Krell KSA-150, KSA-250 Owners 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 set­up, 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 generally be accommodated,
guaranteeing consistent performance in all environments.

The KSA-150 and KSA-250 are protected by a series of opto-coupled, non­intrusive circuits that constantly evaluate the amplifiers operation. Appropriate

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protective action exists f or 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 adju sted 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 dou bling 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.