3.1.7 VU-Meter adjustment
Peak record level is defined as the level at which the signal contains 3 % of third
harmonic due to tape distortion. This should correspond to an output level approx. 3
db above the reference level of the calibration tape.
Where a distortion analyser is available, the alignment procedure is as follows:
Record a 1 kc/s signal via the radio input with the record level control wide open and
adjust generator level until a distortion factor of 3 % can be measured on the cathode
follower output. A “lead” (higher sensitivity) of 7 db is required on the VU-Meter to
compensate for its ballistic characteristic. The generator level should now be
attenuated by 7 db and the trimpot on the meter amplifier adjusted for 0 VU-
indication on the meter. Adjustment is made with the trimpots P 8 and P 9 (fig. 14)
for channel I and II respectively.
Lacking a distortion analyser, a reasonably accurate alignment is possible by the
following method:
Note the output level produced from the reference section of the calibration tape.
Record a signal of identical frequency, adjusting the input level until a level 4 db
below reference level appears on the cathode follower output. Now set the trimpots
of the meter-amplifiers to obtain a 0 VU reading on the meters.
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