Warranty
Knoll Systems warrants MA1250 amplifiers sold in the USA and Canada by
authorized Knoll dealers to be free of defects in materials and workmanship. This
warranty extends for three full years from the date of purchase by the original
consumer. Any products returned to Knoll Systems and found to be defective by
Knoll Systems within the warranty period will be repaired or replaced at Knoll
Systems decision, at no charge. Knoll Systems will not be responsible for the
actual cost of installation or removal of the product, nor for any incidental or
consequential damages. Some states do not allow the exclusion or limitation of
incidental or consequential damages, so the above limitation may not apply to
you. This warranty gives you specific legal rights. You may have additional legal
rights that vary from state to state.
MA1250 Amplifier
Installation Instructions v1.2
12 Channel Amplifier
Warning: To be installed and/or used in accordance with appropriate
electrical codes and regulations.
Description: The MA1250 is a member of the long line of Knoll multi-
channel amplifiers. Designed primarily for the custom install industry, it
is used to power speakers with different or similar sources in multiple
rooms. With 12 channels rated at 50 watts per channels at 8 ohms, the
MA1250 packs some serious punch. Each channel has a gain control.
The MA1250 can be turned on and off via the front panel power switch
or via the 12 VDC trigger. MA1250 channels 3-12 can be linked to
channel 1-2 individually using the link switches. MA1250 amplifiers
designed to meet the amplifier needs of custom installed systems
where high-quality sound is a specific requirement.
Specifications:
Inputs
12 Gold RCA jacks with adjustable gain
50k ohms
Input impedance
Outputs
detachable plug
Output power
Peak output power
Ideal impedance
Frequency response
S/N ratio
50 watts RMS per channel (8 ohms)
100 watts per channel (8 ohms)
4 - 8 ohms
Key Features:
1. Size efficiency. The MA1250 consists of a total of 12 power
amplifiers in one 3-1/2” high enclosure. Each power amplifier
channel can deliver 50 watts RMS into an 8-ohm load.
2. Automatic protection circuitry. Each MA1250 channel is
individually and fully protected against low impedance,
overheating, overloading, overvoltage and undervoltage. The
protection circuitry automatically restores the amplifier channel
as soon as its parameter returns to the safe operating area.
3. Individual input gain adjustment. Each channel features
an input gain adjustment pot to adjust each channel for gain
and speaker sensitivity variations. The gain adjustments are on
the rear of the MA1250 so installers normally set the gain.
4. External power on/off. The MA1250 can be turned off and
on by external controllers. To activate external power on, apply
a 12 VDC current to the trigger jack (the MA1250 power switch
is in the off position for external power control).
10 Hz - 40 kHz +/- 1dB (1w)
over 105 dB A weighted (50 watts)
less than 0.1% 20 Hz to 20 kHz
less than 0.01% 60 Hz 7 kHz 4:1 (SMPTE)
12 VDC 35mA on 3.5mm mono jack
17" x 3.5" x 11.5" (432 x 89 x 292mm)
quiet 26 dBA
THD distortion
IMD distortion
Trigger control
Dimensions
Fan Noise
Power
750 watts at 117 VAC or 230 VAC
21 lbs (9.5 kg)
Weight
Note: Specifications subject to change without notice.
5. Stackable 17" chassis.
6. Link Feature. Certain installations require that some or all of
the stereo channels play the same content. Instead of using Y
cords, "link" cascades any or all of channels 2-6 to channel 1
(l/r).
Knoll Systems
145 Tyee Drive Point Roberts, WA 98281
12140 Horseshoe Way, Richmond, BC V7A 4V5
Tel: (604) 272 4555, fax (604) 272 5595
Made in Canada
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Knoll Systems service information
The MA1250 amplifier does not contain any user serviceable parts
inside. If you suspect a problem that may require servicing, contact us
Installation
Installing the MA1250 should be relatively easy. With a bit of
planning, the MA1250 will give trouble free service for years.
1. The most important consideration when installing the
MA1250 is cooling. The MA1250 has a lot of power packed into
a small chassis size. When installing it in an equipment stack, it
should be the top component. It needs at least 3"-5" of space
above the amplifier to allow for adequate convection cooling.
Troubleshooting
If a problem is encountered with the MA1250, the most
expedient procedure is to locate the problem and if possible
repair it before requesting service. Be sure to carefully check
other system components such as controllers, CD players,
volume controls, wiring, speakers, etc. that may be at fault.
2. Amplifiers should always be the top components in system.
Problem
Action
Power LED does
1. Check that the MA1250 is plugged in.
3. If MA1250 channels frequently shutdown due to overheating,
install a fan directed up from the MA1250 bottom center.
not light - no sound 2. Test the AC outlet with a lamp.
3. If remote on/off is used, check that
the trigger voltage is at 12 VDC.
4. Never operate the MA1250 on its side, as the cooling
potential drops significantly when operated on the side.
4. Check MA1250 power button on (in).
Sound cuts out
1. Verify speaker impedance is 4-16 ohms.
Changing speakers may be required.
2. Check if the MA1250 feels hot. If it's
hot increase cooling - see Installation.
5. Connect the MA1250 inputs to the source component outputs
with good quality, short as possible RCA jack cables. Connect
each channel individually.
6. Connect the MA1250 speaker outputs to speakers using good
quality speaker wire. Minimum 16 gauge copper wire is
recommended with 14 gauge minimum for runs over 30' (10m).
Sound is distorted
1. Turn the volume down.
2. Check speakers for damage.
3. Check inputs for proper levels.
MA1250 gain and source output level
may have to be adjusted.
Note: Ideally the MA1250 likes 6-8 ohm loads. Connecting
to 4 ohm loads won't hurt the MA1250 but those channels
connected to 4 ohm loads may occasionally shutdown due
to overloading. Never connect the MA1250 to less than 4
ohms.
4. Speakers may be less than 4 ohms.
MA1250 does
not turn off
1. Push MA1250 power switch off (out)
2. If trigger is being used, power switch
needs to be set to off (out) position
or amp is on all the time.
7. Individually adjust the channel gains as required. Ideally, all
gains are fully on (fully clockwise).
3. Try disconnecting trigger jack.
8. Make sure the speakers in each room are connected in phase
with the amplifier + going to the speaker + . Out of phase
speakers give unstable imaging and poor bass response.
Trigger does not
work
1. Measure trigger voltage with a volt
meter. It needs to be 11-15 volts DC
to work (current is about 35mA total
per amp). See page 5 for details.
9. Connect trigger if being used to a 12 VDC source (about
35mA) using a 3.5mm mono jack. 5 VDC triggers will not work.
Speaker pops when 1. Speaker may need resistor placed
amp turned on or off
across terminal. Suggest 2k0 1/4 w.
Discharges speaker internal cap.
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10. Connect the AC power into an outlet that supplies at least
six amps (750 watts) dedicated to each MA1250.
Caution: Never listen to sound that is distorted. If distorted
sound is heard, turn the volume down immediately or speaker
and/or amplifier damage could occur that is not covered by the
warranty. If this problem persists, contact your dealer.
The trigger is 12 VDC (35mA per MA1250) via 3.5mm
mono jack. 5 VDC trigger outputs will not work. To
connect the trigger to a receiver use a 12 VDC power
supply (we suggest Knoll PS1202 power supply with an
adaptor). Plug the power supply into the switched outlet
on the rear of the receiver. Connect the 12 volt wire to a
3.5mm mono jack. Plug the jack into the rear of the
MA1250. 12 VDC polarity is not important. Make sure the
amplifier power switch is off (out). When the receiver is
switched on, the MR1250 amplifier is switched on.
User adjustments and service: There are no user
adjustments on the MA1250. Your installer may make certain
gain level adjustments on the rear panel.
Caution: The MA1250 contains no user serviceable parts, so do
not attempt to open or repair the MA1250. Refer servicing to a
qualified technician only or contact the factory for information.
12 VDC
Trigger
Input
Input
Input
2
1
3
4
6
5
Output
Output Output
Output Output
Output
L
L
L
Gain
Gain
Gain
Gain
Gain
Gain
R
R
R
4R
2R
3R
4L
5R
6R
6L
1L1R
2L
3L
5L
Link (out position)
cascades channel 1
to chanels 2-6
120 VAC
8 Amps
MA1250
The Link button is normally set to the in
position to give all six stereo inputs individual
sources. When the Link button is set to the
out position, that input Left/Right is linked or
cascaded to input #1 (without the use of Y cords). Any or
all combination of linked inputs 2 to inputs 6 are possible.
When all inputs are linked to input 1 the input impedance
is about 4000 ohms.
Caution: NEVER connect the
MA1250 to impedances
less than 4 ohms or amplifier
damage not covered
by the warranty may occur.
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