Conrad-Johnson ART 27A User manual

Conrad-Johnson ART 27A Amplifier Owner’s Manual 1
Thank you for selecting the ART 27A Amplifier to power your audio
system. The ART 27A Amplifier draws on four 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
dynamics, textures, tonalities, and ambience of live musical
performances. With the ART 27A Amplifier, we believe that you
will experience the excitement of discovery in hearing more from
your favorite recordings than ever before.
At conrad-johnson, we expect our products to be a source of
satisfaction and of pride to their owners for many years to come.
Accordingly, 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 ART 27A Amplifier is quite
straightforward, please take a few minutes to read this manual for
useful information 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
product to the fullest. To this end, our staff stands ready to answer
any questions you may have about the function and application of
your ART 27A Amplifier, and to provide any needed service both
during, and after the warranty period. Our goal is to heighten your
enjoyment of recorded music.

Conrad-Johnson ART 27A Amplifier Owner’s Manual 2
Limited 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
original 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, fuses, and batteries).
Exclusions. The following are not covered under this warranty:
a) Units which have been damaged by misuse, abuse, or
accident.
b) Units which have been modified, altered, or improperly
repaired 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
incidental 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
express warranty. Some states do not allow limitations on the
duration 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 which vary from state to state.

Conrad-Johnson ART 27A Amplifier Owner’s Manual 3
Conrad-Johnson products purchased outside the United States are
covered by warranty terms of the importing distributor in the
country in which the product was originally purchased, which may
differ from the terms set out herein. Importing distributors are not
obligated 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.
2800K Dorr Avenue
Fairfax, VA 22031
The conrad-johnson service department can also be reached by e-
mail at [e-mail] or by phone at 703-698-8581.
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.

Conrad-Johnson ART 27A Amplifier Owner’s Manual 4
Installation
As is the case with any vacuum-tube power amplifier, the ART 27A
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 ART 27A 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 ART 27A Amplifier will have the
correct operating 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 ART 27A
Amplifier to minimize its susceptibility to radio frequency
interference and other forms of EMI. Choice of materials, physical
layout, grounding practice, and power supply design have all been
specified with a view to reducing the impact of electromagnetic
fields on the performance 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 objective 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 installations where EMI is not a problem.
Care in installation can often avoid EMI induced problems. The
following practices should generally be observed in any
application, 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

Conrad-Johnson ART 27A Amplifier Owner’s Manual 5
center conductors, and a separate external shield connected at
only one end).
Physical location and cable “dress” can be an important factor in
minimizing hum pickup. The installation should situate the
preamplifier 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.
Connection
INPUT: Connect the preamplifier to your ART 27A 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
"double banana" plug. They will also accept spade lugs, bare wire,
or pin connectors.
In a stereo system, 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 synchronously - in and out together.
Terminals on speakers are usually coded - one designated "C",
"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 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 switching the "+" and "-" leads
at one speaker only.

Conrad-Johnson ART 27A Amplifier Owner’s Manual 6
Vacuum Tube Replacement
The ART 27A Amplifier uses seven vacuum tubes of two different
types: three type 6922 (V1, V2, V3,) and four type KT88 (V4, V5,
V6, V7.)The ART 27A amplifier was designed exclusively for the
use of KT88’s. We know of no vacuum tubes available which will
improve the sonic performance of your ART 27A Amplifier.
Note: To maintain performance and reliability, KT88 output
tubes for the ART 27A must be replaced with matched pairs
selected for use with this amplifier.We highly recommend that
you purchase replacement tubes from conrad-johnson design.
We anticipate tube life to accommodate two to three years of
operation without degradation in normal use - if the amplifier is
switched off when not in use. If it is left on at all times, tube life can
be exhausted in a matter of a few months.
The ART 27A Amplifier has been designed to make tube
replacement as simple as possible. No a-c balance adjustment is
necessary. It is necessary to re-bias the amplifier when the output
tubes are replaced. The ART 27A Amplifier has built in bias
indicators so that no instruments are required to make this
adjustment.

Conrad-Johnson ART 27A Amplifier Owner’s Manual 7
Adjusting Output Tube Bias
Biasing the amplifier is a simple procedure that can easily be done
by the owner. Only a plastic bias tool is required (one has been
included with your amplifier for this purpose). After installing 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 turned fully down. Turn the amplifier on. After three
minutes, turn each of the four bias adjustment controls (located
near the output tube socket) clockwise until the associated
indicator LED turns on “AMBER.” Do not turn the bias adjustment
control any further in the clockwise direction once the LED turns on
“AMBER.” If the LED turns on “RED”, turn the bias adjustment
control counterclockwise until the LED turns on “AMBER”.
After the amplifier has warmed up thirty minutes, the procedure just
described should be repeated. NOTE: It is normal for these LEDs
to flash or flicker “RED” when the amplifier is in use. This biasing
procedure should be performed whenever the amplifier's output
tubes are replaced and after each six months of average use.
PLATE FUSE: Your ART 27A Amplifier has been fitted with plate
supply fuses that are installed to protect the amplifier circuitry in
the event of output tube failure. The fuse holders are physically
located on the back panel, near the speaker connectors. The cap
unscrews counter-clockwise to remove the fuse (BBS ¾ ).
What happens when the fuse blows? A blown plate fuse usually
indicates a marginal output tube and an attempt should be made to
identify and replace it, by replacing the fuse and turning on the
amp while watching the output tubes carefully; look for a bright
white or blue flash inside the tube. If the tubes have more than
1,500 hours on them, a complete replacement 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
Replacement fuses are available from conrad-johnson dealers and
directly from conrad-johnson design.

Conrad-Johnson ART 27A Amplifier Owner’s Manual 8
Getting The Most From Your ART 27A Amplifier
In a system of commensurate high quality components, the
Conrad-Johnson ART 27A 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
almost 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 terms of 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 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 inverting. 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 inversions is even (or zero).
The ART 27A Amplifier is phase correct (non-inverting). If your
system has an odd number of inversions, (for example, if you have
a phase inverting preamplifier) then you must add one phase
inversion. This is conveniently done by reversing the positive and
negative connections 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.

Conrad-Johnson ART 27A Amplifier Owner’s Manual 9
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 strangle the system to the point where it
becomes little better than average. To complicate matters, our
experience suggests that the choice of interconnects will be
system dependent - 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 ART 27A Amplifier before listening: The sonic
performance of the ART 27A Amplifier improves noticeably as the
unit warms up. The midrange becomes more lucid, the highs
smoother, and the soundstage 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 ART 27A Amplifier, do not hesitate to call Customer
Service at [phone].

Conrad-Johnson ART 27A Amplifier Owner’s Manual 10
Specifications
Power: 36 Watts rms both channels driven into 4 ohms from 30Hz
to 15KHz at no more than 1.5% total harmonic distortion.
Sensitivity: 0.6 V rms to rated power
Small Signal Distortion: less than .25% at mid-band
Frequency Response: 20Hz to 20 kHz +0/-.25 dB
Hum and Noise: < 200 uv
Phase: phase correct
Input Impedance: 100 kOhms
Tube Complement: 3 x 6922, 4 x KT88
Important Note: output tubes must be replaced with matched pairs
selected for use in this amplifier.
Mechanical
Dimensions: 17.5"D x 19"W x 8.875"H
Net Weight: 63 lb net
Fuses
The ART 27A Amplifier power transformer is protected by a fuse
on the ac power line (F5, located in a compartment in the ac line-
cord receptacle mounted on the back of the amplifier), and by four
separate internal fuses on the secondary circuits of the transformer
(F1 –F4) located on the bottom of the pc board. A failure of any of
these fuses is a symptom of a more serious problem, and a
competent service technician should be consulted. In no event
should fuses be replaced with a value or type different than that
originally supplied. The correct fuse values and types are:
F5: 5x20mm 12 amp T-type if configured for 100 or 120V:
5x20mm 6.3 amp T-type if configured for 220 or 240V.
F4: 5x20mm 3.15 amp T-type
F1 5x20mm 200ma T-type
F2, F3 5x20mm 400 MA type