Conrad-johnson design MV50 User manual

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

Replacement fuses and tubes are available from conrad-johnson deal-
ers.
SPECIFICATIONS:
Power: 45 watts per channel RMS both channels driven into 8 ohms
from 30Hz to 15KHz at no more than 1% total harmonic distortion or
intermodulation distortion.
Sensitivity: 750 mv to full power.
Small Siganal Distortion: Less than .1% at midband
Phase: Phase correct (non-inverting)
Frequency response: 20Hz to 20KHz +0, -.5dB
Hum and noise: 90dB below full power output.
Input impedance: 100K ohms.
Dimensions: 11.5D x 19W x 9H inches.
Weight: 39 lbs.
MV50 Owner’s Manual 11

SERVICE
In the event your conrad-johnson MV50 stereo amplifier requires serv-
ice, repack it with the original packing material and ship via truck freight
Service to: conrad-johnson design, inc.
Service Department
2800R Dorr Avenue
Fairfax, VA 22031
Be sure to enclose a note explaining the problem you are having in as
much detail as possible. If the problem is intermittent, please indicate. If
you do not have the original packing material, replacements are avail-
ablefromconrad-johnsondesignatanominalcharge.Iftheunitisunder
warranty, be sure to enclose a copy of your receipt as proof of purchase.
MV50 Owner’s Manual 12