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Old 5th December 2001, 09:13 PM   #1
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Hello,
While tweaking my AMC CD-8B analog output stage I began looking into improving the clock. This unit uses a single PCM1716 dac. The TI spec-sheet specifies a 16.340MHz clock, but the crystal in the unit is the more common 16.344Mhz. Is this a problem and should I try to find a 16.340MHz XO?
16.344Mhz is more easily available, is this perhaps why AMC used this crystal? I realize the %difference is miniscule, but thought I should check before ordering a new XO. Any advice is appreciated.

-Thank you.
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Old 5th December 2001, 10:16 PM   #2
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Hello

You can "pull down" a crystal by connecting in series a small coil, say 5 or 10 turns of thin ennameld copper wire, on a small plasic tube (1/8 or 1/4") Cut and try... When all is ok, you must use glue in order to minimize vibrations effects, which can cause some jitter...


Regards, P.Lacombe.
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Old 6th December 2001, 02:46 AM   #3
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16.9344MHz is a right fequency for CD player.
44.1K(sampling rate of CD) * 384 = 16.9344MHz
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Old 6th December 2001, 08:18 AM   #4
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I agree, odd then that TI spec's 16.9340 for this particular chip and a few other listed on their site. Perhaps a typo or bad math on their part.
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Old 6th December 2001, 10:12 AM   #5
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yes! I think the better way to check the frequency clear. Is check for the mark on the crystal which they using on the PCB.

For the formula the frequecy should be 16.9344MHz. And may be they just show the spec in the simple way and less some value only!
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Old 6th December 2001, 01:00 PM   #6
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In earlier CD players, some manufacturers used a crystal running at a slightly faster frequency than required. I recently upgraded my CD player, an eleven year old Carver, with the LClock XO2 from LC Audio. The crystal in my CDP was running at 8.6432 MHz, and LC only had a frequency of 8.4672 MHz available. Lars told me that some manufacturers used a faster clock speed to make the sound seem lighter or more lively, but this practice has been largely discontinued. This just goes to show how the clock speed does not have to be exact. Get the common frequency, for you it would be 16.9344 MHz. It's hard to tell what a manufacturer will do to cover up a mistake in design.
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Old 6th December 2001, 01:31 PM   #7
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hmm i believe that some dacs can have difficulty locking on if the clock is mor tan +-100ppm off....

/micke
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