Knoll MX1255 User Manual

Warranty

Inputs

12 Gold RCA jacks with adjustable gain

Input impedance

50k Ω

Outputs

detachable plug

Output power

55 watts RMS per channel (8 Ω)

Bridged Power (channel 6)

180 watts RMS (8 Ω only)

Peak output power

100 watts per channel (8 Ω)

Ideal impedance

4 - 8 Ω

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)

Knoll Systems warrants MX1255 amplifiers sold in the USA and Canada by
authorized Knoll dealers to be free of defects in materials and manufacturing.
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:

Note: Specifications subject to change without notice.

Knoll Systems

145 Tyee Drive Point Roberts, WA 98281
14-7163 Vantage Way, Delta BC V4G 1N1
Tel: [phone], fax [phone]

Made in Canada/Fabrique au Canada

MX1255 Amplifier

12 Channel Amplifier
Installation Instructions v7.3

Warning: To be installed and/or used in accordance with appropriate

electrical codes and regulations.

Description: The MX1255 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 55 watts per channels at 8 Ω, the
MX1255 packs some serious punch. Each channel has a gain control.
The MX1255 can be turned on and off via the front panel power switch
or via the 12 VDC trigger. MX1255 channels 2-6 can be linked to
channel 1 individually using the link switches. MX1255 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 MX1255 consists of a total of 12 power

amplifiers in one 3-1/2” high enclosure. Each power amplifier
channel can deliver 55 watts RMS into an 8-Ω load.

2. Automatic protection circuitry. Each MX1255 channel is
individually and fully protected against low impedance,
overheating, overloading, over voltage and under voltage. 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.

4. External power on/off. The MX1255 can be turned off and
on by external controllers via its 12 VDC trigger jack.

5. Stackable 17" chassis. 19” rack ears available.

6. Link Feature. Certain installations require that some or all of

the stereo channels play the same content. Instead of using Y
cords, the Knoll "link" cascades any or all of channels 2-6 to
channel 1 (L/R).

7. Bridgeable. Channel 6 can be bridged giving 180 watts RMS
into an 8 Ω load for use with subwoofers and speakers that need
more power.

Important Safety Instructions:

1) Read these instructions.

2) Keep these instructions.

3) Read all warnings.

4) Follow all instructions.

5) Do not use this apparatus near water.

6) Clean only with dry cloth.

7) Do not block any ventilation openings. Install in accordance with the manufacturer’s
instructions.

8) Do not install near any heat sources such as radiators, heat registers, stoves, or
other apparatus (including amplifiers) that produce heat.

9) Do not defeat the safety purpose of the polarized or grounding-type plug. A
polarized plug has two blades with one wider than the other. A grounding type plug has
two blades and a third grounding prong. The wide blade or the third prongs are
provided for your safety. If the provided plug does not fit into your outlet, consult an
electrician for replacement of the obsolete outlet.

10) Protect the power cord from being walked on or pinched particularly at plugs,
convenience receptacles, and the point where they exit from the apparatus.

11) Only use attachments/accessories specified by the manufacturer.

12) Use only with the cart, stand, tripod, bracket, or table specified by the
manufacturer, or sold with the apparatus. When a cart is used, exercise caution when
moving the cart/apparatus combination to avoid injury from tip-over.

13) Unplug this apparatus during lightning storms or when not used for long periods of
time.

14) Refer all servicing to qualified service personnel. Servicing is required when the
apparatus has been damaged in any way, such as power-supply cord or plug is
damaged, liquid has been spilled or objects have fallen into the apparatus, the
apparatus has been exposed to rain or moisture, does not operate normally, or has
been dropped.

15).Under no circumstances should the output terminals of the amplifier be short­circuited.

16).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.

17) Where an all-pole MAINS SWITCH is used as the disconnect device, the location
on the apparatus and the function of the switch shall be described, and the switch shall
remain readily operable.

18) A push button is used to turn the power off and on.

19) A LED is used to show when the apparatus is powered on.

CAUTION: These servicing instructions are for use by qualified service personnel only.
To reduce the risk of electric shock do not perform any servicing other than that
contained in the operating instructions unless you are qualified to do so.

WARNING: This product may contain 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
prongs, 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 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.