Conrad-Johnson LP125sa Manuel utilisateur

Conrad-Johnson Owner’s Manual:

LP125sa Vacuum-Tube Stereo Amplifier

conrad-johnson It just sounds right.

LP125sa Owner’s Manual

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

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.

LP125sa Owner’s Manual

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

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

LP125sa Owner’s Manual

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

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.

LP125sa Owner’s Manual

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.

LP125sa Owner’s Manual

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

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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