Knoll MA250 User manual

Stereo Power Amplifier
Version 1.1
INSTALLATION
AND OPERATION
MANUAL
MA250
2
CongratulationsandthankyouforchoosingtheKnöll
MA250power amplifier. The MA250is designed to meet
the amplifier needs where high quality sound is a specific
requirement.
Key Features:
1. Manual and Automatic Power On and Off.
The MA250stereo power amplifier is designed to be
turned on when a video signal is detected, music inputs are
sensed, a 12 volt trigger is activated or the front panel
power switch is pushed on. Power off is automatic in all
modesexceptthefrontpanelpowerbutton.
2. Whole house music override.In homes, yachts,
businessesandmotorhomeapplications(typicallywith
plasma or large screen TV's) the MA250features
amplifierinputs sothatwhole housemusicsystem canbe
heard on the local speakers (without the MA250turned
on).Whenthelocalsource (TV, dish, etc.) needs amp
power,thewholehousemusicisautomaticallyswitchedoff,
the MA250amplifier turns on and plays the local source.
3. Automatic protection circuitry.Each MA250
channel is individually and fully protected against low
impedance,overheating,overloading,overvoltageand
undervoltage.Theprotection circuitryautomatically
restorestheamplifierchannelassoonasitsparameter
returnsto thesafeoperatingarea.
4. Individual input gain adjustment.Each channel
featuresaninputgainadjustmentpottoadjusteach
channel for gain and speaker sensitivity variations. The
gain adjustments are on the rear of the MA250so
installersnormallysetthegain.
5. Stackable 17" chassis.Two MA250's can fit side
by side and stacked for applications requiring more than
twoamplifierchannels.

Installation
Installing the MA250should be relatively easy. With a bit of
planning, the MA250will give trouble free service for years.
1. The most important consideration when installing the MA250
is cooling. When installing it in an equipment stack, it should be the
topcomponent.Itneedsat least 3"-5" of space above the amplifier
to allow for adequate convection cooling.
2. When installing the MA250in a rack we suggest adding a
3-1/2" blank above and below the MA250. In multiple MA250
installations, plan for a 3-1/2" blank (double) between each MA250
and a 3-1/2" blank on the top and bottom. Amplifiers should always
bethetopcomponentsinaracksystem.
3. If MA250channels frequently shut down due to overheating,
installafandirectedupfromtheMA250bottomcenter.
4. Neveroperate the MA250on its side, asthecoolingpotential
drops significantly when operated on the side.
5.ConnecttheMA250inputstothesourcecomponentoutputswith
good quality, short as possible RCA jack cables.
6. ConnecttheMA250speaker outputstospeakersusinggood
quality speaker wire. Minimum 16 gauge copper wire is recommended
with 14 gauge minimum for runs over 30' (10m).
Note: Ideally the MA250is operated into 4-8 ohm speaker
loads. The MA250will not operate into 2 ohm loads.
Do not attempt to mono bridge the MA250
7. Make sure the speakers in each room are connected in phase with
theamplifier + going tothespeaker + . Outofphase speakers give
unstable imaging and poor bass response.
8.Ifconnecting theMA250tothewholehouse soundsystem,
connectthewholehouseamplifieroutputstotheMA250speaker
terminals labeled "AMP INPUTS" using good quality speaker wire.
9. If you are planning to use a video signal to trigger the MA250
power on and off, connect a good quality video wire with an RCA
jacktotheMA250inputlabeled"Video Input". Make sure the music
sensebuttonisinthe"OUT"position.
10. If the music sense or video input is being used to turn the
MA250poweron and off, switch themusicsense button to the
"OUT"position.Adjustthe"Sens"itivitypotontheMA250sothe
amp turns on when quieter passages are playing via the RCA line level
inputs.Adjustthe"Delay" pot sotheampturnsoffareasonable time
afterthemusichasstopped.
3
installation continued...
11.Tousethe 12VDC trigger toturntheMA250on/off,connectthe
triggertothe3.5mmtriggerjack.Setthemusicsenseswitchto"IN".
The front panel power switch is normally off (out position).
12. Individually adjust the channel gains as required. For best noise
and hum cancellation, all MR250gains should be on full (fully cw).
MA2502 Channel Power Amplifier
Inputs: Gold RCA style with adjustable gain
Inputimpedance: 20 k ohms
Outputs: Gold 5 way Binding posts
Output power: 50 watts RMS per channel (8 ohms)
Peak outputpower: 70 watts RMS per channel (4 ohms)
Idealimpedance: 4-8ohmspeakers
Freq.response: 10 Hz - 40 kHz +/- 1 dB (1w)
S/N ratio: over 95 dB A weighted 50 watts
THD distortion: <0.1% 20 Hz to 20 kHz
IMD distortion <0.01% 60 Hz 7 kHz 4:1 (SMPTE)
Trigger control: 12 VDC 35mA (3.5mm input jack)
Power: 140 watts 117 VAC
Dimensions: 8.5" x 3.5" x 10.5"
Weight: 8 lbs (3.6 kg)
Caution: Never listen to sound that is distorted. If
distortedsoundisheard,turnthevolumedownimmediately
or speaker and/or amplifier damage could occur that is
not covered by the warranty. If this problem persists,
contactyourdealer.
User Adjustments and Service: There are no user
adjustments on the MA250. Your installer may make
certainlevel and delay adjustments on the rear panel.
Caution: The MA250contains no user serviceable parts,
so do not attempt to open or repair the MA250. Refer
servicing to a qualified technician only or contact the
factory for information. 4

5
Troubleshooting
IfaproblemisencounteredwiththeMA250,themostexpedient
procedure is to locate the problem and if possible repair it before
requestingservice.Besuretocarefullycheckothersystemcomponents
such as controllers, CD players, volume controls, wiring, speakers, etc.
thatmay beatfault.
Problem Action
Power indicator does 1.CheckthattheMA250ispluggedin.
not light - no sound 2.Testthe ACoutlet witha lamp.
3.ConfirmtheMA250front power button is on
Soundcutsout 1.Verifyspeakerimpedanceis 4-16 ohms.
Changing speakers may be required.
2.Checkifthe MA250feels hot. If it's
hot, increase cooling - see Installation.
3.If music sense is selectedontherear,the
music may level may be too low to activate
and hold the amp on. Turn the source volume
up and the MA250gain controls down to
compensate. Connect a 12 VDC trigger
(trigger mode) or contact the Knöll factory
for information on defeating the music
sense mode.
4.In music or video sense mode,theMA250
rear delay time may have to be increased.
Soundis distorted 1. Turn the volume down
2.Checkspeakersfordamage.
3.Checkinputsforproperlevels.MA250
gain and the music source output levels
may have tobe adjusted.
4.Speakersmayhaveless than 4 ohmrating
and may need to be changed.
MA205doesnot 1. In trigger mode, make sure trigger power is
automaticallyturnoff turning off by removing trigger plug on rear.
Make sure front panel power switch is OUT.
2. In musicsense mode turn off source music
components. If the MA250doesn't turn off
after about 2 minutes remove RCA input
plugs. If the MA250turns off, reconnect
the RCA plugs and try adjusting the
sensitivity down.
In Canada:
12140 Horseshoe Way
Richmond, B.C. V7A 4V5
Knöll Systems
tel [phone]
fax [phone]
Knöll Systems, Richmond, BC & Point Roberts WA
CCOPYRIGHT 1998-2008, Knöll Systems, All Rights Reserved
In America:
145 Tyee Drive
Point Roberts, WA 98281
Limited Warranty
Knöll Systems warrants MA250amplifiers sold in the USA or Canada
by authorized Knöll dealers to be free from defects in materials and
workmanship.Thiswarranty extends forthreefullyearsfrom thedate
ofpurchasebytheconsumer.Anyproductsreturnedfreightprepaidto
Knöll Systems and found to be defective by Knöll Systems within the
warranty period will be repaired or replaced at Knöll Systems option,
at no charge. Knöll Systems will not be responsible for the actual cost
of installation or removal of the product, nor for any consequential or
incidental damages. Some states do not allow the exclusion or
limitation of incidental or consequential damages, so the above
limitation or exclusion may not apply to you. This warranty gives you
specific legal rights. You may have additional rights which vary from
state to state. Knöll products sold outside of the USA and Canada may
be covered by warranties provided by an authorized Knöll distributor.
Pleasecontactthedistributorin thecountrythat theKnöllproductwas
purchased.
*DMS,Powermatch, TransformerfreeandDigicom
are trademarks of Knöll Systems
Printed in Canada

12VDC
Trigger
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AC120V
140 watts
L
R
L GAIN R
IN OUT
Note 1: Ideal speaker impedance is 4-8 ohms.
MA250 REAR PANEL
4-16 ohms
AMPINPUTS TOSPEAKERS
L
R
+
+-
-
Sens Delay
Video
Input Music sense
Out=Active
Connect a video output
such as VCR or plasma
TV to here if the amp is
tobetriggered on when
a video signal is
present.Makesure the
music sense button is in
the out position. For
video sensing without
music sensing turn the
"Sens" pot fully
counterclockwise.
Connect stereo line
level inputs here
Connecttheseunbuffered
stereo line outs to other
amplifier inputs as needed
Connectthe"Amp Inputs"speaker
level inputs to the whole house
audio system or other amplifier
output. The signal here passes
directly to the speakers when the
MA250 amp isn't triggered or
turnedon Connect the "To Speakers" terminals
tothe4-8 ohmspeakers
Connectthis3.5mm
trigger jack if the
amp is to be triggerd
on when a 12 VDC
signal is present.
Polarity can be
reversed.
The music sense (auto turn
on when music is present)
buttonshouldbe OUT
(active)whentheMA250
power is to be triggered
eitherfrommusic sense
from the video signal.
Themusic sensebutton
shouldbeIN when theamp
is turned on and off with
either the front panel
power switch or the 12
VDC trigger.
Adjust the gain
when the system is
on. Best signal to
noise ratio is when
amp gains are on
full (clockwise).
Whenusingmusic sense
only, adjust Sens so the
amp turns on when source
music is at a medium low
volume. Sens is not used
for video on or trigger on.
For video sensing without
music sensing turn the pot
fully counterclockwise.
After amp is on, delay is
used to turn off amp
after source music ends.
Ideal delay adjustment is
about20-40seconds.This
feature is used with video
on or music sense only.