Krell Industries Power Amplifiers MDA-300/500 Quick start guide

A. INTRODUCTION
Thankyou for your purchase of the KRELLMDA-300or
MDA-500poweramplifiers. These amplifiers represent
the latest evolution in amplifier technologyandincorpo-
rate manyinnovative designfeatures.
Toobtain the best performancefrom your MDA-300/
500s, careful attention shouldbe paid to placement,
installation andoperation. Athoro~ughunderstandingo.f
thesedetails will help insure satistactory op.erationand
long life for the MDA-300/500sand related systemcom-
ponents.
This Owner’sReferenceis divided into several sections,
eac.hdesignedto perfo__r~_,a different function.Asyou
.read throughthis. O.w.ners Referenceyouwill become
better acquaintedwith the features andfunctions that
makethe MDA-300/500sa superb value. A Question and
Answersection is also included whereanswersto com-
monquestions are provided. Shouldyouhave any ques-
tions or suggestionsplease feel free to contact yourau-
thorized dealer or the KRELLstaff for assistance.
In the unlikely event that your MDA-3.00/50.0sshould
requireserviceyouwill be pleasedto ~now~tlaat it is .
backedby a.comprehensiveCustomerbatistaction.policy
andoneof the mostadvancedservice facilities in the
industry. For detailed informationon the terms andcon-
ditions of service, pleaseconsult yourwarrantyreg.istra-
tion card, yourauthorized KRELLDealer 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. WARRANTYAND SERVICE INFORMATION
3

B. UNPACKING AND ASSEMBLY
NOTE:Doto the extreme weight of the MDA-300or
MDA-500it is strongly advised that unpackingand
placementis completedby at least twoindividuals.
1. Openthe boxon one end.
2. Foldbackthe flaps on all four sides of the boxand
carefully roll it overonto the exposedend.
3. Pull the boxstraight upand off exposingthe foam
packingmaterial.
4. Pull the foampiece fromthe exposedendof the ampli-
tier.
5. Roll the amplifier carefully ontoits handlesandre-
movethe secondpiece of foam.
Thefollowing items will nowbe visible in each box:
1MDA-300/500monaural amplifier
1 Warrantycard
1ACpower cord
4 or 5 Rubberbottoms (MDA-500has 5 feet)
NOTE:If any of these items are not included please
contact yourauthorized dealer immediatelyf6r assis-
tance.
6. Removethe plastic bag fromthe amplifier.
7. Repeatprocedurefor the secondamplifier.
NOTE:Saveall pac.kin~gmaterials..If youmustship your
MDA-300/500sin the tuture, repackthe unit in its origi-
nal packagingto prevent transit damage.
CAUTION:Donot connect the powercords into the AC
mainsbefore completingthe Installation section.
4

C. BASIC INSTALLATION
AND OPERATION
1. Place the MDA-300/500,on a firm level surface away
fromexcessivedirt or moisture. Ideally the amplifiers ’
shouldbeplacedas close, to the speakersas possible. ,It is
alwayspreferable torun long interconnect cables to tt~e
amplifiers andkeepspeakercable length t.o a minimu~m..
Speakercable doesadd an impedanceat tt~e output ot the
amplifier, regardless of the cable. All KRELLamplifiers
will drive the lowest im. p.edanceswithease. Whenimped-
anceis added,the amphfier’spoweris litera.lly wastedin
driving cable. Longspeaker cables reduce tlae maximum
powerthat can be dehveredto the speakers.
2. Amplifiers dissipate muchof the powerthey consume
in heat. TheMDA-300/500sshould-be installed in a
location that.provides unobstructedventilation. If you
haveto install the units onshelvesor in a cabinet, extra
ventilation m~¢be necessary_. This can be accomplished
with "whisper- type fans. Consultyourdealer for assis-
tance.
Generally,withthe front andrear of a cabinet open,2-3
inches of clearance oneach side and8 inches of clear-
ance abovethe amplifiers should provideadequateventi-
lation.
The exact dimensions for the MDA-300and MDA-500
are in the Specifications Sectionbelow.
3. TheMDA-300/500sshould have a dedicated 20.amp.
line for eachamplifier and shouldonly be operatedwith
the powercords supplied. Useof other powercords may
damagethe amplifiers or void its warranty. Please consult
KREELor your dealer BEFOREusing any devices de-
signedto alter or stabilize the ACpow.erfbr.the MDA-
300/500s. If youhave any questions about placementor
ACpowerconditions please consult KREL-L.
4. Thefeet on the MDA-300/500scanbe used in several
different ways. Theyare madefrom machinedDelrin and
are suppliedwitla separate threadedrubberb~ottoms.The
rubberbottomscan be screwedinto the feet tor protec-
tion of fragile surfaces suchas hardwoodfloors or furni-
ture. For use on rugs, werecommendusing the fee.t with-
out the rubber bottoms. MDA-300/500sfeet can also
accept the KREL.L AMDs(A, coustic MassDamper).
Theseimprovethe amplifier s sonic performancein most
installations.
5

D. INPUT AND OUTPUT
CONNECTIONS
CAUTION:Whenmaking connections to this component
or anyother, makesure ttie poweramplifiers are OFFand
the preamplifier is in the MUTEor STANDBYmode.
1. Connectthe speakercables to the output terminals of
each amplifier. TheMDA-300/500sutilize two sets of
parallel 5 waybindingposts for the left andfight amplifi-
ers. This con_figurationmakescable connectionsand-bi-
wiringsimple.
NOTE:Thebinding, posts are of the highest quality but
w.ill breakif over.tigla.tened.In..se.rt wireor spadeluginto
the connectoranc~tigt~ten until there is no movement
fromthe cable.
CAUTION:Makesure all cable terminations are of the
highest quality, free fromfrayedends, shorts or cold
solderjoints.
2. Connectthe interconnect cables fromyour preampli-
fier to the input of each MDA-300/500.
Thewiring to andfromthe amplifiers, and all compo-
nents in general, shouldbe arrangedin a neat, organized
manner.Specifically, ACwires should be separated from
audio wires. This practice avoids humor ottier unwanted
noise frombeing inducedinto the system.
The MDA-300/500shave balanced and single-ended
inputs. Thebalanced inputs use 3-pin XLRconnectors
and the single-ended inputs use standard RCAconnec-
tors.
CAUTION:Useonly one input to the amplifier at a time.
TheMDA-300/500sare shipped with. shorting pins in the
~LRinputs. Thesepins shoi~ld remainin the XLRinputs
it youare operating the MDA-300/500sin the single-
elided mode.Whenthe shorting pin is inserted, pin 1 and
pin 3 are. shortedtogether. Thesfiorting pins mustbe
removeclto connect the MDA-300/500sfor balanced
operation.
6

Thepin assignment for the XLRis:
pin _1-=shiel-d (ground)
p!n 2 = non-inverting input (hot)
pin 3 = inverting input
NOTE:The RCAcenter conductor for each channel is
wired_in, parallel with pin 2, the non-inv, erted input. Only
oneot these inputs Shouldbe connectecl to a preamplifier.
3. Insert the ACpow6rcord into the receptacle located on
the back of eachMDA-300/500.Insert tile other end into
the wall ACreceptacle. (Refer to section C, Basic Instal-
lation and Operation, for ACpower requirements)
7

E. AMPLIFIER OPERATION
1. Pushthe blackbuttononthe front of bothamplifiersto
turn themon. Theblue LEDon the front panels above
eachswitch will illuminate.
Whenturning on the system,the amplifiers shouldal-
waysbe last.-The MDA-300/50.0sOn/Offswitch is part
of a multi-level turn-oncircuit that goesthroughseveral
steps of protection. Uponturn-on, the amplifier’s outputs
are not connectedto the.speak.ers. Afterttie protect!on
circuits havedeterminedthat the unit has completely
stabilized, the speakerrelays will be engaged.-Youwill
hear a click at this point. Theamplifiers are nowreadyto
use. Theamplifiers will be at temperatureandsoundtheir
best after approximately30 minutes.
2. Withthe preamplifier in the Muteposition, or volume
control fully attenuated, select a source. Turnthe volume
controlup to yourdesired listening level.
3. Understandingthe operationof these amplifiers is very
e.asy. Equallyimportantis an understandingof the care
that should be exercised whenoperating the systemas a
whole,in relation to the enormouspoweroutput of the
MDA-300/500s.Simple mistakes, such as switching
betweenactive sources without mutingthe preampfifier
9utput, or bumping/miscuinga cartridge, can generate
large transients at lowfrequencies.Withthis type of
transient the MDA-300/500scan generate enoughpower
to damagemostloudspeakers. AII switching of sources
should be donewith the preamplifier level e~ther muted
or fully attenuated. Inputs to the amplifier shouldnot be
changedwhilethe amplifier is on.
NOTE:Care must be taken whensetting high playback
levels. Becauseof their tremendousreserve of-clean
power,KRELLamplifiers safely drive speakers to higher
soundpressurelevels than other amplifiers. Thisalso .
meansdriving the speakersto their fimit. Alwaysturn the
level downat the first sign of distortion.
Whenturning the systemoff, the amplifiers should
ALWAYSbe first. This avoids the possibility of a turn-
off transient fromsomeother componentgetting to the
speakers.
8

E PROTECTIONCIRCUITRY
Thereare no fuses in the MDA-300/500s.Theamplifiers
are protected by a series of non-intrusive, opto-coupled
circuits that constantlyevaluatethe amplifier’s operation.
Appropriateprotecti’ce action exists for DCconditions,
stiort circuit, oscillatidn, ACpoweranomalies,high
groundresistance and out-of:phase ground. Collectively
tlae protection circuitry is designedto avoiddamageto
the amplifiers or speakerscausedbyother d.efecti~e
components,faulty wiring, mishandlingof the systemoy
amplifierfailure. Whenthe protection, circuit is engage(l,
the a.mplifierswill shut off andshort tlaeir output.After
resolving either the input or outputproblemthe amplifi-
ers can15eturnedon.
Theamplifiers also havecircuit breakers ontheir
backpanelfor the ACpower.Shouldthe button in the
center of the breakerpopout, pushit in to reset the
breaker.If the amplifiersstill donot comebackon, call
Krell Industries.
9

H. REAR PANEL DESCRIPTIONS
All descriptions are for eachamplifier chassis
INPUTS:
Balancedvia 3 pin XERconnector
Single ended via RCAconnector
XLR PIN CONFIGURATION
p!n 1 Shield (ground)
p.ln 2 Non-invertingor 0 degrees(hot)
pan3 Inverting or 1-80degrees
OUTPUT:
Twopairs of five-waybindingposts in parallel
OTHER:
Standard ACreceptacle
20 ampcircuit breaker
OPTIONS:
Black Faceplate
11

I. QUESTIONS AND ANSWERS
Q. ShouldI leave the MDA-300/500on at all times?
A. Althoughyou could leave the MDA-300/500on at all
times without fear of damageto the amplifier, werecom-
mend.30 minutesof warm-upbefore critical listening and
switchingthe amplifier off whennot in use.
~WhenIpush the powerbutton on the front of the
DA-300/-500,the amplifier doesn’t turn on. What
shouldI c[o?
A. Unplugthe amplifier from the ACreceptacle and
removethe input fromthe amplifier. Checkthe output
connections, then plugthe amplifier backin. Checl~the
circuit breakeronthe-backof the unit andreset it if nec-
essary. Pushthe powerbutton onthe front panel. If the
problempersists, unplugthe unit andcall yourdealer or
Krell industries.
Q. WhenI turn the amplifier on there is a loud hum
throughthe speakers. Therewasnever a humbefore the
MDA-300/500was in the system. Whatshould I do?
A. Often whena newcomponentis introduced into an
audio systema hummay15ec.omepresent. This is often
causedby_a groundloopin tlae system._Tryputting a 3
prongto 2 prongACadaptor (cheate.r plug) on the
powercord, lifting the groundfromthe unit. This sho.uld
makethe humdisappear. If not, try another adaptorelse-
wherein the system.
NOTE:Alwayskeep one major audio component
grounded.
NOTE:Eventhoughthe groundis lifted fromthe power
amplifier,it .is still gr~ou.ndedvia the interconnectcables
throughoutthe rest ot tt~e system.
Q. CanI use special audio powerc~rds on the MDA-300
or MDA’500? ’
A. Youcan experimentwith special powercords as long
as they are groundedon both ends and meetthe
amplifier’s I5 amppowerrequirement.
12

Q. After the amplifier is on for about onehour it be-
comesvery hot. Is this normal?
A. Yes. Dueto the high bias design of the MDA-300/500
it will becomequite warm.After approximately 1 hour
the amplifier will be at its optimumoperating tempera-
ture. If the amplifier should-have a severe temperature
inbalance betweenthe. left and right channel, unplugthe
unit and call your aut~0rized dealer or Krell.
Q. I tried a newpreamplifier in myaudio system and
whenI turned the unit on the MDA-300/500shut off. Is
the amplifier defective?
A. Morethan 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 andthe speakers.
There also could tiave been a bad cable connection or
excessive DCoffset comingfrom the output of the pre-
amplifier. Before turning tile amplifier on, checkthe
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
1Kat 8 ohms
less than .2%
20Kat 8 ohms
less than .4%
INPUT IMPEDANCE
47,000 ohms(47K)
INPUT SENSITIVITY
2.5 volts for 300wattsout
OUTPUT IMPEDANCE
.2 ohms
OUTPUT VOLTAGE
139volts peakto peak
OUTPUT POWER
All read!ngs
are continuousoutput
power, per channeI
8 ohms 300 watts
4 ohms 600 watts
2 ohms 1200watts
1 ohm 2400watts
DIMENSIONS
19.0" WIDE
!9.5" DEEPwith handles
8.5" HIGHwith feet
SHIPPING WEIGHT
105 pounds
MDA-500
GAIN
26dB
SIGNAL-TO-NOISE
106dBunweighted
THD
1Kat 8 ohms
less than .2%
20Kat 8 ohms
less then .5%
INPUT IMPEDANCE
47,000 ohms(47K)
INPUT SENSITIVITY
3.2 volts for 500wattsout
OUTPUT IMPEDANCE
¯ 15ohms
OUTPUT VOLTAGE
179volts peakto peak
OUTPUT POWER
All readings
are continuous output
power, per channeI
8 ohms 500 watts
4 ohms 1000watts
2 ohms 2000watts
1 ohm 4000watts
DIMENSIONS
19.0" WIDE
24.0" DEEPwith handles
8.5" HIGHwith feet
SHIPPING WEIGHT
144 pounds
14

K. WARRANTYAND SERVICE
INFORMATION
Thereare no user-serviceable parts inside the MDA-300/
500. TheMDA-300/500has a limited warranty of f~ve
yearsparts andlabor. Returnfreight is includedin ~the
warranty.Thewarrantyperiod b.egins on thee date ot
p_u_rchaseandis activated withthe return ot the enclosed
Warran.tyCardanda copyof the Sales receipt. Please
return the warrantycardimmediate!yafter successful
installation andoperation are completed.
Thewarrantyfor Krell productsis valid ~n~in t.he coun-
try to whichthey wereoriginally shippedandat tlae
factory. If youtfiink there are problemswithyourunit
pleasecontact yourdealer, distributor or the factory
immediately.
Plea~s.edonot returl?, anyunit to KRELLfor repair with-
out first calling to discussthe problemandto ot~tain a
R..etu..rn Authorizationnumber.-Freightto the factoryor
distrit~utor is yourresponsibili.ty. R.~turnfreight to you
will bepaidb}, the factoryor dlstrit)utor.
Anyunauthorized updates or modifications performedto
the unit will voidthe warranty.
15

KRELL INDUSTRIES
35 HIGGINSDRIVE MILFORDCT 06460
SALES203-874-3139 FAX[phone]
COPYRIGHT1992 KRELLINDUSTRIES
(MDA9204)