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.

AVR400 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.

The post-DAC filters comprise 4 low noise NJM2068 dual op amps, running from the +/- 7V supplies. One op amp is assigned to each channel and performs the dual functions of converting a differential input from the DAC to a single ended output, whilst simultaneously functioning as a three pole 50kHz active filter.

The AM/FM tuner module’s outputs pass through the inductors L310 and L302 (providing 19kHz notch and 38 kHz low pass filtering) and the shunt mute circuits formed by the 330R resistors R354/R369 and the two halves of Q306 plus Q307.

IC101 has a fixed level stereo output for Zone 2 (SUB_L and SUB_R) and a second one, adjustable from 0dB to -18dB in 6dB steps, for the AVR400’s analogue to digital converter (ADC_L and ADC_R).

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Arcam service manual AVR400 Input Board Circuit Description, Analogue inputs, volume control and outputs
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AVR400 specifications

The Arcam AVR400 is a high-performance AV receiver designed to provide an immersive home theater experience. As part of Arcam’s esteemed lineup, the AVR400 combines advanced technology with exceptional sound quality, catering to audiophiles and home cinema enthusiasts alike.

At the heart of the AVR400 is its impressive power amplification, providing 100 watts per channel across 7 channels, ensuring a robust performance capable of driving a wide range of speakers. This power output is complemented by a high-current design, which means the receiver can handle dynamic audio passages without distortion, offering clarity in both subtle and explosive soundtracks.

One of the standout features of the AVR400 is its support for various surround sound formats, including Dolby TrueHD and DTS-HD Master Audio. This allows for an unparalleled audio experience, transporting users right into the heart of the action. Additionally, the AVR400 is equipped with the latest HDMI inputs, ensuring compatibility with a multitude of high-definition sources, including Blu-ray players, gaming consoles, and streaming devices.

The AVR400 also boasts advanced video processing capabilities, supporting 4K pass-through as well as upscaling of lower-resolution content to 4K. This makes it an ideal choice for users looking to future-proof their home theater setup, as it can seamlessly integrate with modern 4K televisions while enhancing the quality of older content.

User-friendliness is another essential characteristic of the Arcam AVR400. It comes equipped with an intuitive on-screen menu system that simplifies the setup process. The inclusion of an automatic calibration system helps optimize speaker settings in accordance with the room acoustics, ensuring users achieve the best sound possible from their setup.

Furthermore, the network features of the AVR400 allow for streaming audio from various online services and wireless devices. Built-in support for DLNA enables users to access their media library wirelessly, while the USB input allows for direct playback from flash drives or external hard drives.

In terms of build quality, the Arcam AVR400 embodies the brand’s commitment to excellence. With a sleek design, high-quality materials, and an engineered chassis that minimizes vibration and interference, the AVR400 is not only visually appealing but also built to deliver performance over time.

In summary, the Arcam AVR400 is a feature-rich AV receiver offering a perfect blend of power, precision, and versatility. Whether for movie nights or music listening, it stands out as a reliable choice for those seeking high-quality audio and video reproduction in their home entertainment systems.
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