When To Use Balanced Connectors; Avoiding Ground Loops - Alesis Q20 User Manual

When to use Balanced Connectors

There are three options for connecting analog audio to the Q20: 1/4Ó unbalanced,
1/4Ó balanced (TRS) and XLR balanced. If your source and destination use balanced
connectors, you should try to stay balanced throughout the chain. Balanced cables
have a higher signal level and have the ability to cancel out hum and noise, which
can make your mixes quieter. XLR connectors have the added bonus of locking into
place, a good idea if you need to move your effects rack from place to place.
Keeping this in mind, your order of preference when connecting the Q20 to a mixer
should be to use the XLR connectors first, then to use balanced 1/4Ó cables, then
unbalanced 1/4Ó cables if your mixer doesnÕt have balanced sends and receives.

Avoiding Ground Loops

In todayÕs complex studio 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 ÒseesÓ 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. Here are some easy helpful hints that a
professional studio installer might use to zap those stray hums and buzzes.
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 donÕt require a lot of current (except power amplifiers), itÕs 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
itÕs not possible to separate the audio and AC wiring in some instances, make
sure that the audio wires donÕt run parallel to any AC wire (they should only
cross at right angles, if possible).
TO ELIMINATE HUM IF THE ABOVE HAS FAILED:
A) Disconnect the power from all outboard devices and tape machines except
for the mixer and control room monitor power amp.
B ) 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.
C) 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!!
D) Keep all cables as short as possible, especially in unbalanced circuits.
If the basic experiments donÕt uncover the source of the problem, consult your dealer
or technician trained in proper studio grounding techniques. In some cases, a Òstar
groundingÓ scheme must be used, with the mixer at the center of the star providing
the shield ground on telescoping shields, which do NOT connect to the chassis
ground of other equipment in the system.
Q20 Reference Manual
Setting Up - Chapter 1
15