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Old 13th December 2013, 07:41 PM   #1
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Join Date: Aug 2012
Location: Tel Aviv, Israel
Default building a Y USB cable - quick question

Hey guys.

Im working on a Y USB cable for my dac (hegel hd2) and i have a simple question..

i know that if the computer dosnt "feel" any voltage through the power supply it wont send a signal, so i know i need to place a between the 5+ 5- on the computers side, qustion is, which value?

thank you!
Tank out
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Old 14th December 2013, 04:38 AM   #2
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Your understanding of bus voltages and device connect indication is incorrect. Referring to the electrical chapter of the relevant USB specification should clarify matters (you don't mention which USB version the HD2 is compliant with).
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Old 14th December 2013, 07:25 AM   #3
marce is offline marce  United Kingdom
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Are you using the y-cable for extra power?
Splitting the signal isn't going to be the best option for signal integrity, this site will have some info though:
USB.org - Welcome
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Old 14th December 2013, 08:57 AM   #4
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For extra power, just connect the power wires (red and black) of the second USB cable in parallel with the first one. Leave the data wires (usually green and white) disconnected. This doesn't comply with the USB spec, because the second cable should negotiate with the hub before drawing more than 100mA, but it can't because its data wires aren't connected to anything. However, it almost always works.

It can be a bit pointless though as most USB hubs have ganged overcurrent protection. On a 4-port hub you can draw the full 2 amps from any port.

A Y cable doesn't do anything useful with the data. You can't plug one USB device into two hosts at once, or have two USB DACs playing the same signal or anything else you might have had in mind.
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Last edited by scopeboy; 14th December 2013 at 09:00 AM.
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Old 14th December 2013, 07:28 PM   #5
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Correct for 1.x and 2.0 ports which don't support battery charging. Incorrect for 3.x ports or ports with charging support. 2A from a four port hub is correct in some circumstances but incorrect in others. The statement about Y cables' data line behaviour is well intentioned and mostly true. But incorrect for compliant implementations.

You should probably refer to the specs for clarity as well.

Last edited by twest820; 14th December 2013 at 07:30 PM.
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