Knoll Systems MR-1250-A Owners manual

MR1250a
MR1250f

12 Channel
Power Amplifier

OPERATION

MANUAL

Version 2.4

Congratulations and thank you for choosing the Knöll
MR1250a power amplifier. The MR1250a is designed to
meet the amplifier needs of multi-zone systems where
high quality sound is a specific requirement.

Key Features:

1. Size efficiency. The MR1250a consists of a total of
12 power amplifiers in one 3-1/2" high enclosure. Each
power amplifier channel can deliver 50 watts RMS.

2. Automatic protection circuitry. Each MR1250a
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 MR1250a so
installers normally set the gain.

4. External power on/off. The MR1250a can be
turned off and on by external controllers such as the
MR640. To activate external power on, apply a 12VDC
current to the trigger jack (the MR1250a power switch is
in the off position for external power control).

5. Stackable 17" chassis. Optional RK1250 rack kit.

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).

7. Optional fan version. For installations that require
a lot of "heavy" use we recommend the MR1250F with an
internal fan. A fan will help to avoid early protection
system distortion.

2

Installation

Installing the MR1250a should be relatively easy. With a bit of
planning, the MR1250a will give trouble free service for years.

1. The most important consideration when installing the
MR1250a/f is cooling. The MR1250a 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.

2. When installing the MR1250a in a rack we suggest adding a
3-1/2" blank above and below the MR1250a. In multiple
MR1250a installations, plan for a 3-1/2" blank (double)
between each MR1250a and a 3-1/2" blank on the top and
bottom. Amplifiers should always be the top components in a
rack system.

3. The RK1250 is an optional 19" EIA rack mount kit for the
MR1250a and MR1250f.

4. If MR1250a channels frequently shut down due to
overheating, install a fan directed up from the MR1250a
bottom center or change it for a MR1250f.

5. Never operate the MR1250a in its side, as the cooling
potential drops significantly when operated on the side.

6. Connect the MR1250a inputs to the source component
outputs with good quality, short as possible RCA jack cables.
Connect each channel individually.

7. Connect the MR1250a 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).

Note: Ideally the MR1250a/f likes 6-8 ohm loads. Connecting
to 4 ohm loads won't hurt the MR1250a but those channels
connected to 4 ohm loads may occasionally shut down due to
overloading. Never connect the MR1250a to less than 4 ohms.

installation continued...

9. 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.

10. Connect trigger if being used to a 12VDC source (about
35mA) using a 3.5mm mono jack. 5VDC triggers will not work.

11. Connect the AC power into an outlet than can supply at
least six amps (750 watts) dedicated to each MR1250a.

MR1250a/f 12 Channel Power Amplifier

Inputs: 12 gold RCA style with adjustable gain
Input impedance: 24 k ohms
Outputs: Gold 5 way Binding posts
Output power: 50 watts RMS per channel (8 ohms)
Peak output power: 100 watts RMS per channel (8 ohms)
Ideal impedance: 4-8 ohms
Freq. response: 10 Hz - 40 kHz +/- 1 dB (1w)
S/N ratio: over 105 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: 12VDC on 3.5mm input jack.
Power: 750 watts 117 VAC
Dimensions: 17" x 3.5" x 10.5"
Weight: 21 lbs (9.6 kg)

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.

User Adjustments and Service: There are no user

adjustments on the MR1250a. Your installer may make certain
gain level adjustments on the rear panel.

8. Individually adjust the channel gains as required. Ideally, all
gains are fully on (fully clockwise).

3

Caution: The MR1250a contains no user serviceable parts, so

do not attempt to open or repair the MR1250a. Refer servicing
to a qualified technician only or contact the factory for
information.

4