BRUEL & KJAER 1013 Instructions And Applications page 28

Fig. 4.2. A.F. Response Recorder Type 3328.
The oscillators may then be used, either when mounted in the combination
unit, or they can be removed from the unit and operated at a convenient
place in the laboratory or workshop.
Use of the Compressor Circuits and Operation.
The voltage applied to the COMPRESSOR INPUT (of Type 1013} should be
greater than 3 Volts for proper operation of the compressor circuits. A
built-in attenuating network automatically feeds the correct voltage to the
two compressor circuits when the two COMPRESSOR VOLTAGE knobs (one
on the 1013 and one on the 1017 oscillator) are set to approximately the
same value on the scales.
When the compressor circuits of the instruments are used it is recommended
to check the proper operation of the circuits during cross-over before
commencing the actual measurements. This can be done simply by observing
the voltage on the meter of the compressor amplifier. It should be constant
when passing the cross-over frequency.
The two oscillators are insulated from the combination unit to avoid ground-
loops. It is essential for correct operation that ground-loops are also avoided
in the external loop when the compressor circuits are utilized. The measuring
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