Weird noise through bass rig/PT? Grounding issue maybe?

[Travisx2112]

Hi there!

I didn't quite know where to put this, so mods or admins feel free to move it if need be.

I'm a new user to Pro Tools as of two days ago. I was super excited to get it, as I've been using GarbageBand and hate it.

My rig is as follows:
iMac 21.5 inch, with 4gb RAM
MOTU 828 MK3
a BOSS LS-2 Line Selector, which goes through the following
Sansamp RPM:
EHX Big Muff Bass
Digitech Whammy

and the other half is just a Sansamp RBI on it's own.

When I have the output from the LS-2 plugged into the input of the MOTU, there's a high pitched noise, like that of an onboard soundcard from a laptop, for example. It doesn't do it, however, if the output is plugged directly into the bass. Also, it doesn't make any noise with my keyboard, which is also plugged into the MOTU as well.

So, Last night, I took the output cable, and touched it to metal peices of equipment through the chain (for example, the footswitch on the digitech whammy) even with the Whammy's power unplugged, and the noise was still there! Does that mean it's a grounding issue? So I then unplugged a patch cable from the Big Muff to the Whammy, and the noise upon contact dissapeared.

Now, here's another thing to note, too. In Garageband, there is still a similar noise, but it doesn't sound the same. I don't think it's a software issue though, because it dissapears if I change the cable routing, as I've said before. Everything is plugged into two power bars (of which one is daisy chained to the other.) Oh, it also appears if I just use the RBI side of the LS-2, and also if I only plug in the chain from the RPM. I haven't tried it yet with just the RBI.

Any ideas? Is it a grounding issue?

Thanks in advance for the help!

[albee1952]

High frequency noises are likely not grounding(which usually manifests as a 60 or 120 cycle hum). More likely its some other noise being induced into the unbalanced cables you have with some of the rig. Could be drive noise, RF, EMI, etc. Does the iMac have wifi? Can you turn it off? Try moving cables around. If you have a bunch of wall warts and such near your audio cables, try moving them. Try hardware bypassing one piece at a time and maybe you can pin it to a pedal or a certain cable.

[Travisx2112]

Ooh. I was wondering that too, about the cycles!

All of the cables are unbalanced in the rig, and there are a lot of wall warts plugged in near eachother. Should I try some balanced cables instead? I was reading last night that that can help eleviate issues like this.

[Travisx2112]

So, an update. I was talking to a friend about the issue and he said it is a grounding issue and told me to try removing the ground prong on the detachable power cords for my Sansamps. This worked perfectly! However, this is obviously unsafe, so I'm wondering if there's a box I can buy or anyhting to do the same thing without getting rid of the ground prong in the plug?

[Travisx2112]

Anyone?