Generator Output Circuit
Figure 6-2 shows a simplified diagram of the output circuitry of the
Portable One Plus analog 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 40 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 20 Ω source resistance is
switched in series with the high terminal in unbalanced mode to
preserve the same source impedance as in balanced mode.
When the generator output is turned off, a floating 40 Ω resistor is
connected in place of the generator to back-terminate the output
connector so that proper noise measurements can be made.
Output impedance selection is made by switching buildout resistors at
the output connector.
When generator monitor inputs are used, the connection (labeled GEN
MON in the diagram) is made directly across the output connector
terminals.
Note that the power amplifier, output transformer, and output
attenuator are common to both channels.
6 Diagrams
Detailed Technical Diagrams Generator Output Circuit
6-4 Portable One Plus Access User's Manual
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