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Old 11th May 2008, 11:08 AM   #1
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Default Slow playback after replacing crystal on soundcard

I tweaked with my cmi8788 based soundcard by replacing traditional crystal oscillator with Rakon brand oscillator chip at same 24.576mhz.

I thought that if i could supply oscillator chip via clean power source then it would be an improvement.

I removed two little capacitors and crystal and applied oscillator chip like schematic below.

It worked but playback is too slow. Rebecca Pidgeon sings like Hulk Hogan.

I tried 10 nf cap, 100r resistor at output and 3.3v supply but same result.

I used oscillator chip from an old soundcard. Maybe it's a faulty or non accurate chip.. have you any idea?
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Old 12th May 2008, 03:47 PM   #2
kevinkr is offline kevinkr  United States
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Have you measured the oscillator to make sure it is actually producing a 24.576MHz output? You might also try a new oscillator module from one of several sources like Tent Labs, etc.
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Old 12th May 2008, 08:12 PM   #3
Eric_R is offline Eric_R  Sweden
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Why don't you remove the 1M resistor also, it leaks signal from XO to XI.
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Old 12th May 2008, 11:52 PM   #4
wa2ise is offline wa2ise  United States
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Quote:
Originally posted by Eric_R
Why don't you remove the 1M resistor also, it leaks signal from XO to XI.
I agree, that resistor may be what's goofing it up.
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Old 13th May 2008, 10:44 AM   #5
weissi is offline weissi  Europe
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I would also put an series resistor of ~100Ohm between Oscillator Output and CMI8788 Input. Otherwise you might get some ugly overshoot.
But I'have modded my CMI8788 in a similar way, so it should work.
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Old 13th May 2008, 02:15 PM   #6
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Quote:
Originally posted by kevinkr
Have you measured the oscillator to make sure it is actually producing a 24.576MHz output? You might also try a new oscillator module from one of several sources like Tent Labs, etc.
I have no any facilities for measuring. I'm trying to find another one at the moment. If i could find Crystek or Petermann Technik brand low jitter oscillators, it would be good enough instead of expensive ones.

Quote:
Originally posted by Eric_R
Why don't you remove the 1M resistor also, it leaks signal from XO to XI.
First, i tried without it, when this problem occurs, then i resolder it after checking for similar modifications. Then, i will try without it again...

Quote:
Originally posted by weissi
I would also put an series resistor of ~100Ohm between Oscillator Output and CMI8788 Input. Otherwise you might get some ugly overshoot.
But I'have modded my CMI8788 in a similar way, so it should work.
My soundcard is Club3D Theatron DTS (Bluegears B-enspirer). I tried with 100ohm resistor as i mentioned in first message. Which parts did you remove? Did you remove 1M resistor? Can you give a little explanation please?
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Old 13th May 2008, 05:36 PM   #7
weissi is offline weissi  Europe
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I also have the Theatron. Basically I have removed the 1Meg Resistor plus the to ceramic caps and connected the output of the oscillator via a 100Ohm resistor to XI of CMI8788. But I used an 3.3V oscillator. Normally this shouldn't effect the CMI8788 but I don't know if its Ports are 5V tolerant....
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Old 13th May 2008, 07:03 PM   #8
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Quote:
Originally posted by weissi
But I used an 3.3V oscillator. Normally this shouldn't effect the CMI8788 but I don't know if its Ports are 5V tolerant....
Maybe this is the trick. That seems it wouldn't be clear unless getting a new 3.3 oscillator.

Thank you all.
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Old 13th May 2008, 09:17 PM   #9
weissi is offline weissi  Europe
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I have used this one, although not low jitter, but I guess it will work much better than the crystal oscillator that's onboard:

http://at.rs-online.com/web/search/s...duct&R=4785216
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Old 13th May 2008, 11:36 PM   #10
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I ordered Crystek C3391 's from Mouser. I have to find a low noise regulator solution. ON Semi NCP700 looks up for this job with 15uV rms noise level.
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