D.W. Fearn VT-3 - Manual (Page 12)

VT-I/F Vacuum Tube Instrument Interface
D.W. FEARN
14
are required. The ground pin of the power cord is internally connected to the chas-
sis. This configuration is standard in professional equipment and is required by
most electrical codes. If ground loop hum is detected, a careful check of the stu-
dio grounding scheme is needed. The VT-3 is less susceptible to grounding prob-
lems than many studio devices.
The Fuse (2) is a 3AG-type 1 amp for 100/120 VAC operation, and 0.5 amp for
220 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.
CONNECTIONS (See Figure 1 and 2, page 15)
The VT-3 has two identical channels, labeled A and B. They may be used indi-
vidually or simultaneously. These instructions apply to either channel.
The musical instrument output connects to the front panel INSTRUMENT input
(6) via a standard 1/4 inch single-conductor (monaural) phone plug. The input is
unbalanced. Since the input cables carry very low level audio, it is important that
well-shielded cables are used. There should be no additional connectors, patch
jacks, switches, etc. between the instrument and the VT-3 inputs. It is important to
keep the input lines as short as possible. Avoid locating the VT-3 where it will be
subjected to high sound levels or excessive vibration (such as on a drum riser).
If desired, the musical instrument may be simultaneously connected to the input
to an external instrument (guitar) amplifier. The AMP jack (7) is a 1/4” single-con-
ductor (monaural) phone jack wired directly in parallel with the INSTRUMENT
jack.
The OUTPUT connectors (5 and 10) are XLR-3 male wired according to AES
standard: pin 1 is ground (shield), pin 2 is “high” or “+,” and pin 3 is “low” or “-
.” The output is transformer-balanced. The output level is a nominal -30 dBm.
This is somewhat higher in level than a typical microphone.
The back panel of the VT-3 also has XLR output connectors (5) that are wired
in parallel with the front panel XLRs. Signal is present on both the front and rear