AV8 Phono Board

Circuit Description

Refer to circuit diagram L870 sheet 1

The phono board is a simple single stage RIAA amplifier and consists of two channels of high gain amplification, and the ability to switch between moving magnet (MM) and moving coil (MC) settings.

PSU

The unit derives its + 15V regulated rails from the unit it is fitted into with only local decoupling capacitors on board.

Interface

The unit connects to the host unit via a 8 way connector.

Amplification

The left channel has designators beginning with 100, and the right with 200. For the purposes of this description the left channel will be described, as the right channel is the same in all respects.

The amplifier is a small signal class A voltage feedback amplifier with switch able gain. The input consists of an actively loaded differential pair of very low noise PNP transistors (TR106, TR107). These transistors are very specific and should only be replaced with identical parts with the E grade high gain. TR100 and TR101 form a current source for the pair, which sets the quiescent current for the entire amplifier. The active load consists of TR110 and TR111, which forms part of the differential current mirror with TR112, TR113 & TR114. This differential stage also has an active load (TR102 & TR103) to keep gain to a maximum.

Both of these differential stages are designed to have as much gain as possible to enable the single stage design. The RIAA response is achieved in the feedback network: C101, C110, C111, C112, C119, C120 and R115, R112. C115 is used to correct between MM and MC gains as the amplifier is non-inverting.

SW100 switches between MM and MC. Two poles of the switch change between the different loading required for each type of the cartridge: R108 & C109 for MM and added in parallel for MC R104 & C108. The other two poles change the feedback resister value to alter the gain: R105 for MM and added in parallel for MC R123.

The DC offset is controlled by a non-inverting servo built around IC100. The amount of servo current is different for each gain setting via R111 (MM) and R124 (MC) so that the low frequency high pass point remains the same for both settings. However the high pass point for the circuit is set by C113. This gives a warp filter, stops DC start-up thumps from upsetting DC coupled circuitry and an approximation of the RIAA/IEC curve (-2dB @ 20Hz)

The output is class A buffered by a dual mirror follower (TR104, TR105, TR108, TR109). The quiescent current is set by D100 and R118 and R119.

Closed loop stability is achieved with C16, C117, giving symmetrical slewing capability.

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Arcam AV8 service manual Circuit Description Refer to circuit diagram L870 sheet, Interface, Amplification
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AV8 specifications

The Arcam AV8 is a high-performance audio-video receiver that has garnered attention for its exceptional sound quality and versatile features, making it a sought-after option for both audiophiles and home theater enthusiasts. Designed to provide an immersive viewing experience, the AV8 is equipped with a range of technologies that enhance its performance.

One of the standout features of the Arcam AV8 is its support for high-definition audio formats. The receiver can decode various lossless audio formats, including Dolby TrueHD and DTS-HD Master Audio, allowing users to experience studio-quality sound. This capability is complemented by its advanced digital signal processing, which ensures that the audio output is clear and dynamic, enhancing the overall entertainment experience.

The AV8 is built with an emphasis on connectivity and flexibility. It boasts multiple HDMI inputs and outputs, facilitating seamless connections to a variety of devices such as Blu-ray players, gaming consoles, and streaming devices. With support for 4K video pass-through, the AV8 is future-proofed for high-definition content, ensuring compatibility with the latest video technologies.

Another notable aspect of the Arcam AV8 is its user-friendly interface. The receiver is equipped with an intuitive on-screen display that simplifies navigation and setup. Additionally, Arcam has incorporated room calibration technology, which analyzes the acoustic properties of the listening environment and adjusts the audio output accordingly. This feature allows for optimal sound reproduction, tailored to the specific characteristics of the room.

The build quality of the AV8 is exceptional; it features a robust chassis designed to minimize vibration and interference, ensuring high-fidelity sound reproduction. The receiver is designed for ease of use, with remote control functionality and smart home integration options, making it convenient to operate alongside other devices.

In summary, the Arcam AV8 is a powerful AV receiver that combines high-definition audio capabilities, extensive connectivity options, and user-friendly features. With its strong emphasis on sound quality and innovative technologies, it stands out in the competitive landscape of home theater equipment, catering to the discerning tastes of audio enthusiasts and casual users alike. Whether for music or movie playback, the AV8 offers a compelling solution for those seeking an elevated audio-visual experience.
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