Ground loop stuff and digital Hash

Hello, I was working on a problem on here before and a member named “ciptension” was going to try to help me with it but now the forum has changed and I have had to re-register for some reason and don’t have access to the post I started before.

I have a soundcraft 800b. When I hook it up to my mr 816 (through the unbalanced direct outs on a channel) I get a lot of Digital “hash”. It gets recorded. It is only there when I arm a track, gone when not.

Today I discovered that if I went balanced out of the group outs the digital hash is gone but I still have a hum.

I plug headphones into just the board, disconnect everything and bring up a group fader. Still have the hum (nothing else plugged in at this point).

If I lift the ground on the board, still hum on group faders.

anybody have any ideas? 2 seperate problems or one and the same?

Hi There !

Do you have all power sockets connected to the same Phase i.e. same potential against ground ? Are you living in a country where you can turn power socket 180 deg around (not in u.s. or u.k that is).In Studio enviroment you should be okay without balanced cables if phase / grounding is okay.

Try this…power up your system and make sure that hum is audible. Then start disconnecting everything which has the same potential than your music stuff - one by one. At some point you will find a device which is causing your headache. That includes power supplies and all the wiring between your mixer and audio interface. One by one.


I live in canada. I’m not sure if I can flip the phase 180 deg. I did manage to get rid of the digital hash going through the board out balanced outs … But seeing as I still have this hum on the mixer when Nothing is plugged into it except headphones I’m not sure what could be the problem there. I guess I have to start pulling every channel and see if one of them is shorting out the ground to all?

I feel like I am so close now. Excuse all the posts but can anyone follow this:
I have narrowed it down to unbalanced cable in interface connected to anything else that has power and this digital noise happens. If I
Plug in a guitar direct to interface it’s not there. If I take the other end of the cable and touch the chasis of the mixer while everything is unplugged it’s not there.

If I plug my powered speakers into the mixer and the mixer is still unplugged (no power) the noise starts when unbalanced cable touches chasis or plugged in. Heck I can touch the metal on my powered speakers and it’s there.

So it’s not an issue between the board and the interface.

Any ideas?

Well, it’s solved sort of.
The problem is grounding between the Imac, ungrounded MR816, and connecting to anything else grounded.

If I take the ground off the Imac and connecting everything the sound is gone.

So what is the solution now?

Hello Cactus slim,

I have a setup with a lot of audio hardware merged and had a similar problem.
I looked up a hifi transformer that would do a complete galvanic separation between the devices. Using symetrical cables does not help when you have a ground loop problem.

I found the transformers here in Germany. Try to find something similar in your country
The device I use has Cinch-Cinch connectors. You might consider using stage DI boxes with XLR connectors as they are used on stage. if Cinch-Cinch is not an option for you.

Here is where I found the devices. It’s in German. Try to find something similar at home.

The price is 14 EUR per piece (stereo)
HENRI-electronic GmbH
Am Stadtgraben 11
D-73441 Bopfingen

Pegelwandler (Störgerüschunterdrückung) Ground-Isolator


inkl. MwSt. ohne MwSt.


inkl. ges. MwSt. zzgl. Versandkosten für den ges. Warenkorb.

Marke: Entstörer Audio
41-105-00002 Audio Störgeräuschunterdrückung Cinchstecker_Cinchbuchse

Beschreibung - Technische Daten:
Audio Entstörfilter Stereo Cinch-Stecker auf Stereo Cinchbuchsen mit galvanischer Trennung. Unterbricht auch den Masseweg. Frequenzbereich: 40…32.0000Hz / Ein-Ausgangsimpendanz 10-KOhm / Die Anwendungsmöglichkeit ist sehr vielfältig, PA, Mischpult, Musiker, CAR-Audio usw.

A few manufacturers make things called hum destroyers - which are simply more commercial versions of the above passive transformer. E.g. Behringer HD400 MICROHD Hum Destroyer. Just put them in line and they isolate both sides. But, they are passive so they will effect the signal level and possibly the sound too.

There is also another tried and tested method, and that’s to use signal leads that have the ground disconnected. These should be used in places when there is another ground path present between the two items being connected, thus you don’t need one in your signal cable as well. I made a few of these leads by just clipping the cable in the plug, marking the plug and then trying them in various places until the hum disappeared.

If your equipment is in a rack, you could even try using a Humfree or 4…


Thanks for the ideas. DI’s, or hum destroyers, etc… will not work for me I don’t think. Taking the ground of the actual cables probably would but I’ve never done something like that. In the end I have realized it is the Imac (imac) and that I have 2 weeks left on applecare so my fingers are crossed that they will fix or replace.

I called today Apple and then stopped by an apple certified store and they have had 2 cases of the same problem with a certain batch of Imacs, and mine falls in the timeline of when they were sold. Faulty power and ground problems is what they said.

I can’t isolate individual channels with DI’s as I’d need 16-24 of them. But it did help to solve the problem a bit trying one.

I’m wondering if anyone has had success in getting Apple to do this repair or replace?

I see no reason to run the imac without a ground because it is faulty.

Hopefully it all works out. Thanks everyone.