Conrad-johnson design Classic Sixty User manual

Conrad-Johnson Owner’s Manual:
Classic Sixty Vacuum-Tube Amplifier
conrad-johnson It just sounds right.

Classic Sixty Owner’s Manual
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Thank you for selecting the Classic Sixty amplifier to power your
audio system. The Classic Sixty draws on three decades of re-
search 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 Classic Sixty, we believe that you will ex-
perience the excitement of discovery in hearing more from your fa-
vorite recordings than ever before.
At conrad-johnson, we expect our products to be a source of satis-
faction 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 Classic Sixty amplifier is quite straight-
forward, 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 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
Classic Sixty, and to provide any needed service both during, and
after the warranty period. Our goal is to heighten your enjoyment of
recorded music.

Classic Sixty Owner’s Manual
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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 au-
thorized conrad-johnson dealer. During the warranty period, con-
rad-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 pack-
ing 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.
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Classic Sixty Owner’s Manual
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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 cus-
tomer 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

Classic Sixty Owner’s Manual
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nstallation
As is the case with any vacuum-tube power amplifier, the Classic
Sixty 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 installa-
tions, cooling fans are essential.
All Classic Sixty 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 Classic Sixty 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 volt-
age should be within + 5/-10% of the nominal rated voltage.
Electromagnetic Interference (EMI)
Considerable care has been taken in the design of the Classic
Sixty 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 speci-
fied with a view to reducing the impact of electromagnetic fields on
the performance of this unit. At the same time, however, our pri-
mary goal is the accurate reproduction of recorded music in the
normal home environment, and we have elected not to compro-
mise 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 fol-
lowing 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
center conductors, and a separate external shield connected at
only one end).
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Classic Sixty Owner’s Manual
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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.

Classic Sixty Owner’s Manual
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onnection
INPUT: Connect the preamplifier to your Classic Sixty 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.
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Classic Sixty Owner’s Manual
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acuum Tube Replacement
The Classic Sixty uses seven vacuum tubes of three different
types: one type 6189 (V1), two type 6922 (V2 and V3), and four
type EL34 (V4 through V7). In the Classic Sixty SE, the output
tubes (V4 through V7) are changed to KT120s. Note: the KT120 is
NOT a plug in replacement for the EL34 –the bias circuit must be
revised to make this substitution. The brands of tubes we supply
have been chosen by first selecting those brands which are known
to be most reliable, then by extensive auditioning of these accept-
able brands with the final choices being made solely on the basis
of sonic performance. We know of no vacuum tubes available
which will improve the sonic performance of your Classic Sixty. We
highly recommend that you purchase replacement tube sets from
conrad-johnson design.
We anticipate tube life to accommodate two to three years of op-
eration 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 Classic Sixty has been designed to make tube replacement as
simple as possible. Because the output tubes are individually bi-
ased, replacement tubes need not be matched pairs. No a-c bal-
ance adjustment is necessary. It is necessary to re-bias the ampli-
fier when the output tubes are replaced. The Classic Sixty has built
in bias indicators so that no instruments are required to make this
adjustment.
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Classic Sixty Owner’s Manual
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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 (one has been
included with your amplifier for this purpose). After replacing the
tubes, the amplifier should be connected to a load (your loud-
speakers will work fine) and there should be no signal applied to
the amp. It should be connected to your preamplifier with the vol-
ume control turned fully down. Turn the amplifier on. After about
one minute, turn each of the four screwdriver adjustable controls
(located near the output tube sockets) 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 flash or flicker when the amplifier is in use. This biasing proce-
dure should be performed whenever the amplifier's output tubes
are replaced and after each six months of average use.
PLATE FUSE: Your Classic Sixty 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 in-
side the chassis at the ends of the vertically mounted power supply
pc board. The fuses are 5x20mm 800mA T-type ceramic fuses.
LEDs labeled FUSE OUT are located on the top of the chassis,
one on either side of the center transformer. If a plate fuse blows,
the associated LED will light. The sonic effects of a blown fuse are
very low, very distorted sounds from the speaker being driven by
that channel.
WARNING: the Classic Sixty operates at high voltages. The chas-
sis should only be opened by qualified, experienced persons.
NEVER remove the bottom cover of the chassis without first un-
plugging the unit from the ac mains and allowing ample time for
power supplies to drop to safe voltages.
Replacement fuses are available from conrad-johnson dealers.

Classic Sixty Owner’s Manual
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etting The Most From Your Classic Sixty Amplifier
In a system of commensurate high quality components, the
conrad-johnson Classic Sixty 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 al-
ternating 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 anegative transient (an initial
fall in air pressure). In terms of your stereo system, these tran-
sients 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 re-
spond 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 Classic Sixty 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 inver-
sion. This is conveniently done by reversing the positive and nega-
tive connections to your speakers (be sure to reverse both chan-
nels). If you are not sure about the phase of every piece in your
system, you can establish correct absolute phase by careful listen-
ing. When the system is in correct phase, transients will be no-
ticeably cleaner and more sharply defined. The effect is especially
apparent on plucked string sounds. A final warning -not all re-
cordings are phase correct (including some “audiophile” re-
cordings), so listen to several before concluding your investigation
of absolute phase.
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Classic Sixty Owner’s Manual
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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 ex-
perience 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 Classic Sixty before listening: The sonic performance
of the Classic Sixty 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 Classic Sixty do not hesitate to call Customer Service at
[phone].

Classic Sixty Owner’s Manual
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pecifications
Power: 60 watts per channel RMS both channels driven into 4
ohms from 30Hz to 15KHz at no more than 1.5% total harmonic
distortion or intermodulation distortion (can be re-connected in-
ternally for 8 or 16 ohm loads).
Sensitivity: .7 V rms to rated power
Frequency Response: 20Hz to 20 kHz +0/-.3 dB
Hum and Noise: 96 dB below rated power output
Phase: phase correct
Input Impedance: 100 kOhms
Mechanical
Dimensions: 13.375"D x 17.375"W x 6.625”H
Net Weight: 41 lb net
Fuses
The Classic Sixty power transformer is protected by a fuse on the
ac power line (F1, located in a compartment in the ac line-cord re-
ceptacle mounted on the back of the amplifier), and by four sepa-
rate internal fuses on the secondary circuits of the transformer (F2
– F5) 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 com-
petent 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:
F1: 5x20mm 5 amp T-type if configured for 100 or 120V:
5x20mm 3.15 amp T-type if configured for 220 or 240V.
F2, F3, and F4: 5x20mm 200 mA amp T-type
F5: 5x20mm 3.15 amp T-type
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