Knoll Systems Stereo Amplifier MR1250F User Manual

Warranty  
Knoll Systems warrants MR1250f 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.  
MR1250f 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 MR1250f 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  
MR1250f packs some serious punch. Each channel has a gain control.  
The MR1250f can be turned on and off via the front panel power switch  
or via the 12 VDC trigger. MR1250f 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 MR1250f 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 MR1250f 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 MR1250f so installers normally set the gain.  
4. External power on/off. The MR1250f can be turned off and  
on by external controllers. To activate external power on, apply  
a 12 VDC current to the trigger jack (the MR1250f 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  
 
Knoll Systems service information  
The MR1250f amplifier does not contain any user serviceable parts  
inside. If you suspect a problem that may require servicing, contact us  
Installation  
Installing the MR1250f should be relatively easy. With a bit of  
planning, the MR1250f will give trouble free service for years.  
1. The most important consideration when installing the  
MR1250f is cooling. The MR1250f 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 MR1250f, 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.  
Problem  
Power LED does  
Action  
2. Amplifiers should always be the top components in system.  
1. Check that the MR1250f is plugged in.  
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.  
3. If MR1250f channels frequently shutdown due to overheating,  
install a fan directed up from the MR1250f bottom center.  
4. Check MR1250f power button on (in).  
4. Never operate the MR1250f on its side, as the cooling potential  
drops significantly when operated on the side.  
Sound cuts out  
1. Verify speaker impedance is 4-16 ohms.  
Changing speakers may be required.  
2. Check if the MR1250f feels hot. If it's  
hot increase cooling - see Installation.  
5. Connect the MR1250f inputs to the source component outputs  
with good quality, short as possible RCA jack cables. Connect  
each channel individually.  
Sound is distorted  
1. Turn the volume down.  
6. Connect the MR1250f 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).  
2. Check speakers for damage.  
3. Check inputs for proper levels.  
MR1250f gain and source output level  
may have to be adjusted.  
Note: Ideally the MR1250f likes 6-8 ohm loads. Connecting  
to 4 ohm loads won't hurt the MR1250f but those channels  
connected to 4 ohm loads may occasionally shutdown due  
to overloading. Never connect the MR1250f to less than 4  
ohms.  
4. Speakers may be less than 4 ohms.  
MA1250 does  
not turn off  
1. Push MR1250f 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.  
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.  
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.  
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.  
 
10. Connect the AC power into an outlet that supplies at least  
six amps (750 watts) dedicated to each MR1250f.  
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 MR1250f) 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  
MR1250f. 12 VDC polarity is not important. Make sure the  
amplifier power switch is off (out). When the receiver is  
switched on, the MR1250f amplifier is switched on.  
User adjustments and service: There are no user  
adjustments on the MR1250f. Your installer may make certain  
gain level adjustments on the rear panel.  
Caution: The MR1250f contains no user serviceable parts, so do  
not attempt to open or repair the MR1250f. 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  
M
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  
MR1250f to impedances  
less than 4 ohms or amplifier  
damage not covered  
by the warranty may occur.  
 

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