Conrad-johnson design MV45A User manual

OWNER'S MANUAL
MV45A AND MV75A
VACUUM TUBE POWER AMPLIFIERS
conrad-johnson design, inc.
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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

ADJUSTING OUTPUT TUBE BIAS
Biasing the amplifier is a simple procedure that can readily be done by the owner.
Only a screwdriver is required. 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 fully down. Turn amplifier on. After about one minute, turn each of the four
screwdriver adjustable controls (marked with a "p" in the diagram) 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 for 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 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.

SPECIFICATIONS
MV75A: Power
Stereo: 75 watts per channel, minimum RMS at 4, 8, or 16 ohms from 30Hz to
15kHz, with no more than 1% total harmonic distortion or intermodulation
distortion.
Mono: 150 watts minimum RMS at 4 or 8 ohms from 30Hz to 1kHz, with no
more than 1% total harmonic distortion or intermodulation distortion.
Sensitivity: 2.35 volt to full power
Small Signal Distortion: less than .05% at mid-band
Phase: Phase correct (non-inverting)
Frequency Response: 20Hz to 20kHz to -.5db
Hum and Noise: 100 db below full power output
Input Impedance: 100k ohms
Dimensions: 15 x 10½ x 9"
Weight: 43 lbs.
MV45A
Power: 45 watts per channel, minimum RMS at 4, 8, or 16 ohm from 30Hz to 15kHz,
with no more than 1% total harmonic distortion or intermodulation distortion.
Sensitivity: .80 volt to full power
Small Signal Distortion: less than .1% at mid-band
Phase: Phase correct (non-inverting)
Frequency Response: 20Hz to 20kHz to -.5db
Hum and Noise: 90 db below full power output
Input Impedance: 100k ohms
Dimensions: 14¼ x 9½ x 6½”
Weight: 33 lbs.

Fuses
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 SUPPLIED BY THE FACTORY
MV75A only: The power supply to the output stages of the MV75A are fused to
prevent damage to the amplifier in the event of failure of an output tube. The fuse
holders are located adjacent to the output strips. When one of these fuses opens the
corresponding channel will be dead. An LED adjacent to the fuseholder will light to
indicate a blown fuse. Should the fuse blow, the output tubes in that channel are
suspect and should be replaced.
Fuses: MV75A MV45A
ac line: 7 amp slow blow 5 amp slow blow
output stage: KTK1 (1 amp fast blow) none

SERVICE
If service becomes necessary, the amplifier may be either returned to your dealer or
sent to conrad-johnson for service. In either case, a written description of the
difficulties encountered must be provided. If the problem is intermittent, please
indicate.
To ship the amplifier, MV75A: remove the entire rack panel and protective cover
assembly by removing the switch nut and three machine screws from each side of the
chassis. Next remove,. and separately box, the tubes. The amplifier chassis and the
set of tubes must be packed in the original factory carton and packing materials. The
amplifier should be shipped without its rackplate and cover.
To ship the amplifier, MV45A: remove the protective cover by removing two screws
on each side of the chassis. Next remove and separately box the tubes in their
individual boxes. Pack the boxed tubes into the tube carton. Reinstall the cover over
the tube carton and box the amp in its original factory carton and packing materials.
Shipping cartons and packing materials are available from conrad-johnson at a
nominal charge. Ship by United Parcel Service (UPS) to:
conrad-johnson design, inc.
2733 Merrilee Drive
Fairfax, Virginia 22031
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