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Old 21st January 2003, 07:10 AM   #1
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Default Cdrom Spdif Polarity

Can some knowlegeable memeber please tell me the polarity of the pins on the Molex connector of CDROM spdif output please?
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Old 21st January 2003, 08:29 AM   #2
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One of the pins is ground, this can be easily checked with a multimeter....
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Old 21st January 2003, 03:45 PM   #3
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Quote:
Originally posted by sikkek
One of the pins is ground, this can be easily checked with a multimeter....
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If its so easy, I would have done it. You can see on card. My point is: What is the convention on th CDROM. You can't get at it unless you dismantle. I have a manufacturer that seemed to have reversed polarity by using red on ground!
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Old 21st January 2003, 04:16 PM   #4
Nisbeth is offline Nisbeth  Denmark
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What brand is the drive? Usually you can download specifications from the manufacturers website.

/U.

PS: I think I remember seing something about the polarity of this thing actually being irrelevant, because it is a TTL 0-5V signal, but I'm not entirely sure. Might be worth checking out as well, though.
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Old 21st January 2003, 06:39 PM   #5
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Quote:
Originally posted by Nisbeth
What brand is the drive? Usually you can download specifications from the manufacturers website.

/U.

PS: I think I remember seing something about the polarity of this thing actually being irrelevant, because it is a TTL 0-5V signal, but I'm not entirely sure. Might be worth checking out as well, though.
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Thanks; but CDROM manufacturers tell you nothing about them except basic info anf how great they are.
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Old 21st January 2003, 08:07 PM   #6
Nisbeth is offline Nisbeth  Denmark
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What I meant was a "users manual" which has a picture of the connections on the back of the drive. I have the one for my Pioneer DVD-drive and I found a few for various cd-rw drives from i.e. yamaha and aopen. Look on the manufacturers web-site for "users manuals" or equivalent.

/U.
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Old 22nd January 2003, 05:32 PM   #7
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I beleive this is what you are looking for...

Click the image to open in full size.

From back, digital on left, ground on right. This is from a Lite-On CD-ROM.
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Old 22nd January 2003, 08:02 PM   #8
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Quote:
Originally posted by bstanton010
I beleive this is what you are looking for...

Click the image to open in full size.

From back, digital on left, ground on right. This is from a Lite-On CD-ROM.
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Thanks. What threw me off is that the standard cable is shielded two core, with red not connected, white +ve and black on shield.
Why can't they use 75R coax which should be better. Some manufacturers (high class sound card) don't even shield their cables!
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Old 23rd January 2003, 04:23 AM   #9
MWP is offline MWP  Australia
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Quote:
Originally posted by fmak
Why can't they use 75R coax which should be better. Some manufacturers (high class sound card) don't even shield their cables!
1. Because its 5V TTL which is used over a short distance, PC noise wont effect it.

2. Because its a PC, since when have soundcards produced good quality audio?
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Old 23rd January 2003, 07:14 AM   #10
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The SPDIF output on CDRom drives is not 'normal' SPDIF in electrical sense. Normal SPDIF over coax has an amplitude of +/- 0.5 Volts, the SPDIF out on CDRom drives is TTL level: 0 or 5 Volts. Be carefull when connecting the output to a DAC, not all SPDIF outputs on CDRom drives like to be loaded with a 50 ohm load! (It will draw 100 mA from the output, which is quite a lot for TTL outputs). Better is to use a conversion to go to +/- 0.5 Volts...
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