Weird DI noise through amp/cab

[thebassman]

I have a genz Shuttlemax 9.2 and genz cab.
I have used this setup quite a few times DI'd with no problems, always sounded really good FOH and on stage.
This weekend I played a music festival with stage/engineering etc.
FOH sounded great, but I was getting some really weird noise through my cab. Sounded a bit like distorted earth hum.
This was using the inboard DI on my head, tried post and pre EQ. No change in noise.
I pressed the mute button on the amp, still had noise.
The only way it would stop was if I unplugged the cable from the DI socket.
Any ideas? I'm a bit concerned as I have more gigs coming up in the next few months.
Cheers for any help
Thebassman

[Bill Fitzmaurice]

Symptoms are those of a ground loop. The amp should have a chassis ground lift switch to prevent that.

[thebassman]

[quote name='Bill Fitzmaurice' timestamp='1401139858' post='2460568']
Symptoms are those of a ground loop. The amp should have a chassis ground lift switch to prevent that.
[/quote]

Hi Bill
Thanks for the reply.
Yes, it has got a ground lift switch, got to admit, I didn't try that.
Would this change with different pa set ups? Just curious as I have never had the problem before, with the same amp/cab, but different pa.
Cheers
Thebassman

[Bill Fitzmaurice]

[quote name='thebassman' timestamp='1401141367' post='2460593']
Would this change with different pa set ups? Just curious as I have never had the problem before, with the same amp/cab, but different pa.
[/quote]It can, depending how their inputs are wired. Not all are as they should be. This explains:
http://www.rane.com/note110.html