For people on a low budget (not wanting to buy a LCaudio or Audiocom clock) the following tweak might improve their cd players or dacs that have crystals inside them.
Desolder the crystal, solder say 5 cm fine wire to each leg (I use wire wrap wire)
Solder the wires into the crystals original location.
Bend both wires in a 90 degree angle so the crystal is "dangling" horizontally in the air.
Effectively this will decouple the crystal from a mechanical point of view. Vibrations from transport & pcb will propagate less easy to the crystal, inducing less jitter.
One can see this mechanical sensitivity very easy on a scoop, by just tapping the crystal with your fingernail or small screwdriver.
I've experienced improvements from none to almost as good as a seperate clock. Depends of course on the quality of the local powersupply for the clock gates.
Even on the older "Kwak-Clock" versions the effect was still there.
Only the most recent ones with higher fet current and dual supplies for the comparator are quite immune to the "fingertapping"
Desolder the crystal, solder say 5 cm fine wire to each leg (I use wire wrap wire)
Solder the wires into the crystals original location.
Bend both wires in a 90 degree angle so the crystal is "dangling" horizontally in the air.
Effectively this will decouple the crystal from a mechanical point of view. Vibrations from transport & pcb will propagate less easy to the crystal, inducing less jitter.
One can see this mechanical sensitivity very easy on a scoop, by just tapping the crystal with your fingernail or small screwdriver.
I've experienced improvements from none to almost as good as a seperate clock. Depends of course on the quality of the local powersupply for the clock gates.
Even on the older "Kwak-Clock" versions the effect was still there.
Only the most recent ones with higher fet current and dual supplies for the comparator are quite immune to the "fingertapping"
Can you really confirm your statementrbroer said:
Jitter is MEGAHERTZ!Long wires is a typical no-no if we talk crytal oscillators. What about RFI or EMI from the crystal? Your circuits may pick up the clock signal and really interfere and make things worse!
I think this advice is not very good but if you do have problems with vibrations, let the whole oscillator be suspended in something!
Jitter is not per definition in the MegaHertz range but further I agree with Per-Anders. Long wires are a no-no.
Is a tiny drop of silicone kit under the crystal not better to damp it mechanically ? I've seen crystals in expensive players that had a rubber band around them to damp it. When removed the player did sound different ( worse ). This all was not comparable with a low jitter clock that gave best results.
Of course, Jean-Paul, jitter isn't measured in MHz but what I ment was that jitter is mostly as high frequency phenomina. A crystal is a mechanical device so therefore it's sensitive for vibrations but in a regular CD-player I think the vibrations are rather small, not the one in a x48 data-CD.
What's all this crystal damping stuff, anyhow???
Yes, it makes a difference, but not much. I have measured it. Don't remember the exact amounts, but it didn't help much.
Of course, it may have been enough in your application.
And each brand of crystal is microphonic at different frequencies.
Jocko
Yes, it makes a difference, but not much. I have measured it. Don't remember the exact amounts, but it didn't help much.
Of course, it may have been enough in your application.
And each brand of crystal is microphonic at different frequencies.
Jocko
Speaking of which..............
I getting hungry. Time to bug Phred to go eat pizza.
I need to work out some of the bugs in my phase noise measurement thingie to get the noise floor down. At which point I will post some of my measurements.
Including why the SAA7220 is a piece of junk. Stay tuned..........
Jocko
I getting hungry. Time to bug Phred to go eat pizza.
I need to work out some of the bugs in my phase noise measurement thingie to get the noise floor down. At which point I will post some of my measurements.
Including why the SAA7220 is a piece of junk. Stay tuned..........
Jocko
Re: What's all this crystal damping stuff, anyhow???
dear all,
Yes, it makes a difference (and I take care of that in my XO's, not claiming that further isolation makes no sense, but it also depends on the environment)
Jitter spectrum starts just above 0Hz, that is why some claim a TCXO is required (I am not among that group of people, as long as the absolute frequency error is sufficiently small)
Once you made the crystal immune for environmental noise, let us continue with DAC chips, they behave like piezo's !
enjoy
Jocko Homo said:
dear all,
Yes, it makes a difference (and I take care of that in my XO's, not claiming that further isolation makes no sense, but it also depends on the environment)
Jitter spectrum starts just above 0Hz, that is why some claim a TCXO is required (I am not among that group of people, as long as the absolute frequency error is sufficiently small)
Once you made the crystal immune for environmental noise, let us continue with DAC chips, they behave like piezo's !
enjoy
In a nutshell............
Let's say that you get one of those fancy oscillators........like say the one Guido sells.........and you hook it up to the OSC IN pin of that stinking chip........you are pretty much wasting your time.
The phase noise on the output pin (#9, I believe) is just as bad using a high quality oscillator as the lousy stock version. And it is not a very quiet signal.
If you do use a good oscillator, you must make a new distribution scheme to realise its full potential. You cannot put it through the filter chip to drive the rest of the system.
I'll post how bad the actual numbers are later.
Oh yeah........the decoder chip has the same problem, only not as bad.
Jocko
Let's say that you get one of those fancy oscillators........like say the one Guido sells.........and you hook it up to the OSC IN pin of that stinking chip........you are pretty much wasting your time.
The phase noise on the output pin (#9, I believe) is just as bad using a high quality oscillator as the lousy stock version. And it is not a very quiet signal.
If you do use a good oscillator, you must make a new distribution scheme to realise its full potential. You cannot put it through the filter chip to drive the rest of the system.
I'll post how bad the actual numbers are later.
Oh yeah........the decoder chip has the same problem, only not as bad.
Jocko
If you want a cheap crystal tweek ($0.05), take a sandwich bag and put some sand in it, and place it on top of and around your crystal. It may or may not make a difference, but it's cheap and probably every bit as effective at damping the crystal as hanging it in the air, but it doesn't have the inductance of the long leads.
Sheldon
Sheldon
Megalithic Tweaks
Yeah, try valve springs as mountings instead of cones etc.
A method I used years ago was to place a house brick on top my cd player on the top of my rack.
This dramatically lessened acoustic feedback, but one problem was that the brick was directional - seriously !.
Eric.
fdegrove said:
Yeah, try valve springs as mountings instead of cones etc.
A method I used years ago was to place a house brick on top my cd player on the top of my rack.
This dramatically lessened acoustic feedback, but one problem was that the brick was directional - seriously !.
Eric.
The microphonics problem sounds.......(yes, sounds, because I actually listen to it.........) to be the internal holder vibrating. Doing anything to the can lowers it some, but not that much. Any acoustic energy that arrives at the PCB is just coupled right on into the holder. The solution would need to mechanically isolate the crystal from the PCB as well.
I doubt that a good design could not handle an extra 2 mm or so of wire.
Jocko
I doubt that a good design could not handle an extra 2 mm or so of wire.
Jocko
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