In LEVEL function the filters, additional amplification, and selectable
detectors are excluded from the principal meter circuit so that both
meters become identical.
The secondary meter and reading detector have no selectable filters,
less gain than the primary meter (10 mV minimum signal for
fully-specified performance), and true RMS response only. The
measurement of the secondary reading detector is usually displayed in
the upper center section of the display. It generally shows the level of
the input signal before processing, and its reading may be used to
calculate some relative readings such as THD+N when % or dB units
are selected.
The AC MAINS function works by measuring the input line voltage
through very large resistors connected directly at the power mains
input connector.
The signal monitored by the loudspeaker or headphones is normally
picked off at the selected input channel, following input ranging but
preceding any filtering. An internal resistor may be changed to move
the pickoff point to the end of the principal meter, following all filtering.
Generator Output Circuit
Figure 1-7 shows a simplified diagram of the output circuitry of the
ATS-1 Access generator.
The power amplifier is transformer-coupled to a balanced,
compensated resistive attenuator. This attenuator and an
electronically-variable gain control in the generator circuit are both
controlled by the instrument microprocessor in order to provide the
specific output amplitude selected by the operator. The transformer
center-tap is not dc-connected to the instrument ground.
When the 50 Ω unbalanced mode is selected, signal is taken between
the transformer center-tap and the high terminal of the transformer.
Pin 2 of the generator XLR connectors is hot in unbalanced mode,
working against Pin 3 low. An additional 25 Ω source resistance is
switched in series with the high terminal in unbalanced mode to
preserve the same source impedance as in balanced mode.
1 Description
Generator Output Circuit Description
1-12 ATS-1 Access User's Manual
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