Are you using a laptop ? if so, try to run it on battery.
Are you sure the place has the ground wired correctly ? Buy a cheap tester like this and test every outlet you are using in your setup :

After that, eliminate every piece of gear. Run the monitors alone, put an MP3 player or your phone on it. Hey did you shutdown your phone to hear if it was the problem ??
Try the interface with the monitors alone and go from there ; add the computer, the preamp etc.. step by step you'll find it !! ;)

Sometime it is simple as repositionning or replacing an ac adapter.

ground loop? the tube mics amp is plugged into a different electrical circuit from the interface in the control room?

Hi!

Nope, its a stationary. Why should it be the same issue 2 different places? The new studio is a new building and Norway has good power grids. But yes, I will try cause this is a nightmare.

Thanks!

Stian.

pcrecord, post: 449200, member: 46460 wrote: Are you using a laptop ? if so, try to run it on battery.
Are you sure the place has the ground wired correctly ? Buy a cheap tester like this and test every outlet you are using in your setup :

After that, eliminate every piece of gear. Run the monitors alone, put an MP3 player or your phone on it. Hey did you shutdown your phone to hear if it was the problem ??
Try the interface with the monitors alone and go from there ; add the computer, the preamp etc.. step by step you'll find it !! ;)

Sometime it is simple as repositionning or replacing an ac adapter.

Hi.

I´ve tried both, a separate circuit and the same. Same issue.

Stian

Kurt Foster, post: 449201, member: 7836 wrote: ground loop? the tube mics amp is plugged into a different electrical circuit from the interface in the control room?

Stian, post: 449203, member: 50494 wrote: Hi!

Nope, its a stationary. Why should it be the same issue 2 different places? The new studio is a new building and Norway has good power grids. But yes, I will try cause this is a nightmare.

Thanks!

Stian.

Ok even to another location, you are getting it. Try the list of tests I suggested if you can pinpoint aroud what unit the problem lies, you will then try to change the cables and then power unit(s).

Did the problem just happened without changing anything ?

pcrecord, post: 449207, member: 46460 wrote: Ok even to another location, you are getting it. Try the list of tests I suggested if you can pinpoint aroud what unit the problem lies, you will then try to change the cables and then power unit(s).

Did the problem just happened without changing anything ?

Yep, it started 6 months ago. I thought it was the neighbor installing a new fridge. But since I´ve moved as well I think the problem lies elsewhere. But I will try what you suggest.

Stian

You said the hum is audible especially with tube microphones, but are these phantom-powered tube mics or ones with their own main power supply? How much worse is the hum with a tube microphone over a dynamic mic such as an SM57?

I have a simple piece of kit that I made to help diagnosis of this type of problem that you might consider making up, or at least a variant of it. It's a small metal box with XLRF input and XLRM output connectors and a rotary switch on top. Pin 1 of the XLRs are connected together and also to the box, while XLR pins 2 and 3 on both connectors go through the switch. With the switch in the first position, pins 2 and 3 connect independently between the XLRs as normal. In the next position, 2 and 3 interconnect as in the first position, but are also connected together, shorting the signal, but maintaining PP. The 3rd position has a cheap 1:1 microphone transformer isolating input from output, and in the 4th position, pins 2 and 3 are open circuit on the input connector and short circuit on the output connector. Positions 3 and 4 break the PP supply.

Using this box has enabled me to diagnose many different microphone problems including hum. I have on my "to do" list to add an auxiliary XLRM in the box input side to bring in PP from a separate power supply or other known good source when in switch position 3, very similar to taking the iso output from a mic splitter box.

Before making the box, I used to take the shell off the XLRM end of the mic cable, plug everything in as normal, and then carefully use a small-bladed screwdriver to short out pins 2 and 3 on the input plug. Doing this cut the signal but left the phantom power connected. If noise or hum disappeared when I shorted the signal, the noise or hum was coming from the microphone as though it were a genuine signal. If shorting the pins made no difference, the problem was usually something like a leaky coupling capacitor in the pre-amp input that was unbalancing the PP supply to the microphone.

If you can borrow a mic splitter box (even a cheap unit such as the Citronic MSP-2), you could try the direct and isolated outputs to see if there is any difference in the hum. If your microphone needs PP, you will need to connect the direct output to a source of PP while testing the isolated output.

So, some questions there and a couple of suggestions for things to try.