Krell Industries Power Amplifiers MDA-300/500, MDA-300, MDA-500 Owner's Reference Manual

A. INTRODUCTION

Thank you for your purchase of the KRELL MDA-300 or

MDA-500 power amplifiers. These amplifiers represent
the latest evolution in amplifier technology and incorpo-

rate many innovative design features.

To obtain the best performance from your MDA-300/
500s, careful attention should be paid to placement,
installation and operation. A thoro~ugh understanding o.f
these details will help insure satistactory op.eration and
long life for the MDA-300/500s and related system com-

ponents.

This Owner’s Reference is divided into several sections,
eac.h designed to perfo__r~_, a different function. As you

.read through this. O.w.ner s Reference you will become

better acquainted with the features and functions that

make the MDA-300/500s a superb value. A Question and

Answer section is also included where answers to com­mon questions are provided. Should you have any ques­tions or suggestions please feel free to contact your au­thorized dealer or the KRELL staff for assistance.

In the unlikely event that your MDA-3.00/50.0s should
require service you will be pleased to ~now ~tlaat it is .
backed by a.comprehensive Customer batistaction.policy

and one of the most advanced service facilities in the

industry. For detailed information on the terms and con-

ditions of service, please consult your warranty reg.istra-

tion card, your authorized KRELL Dealer or Distributor.

TABLE OF CONTENTS

4. UNPACKING AND ASSEMBLY

BASIC INSTALLATION AND OPERATION

INPUT AND OUTPUT CONNECTIONS

8. AMPLIFIER OPERATION

9. PROTECTION CIRCUITRY

10. REAR PANEL DES CRIPTIONS

12.

QUESTIONS AND ANSWERS

14. SPECIFICATIONS

15. WARRANTY AND SERVICE INFORMATION

3

B. UNPACKING AND ASSEMBLY

NOTE: Do to the extreme weight of the MDA-300 or

MDA-500 it is strongly advised that unpacking and

placement is completed by at least two individuals.

1. Open the box on one end.

2. Fold back the flaps on all four sides of the box and
carefully roll it over on to the exposed end.

3. Pull the box straight up and off exposing the foam
packing material.

4. Pull the foam piece from the exposed end of the ampli­tier.

5. Roll the amplifier carefully onto its handles and re­move the second piece of foam.

The following items will now be visible in each box:
1

MDA-300/500 monaural amplifier

1 Warranty card
1

AC power cord

4 or 5 Rubber bottoms (MDA-500 has 5 feet)
NOTE: If any of these items are not included please

contact your authorized dealer immediately f6r assis­tance.

6. Remove the plastic bag from the amplifier.

7. Repeat procedure for the second amplifier.

NOTE: Save all pac.kin~g materials..If you must ship your

MDA-300/500s in the tuture, repack the unit in its origi­nal packaging to prevent transit damage.

CAUTION: Do not connect the power cords into the AC

mains before completing the Installation section.

4

C. BASIC INSTALLATION

AND OPERATION

1. Place the MDA-300/500, on a firm level surface away

from excessive dirt or moisture. Ideally the amplifiers ’

should be placed as close, to the speakers as possible. ,It is

always preferable torun long interconnect cables to tt~e
amplifiers and keep speaker cable length t.o a minimu~m..

Speaker cable does add an impedance at tt~e output ot the
amplifier, regardless of the cable. All KRELL amplifiers

will drive the lowest im. p.edances with ease. When imped­ance is added, the amphfier’s power is litera.lly wastedin
driving cable. Long speaker cables reduce tlae maximum
power that can be dehvered to the speakers.

2. Amplifiers dissipate much of the power they consume
in heat. The MDA-300/500s 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 m~¢ be necessary_. This can be accomplished
with "whisper - type fans. Consult your dealer for assis-

tance.
Generally, with the front and rear of a cabinet open, 2-3

inches of clearance on each side and 8 inches of clear­ance above the amplifiers should provide adequate venti­lation.

The exact dimensions for the MDA-300 and MDA-500

are in the Specifications Section below.

3. The MDA-300/500s should have a dedicated 20.amp.

line for each amplifier and should only be operated with
the power cords supplied. Use of other power cords may

damage the amplifiers or void its warranty. Please consult
KREEL or your dealer BEFORE using any devices de­signed to alter or stabilize the AC pow.er fbr.the MDA­300/500s. If you have any questions about placement or
AC power conditions please consult KREL-L.

4. The feet on the MDA-300/500s canbe used in several
different ways. They are made from machined Delrin and

are supplied witla separate threaded rubber b~ottoms. The
rubber bottoms can be screwed into the feet tor protec-

tion of fragile surfaces such as hardwood floors or furni­ture. For use on rugs, we recommend using the fee.t with-

out the rubber bottoms. MDA-300/500s feet can also
accept the KREL. L AMDs (A, coustic Mass Damper).

These improve the amplifier s sonic performance in most
installations.

5

D. INPUT AND OUTPUT
CONNECTIONS

CAUTION: When making connections to this component
or any other, make sure ttie power amplifiers are OFF and

the preamplifier is in the MUTE or STANDBY mode.

1. Connect the speaker cables to the output terminals of

each amplifier. The MDA-300/500s utilize two sets of

parallel 5 way binding posts for the left and fight amplifi-

ers. This con_figuration makes cable connections and-bi­wiring simple.

NOTE: The binding, posts are of the highest quality but
w. ill break if over.tigla.tened. In..se.rt wire or spade lug into

the connector anc~ tigt~ten until there is no movement
from the cable.

CAUTION: Make sure all cable terminations are of the
highest quality, free from frayed ends, shorts or cold

solder joints.

2. Connect the interconnect cables from your preampli­fier to the input of each MDA-300/500.

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 practice avoids hum or ottier unwanted
noise from being induced into the system.

The MDA-300/500s have balanced and single-ended
inputs. The balanced inputs use 3-pin XLR connectors
and the single-ended inputs use standard RCA connec-

tors.
CAUTION: Use only one input to the amplifier at a time.

The MDA-300/500s are shipped with. shorting pins in the
~LR inputs. These pins shoi~ld remain in the XLR inputs

it you are operating the MDA-300/500s in the single­elided mode. When the shorting pin is inserted, pin 1 and
pin 3 are. shorted together. The sfiorting pins must be
removecl to connect the MDA-300/500s for balanced
operation.

6

Thepin assignment for the XLR is:

pin _1-= shiel-d (ground)
p!n 2 = non-inverting input (hot)
pin 3 = inverting input

NOTE: The RCA center conductor for each channel is

wired_in, parallel with pin 2, the non-inv, erted input. Only
one ot these inputs Should be connectecl to a preamplifier.

3. Insert the AC pow6r cord into the receptacle located on

the back of eachMDA-300/500. Insert tile other end into
the wall AC receptacle. (Refer to section C, Basic Instal-

lation and Operation, for AC power requirements)

7

E. AMPLIFIER OPERATION

1. Push the black button on the front of both amplifiers to
turn them on. The blue LED on the front panels above
each switch will illuminate.

When turning on the system, the amplifiers should al-

ways be last.-The MDA-300/50.0s On/Off switch is part
of a multi-level turn-on circuit that goes through several

steps of protection. Upon turn-on, the amplifier’s outputs
are not connected to the.speak.ers. After ttie protect!on

circuits have determined that the unit has completely
stabilized, the speaker relays will be engaged.-You will
hear a click at this point. The amplifiers are now ready to
use. The amplifiers will be at temperature and sound their
best after approximately 30 minutes.

2. With the preamplifier in the Mute position, or volume
control fully attenuated, select a source. Turn the volume
control up to your desired listening level.

3. Understanding the operation of these amplifiers is very
e.asy. 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
MDA-300/500s. Simple mistakes, such as switching
between active sources without muting the preampfifier

9utput, or bumping/miscuing a cartridge, can generate
large transients at low frequencies. With this type of

transient the MDA-300/500s can generate enough power
to damage most loudspeakers. AII switching of sources
should be done with the preamplifier level e~ther muted
or fully attenuated. Inputs to the amplifier should not be
changed while the amplifier is on.

NOTE: 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 the speakers to their fimit. Always turn the
level down at the first sign of distortion.

When turning the system off, the amplifiers should
ALWAYS be first. This avoids the possibility of a turn­off transient from some other component getting to the
speakers.

8

E PROTECTION CIRCUITRY

There are no fuses in the MDA-300/500s. The amplifiers
are protected by a series of non-intrusive, opto-coupled

circuits that constantly evaluate the amplifier’s operation.
Appropriate protecti’ce action exists for DC conditions,

stiort circuit, oscillatidn, AC power anomalies, high
ground resistance and out-of:phase ground. Collectively

tlae protection circuitry is designed to avoid damage to
the amplifiers or speakers caused by other d.efecti~e

components, faulty wiring, mishandling of the system oy
amplifier failure. When the protection, circuit is engage(l,
the a.mplifiers will shut off and short tlaeir output. After
resolving either the input or output problem the amplifi­ers can 15e turned on.

The amplifiers also have circuit breakers on their
backpanel for the AC power. Should the button in the
center of the breaker pop out, push it in to reset the
breaker. If the amplifiers still do not come back on, call
Krell Industries.

9

H. REAR PANEL DESCRIPTIONS

All descriptions are for each amplifier chassis
INPUTS:
Balanced via 3 pin XER connector

Single ended via RCA connector
XLR PIN CONFIGURATION

p!n 1 Shield (ground)
p.ln 2 Non-inverting or 0 degrees (hot)
pan 3 Inverting or 1-80 degrees

OUTPUT:
Two pairs of five-way binding posts in parallel

OTHER:
Standard AC receptacle
20 amp circuit breaker
OPTIONS:
Black Faceplate

11

I. QUESTIONS AND ANSWERS

Q. Should I leave the MDA-300/500 on at all times?
A. Although you could leave the MDA-300/500 on at all

times without fear of damage to the amplifier, we recom­mend. 30 minutes of warm-up before critical listening and

switching the amplifier off when not in use.

~

When Ipush the power button on the front of the

DA-300/-500, the amplifier doesn’t turn on. What

should I c[o?

A. Unplug the amplifier from the AC receptacle and
remove the input from the amplifier. Check the output

connections, then plugthe amplifier back in. Checl~ the
circuit breaker on the-back of the unit and reset it if nec-

essary. Push the power button on the front panel. If the
problem persists, unplug the unit and call your dealer or
Krell industries.

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

through the speakers. There was never a hum before the

MDA-300/500 was in the system. What should I do?
A. Often when a new component is introduced into an

audio system a hum may 15ec.ome present. This is often

caused by_ a ground loop in tlae system. _Try putting a 3
prong to 2 prong AC adaptor (cheate.r plug) on the
power cord, lifting the ground from the unit. This sho.uld
make the hum disappear. If not, try another adaptor else-

where in the system.
NOTE: Always keep one major audio component

grounded.
NOTE: Even though the ground is lifted from the power

amplifier, it .is still gr~ou.nded via the interconnect cables

throughout the rest ot tt~e system.
Q. Can I use special audio power c~rds on the MDA-300

or MDA’500?

’

A. You can experiment with special power cords as long

as they are grounded on both ends and meet the

amplifier’s I5 amp power requirement.

12

Q. After the amplifier is on for about one hour it be­comes very hot. Is this normal?

A. Yes. Due to the high bias design of the MDA-300/500

it will become quite warm. After approximately 1 hour
the amplifier will be at its optimum operating tempera-

ture. If the amplifier should-have a severe temperature
inbalance between the. left and right channel, unplug the

unit and call your aut~0rized dealer or Krell.
Q. I tried a new preamplifier in my audio system and

when I turned the unit on the MDA-300/500 shut off. Is
the amplifier defective?

A. More than likely the amplifier is not defective. When

connecting components you should always keep the
amplifier off. Tile amplifer sensed a bad input signal and

slaut off, protecting itself and the speakers.
There also could tiave been a bad cable connection or
excessive DC offset coming from the output of the pre­amplifier. Before turning tile amplifier on, check the
input cables. If that doesn’t help, bring the preamplifier to
the dealer for testing.

13

J, SPECIFICATIONS

MDA-300

GAIN

26dB

SIGNAL-TO-NOISE

106dB unweighted

THD

1K at 8 ohms

less than .2%

20K at 8 ohms

less than .4%

INPUT IMPEDANCE

47,000 ohms (47K)

INPUT SENSITIVITY

2.5 volts for 300 watts out

OUTPUT IMPEDANCE

.2 ohms

OUTPUT VOLTAGE

139 volts peak to peak

OUTPUT POWER

All read!ngs
are continuous output

power, per channeI
8 ohms 300 watts

4 ohms

600 watts

2 ohms 1200 watts

1 ohm 2400 watts

DIMENSIONS

19.0" WIDE
!9.5" DEEP with handles

8.5" HIGH with feet

SHIPPING WEIGHT

105 pounds

MDA-500
GAIN

26dB

SIGNAL-TO-NOISE

106dB unweighted

THD

1K at 8 ohms

less than .2%
20K at 8 ohms

less then .5%

INPUT IMPEDANCE

47,000 ohms (47K)

INPUT SENSITIVITY

3.2 volts for 500 watts out

OUTPUT IMPEDANCE

¯ 15 ohms

OUTPUT VOLTAGE

179 volts peak to peak

OUTPUT POWER

All readings
are continuous output

power, per channeI
8 ohms

500 watts

4 ohms 1000 watts
2 ohms 2000 watts

1 ohm 4000 watts

DIMENSIONS

19.0" WIDE

24.0" DEEP with handles

8.5" HIGH with feet

SHIPPING WEIGHT

144 pounds

14

K. WARRANTY AND SERVICE
INFORMATION

There are no user-serviceable parts inside the MDA-300/

500. The MDA-300/500 has a limited warranty of f~ve
years parts and labor. Return freight is included in ~the
warranty. The warranty period b.egins on thee date ot
p_u_rchase and is activated with the return ot the enclosed

Warran.ty Card and a copy of the Sales receipt. Please

return the warranty cardimmediate!y after successful
installation and operation are completed.

The warranty for Krell products is valid ~n~ in t.he coun­try to which they were originally shipped and at tlae

factory. If you tfiink there are problems with your unit
please contact your dealer, distributor or the factory

immediately.
Plea~s.e do not returl?, any unit to KRELL for repair with-

out first calling to discuss the problem and to ot~tain a
R..etu..rn Authorization number.-Freight to the factory or
distrit~utor is your responsibili.ty. R.~turn freight to you
will be paid b}, the factory or dlstrit)utor.
Any unauthorized updates or modifications performed to
the unit will void the warranty.

15

KRELL INDUSTRIES

35 HIGGINS DRIVE MILFORD CT 06460
SALES 203-874-3139 FAX [phone]

COPYRIGHT 1992 KRELL INDUSTRIES

(MDA9204)