D.W. Fearn VT-3 - Manual (Page 16)

VT-I/F Vacuum Tube Instrument Interface
D.W. FEARN
18
Fluorescent lights and SCR dimmers are terrible electrical noise generators.
Turn off the fluorescents. If SCR dimmers must be used, they will generally pro-
duce the least noise in their full-on (brightest) position.
Another source of these hums and buzzes is ground loops caused by the inter-
connection of various AC (mains) powered equipment. A properly-wired studio
should not create a ground loop between the VT-3 and the studio equipment, but
often a loop is formed when the VT-3 is connected to an instrument and guitar amp
simultaneously. In this case, use the GND LIFT (8) switch to find the proper posi-
tion for minimum noise. If the guitar amp has a “Ground” switch, experiment with
it as well. Be sure to try all combinations of all switches.
IMPORTANT
When using the VT-3 with the D.W. Fearn VT-1 or VT-2 Vacuum
Tube Microphone Preamplifier, the VT-1/VT-2 Input switch
should be in the -20 dB position (unless the instrument level is
extremely low). With other preamps, use the input pad and/or
reduce the gain of the preamp.
The VT-3 and the guitar amp (if used) should be on the same electrical circuit
(same circuit breaker or fuse) as the studio equipment to minimize ground loop
potential.
Suggestions
You have chosen to use the VT-3 because of the superior sound it provides. To
gain the maximum benefit from your investment, it is important that you hook up
the VT-3 so that other factors do not adversely affect the sound quality.