Krell Industries Monaural Amplifiers KMA-160 User manual

45 ConnairDrive
Orange, CT06477-0533, USA
KMA-160 OWNER, S MANUAL: INSTALLATION & OPERATION INSTRUCTIONS
JUNE. !,.. 19.89
GENERAL INFORMATION
Thank you for purchasing the KMA-160 Monaural Amplifiers. The
KMA-i60 represents the absolute latest evolution in amplifier
technology and has many innovative design features. It is one of four
amplifiers in the new KRELL Programmable Series, the features of
which are are discussed below. There are several aspects of its
operation that require your special attention and understanding
before installation is begun. Also, this document contains much
general information concerning audio system installation in addition
to specifics of the KMA-160.
PURE CLASS A OPERATION AND POWER CONSIDERATIONS
The KMA-160 is rated as delivering 160 watts of Class A power into 8
ohms. One inherent aspect of Class A operation is the need for a
large amount of current from the AC mains. The amplifier at idle
draws 8 amps. However, the Class A rating does not completely reveal
the true, overall power of the KMA-160, both in terms of output power
or AC power consumption. The amplifiers’ maximum output into 8 ohms
is 240 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 KMA-160 will deliver 320 watts per channel into 4 ohms; 640 watts
per channel into 2 ohms and 1280 watts per channel into i ohm. And
there is headroom over these figures! It is capable of driving
impedances below I ohm. Use below i ohm requires adjustment of the
Programmable Low Impedance Limit Set circuit on the Protection Board.
This adjustment is performed by the dealer or distributor.
Given the above, the AC power supplied to the amplifier is crucial to
getting maximum performance. The KMA-160 pair should have a dedicated
20 amp line.
Telephone:[phone]/ FAX:[phone] -

Amplifiers dissipate much of the power they consume in heat. The
KMA-160 should be installed in a location that provides unobstructed
ventilation. If you have to install the units on shelves or in a
cabinet, extra ventilation might be necessary. This can be easily
done with fans in a variety of ways. Generally, with the front and
rear open, 2 - 3 inches clearance each side and 8 inches above the
amplifier, ventilation will be adequate.
The dimensions of the KMA-160 are: 23" wide x 22" deep x 9 high.
The units weigh 80 pounds each; shipping weight is i00 pounds each.
INPUT CONNECTIONS
The KMA-160 has bo~h balanced and single-ended inputs. The balanced
input uses the 3-pin XLR connector and the single-ended input uses
the RCA connector. The pin assignment for the XLR’s is: 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 a
preamplifier.
The input that is not connected to the preamplifier can be used as an
output to a second amplifier for power-biamp applications. Before
proceeding with such an installation you should consult your Dealer
or the factory.
INSTALLATION
After inspection of the amplifiers for any shipping damage they are
ready for instaila~ion. The wiring to and from the amplifiers, and
all components in general, should be arranged in a neat, organized
manner. Specifically, AC wires should be separated from audio wires.
This avoids hum or other unwanted noise from being induced into the
system.
The KMA-160 has four sets of five-way binding post speaker
connectors. These are wired in parallel and have identical function.
It is always preferable to run long interconnect cables to the
amplifiers and keep speaker cable length to a minimum. Speaker cable
does add impedance between the amplifiers, regardless of its guage.
All KRELL amplifiers will drive the lowest impedances with ease. When
impedance is added in any significant amount, amplifier power is
literally wasted in driving the cable, thereby reducing the maximum
power that can be delivered to the speaker.
The feet on the KMA-160 can be used two different ways. They are made
from machined aluminum and are supplied with separate rubber bottoms
and mounting screws. The rubber bottoms can be screwed into the the
feet for protection of fragile surfaces such as hardwood floors or
furniture. For use on rugs we recommend using the feet without the
rubber bottoms.

PROTECTION CIRCUITRY
The KMA-160 has a sophisticated series of circuits that protect it
from dangerous input signals or loads on the output. They also
analyze various amplifier functions to prevent speaker damage caused
if the amp should fail.
When the protection circuit is engaged, the amplifier will stop
functioning. The on/off switch will remain illuminated and in the on
position. Switch it to the off position. After resolving either the
input or output problem and leaving the unit off for a short time, it
can be turned on. The minimum cycle time for the protection circuit
is i0 seconds. Important: if the amplifier does not come on following
this procedure, contact your dealer.
WARRANTY/SERVICE I~;FORMATION
There are no fuses or user-serviceable parts in the KMA-160. The
warranty on the KMA-160 is 5 years for parts and labor, and includes
return freight. Returns can be handled either through a dealer or by
direct contact with the factory. Please do not return any unit to
Krell for repair without first calling to discuss the problem, and to
obtain a Return Aur_horization number if the unit must be repaired.

Once the amplifiers are in place and turned off, connect the speaker
and interconnect cables. The preamplifier should be on at this point,
with level fully attenuated; all other sources should be off. Connect
the AC last.
OPERATION
When turning on the system, the amplifiers should always be last.
The KMA-160 on/off switch is actually a circuit breaker that is
involved in several protection circuits. Upon turn-on the amplifiers’
outputs are not connected to the speaker. After the protection
circuits have determined that the unit has completely stabilized, the
speaker relays will be engaged. You will hear a click when at this
point. The amplifiers are now ready to use. The amplifiers will be at
temperature and sound their best after approximately 15 minutes.
Operating the amplifiers is, obviously, very easy. Equally important
is an understanding of the care that should be exercised when
operating the system as a whole, in relation to the enormous power
output of the KMA-160. Simple mistakes, such as switching between
active sources without muting the preamplifier output, or
bumping/miscuing a cartridge, can generate large transients at low
frequencies. With this type of transient the KMA-160 can generate
enough power to damage most loudspeakers. All switching of sources
should be done with the preamplifier level either muted or fully
attenuated. Also, the inputs to the amplifiers should not be changed
while they are 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 also means driving them to their limit. Always turn the level
down at the first sign of distortion.
When turning the system off, the amplifiers should be first. This
avoids the possibility of a turn-off transient from some other
component getting to the speakers.