Knoll Systems MA-1250 Owners manual

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.

Specifications:

Inputs 12 Gold RCA jacks with adjustable gain

Input impedance 50k ohms

Outputs detachable plug

Output power 50 watts RMS per channel (8 ohms)

Peak output power 100 watts per channel (8 ohms)

Ideal impedance 4 - 8 ohms

Frequency response 10 Hz - 40 kHz +/- 1dB (1w)

S/N ratio over 105 dB A weighted (50 watts)

THD distortion less than 0.1% 20 Hz to 20 kHz

IMD distortion less than 0.01% 60 Hz 7 kHz 4:1 (SMPTE)

Trigger control 12 VDC 35mA on 3.5mm mono jack

Dimensions 17" x 3.5" x 11.5" (432 x 89 x 292mm)

Fan Noise quiet 26 dBA

Power 750 watts at 117 VAC or 230 VAC

Weight 21 lbs (9.5 kg)

Note: Specifications subject to change without notice.

Knoll Systems

145 Tyee Drive Point Roberts, WA 98281
12140 Horseshoe Way, Richmond, BC V7A 4V4
Tel: [phone], fax [phone]

Made in Canada

MA1250 Amplifier

12 Channel Amplifier Installation Instructions v1.0

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 multi­channel 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.

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).

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).

Precautions: The amplifier is a wideband design with

substantial power output capability. Certain precautions must be
taken to ensure proper operation.

1. Never expose the unit to moisture.

2. Never plug an input cable into the amplifier while the
amplifier is turned on.

3. Never apply the “thumb test” (touching the “hot” lead of
the input cable with your finger) to the tip of the input
cable or input jack of the amplifier. RF rectification
and/or hum will be created and could cause damage to
the loudspeakers. Knoll will not be responsible for
damage to the loudspeakers due to improper use of the
equipment.

4. Under no circumstances should the output terminals of
the amplifier be short-circuited.

5. Avoid restricting the airflow around the unit. Good airflow
is necessary to help ensure proper operation.

6. Be sure that the loudspeakers connected can handle the
output power of the amplifier at the loudspeakers rated
impedance. The warranty on the amplifier does not cover
damage to loudspeakers that have inadequate power
handling capabilities.

7. Do not stack other system components or any other
materials directly on top of the unit. The heat dissipating
system of the amplifier depends on free-flowing air
around the chassis.

SAFETY INSTRUCTIONS:

WARNING: TO REDUCE THE RISK OF FIRE OR
ELECTRIC SHOCK, DO NOT EXPOSE THIS UNIT
TO RAIN OR MOISTURE.

Read all the safety and operating instructions before connecting
or using this unit. All warnings on the unit and in this operating
manual should be adhered to. All operating and use instructions
should be followed.

WARNING: This product contains chemicals, including lead,
known to the State of California to cause birth defects or other
reproductive harm. Wash hands after handling.

Hum and noise

In most cases, one of the following suggestions should help you
solve a hum noise in your system. Please try these steps in the
order shown, proceeding from one step to the next if the prior
suggestion does not eliminate the problem.

Suggestion #1

To determine if a cable TV connection is responsible for the hum, first
turn off all the components. Disconnect the cable TV feed to your
system at the first place where it connects to your components.
Alternatively, disconnect the cable TV wire where it is connected at the
wall outlet. Turn your system back on, and listen if the hum has
disappeared. If removing the cable TV feed has eliminated the hum,
you will need to insert a Ground Loop Isolator (Knoll model GB634)
before reconnecting the cable TV feed, or contact your cable TV
operator to see if they can better isolate your cable feed.

Suggestion #2
Turn off all components in your system and then disconnect the input
cables at the amplifier. Turn the amplifier back on to see if the hum is
still present. If the hum disappears, the fault may be in the input cables
used. Try replacing them with cables that have better shielding, and
make certain that the input cables are not running on top of any AC
power cords. Change the cables one at a time to determine if one or all
cables are responsive. If the hum disappears when the input cables are
disconnected but returns after the cables are changed and the system
reconnected, your source device may be causing the problem.

Suggestion #3

Poor grounding of the electrical system in your home may also cause
ground loop problems, particularly when there are multiple components
with three prong, grounded, power cords. Unplug these components
one at a time, and see if one or all of them is causing the problem. The
ultimate solution to this type of problem is to rewire your house with an
isolated, star type-grounding configuration. Knoll understands that this
may be impractical and expensive. In some instances, the use of an
approved AC Power Isolation Transformer (Knoll model PLB200) of
sufficient capacity may solve this problem.

Warning: If you suspect that the grounding system in your
home’s electrical wiring is causing the hum problem, it is
important that you do not make any changes to the wiring. Only
a licensed electrician should make any changes to household
wiring and they must be made in full compliance with all local
building, safety and electrical codes.

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
at www.knollsystems.com/contact.html, or by phone at 800 566-5579.

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.
Problem Action
Power LED does 1. Check that the MA1250 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.

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.

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.

4. Speakers may be less than 4 ohms.

MA1250 does 1. Push MA1250 power switch off (out)
not turn off 2. If trigger is being used, power switch
needs to be set to off (out) position
or amp is on all the time.

3. Try disconnecting trigger jack.

Trigger does not 1. Measure trigger voltage with a volt
work meter. It needs to be 11-15 volts DC
to work (current is about 35mA total
per amp). See page 5 for details.

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.

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.

2. When installing the MA1250 in a rack, we suggest adding a
3-1/2" blank above and below the MA1250. In multiple MA1250
installations, plan for a 3-1/2" blank (double) between each
MA1250 and a 3-1/2" blank on the top and bottom. Amplifiers
should always be the top components in a rack system.

3. If MA1250 channels frequently shutdown due to overheating,
install a fan directed up from the MA1250 bottom center.

4. Never operate the MA1250 on its side, as the cooling
potential drops significantly when operated on the side.

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).

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.

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

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 12 VDC source (about
35mA) using a 3.5mm mono jack. 5 VDC triggers will not work.

11. Connect the AC power into an outlet than can supply 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.

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.

Gain

1L1R

Link (out position)
cascades channel 1
to chanels 2-6

Input

L

R

2

1

Output OutputOutput Output Output Output

Gain

2R

2L

Gain

3R

3L

MA1250

Input

3L4

R

Caution: NEVER connect the
MA1250 to impedances
less than 4 ohms or amplifier
damage not covered
by the warranty may occur.

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.

Gain

Gain

L

Input

5

6

Gain

12 VDC

Tri gg er

4L

4R

5L

5R

R

6L

6R

120 VAC
8 Amps

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.