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--- audio:audio_by_van_alstine_work [2019/08/02 23:03] – [The future] mithat
+++ audio:audio_by_van_alstine_work [2023/01/02 21:54] (current) – [DVA Digital Preamplifier] mithat
@@ Line 11: / Line 11: @@
 New vacuum tube line stage to replace AVA’s existing design originally derived from the Dyna PAS 3.
-**Contribution:** Concept origination, development, and implementation.  I’m pretty sure this was the first commercial application of my vacuum tube computer optimization methods based on my [[https://www.birotechnology.com/articles/VTspice.html|SPICE model optimization work]] (i.e., there were two layers of computer-based optimization: one to model the tubes and the other to optimize the performance of the circuit).
+**Contribution:** Concept origination, development, and implementation.  I’m pretty sure this was the first commercial application of my vacuum tube computer optimization methods based on my [[https://www.birotechnology.com/articles/VTspice.html|SPICE model optimization work]].
-**Discussion:** I thought the time had come for AVA to have a new vacuum tube line-level stage to replace their aging 12AX7A-based design, and they agreed. I based the initial work around two stages of 12AT7A gain using heaps of the SPICE simulation to optimize the circuit behavior for audio reproduction. I originally wanted to apply my design optimization methods to a number of different tube triodes and subjectively evaluate the results, but after hearing the results with the 12AT7A, AVA decided to put the design into production immediately. A variant of this stage remains in production today in the form of AVA’s Fet Valve CFR and FetValve CF RB preamps.
+**Discussion:** I thought the time had come for AVA to have a new vacuum tube line-level stage to replace their aging 12AX7A-based design, and they agreed. I based the initial work around two stages of 12AT7A gain using heaps of SPICE modeling to optimize the circuit behavior for audio reproduction. I originally wanted to apply the design optimization methods to a number of different tube triodes and subjectively evaluate the results. But after hearing the results with the 12AT7A, AVA decided to put the design into production immediately. A variant of this stage remains in production today in the form of AVA’s Fet Valve CFR and FetValve CF RB preamps.
 ===== Transcendence Six =====
@@ Line 19: / Line 19: @@
 [[https://web.archive.org/web/20021019213756/http://avahifi.com:80/root/equipment/preamplifier/transcendence_six_sl.htm|c. 2002]]
-Low-cost hybrid line stage using a computer-optimized 12AT7A gain stage and integrated circuit buffer output.
+Low-cost hybrid line stage using a computer-optimized 12AT7A gain stage and IC buffer output stage.
 **Contribution:** Concept origination, development, and implementation.
-**Discussion:** This was a continuation of the work I started with the Transcendence Five. Historically, AVA had demonstrated some success with two different hybrid approaches. In the first, high-voltage MOSFET buffers were placed inside the main feedback loop of vacuum tube gain stages. In the second, a low-cost opamp stage was used to provide high impedance buffering of a conventional closed-loop tube preamp design. My idea centered around placing a high-speed solid-state buffer IC stage //inside// the global feedback loop. This would allow AVA to offer a preamp with performance that exceeded their tube/MOSFET hybrid at a considerable cost savings. This design was so good that it obsoleted their tube/MOSFET hybrid preamp until I was able to complete work on the Transcendence Seven.
+**Discussion:** This was a continuation of the work I started with the Transcendence Five. Historically, AVA had demonstrated some success with two different hybrid approaches. In the first, high-voltage MOSFET buffers were placed inside the main feedback loop of vacuum tube gain stages. In the second, a low-cost opamp stage was used to provide high impedance buffering of a conventional closed-loop tube preamp design. My idea centered around placing a high-speed solid-state buffer IC stage //inside// the global feedback loop. This would allow AVA to offer a preamp with performance that exceeded their tube/MOSFET hybrid at a considerable cost savings. AVA considered the design so good that it obsoleted their tube/MOSFET hybrid preamp until I was able to complete work on the Transcendence Seven.
 ===== Transcendence Seven =====
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 **Contribution:** Development and implementation. This was a major rethink of the work covered by AVA's [[https://patentimages.storage.googleapis.com/3b/ca/c7/daa969bad4f092/US5017884.pdf|“Fet Valve” patent]] and embodied in their first-generation Fet Valve products.
-**Discussion:** One of the reasons my Transcendence Six design outperformed AVA’s more costly discrete MOSFET hybrid approach was that it used the optimized 12AT7A-based gain stage core initially developed for the Transcendence Five. So a natural progression was to see whether using that gain stage in one of the discrete MOSFET output buffer architectures covered in their patent provided an advantage over the IC-based buffer I designed into the Transcendence Six. In the process of designing the new MOSFET stage, I revisited a number of assumptions made in the original AVA implementation and produced a circuit optimized for this application that was vastly simpler than the one it replaced. AVA thought its performance warranted it being offering as a premium hybrid product.
+**Discussion:** One of the reasons my Transcendence Six design outperformed AVA’s more costly discrete MOSFET hybrid approach was that it used the optimized 12AT7A-based gain stage core initially developed for the Transcendence Five. So a natural progression was to see whether using that gain stage in one of their patented discrete MOSFET output buffer architectures provided an advantage over the IC-based buffer I designed into the Transcendence Six. In the process of designing the new MOSFET stage, I revisited a number of assumptions AVA made in the original implementation and produced an optimized circuit that was significantly simpler than the one it replaced. AVA thought its performance warranted it being offering as a premium hybrid product.
 ===== "T7 CF" =====
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 **Contribution:** Concept origination and development.
-**Discussion:** While working on the Transcendence Seven, I was able to take a deep dive into the tube/MOSFET architecture covered in the AVA Fet Valve patent. One result of this is that I could not find a convincing reason why a power-MOSFET was better suited to buffering the gain stages than a cathode follower, but I was able to come up some reasons a MOSFET might be worse. So I developed an iteration of the Transcendence Seven design using a 12AU7A-based circuit to replace the power-MOSFET stage.
+**Discussion:** While working on the Transcendence Seven, I was able to take a deep dive into the tube/MOSFET architecture covered in the AVA Fet Valve patent. One result of this is that I could not find a convincing reason why a power-MOSFET was better suited to buffering the gain stages over a cathode follower, but I was able to come up some reasons a MOSFET might be worse. So I developed an iteration of the Transcendence Seven design using a 12AU7A-based circuit to replace the power-MOSFET stage.
-At the time I wasn’t given the go-ahead to prototype and test this design. My understanding is the AVA wanted to maintain a commitment to their patented architecture as they felt this gave them marketing distinction. However, this circuit //was// eventually put into production around 2014 as the [[#fet_valve_cf|Fet Valve CF]].
+At the time I wasn’t given the go-ahead to prototype and test this design. My understanding is that AVA wanted to maintain a commitment to their patented hybrid architecture as they felt this gave them marketing distinction. However, this circuit was eventually put into production around 2014 as the [[#fet_valve_cf|Fet Valve CF]].
 ===== Active power supplies for tube and hybrid electronics =====
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 **Contribution:** Concept origination, development, and implementation.
-**Discussion:** To address a concern AVA raised regarding the audibility of B+ power supply shifts caused by line voltage variations and other factors, I developed an active regulation architecture using voltage references and high-voltage power-MOSFETs. The approach was simple and cost-effective enough that several independent regulation stages could be be used to better isolate the individual stages that comprised an entire design. AVA felt that the subjective improvements resulting from the regulated power supplies warranted the adoption of the scheme in all tube and hybrid products. This resulted in the [[https://web.archive.org/web/20040404184016/http://avahifi.com:80/root/equipment/preamplifier/transcendence_five_sl.htm|Transcendence Five SLR]], [[https://web.archive.org/web/20040404191302/http://avahifi.com:80/root/equipment/preamplifier/transcendence_six_sl.htm|Transcendence Six SLR]], and [[https://web.archive.org/web/20040404184915/http://avahifi.com:80/root/equipment/preamplifier/transcendence_seven_ec.htm|Transcendence Seven SLR and ECR]]. The same work was also applied to the [[https://web.archive.org/web/20040404182745/http://avahifi.com:80/root/equipment/amplifier/fetvalve_amps.htm|Fet Valve EXR]] power amplifiers.
+**Discussion:** To address a concern AVA raised regarding the audibility of B+ power supply shifts caused by line voltage variations and other factors, I developed an active regulation architecture using voltage references and high-voltage power-MOSFETs. The approach was simple and cost-effective enough that several independent regulation stages could be used to better isolate the individual stages that comprised an entire design. AVA felt that the subjective improvements resulting from the regulated power supplies warranted the adoption of the scheme in all tube and hybrid products. This resulted in the [[https://web.archive.org/web/20040404184016/http://avahifi.com:80/root/equipment/preamplifier/transcendence_five_sl.htm|Transcendence Five SLR]], [[https://web.archive.org/web/20040404191302/http://avahifi.com:80/root/equipment/preamplifier/transcendence_six_sl.htm|Transcendence Six SLR]], and [[https://web.archive.org/web/20040404184915/http://avahifi.com:80/root/equipment/preamplifier/transcendence_seven_ec.htm|Transcendence Seven SLR and ECR]]. The same work was also applied to the [[https://web.archive.org/web/20040404182745/http://avahifi.com:80/root/equipment/amplifier/fetvalve_amps.htm|Fet Valve EXR]] power amplifiers.
-The Ultra preamplifier ([[https://web.archive.org/web/20060928205449/http://www.avahifi.com:80/root/equipment/preamplifier/UltraSL.htm|c. 2006]]) was essentially a Transcendence Seven SLR with a greater number of regulation stages. Similarly, the first version of the Transcendence Eight ([[https://web.archive.org/web/20060825083341/http://www.avahifi.com:80/root/equipment/preamplifier/Transcendence_Eight_Vacuum_Tube_Preamplifier.htm|c. 2006]]) was essentially a Transcendence Five SLR with more regulators. I wasn’t involved in the development of these particular applications of my regulator design as my ongoing work for AVA went on hiatus just before these products went into development.
+The Ultra preamplifier ([[https://web.archive.org/web/20060928205449/http://www.avahifi.com:80/root/equipment/preamplifier/UltraSL.htm|c. 2006]]) was essentially a Transcendence Seven SLR with a greater number of regulation stages. Similarly, the first version of the Transcendence Eight ([[https://web.archive.org/web/20060825083341/http://www.avahifi.com:80/root/equipment/preamplifier/Transcendence_Eight_Vacuum_Tube_Preamplifier.htm|c. 2006]]) was essentially a Transcendence Five SLR with more regulators. I wasn’t involved in the development of these particular applications of this regulator design as my ongoing work for AVA went on hiatus just before these products went into development.
 ===== Remote control =====
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 **Contribution:** Concept origination, development, and implementation.
-**Discussion:** I was aware that AVA was losing preamplifier sales because they didn’t support any kind of remote control and that AVA regarded even the simplest of remote control functionality an unsolvable problem given their manufacturing quantities and methods. So I decided to solve it. The solution hinged on working with a turnkey supplier of remote control transmitters and pre-programmed receiver ICs and sourcing a motorized potentiometer that was as good as the potentiometers they were using. The result involved minimal changes to the chassis design and a build that was easier than the non-remote approach they had been using.
+**Discussion:** I was aware that AVA was losing preamplifier sales because they didn’t support any kind of remote control and that AVA, given their manufacturing quantities and methods, regarded even the simplest of remote control functionality an unsolvable problem. So I decided to solve it. The solution hinged on sourcing a motorized potentiometer that was as good as the potentiometers they were using and on working with a turnkey supplier of remote control transmitters and pre-programmed receiver ICs. The result involved minimal changes to the chassis design and a build that was easier than the non-remote approach they had been using.
-My original expectation was that AVA would offer the remote as standard equipment on all “big body” preamplifiers. Instead it was offered as a relatively costly option, which they justified because the remote control transmitters were costly, which they were because of the small quantities they ordered them in, which was the case because remote control was offered only as an option.
+My expectation was that AVA would offer the remote as standard equipment on all “big body” preamplifiers. Instead it was offered as a relatively costly option, which they justified because the remote control transmitters were costly, which they were because of the small quantities they ordered them in, which was the case because remote control was offered only as an option.
 ===== Ultimate 70 and Ultravalve power amplifiers =====
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 **Contribution:** Strategization and development. Changes centered on improving loop behavior and power supply regulation, producing a circuit design that has remained in the AVA catalog for over 13 years.
-**Discussion:** AVA felt they needed to produce a revision of their Dyna 70 rebuild offering and asked me to design it. I was proscribed from changing the tube complement or making similar large changes. So I opted to apply some of the insights gleaned from the application of regulated power supplies in tube and hybrid applications to the existing circuit and to revisit some assumptions about pole and zero locations that the original Dyna engineers had made, likely based on the kinds of parts that were available in 1959 and definitely based on the slightly different tube complement. The revisions I developed resulted in the Ultimate 70, and the circuit continues today in different packaging as the AVA Ultravalve amplifier.
+**Discussion:** AVA felt they needed to produce a revision of their Dyna 70 rebuild offering and asked me to design it. I was proscribed from changing the tube complement or making similar large changes. So I opted to apply to the existing circuit some of the insights we gained from the applying regulated power supplies in tube and hybrid applications and to revisit the assumptions about pole and zero locations that the original Dyna engineers had made, likely based on the kinds of parts that were available in 1959 and definitely based on the slightly different tube complement. The revisions resulted in the Ultimate 70, and the circuit continues today in different packaging as the AVA Ultravalve amplifier.
 ===== DAC core for Vision and Vision Hybrid DACs =====
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 **Contribution:** Design and implementation.
-**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.
+**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 abilities---something they had previously considered impossible. So it was probably natural that years later 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 AVA DAC production for seven years until it was replaced by my DAC MK5 design.
+AVA originally wanted to support only 44.1kHz PCM formats with a single coaxial S/PDIF input. Additionally, their manufacturing capabilities precluded the use of microcontrollers. 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 same 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.
+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 SMD package. This design used SMD components exclusively.
 I was not involved in the development of the analog stages for the first DAC products using this board. However, I was responsible for the analog circuits found in the [[#vision_dac_improved|2015 revision]].
@@ Line 105: / Line 105: @@
 **Contribution:** Concept origination and development.
-**Discussion:** Around 2014, finding that hybrid topologies were becoming a marketing liability, AVA revisited my [[#t7_cf|“T7 CF”]] design work without my knowledge. To my original circuit design of 2002, they added grid stopper resistors ahead of the 12AU7A stages (which my original simulations didn’t point to the need for). They released it as the Fet Valve CF, and it remains in production today as the Fet Valve CFR and Fet Valve CF RB.
+**Discussion:** Around 2014, finding that hybrid topologies were becoming a marketing liability rather than as asset, AVA revisited my [[#t7_cf|“T7 CF”]] design work without my knowledge. To my original circuit design of 2002, they added grid stopper resistors ahead of the 12AU7A stages (which my original simulations didn’t point to the need for). They released it as the Fet Valve CF, and it remains in production today as the Fet Valve CFR and Fet Valve CF RB.
 ===== Vision RIAA Phono Preamplifer =====
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 **Contribution:** Development.
-**Discussion:** AVA decided to pursue a stronger presence in the growing phono market by developing a stand-alone phono preamp. I was consulted on the project near the end of its development to determine the best passive component values to be used to yield the best RIAA conformance. I provided some subjective evaluations of the unit while it was being developed as well. I had nothing to do with the preamp’s topology or other design decisions.
+**Discussion:** AVA decided to pursue a stronger presence in the growing phono market by developing a stand-alone phono preamp. I was consulted on the project near the end of its development to determine the best passive component values to yield the best RIAA conformance. I provided some subjective evaluations of the unit while it was being developed as well. I had nothing to do with the preamp’s topology or other design decisions.
 ===== Vision DAC improved =====
@@ Line 131: / Line 131: @@
 [[https://web.archive.org/web/20150427040336/http://avahifi.com:80/|c. 2015]]
-New line stage based on a discrete, class-A, solid-state gain stage I developed as an independent project.
+New line stage based on a discrete, class-A, solid-state gain stage (developed as an independent project).
 **Contribution:** Development and implementation.
@@ Line 149: / Line 149: @@
 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 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.
+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 brought AVA’s production methods more in line with modern approaches.
 ===== Vision SLR, Fet Valve CFR =====
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 Fully remote-controllable chassis and supporting circuitry.
-**Contribution:** Concept origination, development, and implementation. 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.
+**Contribution:** Concept origination, development, and implementation. 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 existing 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 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 far more undeniable.
@@ Line 169: / Line 169: @@
 **Contribution:** Concept origination, development, and implementation.
-**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 new ability to burn microcontrollers in-house, it was natural to apply these toward a limited-feature remote control design for their RB (Real Basic) preamplifer chassis to replace the existing design developed 14 years earlier. As was the case 14 years before, I expected AVA to adopt the remote control as standard equipment on the RB chassis, but again they 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 and AVA's new ability to burn microcontrollers in-house, it was natural to apply these to replace the more expensive and now 14 year old design still being used in their RB (Real Basic) preamplifer chassis. As was the case 14 years before, I expected AVA to adopt the remote control as standard equipment on the RB chassis, but again they decided to offer it as an option, albeit not as costly as the solution it replaced. As of early 2021, they have made it a standard feature for all preamps using this chassis design.
+===== RC3 =====
+c. 2020--2021
+Embedded design for IR remote control sending with silicone membrane switches.
+**Contribution:** Concept origination, development, and implementation.
+**Discussion:** To help address issues with supplier chains in AVA's existing remote control vendors, I decided it would be a good idea if they had the ability to vertically integrate remote control production as needed. This is the first fruit of that endeavor. It is a PCB based around a very low power microcontroller implementation and accompanying firmware that is retrofitted into one of AVA's existing vendor-supplied cases. The solution provides in-house customization of remote control codes and their timing.
+===== DVA Digital Preamplifier =====
+c. 2018--2021
+**Contribution:** Concept origination, development, and implementation.
+**Discussion:** The DVA Digital Preamplifier is effectively an expansion of the DAC MK5. It reworks that product's output stage to provide a [[https://mithatkonar.com/blog/2020/10/14/dacs-and-the-differential-dilemma/|differential output]] as well as some gain while also implementing control of volume and input selection via a touchscreen and remote control. Thus, it eliminates the need for an analog preamp. This is, of course, how many users with primarily digital sources have been doing things for a long time now. It just took a bit of time to convince AVA of the advantages of this. Now that it's done, they are all-in. That said, getting to done was no easy feat. Development was beset by seemingly myriad hurdles, ranging from the [[https://www.strata-gee.com/akm-fire-2020-was-almost-over-then-disaster-struck-again/|fire at the AKM factory]] to the prolonged COVID-19 Great Parts Apocalypse.
+The DVA Digital Preamplifier also brought forth a new design aesthetic and chassis mechanics that I originally intended as a one-off transitional one. As is often the case, it took a good amount of work to convince AVA of the merits of making the change. But once the design was released, it received, for the first time ever for an AVA product, praise in the audiophile press for its aesthetics. Likely as a result of this, AVA asked me to design or redesign faceplates for a variety of new and existing products.
+What this means is that my original plan of transitioning to a completely new design program that takes updated user, business, and manufacturing requirements into full consideration will be delayed. I regard this as an odd manifestation of [[https://www.raymondloewy.org/loewy-biography/|Raymond Loewy's MAYA principle]].
+===== DVA A2D =====
+c. 2021
+**Contribution:** Concept origination, development, and implementation.
+**Discussion:** Coming soon.
+===== DVA R2X =====
+c. 2021
+**Contribution:** Concept origination, development, and implementation.
+**Discussion:** Coming soon.
 ===== The present =====
-I continue to provide ongoing consulting services to Audio by Van Alstine, particularly in the areas of digital audio, small-signal analog audio, low-power amplifier design, and user interface design. For reasons that should be obvious, I'm not at liberty to discuss projects under development.
+I continue to provide consulting services to Audio by Van Alstine, particularly in the areas of digital audio, small-signal analog audio, circuit simulation, and user interface design. For reasons that should be obvious, I'm not at liberty to discuss projects under development.
 ===== The future =====
-Within audio, my work focuses on developing solutions that represent meaningful audio progress rather than chasing coloration signatures that happen to be fashionable. On a more general level, my design interests include a desire to bring greater equity to technological realms and to improve user experiences in every stage of product use. I try to bring all this to bear as much as possible in my work for AVA.
+Within audio, my work focuses on developing solutions that represent meaningful audio progress rather than chasing colorations that happen to be the current fashion. At a more general level, my design interests include a bringing greater equity to all technological realms and improving user experiences in every stage of product use. I try to bring this to bear as much as possible in my work for AVA.