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.
Installing the MA250 should be relatively easy. With a bit of
planning, the MA250 will give trouble-free service for years.
1. The most important consideration when installing the
MA250 is cooling. The MA250 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 MA250 in a rack, we suggest adding a
3-1/2" blank above and below the MA250. In multiple MA250
installations, plan for a 3-1/2" blank (double) between each
MA250 and a 3-1/2" blank on the top and bottom. Amplifiers
should always be the top components in a rack system.
3. If MA250 channels frequently shutdown due to overheating,
install a fan directed up from the MA250 bottom center.
4. Never operate the MA250 on its side, as the cooling potential
drops significantly when operated on the side.
5. Connect the MA250 inputs to the source component outputs
with good quality, short as possible RCA jack cables. Connect
each channel individually.
6. Connect the MA250 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 MA250 likes 6-8 ohm loads. Connecting
to 4 ohm loads won't hurt the MA250 but it may occasionally
shutdown. Never connect a MA250 to less than 4 ohms.
Do not attempt to mono bridge the MA250.
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 MA250 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.