Knoll Systems MA252 User Manual download pdf (Page 3)

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.

Installation

Installing the MA252 should be relatively easy. With a bit of

planning, the MA252 will give trouble-free service for years.

1. The most important consideration when installing the

MA252 is cooling. The MA252 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 MA252 in a rack, we suggest adding a

3-1/2" blank above and below the MA252. Amplifiers should

always be the top components in a rack system.

3. If MA252 channels frequently shutdown due to overheating,

install a fan directed up from the MA252 bottom center.

4. Never operate the MA252 on its side, as the cooling potential

drops significantly when operated on the side.

5. Connect the MA252 inputs to the source component outputs

with good quality, short as possible RCA jack cables. Connect

each channel individually.

6. Connect the MA252 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 MA252 likes 6-8 ohm loads. Connecting

to 4 ohm loads won't hurt the MA252 but it may occasionally

shutdown. Never connect a MA252 to less than 4 ohms.

Do not attempt to mono bridge the MA252.

7. 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.

8. If connecting the MA252 to a whole house sound

system or another amplifier make sure that the other

amplifier is a common ground amplifier and that you use

good quality speaker wire, minimum 16 gauge.

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Knoll Systems MA252 User Manual Page 3

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