DACs, external clocks, and what's what

That's because the MU2 already has a built-in clock section similar to the CC1/CC2. ​​​​​​

My point exactly. It's not likely that Grimm MU2 is the only product or brand to do this.  @phusis 

@erik_squires wrote 

​if your DAC sounds much better with an external clock it says more about the quality of the internal clock. ​​​​​

Exactly. 

@ericrhodes1 wrote:

My point exactly. It’s not likely that Grimm MU2 is the only product or brand to do this.

So? There’s a market for external clocks because they make a difference for the better in existing setups. Buy all the DAC’s and sources you want that you deem don’t need external clocks, i.e.: because you expect they won’t make a difference for the better, and that’s perfectly fine. Problem solved in your case, or..?

Before you jump to that conclusion you should be able to test whether that’s actually true; not all DAC’s and sources offer the opportunity with a Wordclock input for an external clock, but that’s not necessarily to say they don’t need it, and what’s more: you won’t find out either whether an external clock would actually make a difference for the better. 

In the case of the MU2 we know they’ve implemented a very good clock design to begin with, and so I wouldn’t expect an external über-one from another manufacturer to make a worthwhile difference. 

@erik_squires wrote:

I also want to point out hte possibility, that maybe if your DAC sounds much better with an external clock it says more about the quality of the internal clock. 

Being that my DAC is slaved by the source clock, as dictated by its protocol, that’s where the clock function has to be addressed as a first. And, my source happens to have a Wordclock input. Neat. 

It also happens that quite a few expensive DAC’s/sources that are connected to a quality external clock improve sonically because of this. So, ideally this and that is just that. Pragmatically things can be different. 

@phusis distance matters 

I have the Esoteric K-01XDSE and the Stanford Systems Research FS725 rubidium clock.  

Out of interest I Googled to see what others have said about the combo - forgive the length of the somewhat overblown response

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Connecting a Stanford Research Systems (SRS) FS725 Rubidium Frequency Standard to the Esoteric K-01XD SE results in a highly effective, audiophile-approved system upgrade. [1]

The Esoteric K-01XD SE features a highly advanced internal "Master Sound Discrete Clock". However, introducing the SRS FS725—a piece of laboratory-grade scientific equipment—replaces the internal timing with an ultra-stable 10 MHz rubidium atomic oscillator reference. Audiophiles using this exact combination note several key real-world performance benefits: [1, 2, 3]

The Sonic Impacts

• Enhanced Spatial Three-Dimensionality: The most common real-world improvement noted with this exact pairing is a vastly expanded soundstage. Instruments and vocalists snap into a realistic, 3D space, making them feel like physical people performing in your room rather than a flat, two-dimensional stereo image. [1]
• Blacker Backgrounds & Micro-Detail: By virtually eliminating phase noise and timing drift, the absolute silence between notes drops. This lower noise floor uncovers subtle acoustic cues, like the decay of a piano string or the ambient acoustics of the recording room. [1]
• Tightened Low-End Control: Better clocking yields highly accurate transient responses, resulting in a cleaner, punchier, and more texture-accurate bass definition.
• Treble Micro-Detail: The incredibly low phase noise of the rubidium core (<-130 dBc/Hz at 10 Hz) cleans up the extreme treble, smoothing out digital glare while bringing out subtle acoustic ambient cues

Why the SRS FS725 is a "Secret Weapon"

Esoteric sells their own premium external master clocks (such as the G-01XD), which cost upwards of $15,000 to $20,000. Historically, Esoteric clocks utilized scientific rubidium cores similar to what is inside the SRS unit. The Stanford Research Systems FS725 costs a fraction of that price (often found between $2,500 to $4,500) while offering atomic-clock levels of Allan Variance stability and low phase noise. It functions as a high-end audiophile upgrade at a laboratory-equipment price point. [1, 2, 3, 4, 5]

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The difference is perhaps not as dramatic as the AI response above, but the sound is more organic and real.

The SRS FS725 is still a bargain - its list price has not changed!.  Its physics unit was the guts of the Esoteric clock but they now use a very high end OCXO in their external clock. An OCXO chip can cost anything from about $20 to $1,500.

The critical factors of a DAC's clock are frequency stability and "jitter" - very short term frequency stability.  

An OCXO is an oven controlled crystal oscillator - the frequency of a quartz oscillator depends on its temperature (among other things like load capacitance, voltage) and so the OCXO stabilizes the temperature.  There are also TCXOs, temperature compensated crystal oscillators, they measure the temperature and compensate for changes.  OCXOs are more stable.

If you use an external clock the characteristic impedances must match, and the cable is very important.