Scanport Analog Multiplexor; Audio Differential AmpliErs; Headphone Interface; Audio I/O Interface - Kurzweil CUP2 Service Manual

Printed Circuit Boards
Interface PCB

ScanPort analog multiplexor

(page 1, zone A3)
There are eight different sources of analog voltage selected, one at a time, by U10; then passed
to the balanced output amplier, U9, which then drives the selected source voltage to the
ScanPort. The balanced outputs are symmetrical, around 1/2 of the +5ref reference voltage. U7
holds the address of the analog voltage being read during A to D conversion by the Engine
PCB.
Audio differential ampliers
(page 2, zone A5)
Stereo audio from the Engine PCB comes in as a low level, unltered, balanced signal. U16A
(left) and U16B (right) low-pass lters and amplies this and converts it to single ended left
and right signals with typically 50dB of common mode rejection. The single-ended audio
signal is then passed to the Audio PCB through J14.

Headphone interface

(page 2, zone B1)
The Audio PCB supplies the amplied headphone signal through J10. This is passed to the
Control Panel PCB through J7. The headphones jacks are installed on the Control Panel PCB.
When headphones are not in use, J16 should pass the headphone signal back to the speaker
ampliers on the Audio PCB. Transistors Q1, Q2, and associated circuits sense the presence of
headphones and deactivate relay LS1 to ground, the return signal, and thus mute the speakers.

Audio I/O interface

(page 2, zone B3)
RCA connectors for external audio input and output signals are connected directly to the
Audio PCB through J17. Resistors R43 and R44 minimize noise pickup when nothing is
plugged into the left and right input jacks.
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