Differences

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--- audio:audio_by_van_alstine_work [2019/05/22 04:24] – [DAC core for Vision and Vision Hybrid DACs] mithat
+++ audio:audio_by_van_alstine_work [2019/05/22 04:52] – [RB-RC] mithat
@@ Line 75: / Line 75: @@
 **Discussion:** In the mid-1990s, I built AVA a prototype stand-alone DAC that demonstrated to them that producing such a product was within their manufacturing abilities. This ushered in an era of their being able to offer a product that they had previously considered impossible. So it was probably natural that they approached me to design the core circuits that would be used in their next generation of stand-alone DACs. They had preselected the the Wolfson WM8740 as the DAC IC they wanted the design based around, but by the time the design was completed we had moved to the WM8742.
-AVA originally wanted to support only 44.1kHz PCM formats and a single coaxial S/PDIF input. Additionally, their manufacturing capabilities precluded the use of microcontrollers, which would have allowed for advanced use of the receiver and converter ICs. In spite of these constraints, I designed in automatic support for up to 96kHz PCM streams, jumper-configurable support for 192kHz PCM, and support for multiple inputs. Because of this, AVA was able to use this design to meet subsequent customer demands for high-rate audio support and multiple inputs. This board was used unchanged for all their DAC production for seven years until it was replaced by my DAC MK5 design.
+AVA originally wanted to support only 44.1kHz PCM formats and a single coaxial S/PDIF input. Additionally, their manufacturing capabilities precluded the use of microcontrollers, which would have allowed for advanced use of the receiver and converter ICs. In spite of these constraints, I designed in automatic support for up to 96kHz PCM streams, jumper-configurable support for 192kHz PCM, and support for multiple inputs. Because of this, AVA was able to use this design to meet subsequent customer demands for high-rate audio support and multiple inputs. This board was used unchanged for all AVA DAC production for seven years until it was replaced by my DAC MK5 design.
 This would be the first time AVA would use predominantly SMD parts in a PCB design. The previous generation DAC had used a single hand-soldered SOIC package. This design used SMD components exclusively.
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 **Contribution:** New reconstruction and output stage based on a discrete, class-A, solid-state gain stage I developed as an independent project.
-**Discussion:** I had been developing a discrete, class-A, solid-state gain stage as an independent project for a number of years. My goal was to create a design that was free of the issues I kept hearing in opamp ICs. Late in 2014 I thought I succeeded and built a single-stage differential-to-single-ended anti-imaging filter/output stage using the module for the Vision DAC board I had designed earlier for AVA. The results impressed AVA enough that it was immediately adopted for their Vision DAC offerings.
+**Discussion:** I had been developing a discrete, class-A, solid-state gain stage as an independent project for a number of years. My goal was to create a design that was free of the issues I kept hearing in opamp ICs. Late in 2014 I thought I succeeded, and so I built a single-stage differential-to-single-ended anti-imaging filter/output stage using the module for the [[#dac_core_for_vision_and_vision_hybrid_dacs|Vision DAC board]] I had designed earlier for AVA. The result impressed AVA enough that it was immediately adopted for their Vision DAC offerings.
 ===== Vision SL improved =====
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 **Discussion:** Phew! With the Vision DAC incapable of effectively supporting newer in-demand digital audio formats, AVA asked me to design for them a product that would. The original design brief specified support for up to 192kHz PCM sample rates and DSD64. I insisted on a design that provided support for DSD128 as well and that had the infrastructure to support DSD256 once that format matured. (AVA released official support for DSD256 in 2018.)
-Working closely with application engineers at AKM, I was able to develop support circuitry for the AK4490EQ that provided improved low-frequency reference voltage stability; this in turn reduced the low frequency nonlinearity appreciably over more conventional approaches.
+Working with application engineers at AKM, I developed support circuitry for the AK4490EQ whose low-frequency reference voltage stability was significantly greater than the circuits used in AK4490EQ reference designs. This in turn reduced the low frequency nonlinearity of the DAC appreciably over more conventional approaches.
-This would be the first time AVA would use in-house burned microcontrollers --- and it did so in a big way: I ended up using three independent microcontrollers in the final product, one for each of the DAC’s core functions: input selection and control, DAC control, and the user interface. Also notable in this design is the scale to which SMD technology was adopted and the high level of build integration. These required introducing significant changes to AVA’s manufacturing workflow, but this has brought AVA’s production methods more in line with modern approaches.
+This would be the first design that required AVA to use microcontrollers they would burn in-house --- and it did so in a big way: I ended up using three independent microcontrollers in the final product, one for each of the DAC’s core functions: input selection and control, DAC control, and the user interface. Also notable in this design is the scale to which SMD technology was adopted and the high level of build integration. These required introducing significant changes to AVA’s manufacturing workflow, which in turn has brought AVA’s production methods more in line with modern approaches.
 ===== Vision SLR, Fet Valve CFR =====
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 **Contribution:** Concept origination, development, and implementation of a fully remote-controllable chassis and supporting circuitry. New for AVA is minimal-path relay-controlled input selection, custom user interface design and microcontroller programming, and improved manufacturability over the previous generation's less capable chassis. Industrial design subject to AVA’s production and styling constraints.
-**Discussion:** I had two main goals with this project. The first was to bring the remote controllability of AVA preamplifiers up to feature parity with the competition as quickly as possible, and the second was to move AVA away from the costly turnkey remote control solution I adopted for their initial remote control offering. An additional goal was to simplify the assembly of preamplifiers. I had originally planned to work on the first of these goals immediately after completing the volume-only remote control design back in 2004; I had even gotten as far as producing prototype PCBs and a prototype build using relay-controlled input switching. But AVA opted for different priorities at the time, and this work was tabled. In 2017, the case for developing a fully remote-controllable platform was, to put it mildly, somewhat less undeniable.
+**Discussion:** I had two main goals with this project. The first was to bring the remote controllability of AVA preamplifiers up to feature parity with the competition as quickly as possible, and the second was to move AVA away from the costly turnkey remote control solution I adopted for their initial remote control offering. An additional goal was to simplify the assembly of preamplifiers. I originally planned to work on the first of these goals immediately after completing the volume-only remote control design back in 2004. I had even gotten as far as producing prototype PCBs and a prototype build using relay-controlled input switching. But AVA opted for different priorities at the time, and this work was tabled. In 2017, the case for developing a fully remote-controllable platform was, to put it mildly, somewhat less undeniable.
 ===== RB-RC =====
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 **Contribution:** Concept origination, development, and implementation of a low-cost remote controlled volume circuit adaptable to the existing RB chassis.
-**Discussion:** With the availability of a less costly remote control transmitter option that I established for the SLR and CFR chassis as well as the newly founded ability for AVA to burn custom microcontrollers in house, it was natural to apply these toward stripped-down remote control functionality for their RB (Real Basic) preamplifer chassis. The new design replaced the previous volume-only remote control implementation with a significantly less expensive solution. Once again I expected AVA to adopt the remote control as standard equipment on the RB chassis, but they again decided to offer it as an option, albeit not as costly as the solution it replaced.
+**Discussion:** Given the availability of a less costly remote control transmitter that I secured for the SLR and CFR chassis as well as AVA's newly founded ability to burn microcontrollers in house, it was natural to apply these toward a stripped-down remote control design for their RB (Real Basic) preamplifer chassis to replace the previous volume-only remote control first developed 14 years earlier. Again I expected AVA to adopt the remote control as standard equipment on the RB chassis, and again they decided to offer it as an option, albeit not as costly as the solution it replaced.
 ===== The future =====