Technical & Editorial
- 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
Introduction to AVR Build Quality – Part I: Range of Options by Supplier and Price
What does your money purchase inside the chassis of an AVR or Pre-Pro in an audio / video system? In this article, one in a three part series, I attempt to answer this question: I will open the top and look at the parts inside and show how each of the individual parts can affect the audio quality. We will see that dramatic differences exist at a given price point. While this article is focused on electronic components that perform the complex tasks in the audio channel of the AVR, I have always kept in mind the need to make the material understandable to a motivated reader.
Herein, we examine the components embedded in thirty AVRs and Pre/Pros from twelve manufacturers. I draw my observations from service manuals and the technical information found on the manufacturers' websites. Some of my manuals are dated by a couple years, but little has likely changed in the preamp sections of the units on which this article concentrates, with the exception of a handful of products that recently had a DAC upgrade.
It is not possible to focus only on current products because there is often a significant lag between a product's announcement and when I can get access to the schematic or service manual. Access to manuals from some companies is restricted to authorized service centers, or companies may sell them to consumers at very high prices.
For this article, there are no schematics to read, and I have kept the electronics jargon to the level of the features and specifications sections on a manufacturer's website. More technical material is deferred to Part II of this article. Part I covers all the concepts.
My attention centers on the data converters, e.g., DAC, and analog electronics that follow the preamp. Not shown in Figure 1 above are the multiple sets of stereo inputs. In direct mode, the stereo inputs can be connected to the volume control to bypass the digital signal processor (DSP). Alternatively, the inputs can be converted to a digital signal by an analog-to-digital converter (ADC) to drive the DSP. This path is also not shown in the diagram. A direct path for a set of 7.1 analog inputs to electronic volume controls (volume controls that have gain circuits embedded in the volume controls themselves) is also not shown in this diagram.
Many older AVRs had eight ADCs instead of the current standard of two. With eight ADCs, the DSP could process 7.1-multichannel analog signals. The additional six ADCs were costly. HDMI obviated them by enabling high-resolution multichannel digital signal transfer.
To make the discussion more manageable, I do not highlight quality differences in the stereo ADC path. This may be the subject of a later article.