Conrad-johnson design MV125 Manuel utilisateur

Congratulationson your purchase of the conrad-johnson MV125 ampli-

fier. You have acquired one of the finest pieces of music reproduction

equipment available today. You will find it to be capable of reproducing

with remarkable accuracy the dynamics, tonalities, and textures of live

music performances. The design and materials have been carefully

selected to yield years of unvarying excellence.

Please take a few minutes to read this manual so that you will better

understand the featues and capabilities of your MV125.

MV125 Owner’s Manual 1

LIMITED WARRANTY FOR THE CONRAD-JOHNSON

MV125

1. conrad-johnson design, inc. warrants to the original owner that the

conrad-johnson MV125 will be free from defects in material and work-

manship for a period of three years from the date of original purchase.

2. During the warranty period, conrad-johnson will repair defective units

without charge for labor or parts (with the exception of the vacuum

tubes) subject to the following conditions:

a) The unit must not have been altered or damaged through

misuse, abuse, negligence, accident or improper operation.

b) The purchaser must provide evidence of purchase at the time

service is requested.

c) All repairs must be undertaken at the factory or other service

center designated by conrad-johnson design, inc. Units submitted

for warranty repairs must be shipped in the factory packing carton

to conrad-johnson design or its designated service center, freight

and insurance prepaid by the owner, and will be returned to the

owner, freight and insurance prepaid by conrad-johnson design.

Replacement cartons are available from the factory for a nominal

charge.

d) Normal wear and maintenance are not covered by this warranty.

3. The above warranty may be transferred to subsequent owners pro-

vided that the warranty registration card has been returned to conrad-

johnson design, inc. within 30 days of the original purchase and that the

registered owner provides the factory with a signed notice giving the

newowner’snameandaddressandthemodelandserialnumberofthe

unit.

4. Where permitted by law, conrad-johnson design’s liability shall be

limited to that set forth in this warranty. No other warranty of any kind,

expressed or implied, is made by conrad- johnson design, inc., and all

implied warranties, including merchantability and fitness for a particular

"purpose", which exceed the obligations and time limits set forth herein

are hereby disclaimed. conrad-johnson design, inc. shall not be liable

for incidental or consequential damages. Some states do not allow the

exclusion or limitations on how long an implied warranty lasts, so the

above limitation or exclusion may not apply to you.

MV125 Owner’s Manual 2

5. This warranty gives you specific legal rights, and you may also have

other rights which vary from state to state. Questions about warranty

service should be addressed to:

Service Department

conrad-johnson design, inc.

2800 R Dorr Avenue

Fairfax, VA 22031

REGISTERING THE WARRANTY

Please return the enclosed card to the factory within 30 days of pur-

chase to register the warranty. Proper registration of the warranty is

important! It will enable us to inform you of any alterations in the design

of a given model and of any new products we offer which are likely to be

of interest to you.

MV125 Owner’s Manual 3

CIRCUIT DESIGN

It has been our experience that simple designs with few active stages

when executed with care and great attention to detail will be both more

musical and more reliable than overcomplicated alternatives. Accord-

ingly, the audio circuit of the MV125 is remarkably straightforward. A

triode input amplifier comprised of paralleled sections of a 5751 is direct

coupled to a cathode coupled differential phase inverter using high

current triodes to provide balanced, low impedance drive to the push-

pull output stage. The output stage features ultralinear operation of two

pairsof6550s for high power levels with reducedsourceimpedance.As

a result, the amplifier is capable of supplying the large current demands

of high amplitude musical transients driven into reactive speaker loads.

A substantial main power supply of massive polypropylene capacitors

enables the MV125 to easily meet these extraordinary current de-

mands.Voltageregulatorsforthevoltageamplifiersandphaseinverters

provide nearly absolute isolation of these sensitive stages from the

output stages.

MV125 Owner’s Manual 4

INSTALLATION

Because of the number and type of vacuum tubes, the MV125 dissi-

pates considerable heat. It is essential, therefore, that proper attention

be paid to ventilation. The unit should be mounted horizontally on a flat

hardsurfacesothattheventilation holesin thebottomareunobstructed.

At least six inches of clearance should be provided 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.

The front panel of the MV125 will fit in a standard 19" equipment rack

and is designed to carry the weight of the unit so that it may be rack

mounted. Again, it is important that adequate clearance be provided

above so that ventilation is not impeded. About eight inches of the front

of the rack should be left open above the unit.

To minimize hum pickup, keep the unit well away from the preamplifier

and turntable and route power cords away from input cables.

THE MV125 IS TO BE OPERATED ONLY ON AC LINE VOLTAGE OF

108 TO 125 VOLTS.

The MV125 is optionally available wired for 100 volt, 120V, 220V or 240

volt, 50/60 Hz current.

CONNECTION

INPUT: Connect the preamplifier to your MV125 amplifier at the RCA

type connections located on the back of the amplifier.

OUTPUT: Terminal strips are provided for connection of your loud-

speakers. They will accept bare wire or spade lug connectors.

Three different taps- 4 ohm, 8 ohm, and 16 ohm are provided in addition

to the "C" or ground tap.

Matchingthe rated nominalimpedanceofyour speakers withtheampli-

fier output taps will not necessarily guarantee optimum performance.

The sound with a given set of speakers will vary with the different

MV125 Owner’s Manual 5

impedancetaps. We suggest listening to eachof the three taps to select

the best match for your speakers.

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 should move synchronously-in

and out together. Terminals on the speakers are usually coded-one

designated "C", "earth", "ground", "-" or black, the other designated "+"

or red.

"In phase" connection of the speakers can normally be achieved by

takingcare to connectthewirefrom the4,8,or16 ohm amplifierterminal

marked on each channel to the red or "+" coded terminal on each

speaker, and connecting the "C" tap to the black or "-" coded terminal

on each speaker.

In phase connection of the speakers can be readily ascertained by ear.

With the preamplifier mode switched into the MONO position, play a

recordingof asolovocalist. Withthespeakers inphasethe voiceshould

be clearly focused between the two speakers. With the speakers con-

nected 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.

MV125 Owner’s Manual 6

GETTING THE MOST FROM YOUR

CONRAD-JOHNSON MV125

The conrad-johnson MV125 offers an unparalleled level of sophistica-

tion and refinement in music reproduction, but it cannot transform an

inferior stereo system. Only the very best loudspeaker systems will be

capable of fully revealing the capabilities of this precision instrument.

Proper set-up is important in any high-fidelity system, but with state-of-

the-art components it is essential. Given a system of high quality

components, there remain a number of important details which must be

attended to.

ABSOLUTE PHASE

Musical notes are heard through the ear’s response to waves of alter-

nating rise and fall of air pressure. Musical transients are 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 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

systemiseitherphasecorrectorphaseinverting(includingthecartridge

and speakers-these are normally phase correct). Your MV125 is phase

correct. It is of no consequence if an individual component is phase

inverting, as long as the system as a whole is phase correct. This will be

the case as long as the number of phase inversions is even (or zero). If

your system has an odd number of inversions, then you must add one

phase inversion. This is conveniently done by reversing the positive and

negative connections on either your cartridge or your speakers (be sure

to reverse both channels).

If you are not sure about the phase of every component 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

MV125 Owner’s Manual 7

(including some "audiophile" recordings), so listen to several before

concluding your investigation of absolute phase.

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

stranglethesytemtothepointwhereitbecomesnobetterthanaverage.

To complicate matters, our experience suggests that the choice of

interconnects will be system dependent-those that are ranked first on a

given system may be a poor choice for a different system. Consult your

conrad- johnson dealer for recommendations for your specific system.

QUESTIONS?

If you have any questions about the installation or function of your

MV125 do not hesitate to call Customer Service at (703) 698- 8581.

MV125 Owner’s Manual 8

TUBE REPLACEMENTS

TheMV125 usestwelvevacuumtubes ofthreedifferent types: two5751

(V1 and V2), two 6FQ7 (V3 and V4) and eight 6550s (V5 through V12).

Each type has been carefully chosen for its circuit application. It is well

known that tubes of a given type vary sonically depending on the

manufacturer. We have chosen the brands of tubes that we supply

basedon extensive auditioningofavailablebrands. The choiceofbrand

has been made solely on the basis of sonic performance and reliability

without regard to either cost or prestige. We know of no vacuum tubes

availablewhichwillimprovethesonicperformanceof yourMV125.Also,

the tubes in your amplifier have been tempered by a controlled burn in

procedure that permits them to perform for a greatly extended period

without degradation in normal use. We highly recommend that, when

thetime comes toreplacethevacuum tubes, youpurchasereplacement

tube sets from conrad-johnson design.

The MV125 has been designed to make tube replacement as simple as

posssible. Beacuase the output tubes are individually biased, replace-

ment 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 MV125 has built in bias indicators so that no instru-

ments are required to make this adjustment.

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. A red plastic screw-

driver has been included with your amplifier for this purpose. After

replacing the tubes, the amplifier should be connected to a load (your

loudspeakerswillwork fine) andthereshouldbeno signal appliedtothe

amp. It should be connected to you preamplifier with the volume control

turned fully down. Turn the amplifier on. After about one minute, turn

each of the four screwdriver adjustable controls 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

MV125 Owner’s Manual 9

flash or flicker when the amplifier is in use. This is normal and no cause

for alarm.

This biasing procedure should be performed whenever the amplifier’s

output tubes are replaced and also after six months of average use.

FUSES

LINE FUSE: The AC line is fused to protect the power transformer. This

fuse will not fail in normal operation. Failure of the fuse is a symptom of

a more serious problem, so the unit should be taken to a qualified

service center. IN NO EVENT SHOULD THE FUSE BE REPLACED

WITH A FUSE OF DIFFERENT TYPE OR RATING THAN THAT SUP-

PLIED BY THE FACTORY.

PLATE FUSE: Your MV125 has been fitted with plate supply fuses

whicharedesigned to protecttheamplifiercircuitryin the eventofoutput

tube failure. The fuse holders are physically located near the speaker

connectors. The cap unscrews counter clockwise to remove the fuse (

a BUSS BBS-2). 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 6550 tube (one of four for each channel)

and an attempt should be made to identify and replace it, by either (a)

replacing the fuse and turning on the amp while watching the 6550s

carefully; look for a bright white or blue flash inside the tube. If nothing

happens, then (b) lightly tap the 6550s one by one with the plastic

handle of a screwdriver while watching for flashes inside the tube. If all

efforts to identify the bad tube fail, the best course of action is to replace

all 6550s 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 and tubes are available from conrad-johnson deal-

ers.

MV125 Owner’s Manual 10

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