Krell Industries S-275 User manual

THE LEADER IN AUDIO ENGINEERIN

S–275

Stereo Power Amplifier

Instructions for Use

Owner’s Reference

Krell S-275 1

Introduction

Thank you for your purchase of the Krell S-275 Stereo Power

Amplifier. This configurable power amplifier has a discrete signal

path from input to output and employs a wide bandwidth design

with low negative feedback for sonic accuracy throughout the fre-

quency spectrum. All circuits up to the driver stage are balanced

and pure Class A.

Krell’s new surface mount technology (SMT) means that the S-275

is a power amplifier with big power—275 Watts per channel—that

does not require big space. SMT allows individual circuit elements

to be placed very closely together. This shortens signal paths and

allows circuit elements to operate at the same temperature, result-

ing in more accurate signal transfer and enhanced reliablilty.

The S-275 is a slim line design allowing two amplifiers to fit into a

space normally occupied by one. For systems requiring higher

power, the S-275 can be configured for monaural operation by set-

ting a switch on the rear panel. Power output increases to 550

Watts into 8 Ohms. A 6 dB gain switch provides a channel balanc-

ing tool for systems using a combination of balanced and RCA

style connections.This owner’s reference contains important infor-

mation on the placement, installation, and operation of the S-275.

Please read this information carefully. A thorough understanding of

these details will help ensure satisfactory operation and long life

for your S-275 and related system components.

Definition of Terms

Following are the definitions of key terms used in your owner’s ref-

erence manual.

Monaural Operation

Monaural operation combines the output of the left and right chan-

nels to create a more powerful single channel. In the case of the

S-275, the output increases to 550 Watts.

Balanced

A symmetrical input or output circuit that has equal impedance

from both input terminals to a common ground reference point.

The industry standard for professional and sound recording instal-

lations, balanced connections have 6 dB more gain than single-

ended connections and allow the use of long interconnect cables.

Balanced connections are completely immune to induced noise

from the system or the environment.

Single-ended

A two-wire input or output circuit. Use care when using single-

ended connections as the ground connection is made last and

broken first. Turn the system off prior to making or breaking single-

ended connections. Single-ended connections are not recom-

mended for connections requiring long cable runs.

CONFIGURATIONS

INPUT AND OUTPUT

CONNECTIONS

2Krell S-275

Definition of Terms, continued

Off

The component is off when the rear panel button is in the down

position.

Stand-by Mode

A low power consumption status that keeps the audio circuits at

idle. Move the rear panel breaker switch to the on position and the

power status indicator illuminates in red. The component is now

ready to be switched to the operational mode. Krell recommends

leaving the component in the stand-by mode when it is not playing

music.

Operational Mode

When the component is in stand-by mode, press the power button

on the front panel and the power status indicator will change to

blue. The component is in the operational mode and is ready to

play music.

12VDC Trigger

The S-275 may be turned on remotely via a 12 volt trigger.

Connect the 12V trigger output from a compatible device to the

12VDC trigger input. The S-275 will go from stand-by to opera-

tional mode when a 12 volts signal is applied. The S-275 will

return to Stand-by when the 12 volt signal is removed. The S-275

can turn on other devices via 12 volt connection by connecting

them to the 12VDC trigger output. When the S-275 enters opera-

tional mode, it will output 12VDC and remove it when returned to

stand-by.

Input Selection

Put the input select switch in the posistion that matches the con-

nection being used. Krell recommends the use of balanced/XLR

whenever possible. In Mono mode,use the left channel connection.

TECHNOLOGY

Krell S-275 3

OPERATION

4Krell S-275

Unpacking

Follow these steps to safely unpack the S-275:

1. Open the shipping box and remove the top layer of foam. The

S-275 and the S-275 accessory kit containing the following

items are visible:

1 AC power cord

1 packet containing the Quick Setup Guide

and the warranty registration card

2. Grasp the underside of the amplifier and lift it straight out of

the packing box.

3. Place the amplifier in a safe location and remove the protective

plastic wrapping.

f any of these items are not included please contact your authorized

Krell dealer.

Save all packing materials. If you must ship your S-275 in the future,

repack the unit in its original packaging to prevent shipping damage.

Notes

Krell S-275 5

Placement

Before you install the S-275 into your system, review the following

guidelines to choose the location for the S-275. This will facilitate a

clean, trouble-free installation. The S-275 does not require any

type of special rack or cabinet for installation. For the dimensions

of the S-275, see Specifications.

Place the S-275 on a firm, level surface, away from excessive

heat, humidity, or moisture. The S-275 requires at least 1 inch

(2.54 cm) of clearance on each side and at least two inches (5 cm)

of clearance above the component to provide adequate ventilation.

Installations inside cabinetry may need extra ventilation.

The S-275 is not hum-sensitive. Other components may be placed

on or around the S-275 (make sure ventilation grids remain unob-

structed).

Place the amplifier as close to the loudspeakers as possible and

keep loudspeaker cable lengths to a minimum. Loudspeaker cable

adds impedance to the load the amplifier must drive, regardless of

the cable’s gauge. All Krell amplifiers drive the lowest impedances

with ease, but long loudspeaker cables reduce the maximum

power that can be delivered to the loudspeakers.

The S-275 has superb regulation and does not require a dedicated

AC circuit. Avoid connections through extension cords or multiple

AC adapters. High quality 15 amp grounded AC strips are accept-

able. High quality AC line conditioners or filters may be used if

they are grounded and meet or exceed the unit’s maximum power

consumption of 1900 Watts.

The S-275 should be operated with the power cord

supplied and connected directly to the AC power outlet. Please

contact your authorized Krell dealer, distributor, or Krell before

using any devices designed to alter or stabilize the AC power for

the S-275.

AC Power

Guidelines

Power Cord

Figure 1 The S-275 Front Panel

S-275

KRELL

Figure 2 The S-275 rear panel

S-275

KRELL

6Krell S-275

Front Panel

1 Power Button

2 Power Indicator

Rear Panel

3 Mono/Stereo Switch

4 Gain Switch

5 Input Switch

6 Left and Right Balanced

Analog Inputs

7 Left and Right Single-

ended Analog Inputs

8 12 VDC Trigger In/Out

Power

9 Main Power Switch

10 Speaker Connectors

11 Right/Mono Speaker Fuse

12 Left/Mono Speaker Fuse

13 IEC Connector

Front and Rear Panel Description

See Figures 1 and 2 on page 5

Krell S-275 7

1 Power Button

Use this button to switch the S-275 between the stand-by and the

operational modes.

2 Stand-by Indicator

The red stand-by indicator illuminates when the S-275 is plugged

into a standard AC wall receptacle and the rear panel power but-

ton is pressed, indicating that the amplifier is in the stand-by mode

and ready to be switched to the operational mode. The indicator

turns blue when in operational mode

The S-275 back panel provides connections for all inputs and out-

puts, power on/off, and additional remote connections.

3 Mono/Stereo Switch

Set this switch to stereo when using the S-275 as a stereo power

amplifier. Set this switch to mono when using the S-275 as a sin-

gle monaural power amplifier.

4 Gain Switch

In stereo, the amplifier provides 19.8 dB of gain at 0d dB setting

and 25.8 dB of gain at +6 dB setting. In mono, the amplifier pro-

vides 25.8 dB and 31.8 dB of gain at the 0 dB and +6 dB settings,

respectively.

5 Input Switch

Set this switch for the style of connection being used,

balanced/XLR or single-ended/RCA.

6 Left and Right Balanced Analog Inputs

The S-275 is equipped with one pair of balanced inputs via XLR

connectors. Use the left input when in mono mode

7 Left and Right Single-Ended Analog Inputs

The S-275 is equipped with one pair of single-ended inputs via

RCA connectors. Use the left input when in mono mode.

Consult the owner’s reference of the components used in a custom

installation to take full advantage of the remote capability of the S-275.

14 Left and Right Loudspeaker Outputs

The S-275 is equipped with standard binding posts for each ampli-

fier channel. These connectors accept bare wire, pins, banana

Front and Rear Panel Description, continued

8Krell S-275

8. 12 Volt Trigger Input/Output.

Out.The output sends 12 VDC (12 V trigger) to other Krell compo-

nents and other devices that incorporate a 12 V trigger.

In.The input receives 12 VDC (12 V trigger) from other Krell com-

ponents and other devices that incorporate a 12 V trigger.

The 12 VDC output current is limited to 30 ma.

9 AC Power Button

Use this button to change the S-275 from off to the stand-by

mode.

10 Speaker Connections

The S-275 is equipped with standard binding posts for each ampli-

fier channel. These connectors accept bare wire, pins, banana

plugs, or spade lugs. Use the red terminal for the positive connec-

tion and the black terminal for the negative connection. When in

monaural mode, use the left channel’s red connectionfor poitive

and the right channel’s red connection for negative.

11,12 Speaker Fuses

The speaker fuse protects the S-275 in case of overload or mal-

function

13 IEC Connector

The connector is for use with the provided IEC standard 20 amp

power cord.

Krell S-275 9

Krell recommends using balanced interconnect cables. Balanced

interconnect cables not only can minimize sonic loss but are also

immune to induced noise, especially with installations using long

cables. Balanced connections have 6 dB more gain than single-

ended connections. When level matching is critical, keep this gain

value in mind.

Follow these steps to connect the S-275 to your system.

1. Make sure all power sources and components are off before

connecting inputs and outputs.

2. Neatly organize the wiring between the S-275 and all system

components. Separate AC wires from audio cables to

prevent hum or other unwanted noises from being introduced

into the system.

3. Connect the left and right loudspeaker cables to the amplifier’s

left and right loudspeaker output terminals for stereo operation

or positive and negative for mono operation (10).

The S-275 is equipped with standard binding posts for each

amplifier channel. These connectors accept bare wire, pins,

banana plugs, or spade lugs. Use the red terminal for the posi-

tive connection and the black terminal for the negative connec-

tion. When in monaural mode, use the left channel’s red connec-

tionfor poitive and the right channel’s red connection for nega-

tive.

4. Connect the output(s) of your preamplifier/processor to the

appropriate input(s) (6,7) on the S-275.

The S-275 is equipped with one pair of balanced inputs via

XLR connectors and one pair of single ended inputs via RCA

connectors. Set the input switch (5) to the match the input con-

nection Use the left balanced or single ended input when in

mono mode

5. Plug the AC cord into the IEC connector (13) on the back

panel of the S-275. Plug the remaining end into the AC wall

receptacle. Press the Power Button on the rear panel, The red

stand-by indicator (2) illuminates.

Connecting the S-275

to Your System

USING BALANCED

CONNECTIONS

Connection

Steps

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