Conrad-Johnson ART 108A User manual

Conrad-Johnson Owner’s Manual:
ART 108A Amplifier
conrad-johnson It just sounds right.

Conrad-Johnson ART 108A Amplifier Owner’s Manual 1
Thank you for selecting the ART 108A Amplifier to power your
audio system. The ART 108AAmplifier 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 108A 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 asource 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 aview to maintaining optimal
performance over the years. Our reputation for producing among
the industry's most reliable components is anatural consequence
of this engineering approach.
Although operation of the ART 108A Amplifier is quite
straightforward, please take afew 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. Wewant 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 108A 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 108A 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 108A 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 108A Amplifier Owner’s Manual 4
Installation
As is the case with any vacuum-tube power amplifier, the ART
108AAmplifier dissipates a significant amount of heat. Mount the
unit on an amp stand. The ART108A should be unobstructed on all
four sides and top to provide adequate ventilation.
All ART 108A 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 108A 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. The ART108A should be powered "OFF"
when not in use.
Electromagnetic Interference (EMI)
Considerable care has been taken in the design of the ART
108AAmplifier 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.

Conrad-Johnson ART 108A Amplifier Owner’s Manual 5
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 108A Amplifier at
the RCA type connector located on the back of the amplifier.
OUTPUT: Five-way binding posts are provided for connection of
your loudspeakers, with correct spacing to accept astandard
"double banana" plug. They will also accept spade lugs, bare wire,
or pin connectors.
In astereo system, the two channels should be connected in
correct "relative phase". This means that when the samesignal 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 arecording of asolo vocalist (use amono 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 108A Amplifier Owner’s Manual 6
Vacuum Tube Replacement
The ART 108A Amplifier uses eleven vacuum tubes of two
different types: three type 6922 (V1, V2, V3,) and eight type
KT88 (V4-V11).The ART 108A 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
108A Amplifier.
Note: To maintain performance and reliability, KT88
output tubes for the ART 108A must be replaced with
matched quads selected for use with this amplifier.We
highly recommend that you purchase replacement tubes from
conrad-johnson design.
Weanticipate tube life to accommodate two to three years
of operation without degradation in normal use - the amplifier
should be switched off when not in use.
The ART 108A 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 108A Amplifier
has built in bias indicators so that no instruments are
required to make this adjustment.

Conrad-Johnson ART 108A 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 aplastic bias tool is required (one has been
included with your amplifier for this purpose). After installing the
tubes, the amplifier should be connected to aload (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 eight 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 108A Amplifier has been fitted with a
plate supply fuse that is installed to protect the amplifier
circuitry in the event of output tube failure. The fuse holder is
physically located on the back panel, near the speaker binding
post. The cap unscrews counter-clockwise to remove the fuse
(KTK 2).
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 108A Amplifier Owner’s Manual 8
Getting The Most From Your ART 108A Amplifier
In a system of commensurate high quality components,
the Conrad-Johnson ART 108A 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 arise in
pressure. The ear is capable of distinguishing these positive
transients from the musically unnatural alternative of anegative
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 afall 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 awhole is phase correct. This will be the case if the
number of phase inversions is even (or zero).
The ART 108A 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 108A 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 108A Amplifier before listening: The
sonic performance of the ART 108A 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 108A Amplifier, do not hesitate to call
Customer Service at [phone].

Conrad-Johnson ART 108A Amplifier Owner’s Manual 10
Specifications
Power: 160 Watts rms both channels driven into 4 ohms from
30 to 15KHz at no more than 1.5% total harmonic distortion.
Sensitivity: 1.0V 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, 8x KT88
Important Note: output tubes must be replaced with matched
quads
selected for use in this amplifier.
Mechanical
Dimensions: 21.0"D x 19"W x 8.625"H
Net Weight: 89 lb net
Fuses
The ART 108A 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 800 MA type
Power 420 Watts , 120VAC/60HZ , 3.5 Amps
Power 420 Watts , 240VAC/50HZ , 1.75 Amps