Knoll MA252 User Manual

Trigger does not 1. Measure trigger voltage with a voltmeter. It

Line level inputs /outputs

Gold RCA jacks

Input impedance

50k ohms

Speaker inputs /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 95 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 11.75" (431.8 x 89 x 298mm)

Video trigger

0.5 v p-p minimum

Power

175 watts at 117 VAC or 230 VAC

Weight

11 lbs (5 kg)

work needs to be 11-16 volts DC to work (current is

about 35mA total per amp). See page 5 for details.

Speaker pops 1. Speaker may need resistor placed across terminal.
when MA252 is Suggest 2000 ohm 1/4 watt. This discharges the
turned on or off speaker internal capacitor if it has one.

Warranty

Knoll Systems warrants MA252 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:

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

MA252

Stereo Amplifier
Installation Instructions v1.0

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

electrical codes and regulations.

Description: Designed primarily for custom installations, the MA252 is
used to power stereo speakers, usually in a single room. Each channel
has a gain control. The MA252 can be turned on and off using the front
panel power switch, composite video detection, when music is sensed
or the 12 VDC trigger. A special feature of the MA252 is that whole
house music from another amplifier can be heard on the speakers
connected to the MA252. When the local source needs amplifier power
the MA252 senses this, disconnects the other amplifier and amplifies
the local source. The MA252 amplifier is designed to meet the amplifier
needs of custom installed systems where high-quality sound is a
specific requirement.

Key Features:

Manual and Automatic Power On and Off. The MA252 stereo

power amplifier is designed to be turned on when a video signal
is detected, music inputs are sensed, a 12-volt trigger is
activated or the front panel power switch is pushed on. Power
off is automatic in all modes except the front panel power
button.
Whole house music override. In homes, yachts, businesses
and motor home applications (typically with plasma or large
screen TV's) the MA252 features amplifier inputs so that whole
house music system can be heard on the local speakers (without
the MA252 turned on). When the local source (TV, dish, etc.)
needs amp power, the whole house music switches off
automatically and the MA252 amplifier plays the local source.
Automatic protection circuitry. Each MA252 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.
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 MA252 so installers normally set the gain.

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.

Knoll Systems service information

The MA252 amplifier does not contain any user serviceable parts inside.

If a problem is encountered with the MA252, 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. If you suspect a
problem that may require servicing, contact us at
www.knollsystems.com/contact.html, or by phone at
800-566-5579 or 604-272-4555.

Problem Action

Power LED does 1. Check that the MA252 is plugged in.
not light - 2. Test the AC outlet with a lamp.
no sound 3. If remote on/off is used, check that
the trigger voltage is at 12 VDC.

4. Check MA252 power button on (in).

Sound cuts out 1. Verify speaker impedance is 4-16 ohms.
Changing speakers may be required.

2. Check if the MA252 feels hot. If it's
hot increase cooling - see Installation.

3. If music sense is selected on the rear, the
music level may be too low to activate and

hold the amp on. Turn the source volume up
and the MA252 gain controls down to
compensate. Connect a 12 VDC trigger
(trigger mode) or contact Knoll for information
on defeating the music sense mode.

Distorted sound 1. Turn the volume down.

2. Check speakers for damage.

3. Check inputs for proper levels. MA252 gain
and source output level may need adjusting.

4. Speakers may be less than 4 ohms.

MA252 does 1. In trigger mode, make sure trigger power is
not turn off turning off by removing trigger plug on rear.

Front panel power switch needs to be OUT.

2. In music sense mode, turn off source music
components. If the MA252 doesn’t turn off after
about 2 minutes remove the RCA input plugs. If

the MA252 turns off, reconnect the RCA plugs and
turn down the sensitivity.

…continued on last page.