O p e r at i o n
Circuit Breaker/Switch
The IT-20 II has a large black switch on the front panel that is both a precision circuit breaker and an on-off switch. If circuit breaker is tripped, manually reset the unit by turning it off and then back on, to restore power.
Ground Fault Interrupter (GFCI):
The GFCI on the IT-20 II’s front panel is a special kind of circuit breaker that detects an imbalance in the current flowing in the two hot legs. The “missing” current is presumed to be flowing through the ground conductor (the round pin on an AC outlet).
Ground current often indicates a dangerous partial or full short circuit. If an imbalance is detected, the GFCI trips and cuts off power not only to itself, but to all the IT-20 II’s outlets. If this occurs, the button on the GFCI marked “R” (Reset) will pop out. To restore operation, correct the fault and push the button in. You may test the proper operation of the GFCI at any time by simulating a ground fault by pushing the button marked “T” (Test). If the GFC1 is working properly, this will cause the “R” button to pop out and cut off power. You can restore operation after a test by pushing the “R” button in.
Ground Lift Switch
Ground loops are fairly common in many installations because AC cords with safety ground are rarely connected to a single low- resistance buss bar. When there is a significant difference in voltage between a source component’s neutral and ground and a load component’s neutral and ground, the buzz and hum associated with this type of ground current noise (or loop) may take place. Additionally,
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many AC noise contaminants may be present on the AC ground wire. For these reasons Furman’s IT-20 II contains a Ground Lift Switch.
This switch floats the output ground, eliminating ground noise and also, in many instances, the hum and buzz associated with ground loops. The IT-20 II’s GFCI protection circuit assures that even when utilizing the power conditioner in this mode, operation is safe and secure. In fact, even if a connected component has a catastrophic failure, less than 5 milliamps current imbalance from line to ground or neutral to ground will instantly disconnect the voltage output from the IT-20 II. This is far safer than any conventional 120 VAC outlet, and it has numerous noise reducing advantages.
However, ground wiring in any studio, broadcast or club environment can be complex. Because all 14 outlets of the IT-20 II are in parallel, it is still possible to have a ground loop if the two offending products are simultaneously connected to a single IT-20 II. Use of multiple IT-20 II’s may be necessary in extreme cases. Also, for studio and broadcast use, separating all digital processing products from all analog devices is highly recommended and can be accomplished by using two IT-20 II’s.
In the end, it is best to experiment with this switch. Whichever position yields the least noise or clearest audio / video recording or reproduction is the position that should be utilized.
B a l a n c e d AC P o w e r
In much the same way that balanced audio lines can reduce the pickup of hum and other types of electromagnetic interference (EMI), the use of balanced AC power lines in sensitive audio, video, or computer installations can make an enormous difference in system noise and signal integrity. But power distribution in North America, unfortunately, is not balanced. The distribution standards currently in use were derived from
