D.W. Fearn VT-1 Operating instructions manual - page 27

D.W. FEARN 

VT-1 & VT-2 Microphone Preamplifers

27

cate 0 on the meter. This is the standard “0 VU” level for all professional audio recording

equipment built since the early 1970s. “0 VU” on the VT-2 should result in “0 VU” on a prop-

erly aligned recorder. (This reference level can be changed; see the Maintenance Section.)

This is a true VU meter, and conforms to ASA Standard C16.5-1954.

In some applications, or while testing the VT-2, the output level may be considerably higher

than 0 VU. To prevent damage to the meter, it should be turned off under these conditions,

using the Meter switch (5). This switch has no other effect on the operation of the VT-2.

Occasional meter pinning will not damage the meter.

Bench Test

If desired, test the VT-2 before installation. The source generator should be set to -50 dBm,

150 ohms impedance, balanced, and the output should feed a balanced bridging input of the

audio analyzer. Measured bandwidth should be 22 cps to 22 kc to obtain the same readings

as the factory test results. Compare your measurements with the test data supplied with VT-

2. Keep the results for comparison in future maintenance tests.

Initial Set-Up

The VT-2 should be installed as detailed in the Installation section. With the outputs connect-

ed to an appropriate destination (typically to audio recorder inputs), configure the studio to

monitor the VT-2 output. Apply power and wait about twenty seconds for the tube filaments

to get up to temperature. Check for hum, buzz, or other noise. For the first few minutes after

a cold start it is not unusual for the VT-2 to produce hiss, pops, and microphonic “clanks” as

the internal elements of the tubes expand from the heat. Correct any ground loop problems

before proceeding.