Another problem: funny noise

[lockesilver]

Thank you for solving my problem with clipping.
Now I use the non-amplified inputs on the interface and the levels and quality are better. Nice.
However, another thing emerged.

On those other inputs (both 1/4'' and RCA - tried both) there is funny noise in the background. It changes when I manipulate the cables but never stops and I haven't be able to pinpoint at which exact place this is happening...

(example in the attachment)

 

[mjbphotos]

Sounds like a bad connection - change cables, spray some electronics cleaner into the jacks.

 

[lockesilver]

Sounds like a bad connection - change cables, spray some electronics cleaner into the jacks.

Unfortunately it's not that simple. The noise is exactly the same with two different cables on different inputs/outputs. And it isn't happening at all on the amplified input...

 

[mshilarious]

It seems mains-related as it's principally harmonics of 50Hz. But it is very intermittent, which is odd. It could be switching noise on the USB rail or the USB ground, which can be quite noisy unfortunately. Possible solutions are reworking the grounding scheme. First, make sure the Behri and the computer are connected to the same outlet. Also, if it's a laptop, see if it happens running on battery. If neither of those help, the next step is to isolate the Behri from the interface, which means using a transformer. But let's try different grounding schemes first.

 

[lockesilver]

Useful suggestions as always, but I figured out the problem already.

The power cable from the preamp was touching the preamp-interface cable. I don't know how it happened but I'm guessing the electric current in the power cable caused some interference with the signal in the audio cable. As soon as I made the two wires apart the noise disappeared.

 

[mshilarious]

Useful suggestions as always, but I figured out the problem already.

The power cable from the preamp was touching the preamp-interface cable. I don't know how it happened but I'm guessing the electric current in the power cable caused some interference with the signal in the audio cable. As soon as I made the two wires apart the noise disappeared.

Yes that can happen easily in an unbalanced connection. Usually it's OK to cross cables, but never run them parallel. Or in your circumstance, don't let them cross either!

Still a puzzle why that was so intermittent though . . .