D.W. FEARN
VT-12 Microphone Preamplifer
20
Power
The VT-12 is designed to operate from 100, 120, or 220-240 volt, 50/60 Hz power. The unit
will be shipped set for the voltage specified in the order, but may be changed in the field if
necessary. A rear-panel, recessed slide switch changes the input voltage for either 120V or
230V. When the voltage is changed, the value of the fuse on the back panel must be changed
as well. (100V operation is also possible. Call the factory for detailed instructions). The
ground pin of the power cord is internally connected to the chassis. This configuration 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-12 is less suscep tible to grounding problems than many studio devices.
Connections
(see Figure 1)
The INPUT connectors are XLR-3 females wired with pin 1 ground, pin 2 “+” or “high,” and
pin 3 “-” or “low.” The input matches 150 ohm (nominal) microphones and is trans former
balanced.
The OUTPUT connectors are XLR-3 male wired with pin 1 ground, pin 2 “+” or “high,” and
pin 3 “-” or “low.” The VT-12 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 3AG-type 1 amp for 100 or 120 VAC operation, and 0.5 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-12 is operated in close proximity to AM, FM, and TV broadcast transmitters.
Figure 1. The VT-12 rear panel connectors
Summary of Contents for VT-12
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