Conrad-johnson design LP125M Manuel utilisateur

Conrad-Johnson Owner’s Manual:

LP125M Vacuum-Tube Amplifier

conrad-johnson It just sounds right.

LP125M Owner’s Manual 1

Thank you for selecting the LP125M to power your audio system.

The LP125M 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 LP125M, we believe that you will experience the excite-

ment of discovery in hearing more from your favorite recordings

than ever before.

At conrad-johnson, we expect our products to be a source of satis-

faction and of pride to their owners for many years to come. Ac-

cordingly, 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 LP125M 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 prod-

uct to the fullest. To this end, our staff stands ready to answer any

questions you may have about the function and application of your

LP125M, and to provide any needed service both during, and after

the warranty period. Our goal is to heighten your enjoyment of re-

corded music.

LP125M Owner’s Manual 2

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 origi-

nal purchaser, or five years from the date of shipment to the au-

thorized conrad-johnson dealer. During the warranty period, con-

rad-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 which have been damaged bymisuse, abuse, or acci-

dent.

b) Units which have been modified, altered, or improperly re-

paired 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 inci-

dental 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 pack-

ing 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 ex-

press warranty. Some states do not allow limitations on the dura-

tion 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 which vary from state to state.

LP125M Owner’s Manual 3

Conrad-Johnson products purchased outside the United States are

covered by warranty terms of the importing distributor in the coun-

try in which the product was originally purchased, which may differ

from the terms set out herein. Importing distributors are not obli-

gated 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 cus-

tomer 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.

2733 Merrilee Drive

Fairfax, VA 22031

The conrad-johnson service department can also be reached by e-

mail at service@conradjohnson.com, 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

LP125M Owner’s Manual 4

nstallation

As is the case with any vacuum-tube power amplifier, the LP125M

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, cool-

ing fans are essential.

All LP125Ms 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 LP125M will have the correct operating volt-

age 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 LP125Mto

minimize its susceptibility to radio frequency interference and other

forms of EMI. Choice of materials, physical layout, grounding prac-

tice, and power supply design have all been specified with a view

to reducing the impact of electromagnetic fields on the perform-

ance 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 objec-

tive 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 rareinstances of EMI prob-

lems which could be treated locally as needed, rather than com-

promising the performance of our product in the 99.9% of installa-

tions where EMI is not a problem.

Care in installation can often avoid EMI induced problems. The fol-

lowing 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

center conductors, and a separate external shield connected at

only one end).

LP125M Owner’s Manual 5

Physical location and cable “dress” can be an important factor in

minimizing hum pickup. The installation should situate the pream-

plifier 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.

LP125M Owner’s Manual 6

onnection

INPUT: Connect the preamplifier to your LP125M amplifier at the

RCA type connector 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 "dou-

ble banana" plug. They will also accept spade lugs, bare wire, or

pin connectors.

In a stereo system, the two channels should be connected in cor-

rect "relative phase". This means that when the same signal is ap-

plied to both channels, the right and left channels speaker dia-

phragms 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 ter-

minal 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.

LP125M Owner’s Manual 7

acuum Tube Replacement

The LP125M uses six vacuum tubes of three different types: one

type M8080 (V1), one 6922 (V2) and four type 6550 (V3through

V6). The brands of tubes we supply have been chosen by first se-

lecting 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 LP125M. We highly recommend that you pur-

chase replacement tube sets from conrad-johnson design.

We anticipate tube life to accommodate two to three years of op-

eration 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 LP125M has been designed to make tube replacement as

simple as possible. Because the output tubes are individually bi-

ased, replacement tubes need not be matched pairs. No a-c bal-

ance adjustment is necessary. It is necessary to re-bias the ampli-

fier when the output tubes are replaced. The LP125M has built in

bias indicators so that no instruments are required to make this ad-

justment.

LP125M Owner’s Manual 8

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 loud-

speakers will work fine) and there should be no signal applied to

the amp. It should be connected to you preamplifier with the vol-

ume control turned fully down. Turn the amplifier on. After about

one minute, turn each of the four 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 proce-

dure should be performed whenever the amplifier's output tubes

are replaced and after each six months of average use.

PLATE FUSE: Your LP125M has been fitted with a plate supply

fuse that is installed to protect the amplifier circuitry in the event of

output tube failure. The fuse holder is physically located on the

back panel, near the speaker connectors. The cap unscrews

counter-clockwise to remove the fuse (KTK-1). An LED near the

fuse holder will light when the fuse is blown.

What happens when the fuse blows? If one of these fuses should

blow, it usually indicates a marginal output tube (one of two for

each channel) and an attempt should be made to identify and re-

place it, by either (a) replacing the fuse and turning on the amp

while watching the output tubes carefully; look for a bright white or

blue flash inside the tube. If nothing happens, then (b) lightly tap

the output tubes one by one with the plastic handle of a screw-

driver while watching for flashes inside the tube. If efforts to identify

the bad tube fail, the best course of action is to replace both tubes

in the channel that blew the fuse. If the tubes are over two years

old, or have more than 1,500 hours on them, a complete replace-

ment tube set is probably in order.

The sonic effects of a blown fuse are very low, very distorted

sounds from the speaker being driven by that channel.

TO AVOID SHOCK, ALWAYS TURN OFF THE AMPLIFIER

BEFORE REMOVING THE FUSE HOLDER CAP

Replacement fuses are available from conrad-johnson dealers.

LP125M Owner’s Manual 9

etting The Most From Your LP125M

In a system of commensurate high quality components, the

conrad-johnson LP125M 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 al-

ternating 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 tran-

sients 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 re-

spond 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 invert-

ing. 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 inver-

sions is even (or zero).

The LP125M is phase correct (non-inverting). If your system has

an odd number of inversions, (for example, if you have a phase in-

verting preamplifier) then you must add one phase inversion. This

is conveniently done by reversing the positive and negative con-

nections 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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