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Old 5th March 2016, 11:43 AM   #1
Hammer8 is offline Hammer8  United States
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Default DIY Atomic Clock

Hi, for fun I purchased an used SRS PRS10 10Mhz Rubidium clock and would like to connect that to a TEAC 503 DAC. The PRS10 seems to be the cheapest 10Mhz clock out there and luckily, it outputs a 50ohm signal and that is what the TEAC accepts.

Has anyone had any experience with the PRS10? I still need to get a power supply, heatsink and case for it. Any words of wisdom on what parts I should use and how to hook everything up?

Thanks! Hammer8
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Old 5th March 2016, 11:45 AM   #2
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You do realise that the atomic clocks are often don't have good short term (jitter) performance and are generally used as a long term reference to the low jitter clocks?
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Old 5th March 2016, 12:17 PM   #3
Hammer8 is offline Hammer8  United States
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Quote:
Originally Posted by billshurv View Post
You do realise that the atomic clocks are often don't have good short term (jitter) performance and are generally used as a long term reference to the low jitter clocks?
I read that somewhere as well, but srs also makes a clock made for audio, the PERF10, with is also based on the PRS10 I purchased and so I figured it must work! The PERF10 was recently reviewed on ultra audio which is how I got the idea for a diy unit.
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Old 5th March 2016, 12:19 PM   #4
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"condition" that was the word I was looking for. You need to use the atomic reference to condition the (preferably oven controlled) local oscillator.
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Old 5th March 2016, 01:09 PM   #5
Ron E is online now Ron E  United States
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Quote:
Originally Posted by billshurv View Post
"condition" that was the word I was looking for. You need to use the atomic reference to condition the (preferably oven controlled) local oscillator.
To save others the search, that is exactly what the PRS10 does.
http://www.thinksrs.com/downloads/PD...als/PRS10m.pdf
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Old 6th March 2016, 02:56 PM   #6
DF96 is offline DF96  England
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There is no point whatsoever in using an atomic clock for digital audio - except for impressing the ignorant. The very act of putting a crystal clock in a phase lock loop to adjust its long term frequency stability will degrade its short term frequency stability (jitter) so the best thing to do is buy or build a decent crystal oscillator and use that. Or buy an 'atomic locked' oscillator and remove all the locking components.
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Old 6th March 2016, 03:31 PM   #7
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Quote:
Originally Posted by Ron E View Post
To save others the search, that is exactly what the PRS10 does.
http://www.thinksrs.com/downloads/PD...als/PRS10m.pdf
OK that is a lot better than I thought, as designed for cellular, which has very high short term stability requirements, hence the Oven controlled oscillator. But that is to keep carriers in place on narrowband systems in the GHz area and been 15 years so cannot remember the exact requirements.

So it would work as a 10MHz source with low jitter, but like DF96 said, doubtful benefit other than cool factor and a good stand alone OXCO will still be better.
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Old 6th March 2016, 03:36 PM   #8
Hammer8 is offline Hammer8  United States
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Quote:
Originally Posted by DF96 View Post
There is no point whatsoever in using an atomic clock for digital audio - except for impressing the ignorant. The very act of putting a crystal clock in a phase lock loop to adjust its long term frequency stability will degrade its short term frequency stability (jitter) so the best thing to do is buy or build a decent crystal oscillator and use that. Or buy an 'atomic locked' oscillator and remove all the locking components.
Thanks for the advice - wouldn't one think the PRS10 will be better than the standard crystal in the Teac? In their Esoteric line, they sell separate clocks which I think is also based on the PRS10.

Also, does anyone know why some clocks output/inputs are 50ohm and some 75ohm?

For example, my Teac 503 is 50ohm and Teac's own Esoteric line and most other DACs (I think) accept 75ohm signals.

Thank you, Hammer8
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Old 6th March 2016, 05:10 PM   #9
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Consumer grade SPDIF is 75 Ohm, clocks and their signal distribution are 50 Ohm in general. Different stuff.
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Old 6th March 2016, 07:07 PM   #10
modmix is offline modmix  Germany
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Quote:
Originally Posted by Hammer8 View Post
wouldn't one think the PRS10 will be better than the standard crystal in the Teac?
Wouldn't surprised

A while ago I've done some experiments with a PRS10 based DIY clock feeding a Mutec MC-3+. Intriguing.
Much better than a Antelope clock based on LCR-900.
Stability and Noise Performance of Various Rubidium Standards has some measurments.
Experiments using OCXOs with even better phase noise gave better results.
KS-24361 is currently the best I ever had.

Quote:
Originally Posted by Hammer8 View Post
Also, does anyone know why some clocks output/inputs are 50ohm and some 75ohm?
Clock specs rate signal level with a specific load (most often 50ohm). That does not necessarily mean that the clock output impedance is 50ohm.
Much more important is to avoid reflections at the cable end - means: cable impedance should match input impedance as close as possible.
BTW: RG400 is a good 50ohm cable for this application.

hth
Ulli
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