USB connection to DAC: multi stage improvement

Berkeley Audio has an interesting take on this....these guys did the original work and key developers of the HDCD (High Definition Compatible Digital) process.

They felt USB should not be an inherent "built-in" function of a DAC:

Berkeley Audio Design excludes USB connections from their DACs to protect the delicate digital-to-analog conversion circuits from computer-generated electrical noise and clock phase noise. They believe that connecting a DAC directly to a "dirty" USB source inevitably degrades audio performance. [1, 2]

Key reasons for this design philosophy include:

• Electrical Isolation: Computer USB lines carry significant electrical noise. Berkeley isolates this noisy interface externally to prevent it from polluting the master clocks and output drivers.
• Phase Noise: Berkeley engineers believe the human ear is highly sensitive to clock phase noise. Direct USB connections can introduce this jitter into the DAC's master clock, reducing sonic clarity.
• The "Clean/Dirty" Approach: Rather than compromising the DAC's internal board, Berkeley designed the Alpha USB Noise Isolation Device. This external box handles the noisy USB input, electrically isolates the signal, and outputs a pristine, re-clocked signal (via AES/EBU or SPDIF) to the DAC.

Originally, they did not have USB as part of their DAC path, but due to demand they now offer a seperate unit to optimize the digital path for those needing/using USB.

https://www.theabsolutesound.com/articles/berkeley-audio-design-alpha-usb-series-2-noise-isolation-device/

I have their Alpha DAC 3 in my system...it is a keeper.

I can completely relate to the drive to optimize the USB path. Years ago, I was firmly in that same camp, deploying the iFi Micro and Nano iUSB3.0 power supplies, inline iPurifiers, and Gemini split-data/power cables across my main and secondary systems. When you are wrestling with standard computer audio outputs, adding these stages absolutely changes the sound, often bringing a welcome sense of calm and transparency by shifting the leakage current and power supply noise spectrum around.

But for the lurkers following this thread who are looking for true isolation, it’s worth stepping back and looking at the root cause of the problem.

Cascading five different USB isolators, reclockers, and hubs introduces a massive amount of hardware complexity, multiple power supplies, and up to ten physical impedance boundaries where high-speed digital signals can reflect and create deterministic jitter. It’s essentially treating the symptoms of USB's inherent liabilities—packet bursts and erratic CPU polling that generate EMI—with a long chain of hardware band-aids.

I've since discovered a much more elegant, modern way to achieve this goal at the protocol layer rather than the USB hardware layer.

Moving to an architecture like Diretta—specifically running Diretta Direct Stream (DDS) Mode 3 L2 frames over a simple, point-to-point CAT6 or CAT6a patch cable between a Host and Target—provides complete physical and galvanic isolation natively via the network interface. More importantly, it continuously paces the audio data to keep the endpoint’s CPU cycles perfectly flatlined and uniform. By eliminating the erratic processing spikes that plague USB transmission stacks, you stop the electrical noise from being generated at the source, leaving nothing to mitigate.

If you enjoy the science experiment and the puzzle of mixing and matching different isolation chips, the multi-box USB route is certainly a path you can take. But if your goal is an elegant, low-clutter system with maximum isolation, fixing the transmission architecture via a protocol like Diretta renders the entire "decrapifier" chain obsolete.

If you are at all curious, you can read my open source DIY "cookbook" for solving this problem architecturally here: Building a Dedicated Diretta Link with AudioLinux on Raspberry Pi

jmrrobbie1

+1

Upon reading the OP  I immediately thought of the Berkeley Audio USB converter  I have the Alpha Reference 3P and USB converter. Remarkable sound quality and ease of use. For those of you struggling with issues I would recommend giving this a try before attempting a complex solution with multiple devices.

@jhconnor - I would like to hear that 3P Reference some day, and I bet it sounds amazing. What I am curious about is your Alpha USB. Do you have the Reference Series or Series 2?  I want to use one to operate two different DACs in my main system and I am strongly leaning towards the reference based on the reported sound quality.  Does it sound as good as they say? Thanks.

@mitch2 - the Reference 3P is an outstanding improvement over the Reference 3. I owned the Series 1 and 2 USB converters prior to the Reference USB. When I originally upgraded my DAC to the 3P I had the Series 2 USB converter. There was a noticeable improvement in overall space and dimension and clarity. Once I installed the my new Reference USB there was another "step up" in weight, texture and "believability". Because I changed both the DAC and the USB within a short period of time it's hard for me to pinpoint how much of the "change" came from the DAC vs the Converter. The Series 2 is still an excellent piece. I would recommend starting with the Series 2 - it's less than half the price, and seeing what you experience in your system.