Conrad-johnson design MF2550 User manual

MF2550 Owner’s Manual
1
Thank you for selecting the MF2550 amplifier to power your audio
system. The MF2550 draws on three decades of research at
conrad-johnson into the reproduction of recorded music. The result
is a power amplifier with a remarkable ability to recreate the dy-
namics, textures, tonalities, and ambience of live musical perform-
ances. With the MF2550, we believe that you will experience the
excitement of discovery in hearing more from your favorite record-
ings than ever before.
At conrad-johnson, we expect our products to be a source of sat-
isfaction and of pride to their owners for many years to come. Ac-
cordingly, circuit designs, parts and materials for all conrad-
johnson products are selected with a view to maintaining optimal
performance over the years. Our reputation for producing among
the industry's most reliable components is a natural consequence
of this engineering approach.
Although operation of the MF2550 amplifier is quite straightfor-
ward, please take a few minutes to read this manual for useful in-
formation on its installation and operation.
In closing, we’d like to welcome you to the family of conrad-
johnson owners. We want you to enjoy your conrad-johnson prod-
uct to the fullest. To this end, our staff stands ready to answer any
questions you may have about the function and application of your
MF2550, and to provide any needed service both during, and after
the warranty period. Our goal is to heighten your enjoyment of re-
corded music.

MF2550 Owner’s Manual
2
imited Warranty For Conrad-Johnson Components
Conrad-Johnson Design, Inc. will provide service under warranty to
the original owner on products sold new in the United States for the
lesser period of three years from the date of purchase by the origi-
nal purchaser, or five years from the date of shipment to the
authorized conrad-johnson dealer. During the warranty period,
conrad-johnson will repair defective units without charge for labor
or parts (with the exception of vacuum tubes and batteries).
Exclusions. The following are not covered under this warranty:
a) Units that have been damaged by misuse, abuse, or acci-
dent.
b) Units that have been modified, altered, or improperly re-
paired by anyone not specifically authorized by conrad-johnson
design, inc.
c) Units not purchased from an authorized conrad-johnson
dealer in the United States for use in the United States.
d) Normal wear
e) Incidental or consequential damages are not covered under
this warranty. Some states do not allow the exclusion of inci-
dental or consequential damages, so this exclusion may not
apply to you.
Obtaining Warranty Service: To obtain warranty service, the unit
must be shipped, along with evidence of purchase, in factory
packing to conrad-johnson design (or designated service center)
with freight and insurance prepaid by the owner. After repair, the
unit will be returned with freight and insurance prepaid by conrad-
johnson design to any destination in the United States.
All implied warranties, including merchantability and fitness for a
particular purpose are limited in duration to the duration of this ex-
press warranty. Some states do not allow limitations on the dura-
tion of implied warranties so the above limitations may not apply to
you.
This warranty gives you specific legal rights and you may also
have other rights that vary from state to state.
L

MF2550 Owner’s Manual
3
Conrad-Johnson products purchased outside the United States are
covered by warranty terms of the importing distributor in the coun-
try in which the product was originally purchased, which may differ
from the terms set out herein. Importing distributors are not obli-
gated to provide warranty service for products originally purchased
outside their country. Conrad-Johnson will provide warranty service
for products outside the United States, but in these cases, the
customer must pay all shipping, handling and customs costs both
to and from our Service Department.
Questions about this warranty should be addressed to:
Service Department
conrad-johnson design, inc.
2733 Merrilee Drive
Fairfax, VA 22031
The conrad-johnson service department can also be reached by e-
mail at [email protected], by phone at 703-698-8581,
or by fax at 703-560-5360.
Service
If your conrad-johnson audio component requires service, repack it
using the original box and packing material and ship to the Service
Department address above. Boxes and packing materials can be
purchased through our service department if you no longer have
yours. Include with the unit a note describing the problem you are
having in as much detail as possible. It is especially important for
our technician to know if the problem is intermittent. If you want an
estimate of cost for out of warranty service, be sure to request it in
this note. Be aware that requesting an estimate will delay service
to your unit, as we will have to contact you for approval before
commencing service.
Registering The Warranty
Please return the enclosed card to the factory within 30 days of
purchase to register the warranty

MF2550 Owner’s Manual
4
nstallation
As is the case with most power amplifiers, the MF2550 amplifier
dissipates a significant amount of heat. Provision must be made for
adequate ventilation. Mount the unit on a flat, hard surface, taking
care that the ventilation holes in the bottom are unobstructed.
Maintain at least four inches of clearance 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.
All MF2550 amplifiers sold in the United States are configured for
operation on a 60Hz ac power line producing between 108 and 126
volts. Export versions of the MF2550 will have the correct operat-
ing voltage and frequency clearly marked on the back panel of the
unit, near the ac power cord. In all cases, the actual line voltage
should be within + 5/- 10% of the nominal rated voltage.
Electromagnetic Interference (EMI)
Considerable care has been taken in the design of the MF2550 to
minimize its susceptibility to radio frequency interference and other
forms of EMI. Choice of materials, physical layout, grounding prac-
tice, and power supply design have all been specified with a view
to reducing the impact of electromagnetic fields on the perform-
ance of this unit. At the same time, however, our primary goal is
the accurate reproduction of recorded music in the normal home
environment, and we have elected not to compromise this objec-
tive by the application of heavy-handed RFI filters, or by using
grounding practices that reduce RFI at the expense of degraded
audio performance. We find that the approach we have taken has
worked extremely well, resulting in only rare instances of EMI
problems which could be treated locally as needed, rather than
compromising the performance of our product in the 99.9% of in-
stallations where EMI is not a problem.
Care in installation can often avoid EMI induced problems. The
following practices should generally be observed in any applica-
tion, and will be especially important where EMI may be a problem.
Interconnect cables should be kept as short as possible (3 meters
or less), and shielded cable should be used (cable which has two
center conductors, and a separate external shield connected at
only one end).
I

MF2550 Owner’s Manual
5
Physical location and cable “dress” can be an important factor in
minimizing hum pickup. The installation should situate the pream-
plifier well away from the power amplifier, and power (ac mains)
cords should be dressed to remain at least 4" (100mm) away from
input/output cables.

MF2550 Owner’s Manual
6
onnection
INPUT: Connect the preamplifier to your MF2550 amplifier at the
RCA type connectors located on the back of the amplifier.
OUTPUT: Five-way binding posts are provided for connection of
your loudspeakers, with correct spacing to accept a standard "dou-
ble banana" plug. They will also accept spade lugs, bare wire, or
pin connectors.
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 will move synchro-
nously - in and out together. Terminals on speakers are usually
coded - one designated "C", "ground", "-" or black, the other des-
ignated "+" or red. "In phase" connection of the speakers can nor-
mally be achieved by taking care to connect the wire from the "+"
amplifier terminal to the red or "+" coded terminal on each speaker,
and connecting the "-" terminal to the black or "-" coded terminal on
each speaker. In phase connection of the speakers can be readily
ascertained by ear. Listen to a recording of a solo vocalist (use a
mono recording if available). 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 switch-
ing the "+" and "-" leads at one speaker only.
C

MF2550 Owner’s Manual
7
etting The Most From Your MF2550 Amplifier
In a system of commensurate high quality components, the
conrad-johnson MF2550 amplifier offers an unparalleled level of
sophistication and refinement in music reproduction. To get the
best performance out of any audio system, there are a number of
important details that must be attended to.
Absolute Phase
Musical notes are heard through the ear’s response to waves of
alternating rise and fall of air pressure. Musical transients are al-
most exclusively positive: that is, the initial effect is a rise in pres-
sure. 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 terms of your stereo system, these
transients are created by your loudspeakers. If the speakers re-
spond 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
either preserves the phase of the incoming signal, and is said to be
phase correct, or inverts the phase and is said to be phase invert-
ing. It is unimportant whether an individual component is phase
correct or phase inverting, as long as the system as a whole is
phase correct. This will be the case if the number of phase inver-
sions is even (or zero).
The MF2550 is phase correct (non-inverting). If your system has
an odd number of inversions, (for example, if you have a phase in-
verting preamplifier) then you must add one phase inversion. This
is conveniently done by reversing the positive and negative con-
nections to your speakers (be sure to reverse both channels). If
you are not sure about the phase of every piece 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 (including some “audiophile” recordings), so listen to
several before concluding your investigation of absolute phase.
G

MF2550 Owner’s Manual
8
The Importance Of Wires
Interconnect and speaker wires are an important element in your
stereo system. Interconnects are available which will permit a ref-
erence quality system to blossom and fulfill its promise of musical
reality. Others will strangle the system to the point where it be-
comes little better than average. To complicate matters, our expe-
rience suggests that the choice of interconnects will be system de-
pendent - those that are top ranked on one system may be a poor
choice for a different system. Consult your conrad-johnson dealer
for recommendations for your specific system.
Performance Tip
Warm up the MF2550 before listening: The sonic performance of
the MF2550 improves noticeably as the unit warms up. The mid-
range becomes more lucid, the highs smoother, and the sound-
stage expands. The warm up period can be expected to last about
fifteen minutes.
Questions: If you have questions about the installation or function
of your MF2550 do not hesitate to call Customer Service at (703)
698-8581.

MF2550 Owner’s Manual
9
pecifications
Power: 250 watts per channel RMS both channels driven into 8
ohms from 20Hz to 20KHz at no more than 1.0% total harmonic
distortion or intermodulation distortion.
Sensitivity: 2 V rms to rated power
Frequency Response: 20Hz to 20 kHz +0/-.3 dB
Hum and Noise: 100 dB below rated power output
Phase: phase correct
Input Impedance: 100 kOhms
Mechanical
Dimensions: 16.25"D x 19”W x 6.125”H
Net Weight: 52 lb. net
Fuses
Fuses: The output stages are protected by 4 fuses one on the
positive and negative power supplies to each channel. These fuses
are located on the bottom of the main printed circuit board. Be sure
to disconnect the amplifier from the ac mains power (wall outlet)
before removing the bottom cover. Never replace a fuse with a
value or type different from that originally supplied by the factory.
These B+/B- “rail” fuses are 3AG type 6 Amp Fast Blow. In the
event of a fuse blowing repeatedly, contact your dealer or the
conrad-johnson service department.
S