Conrad-johnson design MV45A Manuale utente

OWNER'S MANUAL

MV45A AND MV75A

VACUUM TUBE POWER AMPLIFIERS

conrad-johnson design, inc.

(703) 698-8581

Thank you for your considered purchase of a conrad-johnson vacuum tube amplifier.

In it, you have acquired one of the finest pieces of music reproduction equipment

available today. You will find your amplifier capable of reproducing with great

accuracy the dynamics, tonalities and textures of a live musical performance. The

design and materials have been carefully selected to assure enduring excellence.

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

features and capabilities of your conrad-johnson amplifier.

LIMITED WARRANTY FOR THE conrad-johnson MV45A/MV75A

AMPLIFIERS

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

johnson MV45A or MV75A amplifier will perform to specifications as published

in the owner's manual and that it will be free of defects in materials and

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

2. 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 packing is available from the factory.

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

3. The above warranty may be transferred to subsequent owners provided 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 new 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 are hereby disclaimed. conrad-

johnson design, inc. shall not be liable for incidental or consequential damages.

Some states do not allow the exclusion or limitation of incidental or

consequential damages, or limitations on how long an implied warranty lasts, so

the above limitation or exclusion may not apply to you.

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.

2733 Merrilee Drive

Fairfax, Virginia 22031

ABOUT conrad-johnson design

We are a small company offering exclusively audiophile products designed for our

own use as well as our customers'. We believe that our commitment to the purchaser

of our products is nearly unique in the industry. The services we offer to conrad-

johnson owners include:

•Information - Registered owners of conrad-johnson equipment will be directly

informed of new equipment we have to offer. They will also be informed of any

significant changes in the design of their equipment resulting from our ongoing

development program.

•Factory updating - Should significant design changes be made, conrad-johnson

design will, whenever practical, offer to update existing equipment. This service

will be offered at a reasonable charge to cover parts, labor, and handling.

•Factory service - Any conrad-johnson product may be returned to the factory for

service. All equipment serviced at the factory will perform to its published

specifications when returned. Factory service will be offered at reasonable rates.

•Transferable warranty - conrad-johnson design guarantees its products, not the

owner. Should you decide to sell the product, the warranty may be transferred to

the new owner. (See Registering the Warranty.)

REGISTERING THE WARRANTY

Please return the enclosed card to the factory within 30 days of purchase to register

the warranty. The warranty may be transferred to a new owner if it has been properly

registered initially and if the registered owner sends a signed notice providing the

name and address of the new owner and the model and serial number of the unit.

Proper registration of the warranty is important! Not only will it preserve

transferability of your warranty, it will also 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.

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. Accordingly, the audio circuits of the

MV45A/MV75A amplifiers are remarkably straight-forward. A single triode input

amplifier is direct coupled (MV75A) or RC coupled (MV45A) to a cathode coupled

differential phase inverter made up of high current triodes to provide balanced, low

impedance drive to the push-pull output stage. This 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 reactive speaker

loads. Substantial main power supplies enable the conrad-johnson amplifiers to meet

these extraordinary current demands. Separate voltage regulators for the voltage

amplifiers and phase inverters provide nearly absolute isolation of these sensitive

stages from the output stage.

INSTALLATION

Vacuum tube power amplifiers dissipate considerable heat. It is essential, therefore,

that proper attention be paid to ventilation. The unit should be mounted horizontally

on a flat hard surface. 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.

Optional panels are available to facilitate rack mount installation. Again, it is

important that adequate clearance be provided above the amplifier so that ventilation

is not impeded.

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

turntable and route power cords away from input cables.

THE MV45A/MV75A IS TO BE OPERATED ONLY ON AC LINE VOLTAGE OF

108 TO 125 VOLTS (Also available wired for 100 volt or 230 volt, 50/60 Hz).

CONNECTION

Input: Connect the left and right outputs from the preamplifier to the amplifier inputs

for Channel A and Channel B.

Output: The speaker wires will be connected to the amplifier's output terminals with

one wire connected to the screw terminal marked C and the other to the 4, 8, or 16

ohm screw terminal. Proper connection of the speakers is critical for achieving

optimum performance. There are three criteria for correct connections:

1. Correct Relative Phase: The two channels must be wired in phase. This means that

when the same signal is applied to both channels, the right and left channel 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 taking care to connect the wire from the amplifier terminal marked C on

each channel to the same coded terminal on each speaker.

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

preamplifier mode switch in 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 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.

2. Correct Absolute Phase: Musical transients are positive going - that is they first

create a pressure front in the surrounding air. It is important that your stereo system

reproduces transients in the same way since the ear can distinguish between positive

and negative transients. This means that on a transient the speaker diaphragms should

first move toward the listener - creating a pressure front.

Each component in your system is either phase correct (non-inverting) or phase

inverting . If you know the phase of each component in your system (your MV45A or

MV75A is phase correct) then correct absolute phase is obtained by the following

simple rule:

THE TOTAL NUMBER OF PHASE INVERSIONS IN THE SIGNAL PATH

SHOULD BE EVEN.

If the number of phase inverting components is either none, or even, then simply wire

the speakers in a phase correct manner (amplifier C to speaker "-", amplifier 4, 8, or

16 to speaker "+'.

If the number of phase inverting components is odd, then one more inversion should

be added. This may either be accomplished at the speaker by wiring amplifier C to

speaker "+" and 4, 8, or 16 to speaker "-" or by reversing the positive and ground

leads of the cartridge. The latter method is preferable if one inversion occurs in either

your pre-preamplifier (the HV-1 is inverting) or in your preamplifier phono stage

(but not both). Making the correction at the cartridge will then permit phase correct

tape recording and playback.

If you do not know the phase of each component in your system, try listening with

your speakers hooked up both ways. When correctly phased, plucked strings and

other sharp transients will sound noticeably better defined.

3. Impedance Matching - Matching the rated nominal impedance of your speakers

with the amplifier output' taps will not necessarily guarantee optimum performance.

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

We suggest listening to each of the three taps to select the best match for your

speakers.

Monaural Operation - (MV75A only)

Set the switch on the amplifier to the "mono" position. Connect the output of your

preamplifier to either input (only one input should be used; the other must be left

open.) Connect the speaker to either output as follows: a 4 ohm speaker should be

connected to the 8 ohm terminal, an 8 ohm speaker should be connected to the 16

ohm terminal, or a 16 ohm speaker should be connected to the 16 ohm terminal (in

this case power will be considerably more than 75 watts but will not achieve 150

watts). A single jumper of heavy gauge wire should be connected from the selected

impedance terminal (4, 8, or 16 ohm) to the same impedance terminal on the other

channel's output.

Warning: When the outputs are connected for monaural operation as just described,

the stereo-mono switch must be in the mono position to avoid possible damage to the

amplifier.

TUBE REPLACEMENTS

The MV45A/MV75A amplifiers each use seven vacuum tubes of three different

types. 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 conrad-johnson

amplifier. 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 sonic

degradation. We anticipate one to two years of operation without degradation in

normal use. We highly recommend that, when the time comes to replace the vacuum

tubes, you purchase replacement tube sets from conrad-johnson design.

These amplifiers have 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. Your amplifier has built in bias

indicators so that no instruments are required to make this adjustment.

Tube locations:

Tube complement:

MV75A MV45A

V1 5751 5751

V2,V3 6FQ7/6CG7 12AT7

V4 - V7 6550 6CA7/EL34

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