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Tweakers' Asylum: Re: Crystal oscillator Schematic; I appreciate your criticism by Terry Demol

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Re: Crystal oscillator Schematic; I appreciate your criticism

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> Hi Terry,
> I appreciate your criticism as long it is constructive. In this way > we can make the KWAK-CLOCK even better.

Thanks Elso. I will try and clarify.

We all agree that low jitter is the primary goal of a HQ clock and
the correct measurement of jitter is phase noise in dBC
at a certain frequency away from the carrier (fundamental).
Here is an example of commercially avail VCXO as used in a
DAC reclocking scheme. Ref top RHS of page 2.

http://www.raltron.com/pdfspecs/vc71 72 73.pdf

Note there is more jitter or phase noise closer to
carrier. At 10Hz away from carrier it is -70dBC
and goes to noise floor of -150dBC at 100K.
Now compare previous VCXO to this OCXO at

http://www.raltron.com/pdfspecs/ox3000.pdf

Note phase noise is -90dBC at 10Hz and -155dBC
at even 10K. This is extremely low jitter.
This XO would easily surpass performance
of *any* aftermarket hi end product but at a cost.

There are XO's made for aerospace that can acheive
phase noise specs of -135dBC @ 10Hz! and noise floor
of -175dBC at 1KHz away from carrier. I dare say they
probably cost many thousands of dollars.

Point is, however low jitter spec you want, it's
commercially available now. It just depends on how much
you want to pay and where the point of diminishing
audio returns are.

> > comparator will introduce phase noise i.e. jitter> >
> Well I did the following experiment feeding the output of the low
> jitter Tent clock through the LT1016. The sound slightly improved.

I (we) did same comparison with HQ TCXO on a very low jitter
system and found it worse with 1016.

> As the Tent clock is very low jitter -5ps- I don't believe the
> LT1016 introduces any jitter. What circuit element do you suggest
> instead of the LT1016?

I suggest buying a clipped sine wave XO. Phase noise specs
are available for different OP options so you know
measured degradation.
Which XO does Tent clock use?

> You suggest buying a high quality XO in a can. Well the Tent is such
> a example. I was a bit disapointed by the vague stereo image but
> will give it the benefit of the doubt as I have not yet built the
> dedicated powersupply for it. It is not bad. Can you suggest name
> and make of a low jitter TCXO you can recommend?

Please give details of Tent XO. You need dedicated low noise
supply and ideally as Thorsten stated elsewhere a separate
low cap split bobbin tranny for it. Implemetation is very
mportant. It's not like swapping low speed opamps!

> The latest LC-Audio clock is specified for very low jitter but I can
> not afford it.

Unfortunately any low noise HQ XO will cost money. I suggest that
economies of scale will equate that a commercially avail low noise
TCXO will give better bang for buck than the LC. Also unfortunately
LC or any of the others don't give phase noise specs so we don't
know how much bang for buck we are getting!

> Your suggestion of groundplane to groundplane connection is well
> noted and taken in serious consideration. I will try that! (Walt
> Jung did this with the Audio Alchemy DAC in The Box)
> ELSO

This is very important.

Regards,

Terry


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Topic - Crystal oscillator - Jason 01:31:22 08/16/01 ( 21)