Technical & Editorial
AVR – Audio Video Receiver – Build Quality: Part III – Component Choices for a High Performance Design
- Written by David A. Rich
- Published on 03 March 2014
- AVR – Audio Video Receiver – Build Quality: Part III – Component Choices for a High Performance Design
- Page 2: Introduction to Digital Filtering of an LPCM Signal and DAC digital filter performance*
- Page 3: Building a Pre/Pro with pre-designed boards
- Page 4: A More detailed view of the internal signal flow in the Large Scale Integrated Circuit (LSI) analog AVR chip
- Page 5: Use of the LSI AVR chip in Stereo Applications
- Page 6: Conclusions about LSI AVR block diagrams
- Page 7: Low distortion switching with SSI CMOS switch blocks and separate op-amps
- Page 8: Final Analysis
- All Pages
The overall performance of a Pre/Pro, stereo preamp, or DAC box, is limited by the weakest performing parts in the signal chain. In this article series, I have reviewed the key sections of the signal chain and introduced options that can improve the performance of each stage. Specific ICs were discussed. Some parts, which provide improved performance, have been recently introduced. Part numbers for DACs, op-amps, digital volume controls and ASRCs used can be found on the website or printed literature from some enlightened companies
Those considering the purchase of an expensive component, with a technical background, might consider the purchase of a service manual to see the detailed part selection shown in the schematics. Unfortunately only a few large companies will provide these to consumers at a reasonable price. When I gain access to this material on a piece of equipment under review, I will try to produce a sidebar that highlights the internal construction.
The large number (8-12) of channels of a Pre/Pro makes it impractical to design a unit using the best analog ICs and mono DACs. The price would be so prohibitive that even designers of very high-end home theaters would find it excessive. Another limiting factor on the circuit design for the audio section is the high cost of supporting video functions. For these functions, the dominant cost may be related to development of firmware and license fees.
Often, third parties are contracted for engineering support and design of complete PC boards of subassemblies. The ever changing requirements on the video side gives the product a short shelf life, requiring the development fees to be spread over the smaller number of units produced. Customer support levels become high as a result of HDMI interface issues with other products connected to the unit.
In contrast, stereo units can be produced at a reasonable cost while still use the best performing sub-blocks and can take advantage of advanced circuit techniques, such as balanced volume controls. With the advent of high resolution stereo music files, we are seeing a bifurcation between the build quality of affordable stereo and the most expensive multi-channel equipment.
These issues played out at CEDIA 2013 with few new multi-channel Pre/Pro products exhibited by smaller companies. Instead, dual-domain stereo products for high-resolution audio were introduced in large numbers by companies that have invested the past decade producing high-end Pre/Pros.
The presence of LSI AVR chip in ever higher priced multi-channel products from the Far East points to the need to have multi-channel and stereo units on the same equipment rack.
- Measurements of new products being reviewed at Secrets were used to support the work presented in this article. Each of these products uses a different volume control and two use ESS DACs.
- Chris Heinonen produced the measurements using the Audio Precision APx585 analyser. Units tested included the Pioneer SC-79 AVR which employs the Rohm BD3473KS2 LSI AVR. Additional units included the Marantz AV7705 and Yamaha CX-A 5000 Pre/Pros both using the Renesas R2A15220FP LSI AVR.
- Also tested by Chris Heinonen, was the Arcam AVR750 that uses the SSI implementation with a Cirrus CS3318 digital volume control chip.
- Audio Precision data for stereo preamps used for this article are currently on the website. The products were the Classe CP-800 and Emotiva XSP-1 Stereo Preamplifiers. The units use the TI PGA3310 and MUSES 72320 digital volume controls respectively. Both units used the balanced volume control configuration. These measurements were by Dr. John E. Johnson, Jr.
*These sections appeared in slightly modified form in my review:
I would like to thank Jay Haider for reviewing this article.
* The first two sections (Introduction to Asynchronous Sample Rate Converters (ASRC) for Jitter Reduction and Introduction to Digital Filtering of an LPCM Signal and DAC digital filter performance) are modified from Part 2 of the HK 990 review. The material in these first two sections has been enhanced to cover a number of DACs and ASRCs and not just the parts used in the HK 990.