If the SDP-2 surround processor is not being mounted directly to this rack you may need to fabricate a ground
strap using 16 or heavier gage stranded wire with crimp-on ring lugs on the ends. Securely attach one end of the
ground strap to the SDP-2 using the center top cover retaining screw (found on the rear) as an attachment point.
Attach the other end of the ground strap to the metal equipment rack, in a central location, close to the other
devices in the rack. Make certain the finish on the rack is not insulating the connection.
If mounting the devices in a metal equipment rack is not an option, you may need to fabricate ground straps and
tie some or all of the devices together. Use 16 gage or heavier stranded wire, with crimp-on ring lugs at each end
of the wires. In this instance you will want to create a “star” grounding pattern. This means that each device will
have a ground wire attached directly to the same screw on the SDP-2 surround processor chassis. The center top
cover retaining screw on the back of the SDP-2 can be used for this purpose.
In some difficult installations, you may find it necessary to use a combination of both techniques described above.
Whatever the details of the particular installation, you must reduce all ground path resistance to as close to 0W as
possible. This is the correct method of eliminating hum. Do not try to “break” the ground by defeating the ground
connection on the AC plug. Although this sometimes appears to improve the audible hum, you are actually creat-
ing a potential for much more serious problems associated with floating grounds. Pops and clicks can be one
result. More serious, changes in the AC (from large appliances or peak power usage for example) can cause the
hum to return intermittently after you have left. This can be a real service headache.
Video Devices
Video devices represent a special challenge. This is because they are frequently connected to externally grounded
sources, like cable TV service. Projectors are never installed close to the other equipment, so they are almost
always plugged into a different AC circuit. This is a number 1 cause of ground current related problems. In the
case of cable TV service, one solution is to strap the incoming cable shield directly to the AC receptacle ground.
Another, perhaps easier approach is to install an isolation transformer.
If the source of hum is the remote AC connection of the projector, the best solution is to pull a 12-gage ground
wire along with the video cables. Connect this ground wire between the chassis of the projector and the SDP-2.
4.7
CALIBRATION WALK-THROUGH
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