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Old 28th March 2003, 04:34 PM   #31
A 8 is offline A 8  Sweden
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alvaius,
I just finished my new dac CS8420/DF1704/PCM1704K and made a 24.576 Mhz clock and shapers based on singlegate logic with individual decoupling.
I want to change the clock to a better one and need to decide what to consider.

The clock is directly connected to bitclock in on the dac chips so I expect the clock quality to have a very direct impact on the final result.
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Old 28th March 2003, 04:41 PM   #32
tiroth is offline tiroth  United States
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I think the only argument for very high bandwidth in jitter-sensitive application is that the time spent in the transition region is very short, leading to better rejection of various types of signal modulation. But of course this causes the problems stated. I think it is all a tradeoff.

Murata makes some special ferrite beads that are designed to pass up to a given bandwidth and then sharply reject higher frequencies--they are intended specifically for EMI limiting without screwing up the transitions. I've never tried them in a jitter-sensistive clock path though.
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Old 28th March 2003, 04:50 PM   #33
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Lightbulb 24.576 MHz low jitter Clock

Quote:
Originally posted by A 8
alvaius,
I just finished my new dac CS8420/DF1704/PCM1704K and made a 24.576 Mhz clock and shapers based on singlegate logic with individual decoupling.
I want to change the clock to a better one and need to decide what to consider.

The clock is directly connected to bitclock in on the dac chips so I expect the clock quality to have a very direct impact on the final result.
Hi A8,
You can built my clock i.e the KWAK-CLOCK. If you use the email button below this post I will sent you the schematic.
Only a fundamental mode crystal will work like this one f.a.:
http://www.digikey.com/scripts/us/dk...873&Row=336843
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Old 28th March 2003, 06:49 PM   #34
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Jean-Paul:

I was refering to the tons of test equipment it takes.

JWB:

I have versions with and without the coupling cap. The cap was used to prevent long cables terminated in 75 ohms from mucking things up. Along with build out resistors.

When I get everything here back up and working, I will post some .wav files of the various clock thingies that I have around here. Should prove enlightening.

Ferrite beads act as resistors, that are frequency selective.

Bandwidth can be detrimental, as the peak currents give rise (inadvertant pun!) to ground bounce and crap like that.

I use a sine wave clock, as I pump it all over the lab, and square it up internally.

Jocko
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Old 28th March 2003, 07:22 PM   #35
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Default Re: Who among you actually carried out easurements on.......

Quote:
Originally posted by Jocko Homo
I have, but I no longer have access to all the equipment that you still do, Guido.

So I have to come up with different approaches. In any case, you are right.....it is a lot of work, and most people here don't have our capabilities.

Jocko
Hello Jocko

Oh yes, there are very often more than one sollutions to a given problem.
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Old 28th March 2003, 07:26 PM   #36
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Quote:
Originally posted by alvaius
Sometimes passing perfect square waves is not the best thing to do. That means higher EMI, higher transient currents, etc. that could create their own problems. I have experienced cases where a bit of slew rate limiting has resulted in better system performance, though not specifically in audio, though the output gates on some logic families (on the output of the XO) are prone to ground bounce and a little bit of slew rate limiting could help the final effect.

However, what the issue here may be is more a matter of implementation. If the output of the XO is simply a sine wave (which internally they all are close to at some point), then AC coupling and limiting the bandwidth is not really an issue.

A 8, did you have a specif application or instance in mind?

Alvaius
True about the EMI and bounce, and yes there are perfect trade offs. I have stated that many times, see also:

http://members.chello.nl/~m.heijlige...decoupling.pdf

I would not reccomend distributing a sine wave as that is far more susceptible due to the lower dV/dt.

My XO's put out a square wave

all the best
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Old 29th March 2003, 06:03 AM   #37
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Default The problem with square waves.......

I use a cheap TV in my lab to detect EMI problems. A lot of stuff that I see generates tons. With all the clock signals I have going every which way, unless it was a ridiculously low level, it would mask the EMI the I am trying to detect. So sine wave it is. I have yet to see any phase noise detriment this way, and since I don't have a $40K 'scope to measure jitter with..........

The all time winner for generating EMI was the Audio Alchemy "Jitterbug". Took every VHF channel off of the air.

The original Arcam "Black Box" was a close second. Never measured the subsequent versions.

Jocko
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Old 29th March 2003, 12:59 PM   #38
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Default Re: The problem with square waves.......

Quote:
Originally posted by Jocko Homo
I use a cheap TV in my lab to detect EMI problems. A lot of stuff that I see generates tons. With all the clock signals I have going every which way, unless it was a ridiculously low level, it would mask the EMI the I am trying to detect. So sine wave it is. I have yet to see any phase noise detriment this way, and since I don't have a $40K 'scope to measure jitter with..........

The all time winner for generating EMI was the Audio Alchemy "Jitterbug". Took every VHF channel off of the air.

The original Arcam "Black Box" was a close second. Never measured the subsequent versions.

Jocko
Hello Jocko,

Does your TV "spectrum analyser" have an aerial antenna or cable ? In the latter case I am pretty sure the Audio Alchemy and the Arcam are not meeting international EMC requirements.....

It is my experience that low EMI also contributes to signal integrity and inmproves sound quality.

all the best,

Guido
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Old 29th March 2003, 02:37 PM   #39
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Default It uses a dipole......

Which can be adjusted.......or moved close to the offending item.

No, I think that it is safe to say that they do not comply. Which is why they sometimes find their way into my shop when a disgruntled owner complains about them.

Yes, it always seems to make things sound better if you fix those problems.

I was unable to do much with the "Jitterbug". It used a DSP chip that caused most of the problems.

Another trick used by us ham radio types is to hit the TX button on a 2 meter handheld rig, and see what happens. Some pieces go nuts.

Jocko
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