Ground Hum due to FW cable? - how to unearth

[harry]

Hello all,

I've had a constant earth hum problems in my studio and now with my firewire interface (Steinberg mr816) - and noticed that when the I/o is connected to my monitoring setup, it doesn't hum at all when I disconnect the FW cable from the computer.

I want to try and cut the shield of one end of the FW cable - google tells me it is pin 2.

Has anyone got any experience with this?

I have tested the card in the past and found that the hum doesn't get into the inputs of the soundcard just into the mixer when I monitor the main soundcard outs (recordings are fine - just record tested each channel without anything plugged in and normalised the signal - all I get is nice white noise... no earth hum at all)

I'm only checking all this stuff as somehow earth hum got into my last recording (think my space echo causes this) and I wanted to get to the bottom of everything...

Along the way, I have noticed that when my soundcard is patched into my bantam patchbay, I get the occasional low level pop / click in the audio.... was thinking this might be digital glitches, but have since ruled this out (3 hours of various recordings with nothing plugged in... then normalised - nothing but whitenoise and no glitches.. (DPC checker results are good - windows defender and wifi card switched off..) could it be static electricity flying around the bay (everything switched off) or the crap Ningbo connectors I used are perhaps a wee bit intermittent?

Just checked this stuff out on my mates 'holy and perfect' apple laptop / ensemble combination for glitches artifacts - and found that he had some severe earth hum coming in to his ensemble... seems that this is a subtle problem that gets a lot of people - and it is not obvious until 24 tracks with -68db 60hz hum are mixed together...

h.a.r.r.y.a.r.v.a.n.i.t.i.s

[Paul Maybury]

Hi Harry, I have had success in the past with lifting the earth on Firewire cables.
They are a potential source of earth loop hum.
Cheers,
Paul

[harry]

Hey Paul,

I cut the shields - very hard to do, and disconnected the ground / power pins..
Thing is - I have 2 identical soundcards - when I plug the cable into the 1st one... it doesn't work, BUT... it does when plugged into the 2nd.

[Kurt]

With a chain of various leads and adaptors you could change it to 4 pin and back again. The 4 pin plug doesn't have the 2 power pins that the 6 pin does.

[harry]

Hey Kurt,

Great idea - been scouring ebay for the appropriate connectors... my local computer shop doesn't sell them anymore... oh well

[Paul Maybury]

Oh yeah, what Kurt said. tried that too, and it can work. Certainly easier than lifting the shield.
If I remember rightly, my Motu 24 i/o PCI card uses firewire cables, but it isn't a firewire interface and the 6 to 4 to 6pin didn't work, but lifting the shield did. With some RME firewire interfaces, the opposite was true.
Cheers,
Paul