Conrad-Johnson ART 27A Bedienungsanleitung

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 service@conradjohnson.com 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 (703) 698-8581.

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