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andy.m2
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Posts: 6



(03/15/09 09:08 AM)

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FireWire 4-wire cable to break "ground loop"
My audio setup is made up of FireWire devices only:
Windows XP PC with a FireWire card using a Texas Instruments chipset
M-Audio FireWire 410 audio interface (with external power supply)
Yamaha S90 ES synth with mLAN card (powered from mains)

All the peripherals are powered from the same AC outlet.

When I connect all the peripherals to an audio mixer I hear, in the audio output, a “digital hash” noise. A ticking or tweeting noise, especially when I move the mouse or start a new program. This noise is due to a “ground loop”.

I read that to in order to solve “ground loop” problems one has to “break the loop”, preventing ground levels in the different devices from contacting each other.

In order to “break the loop” I created a FireWire 6M-6M cable with just 4 wires. I cascaded a FireWire 6M-4M cable (with just 4 wires) and a FireWire 4F-6M adapter. Using this cable I connect FireWire devices with a 6 pin connector, but only with the 4 signal ping. The DC voltage and the ground don’t go from a device to another. All the devices are powered, so they don’t need to get the DC voltage from the FireWire cable.

When I connect the devices using this cable I no longer hear the “digital hash” noise. So the “ground loop” problem seems solved. But the FireWire devices do not work with cable. The PC doesn’t even recognize them.

Is it possibile that FireWire devices, when connected to each other, are able to “expose” their features and tell if they have a 4 or 6 pin connector? If two devices at the ends of a cable have a 6 pin connector, but they don’t see the DC voltage because they are connected using only 4 wires, can they stop working? I think this is not likely to occur. If this happened, all the FireWire 4 to 6 pin adapters would make no sense.

Why do FireWire devices, having 6 pin connectors, not work when they are connected with only 4 wires, so that DC voltage and ground are not connected?

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