17
O P E R AT I O N
REAR PANEL CONTROLS (see Figure 1, page 14)
Power switch (1)
Primary power is applied to the VT-I/F circuits when the Power switch (1) is in
the up position. The amber pilot lamp (5) on the front panel indicates that the unit
is on. It takes about twenty seconds for the Interface to start working, but it is sug-
gested that you turn on the power at least five minutes prior to use. The tubes are
often noisy until all the internal elements reach a stable operating temperature.
FRONT PANEL CONTROLS (see Figure 2, page 15)
The only controls on the VT-I/F are the GND LIFT switches. These connect or
disconnect pin 1 of the OUTPUT connectors to the unit internal ground. In most
situations, the GND LIFT switch (3) will remain in the down (pin 1 to internal
ground) position. In some situations, particularly when an external instrument
amplifier is connected to the AMP jack, a ground loop may occur. This causes a
hum or buzz in the recording equipment. Placing the GND LIFT switch in the up
position may help alleviate this.
The musical instrument is connected to the INSTRUMENT jack (2), an option-
al guitar amp is connected to the AMP jack (1), and the external preamp (VT-1/VT-
2 or other) is connected to the OUT jack (4).
HUMS AND BUZZES
Unfortunately, it is the nature of high-impedance, unbalanced instrument output
to be highly susceptible to hum and buzz. Some of this is often unavoidable — the
instrument pickup(s) are very sensitive to the omnipresent AC fields in our envi-
