Alesis ModFX Metavox Specifications download pdf (Page 43)

Troubleshooting

Avoiding ground loop noise

In today’s studio, where it seems every piece of equipment has its

own computer chip inside, there are many opportunities for

ground loop problems to occur. These show up as hums, buzzes

or sometimes radio reception and can occur if a piece of

equipment "sees" two or more different paths to ground. While

there are methods to virtually eliminate ground loops and stray

radio frequency interference, most of the professional methods are

expensive and involve installing a separate power source just for

the sound system. Alternatively, here are some helpful hints that

professional studio installers use to keep those stray hums and

buzzes to a minimum.

KEEP ALL ELECTRONICS OF THE SOUND

SYSTEM ON THE SAME AC ELECTRICAL

CIRCUIT.

Most stray hums and buzzes happen as a result of different parts

of the sound system being plugged into outlets of different AC

circuits. If any noise generating devices such as air conditioners,

refrigerators, neon lights, etc., are already plugged into one of these

circuits, you then have a perfect condition for stray buzzes. Since

most electronic devices of a sound system don’t require a lot of

current (except for power amplifiers), it’s usually safe to run a

multi-outlet box or two from a SINGLE wall outlet and plug in all

of the components of your system there.

KEEP AUDIO WIRING AS FAR AWAY FROM AC

WIRING AS POSSIBLE.

Many hums come from audio cabling being too near AC wiring.

If a hum occurs, try moving the audio wiring around to see if the

hum ceases or diminishes. If it’s not possible to separate the audio

and AC wiring in some instances, make sure that the audio wires

don’t run parallel to any AC wire (they should only cross at right

angles, if possible).

TO ELIMINATE HUM IF THE ABOVE HAS FAILED:

1. Disconnect the power from all outboard devices and

tape machines except for the Metavox, the mixer and

control room monitor power amp.

2. Plug in each tape machine and outboard effects device

one at a time. If possible, flip the polarity of the plug of

each device (turn it around in the socket) until the

quietest position is found.

3. Make sure that all of the audio cables are in good

working order. Cables with a detached ground wire will

cause a very loud hum!!

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Alesis ModFX Metavox Specifications Page 43

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