USB and DACs

[elira]

As most of you may know, a DAC (Digital Analog Converter) is a device that transforms a Digital stream to an analog signal. The digital stream is usually a PCM stream that comes from a computer via USB. As most of you I was very skeptical about boutique USB cables that cost hundreds of dollars even thousands and that claim better sound.

If you know a little about how digital signal work, they travel through an analog signal, and there’re two main components an emitter and a receiver. The emitter converts a bunch of ones and zeroes to an analog signal where a one is represented by some voltage, and the zero is usually represented by zero volts.

In the specific case of USB this signal is represented by something around 500mV for ones and 0 volts for zeroes. So as long as that signal arrives intact to the DAC everything should be ok, and in theory any USB 2.0 rated cable should be enough to guaranty that you don’t miss any data. As you can imagine the voltage between the two data lines can fluctuate up to some degree without altering one bit (around 200mV).

Another important part of USB is that it provides power lines, with 5V and up to 500mA. Most USB DACs use this to power the DAC circuit and some of them use it to also power the amp. As long as this power is clean we don’t have to worry about.

After all these facts, one can imagine that USB is pretty robust and it should just work with any USB cable that meets the standard, some people claim that as it’s a digital connection if there’s a problem with the connection it will just stop working (like in HDMI connections).

Now let go to some anecdotic data, about a couple of weeks ago I attended a Woo Audio event where they were showing some of their amps, included the WA8 (DAC/amp), and there were also some Kimber cables, at the beginning I just ignored the cables under the assumption that it doesn’t matter. I took my MacBook Pro, connected a WA8, connected my GS2000e, opened Tidal in chrome and started listening some music (Cinema by Andrea Bocelli). The first thing I noticed is that it was clearer than my Schiit gear, usually I felt that music coming from my gear was too harsh but I assumed it was because of bad recordings or just the Grados being too harsh. So I assumed all the magic was coming from the tube amp, a very nice tube amp by the way.

After listening to some songs one of the guys that was showing the Kimber cables approached to me and asked me if I was willing to test the cables, I said yes, and listened the next song using the Kimber cable (that was already connected). After that I asked him for the other cable, a very standard black cable, I connected it and played the same song. Then I started listening the same harshness I listen with my own gear, then I returned to the Kimber cable and verified that the distortion was gone. After that I asked for the price of that magic cable, and it was crazy expensive around 600 dollars, obviously I’m not going to pay that kind of money for a cable.

Something was clear, some kind of noise was coming to my gear through the USB. At home I took out some RCA cables and started moving things around, first thing I noticed was that my Chrome Cast Audio sitting right next to the Bifrost was causing most of the interference, then I placed it away from the power conditioner and other devices and put it next to my Corda Jazz, and suddenly it was fixed, everything was clear and the harshness was fixed, no more distortion. I had to do some re arrangements to place it far from other devices, and everything is ok now.

At work my problem was harder to fix, obviously the interference was coming through the cable, because my Jotunheim sits far from the computer and other devices. Being it a workstation obviously not designed for audio signals, the problem was being caused mainly by the USB port in the computer. As you may know the Jotunheim DAC gets powered from the USB and that way the amp section is isolated from the USB. But that means that noise in the USB power lines get to the Jotunheim DAC, probably generating some of the distortion. So to test it I bought a Wyrd, which sends clean power to the DAC, and retransmits the digital signal using a precise oscillator (the thing that sets the timing of the transmission). And the result is amazing, now everything sounds better, more detail and less distortion.

I’m sharing this just in case it is useful for someone. At the end seems like the USB connection is not as robust as I was expecting, and seems like the Bifrost is a little sensitive to external signals. Results may vary depending on the environment and the specific DAC implementation, but now you know that some interference can come through the USB.
 

[seduce_me]

Schiit's USB implementation is bad. You can get lynx card for cheap to get a clean output or get the Schiit Eitr. If you have a Schiit DAC, upgrade to Gen 5 and get 2 years warranty.

 

This whole USB decrapification can get out of hand real quick. TBH, it's not about what gives a sonic improvement, it's more about fixing the problems of USB. 

[elira]

6 minutes ago, seduce_me said:

Schiit's USB implementation is bad. You can get lynx card for cheap to get a clean output or get the Schiit Eitr. If you have a Schiit DAC, upgrade to Gen 5 and get 2 years warranty.

 

This whole USB decrapification can get out of hand real quick. TBH, it's not about what gives a sonic improvement, it's more about fixing the problems of USB. 

Yeah, I'm planning on getting the Gen 5 for my Bifrost, but the Jotunheim is only USB (Gen 2) so the only viable option seems to be a Wyrd or something similar.

 

I got surprised how bad USB can be, but everything seems ok at least for now, I'm not planning any changes in the near future.

 

Regarding the improvement, you're right, if you have a good signal and a DAC that can decode it properly then USB decrapifiers are useless.