Krell Industries S-275 User manual

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 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.
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 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
12
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