D.W. Fearn VT-7 - Manual (Page 14)

D.W. FEARN
VT-7 Compression Amplifier
18
Power
The VT-7 is designed to operate from 100, 120, or 220-240 volt, 50/60 Hz power. The unit
will be shipped for the voltage specified in the order, but may be changed in the field if nec-
essary. (See the Maintenance section for detailed instructions on changing the primary volt-
age). The ground pin of the power cord is internally connected to the chassis. This configu-
ration is standard in professional equipment and is required by most electrical codes. A
grounding screw is provided on the back panel for installations that use separate chassis
grounding. If ground loop hum is detected, a careful check of the studio grounding scheme
is needed. The VT-7 is less susceptible to grounding problems than many studio devices.
Connections
The INPUT connectors are XLR-3 females wired with pin 1 ground, pin 2 “+” or “high,” and
pin 3 “-” or “low.” The input matches 600 ohm (nominal) line level (+4dBm nominal) bal-
anced or unbalanced signals. The input uses a top-quality Jensen line bridging transformer.
The OUTPUT connectors are XLR-3 male wired with pin 1 ground, pin 2 “+” or “high,” and
pin 3 “-” or “low.” The VT-7 is optimized for feeding balanced bridging inputs. (Virtually all
modern audio equipment has bridging inputs.) The output is transformer-balanced.
The “GND” terminal is for use when an external grounding scheme is utilized.
The Fuse is a 5x20mm-type slow-blow 2 amp for 100 or 120 VAC operation, and 1 amp for
220-240 volts.
The AC input connector is used with the mating line cord (supplied). For 120 VAC operation,
this cord is a Belden 17250 or equivalent.
The unit does not utilize any RFI filtering, and no RFI has been experienced, even when the
VT-7 is operated in close proximity to AM, FM, and TV broadcast transmitters.
Input and Output Connections
Gold-plated XLR connectors are used for inputs and outputs. The input connectors are
female and the outputs male.
All connectors are wired according to AES standard: pin 1 is ground (shield), pin 2 is “high”
or “+,” and pin 3 is “low” or “-.” A positive voltage on pin 2 of the input will result in a posi-
tive voltage on pin 2 of the output.
Grounding and Shields
A full discussion of proper studio wiring schemes is beyond the scope of this manual, but, in
general, whether the shield is connected to pin 1 of the output connector depends on the
standard in your studio. The shield should be connected to ground at only one end of the out-
put cable; however, although not recommended, the shields can often be connected at both
ends without a problem.