teach

mayday! digital noise/static

12 posts in this topic

Hi all, new member here, joined specifically for help with this topic.

 

Quick background info: I am a technician in a college and am having trouble with our studio setup. I do not have a music background, we have only run this music course for 2 years, I am generally good with this sort of stuff and have learned alot since running the course, but I am stuck on this and need help!

 

I am currently experiencing issues with digital noise/static (best I can describe) only when using a preamp mic. Through lots of testing I have managed to figure out that it is the power/wall socket that seems to be providing the feedback. If I use an SM58 (no preamp just an XLR cable) it is fine, no static. But when I use a preamp mic, as soon as I connect the power cable, I get a digital hum/static which is terrible, and this is before the amp is even turned on.

Any clues??

My guess was that its something to do with how the sockets are wired up, grounding issue?  thats as far as I got lol     

 

thanks in advance

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Yes, you have grounding issue. Check your preamp,  maybe you have some switch called "DI" on it ? Upload some pictures with the preamp  and the power plug (cable). 

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ok i've taken pics, but can't figure how to upload them. Tried what I ususally do for forums - upload to photobucket then paste in the URL...says I can't do that on here

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Use the EDIT, Full Editor Function  and after that Attach files, or More Reply Options, there you will have attach files option.

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Damn.. you are using 110 v , and the preamp doesn;t have DI. It's a hard one.. next time try to separete more the stage box ( multicore) from the power  cables. Try to eliminate the ground from your power socket where are you using the preamp, see if you still have that noise, or you need something to lift the ground. You can buy a UPS , but is not cheap, or isolation box, DI, the cheapest ideea is to eliminate the ground.  I don;t know if that is a preamp, looks more like a multi-pattern switcher who provides phantom power, are you using 48v (phantom power) for that mic?

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apologies, some of that went over my head. I'll try my best to tell you my setup...

 

we use 3 types of Gemini mics for studio recording - Gemini ll, Gemini 5 and Gemini Z5600a - all of which have their own preamp power boxes (or whatever they actually are). They have their own unique cable which connects the mic to the preamp, and then a standard XLR cable is used to connect it to the snake patch bay on the wall. We keep this in our "live room" - it has 16 channels and is split between 2 booths (8 in each booth). The snake runs through to the other booths is connected up to a m-audio profire interface, which is connected to a mac pro via firewire.

 

As said before, standard XLR and SM58 works fine, no humming. Using a the gemini, as soon as the box in connected to the power cable, humming begins.

 

no I dont think I am using phantom power. I also sometimes use the same gemini setup, but instead of connecting XLR into snake patch, it goes straight into the back of keystudio midi keyboard. So doesn't require phantom power, just its own box.

 

How do you eliminate the ground, or lift it as you said. Sorrymate my knowledge is pretty basic.cheers

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It's a ground reference issue to me. Don't 'ground lift' - it's dangerous to remove earth pins unless the equipment was designed that way. It may stop the hum, but you may also get an electric shock or the equipment may kill someone if it ever faults electrically.

 

Try these things:

1. From the case of the mac, run a piece of cable to the case of the Profire interface. If hum stops... move no further.

2. Hum still there? Connect the pre-amps only 1 at a time. Run a cable from the Profire at the same point you connected the Mac to the pre-amp. Maybe loosen a screw on each device and wrap the cable around it. Noise gone? Try the other pre's without the cable and then with.

 

If you see a little spark as you connect the ground cable between devices with power on them, it's 100% a ground issue. The best long term solution will be to ensure the power points in the different rooms are all connected to the same earth point. This doesn't always fix audio interfaces, though, as they us DC plugs and typically don't have a ground - in which case the cable from the PC to the case of the audio interface should solve the issue.

 

If it's not practical or cost effective to have the earth all connected to the same place and you've tried the PC to Profire link cable... there are things called "isolating transformers" that are designed to provide isolation on 110/240V AC and should stop any hum coming through the electrical system. It's more likely to me, though, that it's a PC/Firewire and Audio interface issue.

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Yup, he is right, can be dangerous at some points to remove the ground. Try what jester said , if doesn;t work we will think on something else. 

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