Avr360 Input Board Circuit Description; Analogue Inputs, Volume Control And Outputs - Arcam AVR360 Service Manual

fitted in front of its input to minimize switching transients and it is powered from the +/-15V supplies
generated on the Power Supply Board.
The L and R headphones outputs go via BN93 to the Headphones Board, after passing through relay
RL902 which is normally off. A positive voltage from the μP at the emitter of pnp Q911 turns on Q911
and generates the same positive voltage at the base of the npn transistor Q909. Because its emitter is
connected to the -15V rail this pulls the relay on.
The FRONT AUX and MIC inputs come from the Headphones Board and through the microphone relay
RL901. When the relay is off the AUX line level L and R signals are switched through to the unity gain
buffer IC904 and then on to the Input Board via pins 3 and 1 of CON101. When the relay is closed (in
the same manner as described above for RL902) then the L front input is routed to the low noise micro-
phone amplifier IC903. This operates as two cascaded virtual earth amplifiers, each with a voltage gain
of approximately 21 (R961/960 and then R965/962). Note the MIC line is biased at +6V via resistors R956,
R957 and R958. The amplified signal is output to the Input Board on pin 5 of CON101.

AVR360 Input Board Circuit Description

The Input Board comprises a 4 layer PCB; this is attached directly to the back panel via its various sock-
ets and to the heatsink by two steel brackets. It is positioned underneath the HDMI Board and above
the Main Board. 5 ribbon cable sockets connect it to the other 4 boards. CN71 connects it to a daughter
board containing two 9 Pin D socket connectors (an RS232 serial port and an iPod dock interface), plus
two 12V trigger sockets and 2 IR receiver sockets. Note some passive components are mounted on the
underside of the PCB.
The Input Board circuitry is shown on pages 2 – 5 of the schematic diagram.
Page 2 covers the analogue inputs, volume control and line level outputs.
Page 3 covers the SPDIF (digital) inputs, clock recovery, audio DSPs and the codec (stereo ADC plus
8-channel DAC).
Page 4 covers the system microprocessor and a slaved support microprocessor
Page 5 covers interfaces to the DAB/Ethernet module, and the boot loader microprocessor used to
update the system SW via USB.

Analogue inputs, volume control and outputs

IC101 is a Renesas R2A15218FP analogue multiplexer and volume control, with a gain range of +42 to
-95dB in 0.5dB steps. It is digitally controlled from the system microprocessor via the I2C bus on pins 49
and 50. A high logic signal on pin 51 enables the system mute. IC101 has +/- 7V supplies generated from
the +/-15V rails with the regulators IC102 and IC103.
All stereo external line level inputs using phono sockets are routed to IC101 via 100R/220pF low pass
CR filters. IC101 also handles the AUX-L, AUX-R and the (mono) MIC_SIGNAL setup microphone inputs
coming from the front panel, plus the internal stereo outputs from AM/FM tuners (TUN-L and TUN-R)
and the DAB/ethernet receiver (VENICE_L and VENICE_R). IC101 additionally switches two multichannel
signals - the 8 channel direct input and the outputs from the 8 post-DAC filters. Note that the +/- 7V
power supply limits the input signals to approximately 4V rms before overload occurs.
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