Differences in sound: DAC vs. DAC + Pre-amplifier

[tedwoods]

On 6/6/2020 at 10:41 PM, barrows said:

The above is not possible, the clock frequencies required for Ethernet transmission and audio data are different.

 

While I agree that a direct ethernet connected DAC is a desirable thing, in practice it is very difficult to implement a good Ethernet interface inside a DAC.  By no means am I suggesting it is impossible to do so, but doing so does require paying attention to a lot of details.  Decoding Ethernet data to digital audio samples requires quite a bit of processor power, quite a bit more than, for example, USB audio processing to digital audio data.  And even USB interfaces inside DACs benefit a lot from careful implementation and isolation.  For example, a typical USB interface requires around only 200 mA of power at around 5 VDC, whereas even a less capable (sample rate limited) Ethernet interface requires at a minimum 500 mA of power at 5 VDC, and a better Ethernet interface (like Sonore's optical) requires well over 1 A at 7 VDC to work with higher sample rates.  This power requirement transfers fairly directly into processor noise, inside the DAC chassis.

Currently, most DACs (not all) with inbuilt Ethernet interfaces are both sample rate limited, and not adequately isolated from the DAC circuitry.  Mostly this is because most DAC companies are quickly adding Ethernet interfaces using relatively affordable, off the shelf modules, of limited performance.  One exception is Lumin, and another is Linn, although while the Linn Klimax DS provides superb performance, it is still sample rate limited.

 

The way to do it right:

 

1. Design your own Ethernet interface (preferably with optical input for noise isolation), capable of all sample rates to PCM 768 and DSD 512 (or higher).  And be sure to use high end design approaches all around, many low noise regulated supplies, high precision ultra low phase noise oscillator, etc, etc.  Not an affordable off the shelf module.  Designing such a module requires an engineer highly skilled in high speed circuit engineering, preferably someone with extensive computer mother board design expertise, typical engineers at audio companies do not have the required expertise for this, so the dAC manufacturer will likely have to sub-contract a suitable engineer for the project.

 

2. Make sure the digital audio output (I2S) from he Ethernet interface is fully galvanically isolated from the rest of the DAC.  Note that to provide full galvanic isolation it is also necessary to supply power to the Ethernet interface from a dedicated supply, preferably from a separate dedicated transformer.

 

3.  Make sure the Ethernet interface is physically shielded in a separate sub enclosure to reduce the amount of airborne RF pollution on the inside of the DAC chassis which can couple into the analog outputs.  Note that both Lumin X-1, and Linn Klimax DS do appear to address this need, as does the Mola Mola Tambaqui.

 

I would expect to pay around a $2K USD premium for a really good Ethernet interface inside a DAC, all other things being equal. This can come at some savings if the DAC maker is willing to forgo other inputs altogether, which would be my preference for best sound quality: simple has its advantages.  An Ethernet only input might be able to come with a $1.5K USD premium over the same model DAC with only typical inputs.

 

 

Why put an ethernet to i2S interface inside a DAC?

Isn't it better to have an external device doing that and the DAC only having an i2S input, like what Aqua are doing with their LinkQ?

https://www.aquahifi.com/Introducing_LinQ.html

Or maybe design an external optical to i2S converter...?

[tedwoods]

1 hour ago, barrows said:

Still, my "Ultimate DAC concept" would have an optical Ethernet input (only), which was well isolated from the rest of the DAC internally: with its own separate power supply, inside its own separate shielded sub enclosure, and completely galvanically isolated from the the rest of the DAC.  Then you can have a single master clock for the DAC section, adjacent to the conversion stage, and this clock can remain clean and undisturbed by any other clocks.  (As any other clock frequencies used will be in the isolated Ethernet receiver section).

That would be a very interesting solution, to say the least...