© 2003 TDM Audio, Inc.
Graphic Equalizer Owner’s Manual
Page 15
the power amplifiers are plugged into a different outlet 100 feet away at the stage. The mixing
console is connected by shielded cable to the amplifiers and the shield is grounded. This causes
both the mixer and the amps to be individually grounded, and each gets another ground from the
other through the shielded cable. The result is a small, 60 Hz AC current flowing through the
shield.
A problem like this can be fixed in several different ways. The mixer ground can be lifted. This
is commonly done by plugging the mixer’s three-prong plug into a two-prong grounding adapter
(you can get these at any hardware store), and plugging that into the outlet. This effectively
disconnects the mixer’s ground lead from the outlet so that the mixer is now grounded only to
the amplifiers. The ground can also be lifted at the amplifiers so that they are grounded only to
the mixer. If the cable connecting the mixer to the amplifiers is a balanced (3-wire) type, the
ground can be floated at either end of this cable by disconnecting the wire connected to pin 1 of
the XLR adapter at one end or the other (but not both). Sometimes, because of the particular
setup, you will have to try several of these options before finding one that works.
CAUTION: Check local codes and regulations for rules
pertaining to electrical grounding. It may be illegal in some
places to lift the ground of a piece of equipment—especially if
this piece of equipment is installed in a public venue.
Another common cause of ground loops is direct input (or DI) boxes. These let you plug an
instrument such as a guitar or bass directly into a microphone input. The problem is that the
musician playing the guitar or bass might be using an amplifier or some other signal processing
equipment on the stage that is plugged into a grounded outlet. This creates a ground loop
between their rig and the grounded outlet that the mixing console is plugged into. Fortunately,
many DI boxes have a ground lift switch that you can use to break this ground loop. Because
they are so convenient, ground lifts on DI boxes are often the first option tried when a hum or
buzz surfaces.
If you suspect that there is a problem with your TDM 15GE-2 equalizer that is causing a hum or
buzz, try removing the unit from the system and plugging its outputs directly into power
amplifiers with speakers attached. Make sure that the TDM 15GE-2 equalizer is plugged into the
same electrical outlet as the amplifier. If the hum or buzz is still present, there might be a
problem with the unit. In this case, contact your vendor, or call TDM for support and/or service
(see
Contacting TDM
). If the hum or buzz is not still present, the problem is somewhere else in
the system, and is probably a ground loop.
Contacting TDM
If you have a problem with your TDM 15GE-2 equalizer that you cannot solve using this
troubleshooting guide, contact the vendor where you purchased the unit. If you need further
assistance, you can call TDM at (818) 765-6200 during normal business hours (9 AM to 5:00 PM
Pacific time). Our FAX number is (818) 765-8262. Our email address is [email protected]
and our Web site is TDMAUDIO.COM. Your satisfaction is our business, and we are happy to
help you get the most out of your TDM 15GE-2 equalizer.
