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
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