Specifications

12
There is a gain adjustment potentiometer with a range of about plus-minus 3dB located
on top of the shielded input transformer, reached by removing the instrument from its
case or dust shroud. With this adjustment, the analyzer may be recalibrated with a test
signal, or adjusted to read directly with a microphone having a sensitivity different from
the standard value.
The maximum signal that be inserted at the
"Microphone"
input is 8.2 mVrms sine
wave. Above this value, the overload indicator will be actuated. This is an indicator light
marked
"Overload"
on the front panel. This may be the case when using a buffered
microphone, or when the system is being tested with an external signal generator.
3. Operation From the
"Line"
Input
The
"Line"
input jack is designed for signal material at a normal line level. The input
impedance at the jack is 20 kilohms. It is a
BRIDGING
input for a 600ohm line and does
not terminate the line. Source impedances other than 600ohms may of course be used.
The input is single-ended and grounds the low side. A voltage of 2.6 volts at the
"Line"
input jack will give a reading of 100dB-SPL on the broadband readout. All the gain
controls function on
"Line"
input and a typical operating range from 2.6mv to 8.2 volts
rms sine wave.
4. Overload Indicator
The
"Overload"
light glows whenever signals are clipped in either the Microphone
amplifier of the line amplifier stage. Reduction of the input signal or proper adjustment of
the
"dB-SPL"
control should be made to prevent amplifier overload.
5. Over-Range on the Display
Each channel of the display raster has a light at the top of its column to give a row of
LED'S
marked
"O-R".
This does
NOT
indicate an amplifier overload condition, but that
a particular channel is off scale on the high side. If a channel is too low to actuate the
display, that channel will be dark. To accommodate the full 40dB display range, it will be
necessary to have part of the display actuating the
"0-R"
in order to view the lower
amplitude parts of the spectrum. Of course, care must be taken that the amplifier
"Overload"
indicator does not light.