Hollywood 24CX-3 User Manual

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© 2003 TDM Audio, Inc. 
Electronic Crossover Owner’s Manual 
Page 22 
two different grounds. The problem is most often caused by a single piece of equipment 
grounded to two different power sources that are located some distance apart. For example, a 
mixing console is plugged into a grounded outlet at the back of an auditorium, and 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.  
A problem like this can be fixed in several different ways. The mixer ground could 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 could 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 publicly. 
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 
person 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 setup 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 24CX series crossover 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 24CX series crossover 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 24CX series crossover 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 support@tdmaudio.com 
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 24CX series crossover.