Can I use S.S. 10M Rubidium Audio Clock alone in my K-03X?

Yes you can use the K-03x, K-01x or any other Esoteric device that accepts a 10Mhz master clock input sync connection with an SRS PERF10 or other 10Mhz master clock. You won't get the 44.1 or multiples of that clock frequency like the G-series clocks give you, but what you do get as I understand it is a rock solid clock sync pulse signal from the atomic master that will improve all aspects of the performance in and of itself. Further, if you ever get a G-03 or G-02 or G-01 Esoteric clock, you can hook the 10Mhz atomic master clock into that and then all the other Esoteric devices get sync'ed off the G-series clock baselined with the atomic clock's 10Mhz pulse. This combo is reported to be the ultimate combination but I've not owned it personally...

I've done a lot more research in this regard and have had a number of conversations with SRS as well as other options. The lead-time on the PERF10 or FS725 is longer than I would like to wait personally and my RFQs out to LibertyTest, AllTest and other certified/used equipment vendors for a PERF10 or FS725 have come up dry at the present time. I stumbled on Cybershaft Japan as an option via listings on various sites. It seems they make OCXO, Rudidium-only and OCXO+Rb clock units (single port each standard) for high-end audio, video and studio purposes at an extremely aggressive price point (the Rb-only unit is about $1300-$1500 USD depending upon JPY->USD conversion rate). They are rated for 100-120V and 50-60Hz use which makes them perfect for US or Japanese usage. The Rb-only unit has a single FIFTY (50)-ohm BNC clock output; they supply all their test and calibration results with each unit plus a 1 year unconditional warranty.  I have taken the plunge and ordered one as of yesterday; this should be a very nice and affordable test.  I plan to use this 10Mhz reference clock sync to drive my Esoteric D-02's clocking baseline while leaving the D-02 to sync itself and the P-02 transport together at 22.5792 Mhz.  This should surpass the already great performance of the D-02 clock circuit by a clear margin.  Unlike the PERF10 or particular FS725, this Cybershaft unit seems to have a better internal PSU but I'm not discounting the potential move to another HDPlex power supply with a retrofit in the future to get an even better bespoke PSU to drive the Rb-clock.  I will report back and let you know my findings between mid-late April after I receive it and break it in.  They state specific compatibility with Esoteric D-02, D-03, D01, G-01, G-02, G-03x, G-02s, K-01, K-01X, K-03 and K-03X.  You may read more here (use Google Chrome and let it translate the page);

www dot cybershaft dot jp

Hello!  Were you going to add something more in the way of comments?

In the way of an update, I have the Cybershaft Rb+OCXO 'dual master clock' offering up and running as of late and I am extremely impressed by the build quality of the unit and the customer service provided by Hasegawa-san at Cybershaft.  He goes to great lengths to ensure all questions are answered and provides unit-specific test data for ALL testing of the unit including Allen Deviation, reference measurement devices used, etc....It's the most specific and open backing of what a unit truly does after it is built I have ever seen.  The price point of the unit is a fraction of the other offerings in the space (that provide 10 Mhz atomic-precision master clocking) and frankly when I saw the unit, it's quality, appearance and sheer weight coupled with the exceptional customer service, I don't fee that I am missing out on a single thing compared to the offerings from Stanford Research, Isochrome/Antelope or others. I currently have this connected as follows;

Cybershaft Rb-output=>10Mhz=>Esoteric D02 (WRD CLK IN, 10Mhz)=>Esoteric P02 (MCLK frequency from the D02).

Put another way, the Cybershaft clock is providing an atomic-precision baseline for the clocking circuit of the D02.

All the specs and other technical aspects aside, there was an immediate improvement in the natural/liquid nature of the sound when I enabled the 10Mhz input signal from the Cybershaft to drive the WRD CLK Input of the D02 over the D02 alone. All was extremely good before but I find a touch more precision in image size and placement (of instruments and voices) and an even more musical presentation overall of the system as a whole.

I am very happy to have stumbled on the company out of Japan that as it turns out produces alot of these and similar devices for broadcast and recording audio and video firms and audiophile users in Asia.  My hat is off to Hasegawa-san and his team for building on hell of a component at a fair price and topping that with some of the best customer service and attention to detail I have ever seen!

If your DAC or clock can accept a 10-Mhz clock master input signal, I highly recommend looking up this company and their Rb-only or Rb+OCXO (dual clock outputs) offering. You will not be sorry!

FYI...for anyone interested, the model designation of the Rb+OCXO dual master clock is RBOCXO-01