Conrad-johnson design MV50 Manual de usuario

Congratulations on your purchase of the conrad-johnson MV50 ampli-

fier. You have acquired one of the finer pieces of musical reproduction

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

withgreataccuracythedynamics,tonalities,andtexturesoflivemusical

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 MV50.

MV50 Owner’s Manual 1

LIMITED WARRANTY FOR THE CONRAD-JOHNSON

MV50

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

conrad-johnsonMV50willbefreefromdefectsinmaterialandworkman-

ship 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

registeredownerprovides thefactorywithasignednoticegiving thenew

owner’s name and address and the model and serial number of the 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

areherebydisclaimed.conrad-johnsondesign,inc.shallnotbeliablefor

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.

MV50 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.

MV50 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 MV50 is remarkably straightforward. A

single triode input amplifier is direct coupled to a cathode follower. This

arrangement offers exceptional phase linearity. This stage 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 which

permits high power levels while greatly reducing the source impedance

of the stage. As a result, the amplifier is capable of supplying the large

current demands of high amplitude musical transients driven into reac-

tive speaker loads. A substantial main power supply enables the MV50

to easily meet these extraordinary current demands. Voltage regulators

for the voltage amplifiers and phase inverters provide nearly absolute

isolation of these sensitive stages from the output stages.

MV50 Owner’s Manual 4

INSTALLATION

Because of the number and type of vacuum tubes, the MV50 dissipates

considerableheat.It isessential,therefore,that properattentionbepaid

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

surface so that the ventilation holes in the bottom are unobstructed. At

least four 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 MV50 will fit in a standard 19" equipment rack and

isdesignedto carrytheweightof theunitsothat itmayberack 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 MV50 IS TO BE OPERATED ONLY ON AC LINE VOLTAGE OF

108 TO 125 VOLTS.

The MV50 is optionally available wired for 100 volt, 120V, 220V or 240

volt, 50/60 Hz current.

CONNECTION

INPUT: Connectthepreamplifierto your MV50amplifierattheRCA type

connections located on the back of the amplifier.

OUTPUT: Terminalstripsareprovidedforconnectionofyourloudspeak-

ers. 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.

Matching the rated nominal impedance of your speakers with the ampli-

fier output taps will not necessarily guarantee optimum performance.

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

MV50 Owner’s Manual 5

impedance taps. We suggest listening to each of 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

takingcaretoconnectthewirefromthe 4,8, or 16 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

record of a solo vocalist. With the speakers in phase the voice should

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.

MV50 Owner’s Manual 6

GETTING THE MOST FROM YOUR

CONRAD-JOHNSON MV50

The conrad-johnson MV50 offers an unparalleled level of sophistication

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. Before attempting to evaluate the MV50, be

sure that your phono system has been set up carefully according to

manufacturer recommendations. Adjustment of the cartridge vertical

tracking angle can be especially critical with modern stylus configura-

tions.

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

system is either phase correct or phase inverting (including the cartridge

andspeakers-theseare normallyphasecorrect).It isofnoconsequence

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

MV50 Owner’s Manual 7

system is in correct phase, transients will be noticeably cleaner and

moresharplydefined.Theeffect isespeciallyapparentonpluckedstring

sounds. A final warning-not all records are phase correct (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

stranglethesytemtothe point where itbecomesnobetterthanaverage.

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?

Ifyouhaveanyquestions about the installationorfunctionofyourMV50

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

MV50 Owner’s Manual 8

TUBE REPLACEMENTS

The MV50 uses eight vacuum tubes of three different types: two 5751

(V1 and V2), two 6FQ7 (V3 and V4) and four EL34s (V5 through V8).

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

based on extensive auditioning of available brands. The choice of brand

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

available which will improve the sonic performance of your MV50. 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

withoutdegradationinnormaluse. We highly recommendthat,whenthe

time comes to replace the vacuum tubes, you purchase replacement

tube sets from conrad-johnson design.

The MV50 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 MV50 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

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

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

MV50 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 each 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

amoreseriousproblem,sotheunitshouldbetakentoaqualifiedservice

center. IN NO EVENT SHOULD THE FUSE BE REPLACED WITH A

FUSEOFDIFFERENTTYPEORRATINGTHANTHATSUPPLIED BY

THE FACTORY.

PLATE FUSE: Your MV50 has been fitted with plate supply fuses which

are designed to protect the amplifier circuitry in the event of output tube

failure. The fuse holders are physically located near the speaker con-

nectors. The cap unscrews counter clockwise to remove the fuse ( a

BUSS BBS-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 EL34 tube (one of two 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 EL34s

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

happens, then (b) lightly tap the EL34s 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

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.

MV50 Owner’s Manual 10

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