Krell Industries Power Amplifier KSA 150 / 250 User manual

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KRELL,
THE LEADER IN AUDIO ENGINNERING
KSA –150 /250 OWNER’S MANUAL
INTRODUCTION
Thank you for your purchase of the new Krell KSA-150 or KSA-250 Power
amplifier. The KSA-150 and 250 represent the absolute latest evolution in
amplifier technology. They have many innovative design features in addition to
Krell refined Class A power and direct-coupled circuitry from input to output.
There are several aspects of the KSA-150 and KSA-250’s operation that require
your special attention before installation. Because of the high level of
performance capabilities of the KSA-150 and 250, careful placement and
installation are crucial. Your thorough understanding of the operation and
interrelation of your new amplifier with your audio system will ensure its
maximum performance and long life.
ABOUT THE OWNER’S MANUAL
The Owner’s Manual is divided into various groups of information. The purpose
of the manual is to familiarize you with the product and guide you through its set-
up, installation and operation in a logical progression.
TABLE OF CONTENTS
A. General Information: A description of the basic design and
performance features of the KSA-150 and KSA-250
B. Power Considerations: Your new power amplifier and its electrical
requirements
C. Unpacking
D. Installation: Cautions, unit location guidelines, and connection of inputs
and speakers
E. Operation
F. Protection Circuitry
G. Warranty and Service Information

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A. GENERAL INFORMATION
The latest generation of high-resolution source components and speakers places
new demands on the power amplifier. The Krell KSA 150 and KSA-250 meet
these challenges with fresh design sophistication and long-term value. Both
products can drive any speaker with an effortless quality that makes their power
seem endless. Extreme clarity is maintained at all power levels. They both utilize
Krell refined high-bias Class A and direct-coupled circuitry from input to output.
Their power supplies and output stages are massive. High voltage rails with
extensive regulation are provided for the input circuitry. All materials and
electronic components are of the finest quality and operate within their optimum
performance ranges. Virtually all hand wiring has been eliminated, resulting in a
dramatic improvement in sonic clarity.
The KSA-150 and KSA-250 both utilize Class A circuitry throughout the audio
and power supply regulation stages. Class A gain stages deliver excellent sonic
performance under diverse conditions because all active components are
turned on at all times. This allows each component to operate in its most linear
and precise regions. The amplifiers are able to respond to the full range of input
signals with equal accuracy.
The KSA-150 and the KSA-250 are conservatively rated at 150 and 250 watts
per channel into 8 ohms, respectively. The 150 will actually generate 220 watts
into 8 ohms, and the 250 will generate 320 watts into 8 ohms. The 8-ohm power
ratings do not account for the amplifiers superb sonic performance nor describe
their maximum power. The Krell definition of power and the ability to drive low
impedances is that the output must double into successively low impedances.
The immense power supplies in both products allow them to double their power
into one ohm.
There are many advances in thermal construction and control circuitry in the
KSA -150 and KSA-250. All heat bearing structural components and external
heat sinks have been designed in-house to improve thermal tracking and cooling.
This construction provides very low thermal resistance between the output
transistors and the heat sinks, resulting in superior thermal tracking. It also
results in a considerable reduction in overall size. Greater amplifier life
expectancy is an added design benefit.
Automatic self-adjusting bias and DC offset control circuitry have been developed
for the KSA-150 and the KSA-250. These circuits compel the amplifiers to
conform to their intended operational parameters under all AC mains conditions.
A variation of approximately 10% in the AC can generallybe accommodated,
guaranteeing consistent performance in all environments.
The KSA-150 and KSA-250 are protected by a series of opto-coupled, non-
intrusive circuits that constantly evaluate the amplifiers operation. Appropriate

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protective action exists for a wide range of problematic conditions. Collectively,
the protection circuitry is designed to avoid damage caused by other defective
components, faulty wiring, mishandling of the system or amplifier failure.
Krell is committed to balanced operation in all products. Balanced systems have
long been standard in professional audio applications and the same advantages
apply to home audio equipment. There is a 6dB increase in gain without an
increase in noise and there is a decrease in overall system noise caused by stray
AC and RF fields. Sonic performance is drastically improved, particularly in
dynamic and soundstage presentation.
B. POWER CONSIDERATIONS
The KSA-150 is rated as delivering 150 watts per channel into 8 ohms. The
amount of Class A power is adjusted for the finest sonic performance with a
minimum of generated heat and energy consumption. The amplifier’s maximum
power into 8 ohms is 220 watts per channel. The KSA-250 is rated as delivering
250 watts per channel into 8 ohms. The amplifier’s maximum power into 8 ohms
is 320 watts per channel.
That every Krell product uses Class A circuitry in all gain and supply stages is a
foundation of our design philosophy. A second design commitment that relates to
amplifiers is that every unit be capable of doubling its output into successively
lower impedances. The KSA-150 will deliver 300 watts per channel into 4 ohms,
600 watts per channel into 2 ohms and 1,200 watts per channel into 1 ohm. The
KSA-150 is fully capable of driving impedances below 1 ohm. The KSA-250 will
deliver 500 watts per channel into 4 ohms, 1,000 watts per channel into 2 ohms
and 2,000 watts per channel into 1 ohm. The KSA-250 is capable of driving
impedances below 1 ohm.
Given the above, the AC power supplied to the amplifier is crucial to getting
maximum performance. The KSA-150 will operate at its peak with a dedicated
20-amp line, although this is not a requirement. Additionally, the KSA-150 should
only be operated with the power cord supplied with the unit. Use of other power
cords may damage the amplifier and void its warranty. The KSA-250 requires a
dedicated 20-amp line. It too, should only be operated with the power cord
supplied with the unit.
Please consult Krell or your dealer before using any devices designed to alter or
stabilize the AC power for the KSA-150 or KSA-250.
C. UNPACKING
Remove the unit, power cord and accessories from the shipping container. Store
all packing materials in a cool, dry place for future use. Inspect the unit for
shipping damage. If any damage is evident, contact your dealer immediately. If
the unit is in proper condition, proceed with the installation.

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D. INSTALLATION
1. CAUTIONS: These are important points of which you should always be
aware.
•Do not connect the power cord into the AC mains before completing
the entire installation.
•The unit must always be turned off while making connections.
•Krell XLR and custom RCA connectors are made to very exacting
standards. Connectors of lesser quality may damage the amplifiers
or cause poor connections. Please check with your dealer or Krell
about the use of any other connectors.
2. UNIT LOCATION GUIDELINES
With the power cord disconnected from the AC mains, lay out the pre-amp to
power amplifier interconnect and speaker cables to best determine the
placement for the amplifier. As mentioned earlier, the KSA-150 operates at its
peak with a dedicated 20-amp line and the KSA-250 requires a dedicated 20-
amp line. Consult a licensed electrician for installation of a dedicated line.
Amplifiers dissipate in heat much of the power they consume. The KSA-150 or
KSA-250 must be installed in a location that provides unobstructed ventilation. If
the units will be installed on shelving or in a cabinet, extra ventilation is
necessary. This can be accomplished with the use of ‘whisper’-type fans in a
variety of ways. Consult your dealer for assistance. Generally, with the front and
rear of the installation shelving or cabinetry open, 8 inches of clearance on the
sides and top of the amplifies should provide adequate ventilation.
The dimensions of the KSA-150 are: 19” wide X 16.75” deep x 8.5” high. Add
2.5” of depth for front and rear handles. The unit weighs 90 pounds. Shipping
weight is 105 pounds. The dimensions of the KSA-250 are: 19” wide x 21.5” deep
x 8.5” high. Add 2.5” of depth for front and rear handles. The unit weighs 140
pounds. Shipping weight is 144 pounds.
3. CONNECTION OF INPUTS AND SPEAKERS
Note: The KSA-250’s AC power cord may be connected to the amplifier at this
time, but do not yetconnect the power cord to the AC mains.
The KSA-150 and KSA-250 have both balanced and single-ended inputs. The
balanced inputs use 3-pin XLR connectors and single-ended inputs use RCA
connectors. The pin assignments for the XLRS are: pin 1 = signal ground: pin 2 =
non-inverting input: pin 3 = inverting input. The RCA connector is wired in parallel
with pin 2, the non-inverted input. Only one of these inputs should be
connected to the preamplifier.

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The input that is not connected to the preamplifier may be used as an output to a
second amplifier for power bi-amp applications. Before proceeding with such an
installation, you should consult your dealer or Krell.
The KSA-150 and KSA-250 are shipped with shorting pins in the XLR inputs.
These pins must remainin the XLR inputs if the units are to operate in the single-
ended mode. These pins must be removed to connect either unit for balanced
operation. The shorting pin connects pins 1 and 3 and grounds the inverted input.
The wiring to and from the amplifier, and all components in general, should be
arranged in a neat, organized manner. Specifically, AC wires should be
separated from audio wire. This insures the avoidance of hum or the introduction
of other unwanted noise into the system.
It is always preferable to run long interconnect cables to the amplifier and to keep
speaker cable length to a minimum. Speaker cable does add impedance
between the speakers and the amplifier, regardless of the wire gauge. All Krell
amplifiers will drive the lowest impedances with ease. When impedance is added
in any significant amount, (for instance with excessive cable length) amplifier
power is literally wasted in driving the cable, thereby reducing the maximum
power that can be delivered to the speakers.
The feet on the KSA-150 or KSA-250 can be used three different ways. They are
made from machined Delrin and are supplied with separate rubber bottoms and
mounting screws. The rubber bottom can be screwed into the Delrin for the
protection of fragile surfaces such as hardwood floors or furniture. For use on
rugs or carpeting, using the feet without the rubber bottoms is recommended.
You may purchase, from your authorized dealer, a set of Acoustic Mass
Dampers (AMDs). AMDs are custom-machined stainless steel feet fitted with a
threaded insert and a washer made from acoustically absorbent material. When
threaded into the Delrin feet, the AMS will decouple the amplifier from vibrations
present on the surface where the unit is installed.
Once the amplifier is in place, and turned off, you can begin to connect the
interconnect and speaker cables. The preamplifier should be off, with the level
fully attenuated (turned down). All other sources should be off. The two sets of 5-
way binding posts for each channel’s output are wired in parallel to allow easy bi
wiring.
You may now connect the AC.
E. OPERATION
Activate the system by turning on the source components and preamplifier with
the volume fully attenuated (turned down). The amplifier must always be turned
on last. Just after turn-on, a soft click will be heard. This is the main power relay

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closing. At this pint the amplifier’s outputs are not connected to the speakers.
After the protection circuits detect that the unit has completely stabilized, the
speaker relays will engage. Another click will be heard at this point. The amplifier
is now ready to use. The amplifier will be at temperature and sound its best after
approximately 15 minutes.
Operation of the amplifier is simple. It is important to note that care must be
taken in the operation of the whole system in relation to the significant power
output of either amplifier. Mistakes, such as switching between active sources
without muting the preamplifier output or bumping/miscuing a phonograph
cartridge, can generate large transients at low frequencies. When this type of
transient activity occurs, the amplifiers can generate enough power-surge to
damage most loudspeakers. All switching of sources should be done with the
preamplifier level either muted or fully attenuated (turned down). Inputs to the
amplifier should never be changed while the amplifier is on.
Care must be taken when setting high playback levels. Because of their
tremendous reserve of clean power, Krell amplifiers safely drive speakers to
higher sound pressure levels than other amplifiers. This often results in driving
the speakers to their limit. Always turn the volume level down at the first sign of
distortion.
When turning off the system, the amplifier should always be first. This avoids the
possibility of a turn-off transient occurrence from some other component to the
speakers.
F. PROTECTION CIRCUITRY
The KSA-150 and KSA-250 have a sophisticated series of circuits that protect
them from dangerous input signals or loads on the output. These circuits also
analyze various amplifier functions to prevent speaker damage that may be
caused if the amplifier fails to function properly.
There are two protection modes: Input and Output. When the Input Protection is
engaged the amplifier will remain on, with the front panel LED illuminated, but it
will not pass a signal. This indicates a problem with the input signal caused by
the preamplifier or source component. This is most often a DC condition. The
amplifier will resume passing signal when the problem is resolved.
When the Output Protection is engaged the amplifier will turn off, with the front
panel LED turning off as well. This usually indicates a problem with the speaker
wires, their connection, or the speakers themselves. Once the problem is located
and resolved the amplifier will turn on normally with activation of the front panel
switch. The Output Protection will also engage if the amplifier fails. If the amplifier
will not turn on with all inputs and outputs disconnected, please contact your
dealer or Krell Service.

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IMPORTANT NOTES REGARDING PROTECTION CIRCUITRY
1. When the Output Protection circuitry has been engaged, allow at
least 20 seconds before turning on the amplifier again. Repeated
fast cycling of the On/Off switch can damage the amplifier and void
the warranty.
2. If the amplifier does not come on following the procedure above,
please contact your dealer.
3. There is a circuit breaker on the amplifier real panel. This breaker
protects the amplifier in the event of catastrophic failure. If the
circuit breaker engages, contact your dealer or the Krell Service
Department. Do not attempt to reset the circuit breaker.
G. WARRANTY AND SERVICE INFORMATION
There are no fuses or user-serviceable parts in the KSA-150 or KSA-250. Both
amplifiers have a limited warranty of five years from the date of purchase for
parts and labor. Return freight is included in the warranty. Please return the
warranty car immediately after successful installation and operation are
completed.
The warranty for Krell products is valid only in the country to which they were
shipped and at the Krell factory in Orange, Connecticut, USA. If there are
problems with any of your Krell products, please contact your authorized Krell
dealer or the Krell Service Department.
Please do not return any unit to Krell without first having contacted the Krell
Service Department and receiving a Return Authorization Number. Units should
be shipped in Krell packing. Packing materials may be purchased through the
Krell Service Department. Freight charges to the factory or distributor are the
responsibility of the customer. Krell or the dealer/distributor will pay return freight
charges on warranty repairs.