the VCAtt integrated circuit. OUT 1 and OUT 2 (from VCAtt) feed U405B
where they are combined into single-ended signal feeding the MIX Control
VR407 through capacitor C417.
The VCAtt output is controlled by the type and amount of voltage present on
the VC terminal. When VC is 0 VDC, VCAtt output exhibits no attenuation.
Resistors R450, R404, and R468 set up a negative bias voltage on VC that pre
attenuates VCAtt approximately 10 dB. This action allows for the integration
of modulation signals from the Harmonics Generator (Section 6.2.2) and
Downward Expander circuit (6.2.3).
VR408 and VR409 are used to null any residue signal from VC before it
reaches the OUT1 and OUT2. Refer to the Nulling and Test Procedures in
Section 7.0 for further information.
6.2.6 Series Connected LED's
RELAY BYPASS, SPR, SOLO and Ax switches contain dry contact closures to
ground to activate individual modes. However, an individual LED indica
tor, associated with a chosen mode, is activated by removing a short circuit
bridge from the LED terminals. A constant current source, Q401, provides 15
mA of current to a series connection of LD401-402 and LD406-409. All
mentioned LEDs, except LD409, are extinguished by sorting the LED termi
nals. LD409 is controlled by Q403 which follows the REMOTE BYPASS
logic. The benefit of the constant current design is a reduction in the power
supply requirements and a constant illumination brightness for any LED in
the series chain.
6.3 Power Supply
The Power Supply circuit consists of a combination Corcom Fuse/RF Filter/
Voltage Selector assembly, a toroid AC transformer, and a AC/DC power
convertor board. The circuit board contains a full wave rectifier, rectifier
filter capacitors, and conventional +15 and -15 VDC regulators with overvolt-
age/short circuit protection diodes. Regulated +15 VDC, ground, and -15
VDC is routed to separate sets of wired connectors for individual connection
to the Main Audio and Control boards.
Circuit Description
6-7
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