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D.W. Fearn VT-4 Vacuum Tube LC Equalizer
Input and Output Connections
Gold-plated XLR connectors are used for inputs and outputs. The input connector is
female and the output 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 positive 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, the Input mating XLR connector must have the cable shield connected to
pin 1.
Whether the shield is connected to pin 1 of the output connector depends on the stan-
dard 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.
Input
Since the input cable will be carrying very high-quality audio, it is important that a
well-shielded cable is used.
Output
The output of the VT-4 is line level, transformer balanced. Note that vacuum tube
equipment is more sensitive to load impedance than solid state units. The VT-4 design
was optimized for feeding a balanced bridging input (20k ohms or greater). When feed-
ing a 600 ohm load, there may be a slight degradation of some of the specifications. In
modern studio equipment, bridging line inputs are universal. If the device being fed by
the VT-4 has an input termination switch, that switch should be in the “off” position.
The VT-4 can feed balanced or unbalanced inputs with no need for any modification in
output wiring. Either pin 2 or 3 can be grounded, although pin 2 is normally used as the
”hot” and pin 3 grounded in unbalanced configurations.
