Technical Articles and Editorials
- Written by Dr. David A. Rich
- Published on 23 September 2013
- AVR - Audio Video Receiver - Build Quality: Part I
- Page 2: Understanding DAC Specifications
- Page 3: Digital Reconstruction Filter
- Page 4: Number of DACs per Chip
- Page 5: Improved Distortion and Noise Performance with Balanced DAC Output
- Page 6: Enhanced Distortion Performance with Current Mode DACs
- Page 7: Multiple DACs Combined to Produce a Single Channel
- Page 8: Chart Presenting Build DACs used in AVRs Across Manufacturers and Price
- Page 9: The Right Side of the Chart: More Details about the AVRs and Pre/Pros
- Page 10: The concept of Effective Bits
- Page 11: Single Chip Analog AVR LSI
- Page 12: Enhanced Performance with SSI Parts
- Page 13: Limitations of Operational Amplifier Performance with the Single Chip Analog AVR LSI
- Page 14: Limitations on the Performance of Semiconductor Switches with the Single-Chip Analog AVR LSI
- Page 15: Use of Relays to Achieve Better Performance
- Page 16: A Very Brief Look at Changes in Power Amps in AVRs
- Page 17: Conclusions
- All Pages
When the hood is lifted on AVRs that are currently in production or have recently been discontinued, we find changes have occurred in the analog section (excluding the power amp) in medium to higher-priced products.
Intuition suggests the quality of the DAC in an AVR moves inversely with the added features list over time, i.e., to keep prices constant as features are added, DAC quality suffers. I was surprised to discover that the intuition turns out to be incorrect. Only after completing the exercise of compiling the products list did I fully appreciate the tradeoffs between functionality and cost control. In many cases, DAC quality is not the point of vulnerability; instead, the pinch point is the substitution of the SSI chips for the single-chip analog AVR LSI.
A key takeaway: circuit quality in the direct mode (stereo or 7.1) is almost always invariant to AVR prices in the range of $400 to $2,000. As examples, the $250 Yamaha RX-V367 and Marantz AV8801 ($3000) use the same Renesas LSI chip (R2A15220FP). With the LSI analog chip in these products, the sound of the direct mode is relatively constant, although a more robust power supplies, addition a quality output buffer and enhanced DC blocking capacitor quality can make small differences.
Unfortunately it is not possible to actually do this listening test just proposed in practice because the Yamaha RX-V367, like almost all low cost AVRS produced today, does not have preamp outputs. The experiment would be possible using the older RX-V665 ($550)
Even a low-cost stereo integrated amplifier will offer better performance in its analog input to its preamp output than an AVR in direct mode, since stereo products are made from SSI chips and, occasionally, relays. Value-priced stereo preamps with exceptional internal parts quality, including the electronic volume control chip, such as the Emotiva XSP-1 recently reviewed in Secrets (link shown below), will reveal any coloration of the LSI chip in the AVRs in direct mode.
The LSI analog chip also degrades the performance of the AVR when listening to the DAC for reasons outlined above.
Using multiple SSI analog chips was, a technique found in all top of the line AVRs for Japan but now only one is left. The use of multiple SSI analog chips remains in Pre/Pros designed and built in North America. Unfortunately, these units have higher prices. I cannot make definitive statements about top of the line units designed in the UK since I have no current service manuals
Most, not all, manufactures now fail to provide specific chip numbers on their website for components like the DAC, ADC, electronic volume controls, and opamps, leaving the consumer limited visibility with respect to parts quality. They have never specified the IC used for the multichannel electronic volume control if it is produced by Renesas, Rohm, or JRC.
A significant delay can occur between the time a product is released and when I gain access to the service manuals. Thus most of the products examined for this article are discontinued
Part II of this article will provide more technical information about:
- Construction options for improving performance of an AVR, Pre/Pro and stereo units with better performing analog SSI circuits.
- Signal flow in the LSI analog AVR chips.
I would like to thank Peter Aczel, Jim Clements, Howard Ferstler, Jay Haider, Stephen Hornbrook and Robert Kozel for reviewing this article.