SK1000

Pin1

P18V

Pin2

AGND

Pin3

N18V

Pin4

P21V

Pin5

AGN

Pin6

N21V

SK1001

 

Pin1

P12V

Pin2

DGND

Pin3

N12V

Pin4

DGND

Pin5

P5V

Pin6

DGND

Pin7

P3V3

Pin8

DGND

SK1002

 

Pin1

PSU SYNC

Pin2

PSU GOOD

Pin3

PSU KILL

Pin4

DGND

SK1003

 

Pin1

P36VF1

Pin2

0VF1

Pin3

P36VSET

Pin4

P5VF2

Pin5

OVF2

Pin6

P5VF2SET

Pin7

N/C

ADC

Refer to circuit diagram L896 Sheet 2

The signals to the ADC are converted to balanced by the three opamps that also correct the level to the input of the ADC so that 2VRMS on the input of the first opamp provides a full-scale input to the ADC. 2.45V p-p (Note: not RMS)

A bias is added to the incoming signal so that it can be input to the ADC analogue section which operates on a single 5V rail. The bias is generated by the potential divider R216 and R217 this is 1.75V it is amplified by 1.43 by the opamp to give approximately 2.5V at the output of the opamps IC202 and IC203.

The diodes D200, D201, D202, D203 prevent over voltage signals from being presented to the input of the ADC, they do not protect the ADC if one of the opamp fails, as the diode will blow as well. The ADC itself is set to operate as a master for the I2S interface and to have its internal high pass filter enabled.

Data is output from the ADC on pin 15, it also generates a bit clock at 64xFS on pin 14 and a word clock at Fs on pin 13. The master clock on pin 17 is an input and should be at 256xFs.

DAC

Refer to circuit diagram L896 Sheets 3,4,5,6

The DAC sheets are all essentially the same and so are only described once below. The Sub DAC output has some minor differences that are described in the text.

The DAC is a 24bit 192KHz part it consists of a serial interface port, digital interpolation filter, multi bit sigma delta modulator

and stereo DAC. The DAC is in hardware configuration mode (the control of emphasis and serial interface mode is set by pulling pins high and low on the DAC). The serial interface is set to I2S. The pins DM0 and DM1 control the de-emphasis filters and are controlled via a serial to parallel latch (IC905) connected to the micro.

DAC reset is used to initialise the part and is under the control of the microprocessor via a latch (IC905), it is an active low signal. DAC MUTE on the same latch is an active low signal and forces a soft mute of the output of the DAC.

The serial audio data interface consists of the DAC I2S LRCLK, DAC I2S BCLK and DAC I2S DATA.

DAC I2S LRCLK is the left right clock for the audio frames it should be a square wave at the sampling frequency. The signal is low during the left frame and high during the right frame.

DAC I2S BCLK is the bit clock for the data and data is clocked into the DAC on the rising edge of this clock. The bit clock operates at 64 times the left right clock.

DAC I2S DATA is the actual audio data it is should be presented in I2S format that is one bit offset MSB first data of up to 24bits. Each data frame consists of 32bits one offset bit 24 data bits and 7 empty zero bits. (If the actual data is less than 24 bits (i.e. from CD) the unused bits may also be empty zero.)

The output of the DAC is differential on the pins 16,17 for left and 12,13 for right. This signal passes into a second order multiple feedback type balanced to single ended filter. The filter is a second order Bessel function with a three dB point of approximately 75KHz. This filter has been reworked on the Bass output to have a three dB point of approximately 300Hz to reduce the HF noise introduced by the bass management section. The filter is unity gain however the balanced to single ended conversion introduces a gain of two. The output of the balanced to single ended converter should be 2Vrms for a full scale input. Following the filter is a buffer stage. The buffer stage performs two functions, it is a virtual earth mixer used to mix bass information into the other channels when a sub woofer is not present. Switching the CMOS switch 74HCT4053 controls the mix. The control of the CMOS switch is under microprocessor control via a latch (IC904). The second function of the buffer is to provide a ground sense to the Audio board. This allows the two boards to be loosely connected via a high impedance without introducing hum. The difference between the grounds on the two PCBS is sensed by the positive input of the opamp and added into the signal, this effectively removes any ground variation between the two PCBS. The full-scale output of the DAC should produce 2v RMS at the output of the buffer stage.

DAC performance specification

THD better than -95dB (0.0018%)

Noise level at output of buffer better than -100dB ref 2VRMS or 94dBV

Frequency response +/- 0.4dB 10Hz to 20KHz

The other components on the circuit are decoupling for the DAC, OPAMP and CMOS multiplexer. VMIDR and VMIDL are the output bias chains and should be at approximately half the Analogue Voltage rail (2.5V). AVDDL and AVDDR are the logic supply rails for the digital filter and the switched capacitor filter.

DSP

Refer to circuit diagram L896 Sheet 7

This is the Digital signal Processor sheet. IC701 is the main DSP it decodes the in coming data stream to provide the 5 channels of discrete audio from Dolby Digital, DTS or MPEG encoded material or a matrix decode of stereo information to 4 or five channel. The decoded data is passed to the second DSP IC702 that performs post processing on the signal, performing the THX equalisation Tone controls and Bass management.

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Image 37
Arcam AV8 service manual Adc, Refer to circuit diagram L896 Sheets 3,4,5,6

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.