Contacting TDM

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.

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.

Electronic Crossover Owner’s Manual

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