjustment is necessary. It is necessary to re-bias the
amplifier when the output tubes are replaced. The LP125sa has
built in bias indicators so that no instruments are required to make
this adjustment.
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LP125sa Owner’s Manual
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Adjusting Output Tube Bias
Biasing the amplifier is a simple procedure that can easily be done
by the owner. Only a plastic screwdriver is required (one has been
included with your amplifier for this purpose). After replacing the
tubes, the amplifier should be connected to a load (your
loudspeakers will work fine) and there should be no signal applied
to the amp. It should be connected to your preamplifier with the
volume control turned fully down. Turn the amplifier on. After about
one minute, turn each of the eight screwdriver adjustable controls
(located near the output tube sockets) counterclockwise until the
associated indicator LED just goes off. Clockwise rotation may be
necessary first to turn the LED on; do not turn the adjusting screw
any further in the clockwise direction once the LED has come on.
After the amplifier has warmed up thirty minutes, the procedure just
described should be repeated. NOTE: It is normal for these LEDs
to flash or flicker when the amplifier is in use. This biasing
procedure should be performed whenever the amplifier's output
tubes are replaced and after each six months of average use.
PLATE FUSE: Your LP125sa has been fitted with plate supply
fuses that are installed to protect the amplifier circuitry in the event
of output tube failure. The fuse holders are physically located
inside the chassis at the ends of the vertically mounted power
supply pc board. The fuses are 5x20mm 1A F-type (fast blow)
ceramic fuses. LEDs labeled FUSE OUT are located on the rear of
the chassis, one on either side of the center transformer. If a plate
fuse blows, the associated LED will light. The sonic effects of a
blown fuse are very low, very distorted sounds from the speaker
being driven by that channel.
WARNING: the LP125sa operates at high voltages. The chassis
should only be opened by qualified, experienced persons. NEVER
remove the bottom cover of the chassis without first unplugging the
unit from the ac mains and allowing ample time for power supplies
to drop to safe voltages.
Replacement fuses are available from conrad-johnson dealers.

LP125sa Owner’s Manual
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etting The Most From Your LP125sa Amplifier
In a system of commensurate high quality components, the
conrad-johnson LP125sa amplifier offers an unparalleled level of
sophistication and refinement in music reproduction. To get the
best performance out of any audio system, there are a number of
important details that must be attended to.
Absolute Phase
Musical notes are heard through the ear’s response to waves of
alternating rise and fall of air pressure. Musical transients are
almost exclusively positive: that is, the initial effect is a rise in
pressure. The ear is capable of distinguishing these positive
transients from the musically unnatural alternative of a negative
transient (an initial fall in air pressure). In terms of your stereo
system, these transients are created by your loudspeakers. If the
speakers respond to musical transients by first moving out, they
are creating a rise in pressure, and the system is said to be phase
correct. If they respond by moving in, they create a fall in pressure
and the system is said to be phase inverting. Each component in
the stereo system either preserves the phase of the incoming
signal, and is said to be phase correct, or inverts the phase and is
said to be phase inverting. It is unimportant whether an individual
component is phase correct or phase inverting, as long as the
system as a whole is phase correct. This will be the case if the
number of phase inversions is even (or zero).
The LP125sa is phase correct (non-inverting). If your system has
an odd number of inversions, (for example, if you have a phase
inverting preamplifier) then you must add one phase inversion.
This is conveniently done by reversing the positive and negative
connections to your speakers (be sure to reverse both channels). If
you are not sure about the phase of every piece in your system,
you can establish correct absolute phase by careful listening.
When the system is in correct phase, transients will be noticeably
cleaner and more sharply defined. The effect is especially apparent
on plucked string sounds. A final warning - not all recordings are
phase correct (including some “audiophile” recordings), so listen to
several before concluding your investigation of absolute phase.
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LP125sa Owner’s Manual
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The Importance Of Wires
Interconnect and speaker wires are an important element in your
stereo system. Interconnects are available which will permit a
reference quality system to blossom and fulfill its promise of
musical reality. Others will strangle the system to the point where it
becomes little better than average. To complicate matters, our
experience suggests that the choice of interconnects will be
system dependent - those that are top ranked on one system may
be a poor choice for a different system. Consult your conrad-
johnson dealer for recommendations for your specific system.
Performance Tip
Warm up the LP125sa before listening: The sonic performance of
the LP125sa improves noticeably as the unit warms up. The
midrange becomes more lucid, the highs smoother, and the
soundstage expands. The warm up period can be expected to last
about fifteen minutes.
Questions: If you have questions about the installation or function
of your LP125sa do not hesitate to call Customer Service at (703)
698-8581.

LP125sa Owner’s Manual
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pecifications
Power: 125 watts per channel RMS both channels driven into 4
ohms from 30Hz to 15KHz at no more than 1.5% total harmonic
distortion or intermodulation distortion (can be re-connected
internally for 8 or 16 ohm loads).
Sensitivity: 1 V rms to rated power
Frequency Response: 20Hz to 20 kHz +0/-.3 dB
Hum and Noise: 100 dB below rated power output
Phase: phase correct
Input Impedance: 100 kOhms
Mechanical
Dimensions: 18.88"D x 19”W x 7.63”H
Net Weight: 82 lb net
Fuses
The LP125sa power transformer is protected by a fuse on the ac
power line (F5, located in a compartment in the ac line-cord
receptacle mounted on the back of the amplifier), and by four
separate internal fuses on the secondary circuits of the transformer
(F1 – F4) located on the bottom of the pc board. A failure of any of
these fuses is a symptom of a more serious problem, and a
competent service technician should be consulted. In no event
should fuses be replaced with a value or type different than that
originally supplied. The correct fuse values and types are:
F1, F2, and F3: 3AG ¼ Amp Slow-Blow
F4: 3AG 4 Amp Slow-Blow
F5: 5x20mm 10 amp T-type if configured for 100 or 120V:
5x20mm 5 amp T-type if configured for 220 or 240V.
The output stages are protected by plate fuses in series with
the output tubes. These are 5x20mm 1 A fast-blow ceramic
fuses, located inside the chassis in fuse holders mounted on
the vertical power supply board.
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