Maximum cable length for I2s? - diyAudio
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Old 27th June 2010, 09:52 PM   #1
Ryssen is offline Ryssen  Sweden
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Default Maximum cable length for I2s?

Been searching the forum on this subject,and some say after 10cm the signal gets worse,use LVDS for longer cables.And some say LVDS is overkill...that I2s can bes used for longer length.
Opinions on this?
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Old 27th June 2010, 11:13 PM   #2
Sandor is offline Sandor  Italy
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I used 75 cm (about 3 inches) long cables to connect my modded cdplayer to my TDA1541-based dac. Cables were self-made using RG59 coaxial cable and BNC connectors. Observed at the scope, the signals at the dac end looked good, and almost identical to the ones at the player end. No problem, good sound.
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Paul
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Old 28th June 2010, 12:09 AM   #3
glt is offline glt  United States
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75 cm or 7.5 cm?
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Old 28th June 2010, 02:30 PM   #4
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Depends of the output/input impedances. If they are low and adapted with the cable, then you don't need LVDS for 2-3 feet.
I would suggest twisted CAT5E cable with 100 ohms resistor on the receiver side. And of course with the I2S output buffered to be capable of driving that load.
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Old 28th June 2010, 09:45 PM   #5
Ryssen is offline Ryssen  Sweden
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Quote:
And of course with the I2S output buffered to be capable of driving that load.
How is such a buffert constructed?
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Old 28th June 2010, 10:02 PM   #6
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Use 74HC(T) or 74AC(T) 244/245 buffers...
- clock lines can beterminated by using 100 Ohms and 100pF in series (so the DC-resistance isn't that low) and
- data lines with 220 Ohms to Vcc and 330 Ohms to GND (see SCSI), perhaps coupled via 100pF to the line.

!! But LVDS is preferrable !! or you must a 100MHz (minimum !) scope to check if termination is ok.

Don't forget, that the MCLK must be treatened as an analog signal ! (else you would get jitter problems and therefore noise or FM modulated to the signal (not detectable by common used notch filters analyzers !)
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Old 29th June 2010, 10:26 AM   #7
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pics for better understanding. The value of C depends on the frequency to be terminated
Attached Images
File Type: jpg Terminating_Data-CLock.jpg (29.6 KB, 387 views)
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