Krell S-275 Owners Reference

THE LEADER IN AUDIO ENGINEERIN

G

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 fre­quency 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, result­ing 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 set­ting a switch on the rear panel. Power output increases to 550
Watts into 8 Ohms. A 6 dB gain switch provides a channel balanc­ing tool for systems using a combination of balanced and RCA
style connections.This owner’s reference contains important infor­mation 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 ref­erence manual.

Monaural Operation

Monaural operation combines the output of the left and right chan­nels 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 instal­lations, balanced connections have 6 dB more gain than single­ended 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 single­ended connections as the ground connection is made last and
broken first. Turn the system off prior to making or breaking single­ended connections. Single-ended connections are not recom­mended for connections requiring long cable runs.

CONFIGURATIONS

INPUT AND OUTPUT
CONNECTIONS

2 Krell 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 opera­tional 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 opera­tional 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 con­nection 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

4 Krell 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.

I

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 unob­structed).

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 accept­able. 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

6 Krell 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

12

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 but­ton 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 out­puts, 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 sin­gle 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 pro­vides 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 ampli­fier channel. These connectors accept bare wire, pins, banana

Front and Rear Panel Description, continued

8 Krell S-275

8. 12 Volt Trigger Input/Output.

Out.The output sends 12 VDC (12 V trigger) to other Krell compo­nents and other devices that incorporate a 12 V trigger.

In.The input receives 12 VDC (12 V trigger) from other Krell com­ponents 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 ampli­fier channel. These connectors accept bare wire, pins, banana
plugs, or spade lugs. Use the red terminal for the positive connec­tion 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 mal­function

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 single­ended 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 posi­tive connection 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.

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 con­nection 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

10 Krell S-275

The S-275 Amplifier is easy to operate. However, great care
should be exercised when operating a system that includes the S­275, because of the amplifier’s power output. Switching between
active sources without muting the preamplifier output, or bump­ing/miscuing a device, can generate large transients at low fre­quencies. The S-275 may generate enough power with these tran­sients to damage most loudspeakers. To avoid damage, be sure to
switch all sources with the preamplifier level either muted or fully
attenuated.

Krell amplifiers have large reserves of clean power and can safely drive
loudspeakers to higher sound pressure levels than other amplifiers.
However, use care when setting high playback levels and lower the vol­ume level at any sign of loudspeaker distress.

When powering up any system, always turn amplifiers on last.
When powering down, always turn amplifiers off first.

When the amplifier is in stand-by mode, with the red stand-by
LED (2) illuminated, turn the amplifier on by pressing the
power button on the front panel or the power key on the
remote control (1). There is an audible click. The blue power
LED (2) illuminates. The S-275 is now in the operational mode
and ready to play music.

Operating Your S-275

Q. Should I leave my S-275 on at all times?

A. Krell recommends leaving the amplifier in the stand-by mode,

ready to play music. If you are not going to play music for a
long time, you may turn off the rear panel power button.

Q. When I turn on the amplifier there is a loud hum through the

loudspeakers. What should I do?

A. Check all cable terminations, making sure they have solid sol-

der joints and are of sound construction.

With the amplifier off, remove the interconnect cables, then
turn the amplifier on. If the hum disappears, turn the amplifier
off and reinsert one of the interconnect cables. Turn the
amplifier back on. If the hum reappears with one or both
cables reinserted, there may be a defective cable. Have the
interconnect cables checked before proceeding.

. If the interconnect cables are sound, you may be experiencing

a ground loop. Please contact your authorized Krell dealer,
distributor, or Krell for suggestions on how to solve this
problem.

Questions and Answers

Krell S-275 11

This Krell product has a limited warranty of five years for parts and labor on circuitry from
date of purchase or six years from date of original shipment from the Krell factory. Should
this product fail to perform at any time during the warranty, Krell will repair it at no cost to
the owner, except as set forth in this warranty.

The warranty does not apply to damage caused by acts of God or nature.

The warranty on this page shall be in lieu of any other warranty, expressed or implied,
including, but not limited to, any implied warranty of merchantability or fitness for a
particular purpose. There are no warranties which exceed beyond those described in this
document. If this product does not perform as warranted herein, the owner’s sole remedy
shall be repair. In no event will Krell be liable for incidental or consequential damages
arising from purchase, use, or inability to use this product, even if Krell has been advised of
the possibility of such damages.

Proof of purchase in the form of a bill of sale or receipted invoice substantiating that the unit
is within the warranty period must be presented to obtain warranty service. The warranty
begins on the date of retail purchase, as noted on the bill of sale or receipted invoice from
an authorized Krell dealer or distributor.

The warranty for Krell products is valid only in the country to which they were originally
shipped, through the authorized Krell distributor for that country, and at the factory. There
may be restrictions on or changes to Krell’s warranty because of regulations within a
specific country. Please check with your distributor for a complete understanding of the
warranty in your country.

If a unit is serviced by a distributor who did not import the unit, there may be a charge for
service, even if the product is within the warranty period.

Freight to the factory is your responsibility. Return freight within the United States (U.S.A.) is
included in the warranty. If you have purchased your Krell product outside the U.S.A. and
wish to have it serviced at the factory, all freight and associated charges to the factory are
your responsibility.

Krell will pay return freight to the U.S.A.-based freight forwarder of your choice. Freight and
other charges to ship the unit from the freight forwarder to you are also your responsibility.

Krell is not responsible for any damage incurred in transit. Krell will file claims for damages
as necessary for units damaged in transit to the factory. You are responsible for filing claims
for shipping damages during the return shipment.

Krell does not supply replacement parts and/or products to the owner of the unit.
Replacement parts and/or products will be furnished only to the distributor performing
service on this unit on an exchange basis only; any parts and/or products returned to Krell
for exchange become the property of Krell.

No expressed or implied warranty is made for any Krell product damaged by accident,
abuse, misuse, natural or personal disaster, or unauthorized modification.

Any unauthorized voltage conversion, disassembly, component replacement, perforation of
chassis, updates, or modifications performed to the unit will void the warranty.

The operating voltage of this unit is determined by the factory and can only be changed by
an authorized Krell distributor or at the factory. The voltage for this product in the U.S.A.
cannot be changed until six months from the original purchase date.

In the event that Krell receives a product for warranty service that has been modified in any
way without Krell authorization, all warranties on that product will be void. The product will
be returned to original factory layout specifications at the owner’s expense before it is
repaired. All repairs required after the product has been returned to original factory specifi­cations will be charged to the customer, at current parts and labor rates.

All operational features, functions, and specifications and policies are subject to change

Warranty

To register your product
for warranty benefits,
please complete and return
the Warranty Registration
Card enclosed in the ship­ping box within 15 days of
purchase. Thank you.

12 Krell S-275

Return Authorization
Procedure

If you believe there is a problem with your component, please con­tact your dealer, distributor, or the Krell factory to discuss the
problem

before

you return the component for repair. To expedite
service, you may wish to complete and e-mail the Service Request
Form in the Service section of our website at:

http://www.krellonline.com

To return a product to Krell, please follow this procedure so that
we may serve you better:

1. Obtain a Return Authorization Number (R/A number) and ship-

ping address from the Krell Service Department.

2. Insure and accept all liability for loss or damage to the product

during shipment to the Krell factory and ensure all freight (ship­ping) charges are prepaid.

The product may also be hand delivered if arrangements with the
Service Department have been made in advance. Proof of pur­chase will be required for warranty validation at the time of hand
delivery.

Use the original packaging to ensure the safe transit of the product
to the factory, dealer, or distributor. Krell may, at its discretion, return
a product in new packaging and bill the owner for such packaging if
the product received by Krell was boxed in nonstandard packaging
or if the original packaging was so damaged that it was unusable. If
Krell determines that new packaging is required, the owner will be
notified before the product is returned.

HOW TO RETURN
A PRODUCT

IMPORTANT

To purchase additional packaging, please contact your authorized
Krell dealer, distributor, or the Krell Service Department for assis­tance.

HOW TO PURCHASE
ADDITIONAL PACKING

To contact the Krell Service Department:

TEL [phone]

Monday-Friday, 9:00 am to 5:00 pm EST
FAX [phone]
E-MAIL [e-mail]
WEBSITE http://www.krellonline.com

HOW TO EXPEDITE
SERVICE

Krell S-275 13

FREQUENCY RESPONSE

20 Hz–20 kHz

+0 dB, -0.08 dB - Stereo

+0 dB, -0.12 dB - Mono

SIGNAL-TO-NOISE RATIO

“A” weighted

115 dB

TOTAL HARMONIC
DISTORTION (THD)

1 kHz <0.03%

20 kHz <0.20%

GAIN

Selectable, 25.8 or 19.8 dB - stereo

Selectable, 31.8 or 25.8 dB - mono

INPUT SENSITIVITY

Selectable, 2.4 V or 4.8 V - stereo

Selectable, 1.7 V or 3.4 V - mono

INPUT IMPEDANCE

20 kOhms single-ended

20 kOhms balanced

OUTPUT IMPEDANCE

<0.067 Ohms - stereo

<.15 Ohms - mono

POWER CONSUMPTION

Idle 80 W - stereo, 65 W mono

Max. 1,900 W

TRANSFORMER

1,650 VA

INPUTS

1 pair balanced via XLR connectors

1 pair single-ended

via RCA connectors

OUTPUTS

2 loudspeaker via 5-standard

binding posts

OUTPUT VOLTAGE

Peak to peak 133 V - stereo

Peak to Peak 188V mono

OUTPUT POWER

275/550 WPC 8/4 Ohms - stereo

550/1,100 WPC 8/4 Ohms - mono

REMOTE CONTROL

1 12 VDC trigger Ouput

1 12 VDC trigger Input

Krell Industries, LLC.
45 Connair Road
Orange, CT 06477-3650 USA

TEL [phone], FAX [phone]
E-MAIL [e-mail]
WEB SITE www.krellonline.com

S-275

Stereo Amplifier

v 1.0

Specifications

All operational features, functions,
specifications, and policies are
subject to change without
notification.