Learn About the AV8 Phono Board for Arcam Home Theater Systems: FMJ A32 & P35

Arcam Understanding the AV8 Phono Board in Home Theater Systems

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.

FMJ A32, P35/3, P35 specifications

The Arcam P35 is a high-performance power amplifier that has gained recognition among audiophiles and home theater enthusiasts alike for its exceptional sound quality and robust build. Designed to deliver superior audio performance, the P35 is a testament to Arcam’s commitment to engineering excellence and innovative technology.

One of the standout features of the Arcam P35 is its Class G amplification technology. This unique design offers the efficiency of Class D amplifiers while maintaining the warm, rich sound that Class A amplifiers are known for. By utilizing two sets of output transistors for different power levels, the P35 provides additional power when needed without compromising sound quality at lower volumes. This results in remarkably low distortion levels and an impressive dynamic range, making it suitable for everything from subtle acoustic tracks to explosive movie soundtracks.

The P35 is capable of delivering 120 watts per channel into 8 ohms, and an even more powerful 240 watts per channel into 4 ohms. Such power ensures that it can drive even the most demanding speakers with ease. Moreover, the amplifier features both balanced and unbalanced inputs, providing flexibility for various audio setups. The balanced XLR connections help to minimize noise and signal degradation for a clearer sound, particularly in professional settings.

In terms of build quality, the Arcam P35 boasts a robust chassis that minimizes resonance and vibration. The solid construction not only enhances durability but also contributes to an overall cleaner sound. The component selection is top-notch, utilizing high-quality capacitors and transistors designed to withstand the rigors of constant use while delivering exceptional audio fidelity.

An additional characteristic worth noting is Arcam's emphasis on user-friendly design. The P35 features a straightforward layout, allowing for easy setup and operation. It is also equipped with an LED status indicator that provides visual feedback on the amplifier's operational state.

Overall, the Arcam P35 is a powerful and sophisticated amplifier that excels in delivering an immersive audio experience. With its advanced Class G technology, versatile connectivity options, and exemplary build quality, the P35 stands out as an ideal choice for both stereo and home theater applications. Whether you're a casual listener or a serious audiophile, the Arcam P35 is sure to impress with its musicality and performance. Through meticulous engineering and attention to detail, Arcam has successfully created an amplifier that meets the high expectations of audio enthusiasts around the world.