Lexicon RV-8 Service Manual page 84

RV-8 Service Manual
L/R, Center, Sub, L/R Side, L/R Rear) whereas MAIN_DIRECT_SEL/ selects the 5.1-analog inputs
directly. The rear channels are switched with separate controls REAR_DACOUT_SEL/ and
REAR_DIRECT_SEL/.
The output from the analog switch goes to a –6dB level shifter and ADG451 output mute switch. The
outputs pass through DC-blocking caps and relays before going to the RCA connectors. The relays mute
the Main outputs during a power cycle and whenever the unit is in Standby or powered off. The relays are
controlled by the MAIN_MUTE_RLY/ signal.
Control Registers (sheet 14)
A Xilinx CPLD hold the control registers for the board. The main board writes to them via a SPI data bus
(ADA_SCLK, ADA_SDATA_OUT, ADA_LATCH). Their function is loosely related to the function and
numbering of the MC-12 registers. The control register output bits provide relay control, 5.1 direct mux
selection, analog source selection, A/D control, DAC reset control, output selection, independent zero
crossing enable and mute for inputs and outputs.
Three-bits of data are returned to the main board through the SPI port (HEADP_PRES, TUN_TUNED,
TUN_STEREO). A serial stream from the tuner for status and RDS data is also available
(TUN_SDATA_OUT).
Amp Select and I/O Connectors (sheet 15)
The Main Board Digital connector is the source for the clocks and data for the A/D and D/A converters.
The MCLK is at 256x the sample rate (FS). Each converter gets MCLK through a separate buffer and
source resistor. The SCLK (64xFS) and LRCK (1xFS) are distributed directly to the DACs. All of the D/A
converters operate in I S mode. J20 and J22 provide a row of test points for quick access to all the
2
clocks.
J23 and J24 are ribbon connectors from the Mic/Phono Board and Tuner board respectively. The left and
right signal pairs are buffered differentially and presented to the input muxes through these connectors.
The tuner is controlled through the SPI port signals ADA_TUNER_CE/, ADA_SDATA_OUT, and
TUN_SCLK.
Power Supply Connections and Regulators (sheet 16)
There is a separate feed from the switching power supply to the Analog board. The Analog board has a 4-
pin connector that accepts ±15 volts, +5 volts and a ground connection to the supply. The –15 supply is a
shared daisy chain connection from the supply to the analog and video boards.
Three regulators generate +12V for the tuner, +3.3VD for the convertors and CPLD, and –5VA for the
volume controls and convertors. Heat generated by the –5V regulator is dissipated by a heatsink. Two
voltage regulators create the +5VR supply from the +15V rail. The first regulator regulates to about 10V
and the second regulates to 5V. +5VR is an alternative "clean" 5 volt supply used by the A/D and D/A
converters.
Six DG411 switches select either front L/R or either of the two zones as a source for the headphones. A
high current op-amp with 12dB of gain drives the headphone output at J25. A high impedance headphone
presence detector is shunted to relay ground or the 10K output impedance by a normalling switch in the
socket, and is pulled high when a jack is inserted.
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