Very irritating noise

[Perry100]

Hi,

Being a new member and also from Sweden (meaning my first language isn't English) I apologize if anything written is unclear - feel free to ask.

I did search the forum for any questions similar to mine but couldn't find any - so here goes:

The specifics first: I use Cubase Sx3 on a Toshiba laptop with an Focusrite Saffire soundcard. Up until recently I've only recorded with a tube mic (Golden Age Tc-1) but decided a while ago to try a phantom powered cardiod condenser mic (Studio Projects B1).

The problem: When using the B1 I get a constant hum/noise that I just can't get rid off. I've tried different cables, different rooms (outputs) in my apartment, being as far away as possible from the laptop etc. I've also tried different phantom powered mics and had my soundcard in for a check-up. Nothing. The problem is still there. You can barely hear it when recording, but when fading out (for example a last strum on the guitar) it comes back quickly making it impossible to get a good sound at the end of a song. It's really frustrating since I really enjoy using this type of mic (especially on acoustic guitar).

The solution: Well, that's just it. Is there even a way to solve it? I asked around on a Swedish forum but no one had any ideas (an electrical noise of some sort was the main theory). So I really hope someone here as an idea/solution/trick to somehow get to grips with this. I planned to include a short mp3 file of the "noise" in question - but there doesn't seem to be a way of doing it. So I hope that I've described it good enough for you to get an idea.

I appreciate all the help I can get.

Perry.

 

[mshilarious]

You need to try the B1 with somebody else's preamp or interface (preferably in your studio) and see if it has the same problem. That will verify whether or not the B1 is the problem. That seems likely if other cables and other phantom-powered mics work with your interface.

If it turns out to be the mic, it could be anything from a poor connection from pin 1 to the case, or a bad capacitor, or something else. Once you have established that it's definitely the mic, contact PMI Audio for assistance; they are generally quite good about customer service.

 

[Perry100]

That seems likely if other cables and other phantom-powered mics work with your interface.

Thanks for your response!

I think my english/grammar got in the way there.
I have tried other phantom powered mics (same brand-different models) and it was the same problem.
Although I have considered trying someone elses soundcard to see if the problem lies with the phantom power in my soundcard.
Also, I have thought about taking my whole set-up somewhere else to see if it's a electricity (the wiring in the house) issue.

 

[mshilarious]

Thanks for your response!

I think my english/grammar got in the way there.
I have tried other phantom powered mics (same brand-different models) and it was the same problem.
Although I have considered trying someone elses soundcard to see if the problem lies with the phantom power in my soundcard.
Also, I have thought about taking my whole set-up somewhere else to see if it's a electricity (the wiring in the house) issue.

It's almost certainly sourced from some electrical noise in your house, but that's not the problem. Microphones have to be designed to reject that noise, because it's everywhere. Well, almost everywhere. You could go to someone else's house that has less electrical noise, and maybe your B1 would be quiet there. But that doesn't help you, and it doesn't mean there is not a problem with the mic.

Again, try the B1 into a different preamp or interface in your house, and see if the noise is there. If it is, it's the mic, so contact PMI for assistance.

If it's not, I don't really know what the problem is--could be hard to find. For example, the Focusrite might have noisy phantom power, and the B1 poor power supply rejection. That's just a wild guess, but if so that's would be a design limitation. PMI will be well aware of that if it's the case.

 

[Perry100]

Again - thanks for your reply. You have given me some new hints on what to do and for that I'm grateful. I'll try 'em out and see what comes of it.

 

[dgatwood]

I have tried other phantom powered mics (same brand-different models) and it was the same problem.

If non-phantom-powered mics like your tube mic have no trouble but phantom-powered mics hum, it seems safe to say that the phantom power circuit in your Focusrite is broken. Probably a bad filter capacitor somewhere. I'd expect any noise off the phantom supply to end up in the signal even if there's no mic connected. Try it and see if I'm right.

 

[Perry100]

...it seems safe to say that the phantom power circuit in your Focusrite is broken.

That was my first guess to (even though I'm far from skilled at this subject - as you might have guessed). But I have had it in for a check-up at the Swedish importer. It came back ok. Although I suspect they didn't do a 100% job at it - it came back with a note that said they had upgraded the firmware... (which even I know can be done over the internet).

I tried your suggestion: Activated the phantom power with no mics attached. But there wasn't any increase of noise. With a mic cable and no mic there was a slight increase but not as much as when I have the mic connected.
Would that mean I can rule out the broken phantom power circuit alternative?

Thanks for answering.

 

[Weasel9992]

If non-phantom-powered mics like your tube mic have no trouble but phantom-powered mics hum, it seems safe to say that the phantom power circuit in your Focusrite is broken.

That's the next step in trouble shooting...trying non-phantom powered mics. Have you done that yet?

Frank

 

[Perry100]

Hi Frank,

Yes. As mentioned earlier the other mic I use is a tube mic. No need for phantom power there and no problems either.

Thanks for answering.

 

[Weasel9992]

Hi Frank,

Yes. As mentioned earlier the other mic I use is a tube mic. No need for phantom power there and no problems either.

Thanks for answering.

...and it doesn't require phantom power? Which tube mic is this?

Frank

 

[Perry100]

Which tube mic is this?

It's a Golden Age Projects Tc-1

http://www.goldenagemusic.se/goldenageproject/uk/index.htm

 

[quickmill]

...and it doesn't require phantom power? Which tube mic is this?

Frank

Which tube mics DO require phantom power?

 

[mshilarious]

Which tube mics DO require phantom power?

MT Gefell UM 900.

 

[Weasel9992]

Which tube mics DO require phantom power?

The AT 3060 also.

I mis-spoke about phantom power anyhow...I was thinking about the external power supply and typing something totally different. My mistake.

Frank

 

[Shadow_7]

If you're recording from a laptop, you might try recording on battery power and see if the noise goes away. If it does, you have a power / groundling loop type issue.

Try moving the mic around the room while recording and see if that influences the noise. Might be time to turn off the A/C, cell phone, police scanner, washer, dryer, and other devices if location influences the noise / noise level. There's some interference going on.

Try the mic on other interfaces and preamps and see if it's the mic that way.

If you're using florescent lighting you might turn it off and see if the noise goes away. Some light types tend to influence guitar strings and other like instruments. It might have an affect on other gear as well.

Beyond that you might have a cable or phantom power issue.

 

[dgatwood]

I tried your suggestion: Activated the phantom power with no mics attached. But there wasn't any increase of noise. With a mic cable and no mic there was a slight increase but not as much as when I have the mic connected.

Hmm. Interesting. I'm going to have to think about that one. My first inclination would be induced noise caused by a poor signal ground. Does that Focusrite unit have a three-prong power supply? Does your computer have a three-prong power supply?

 

[Perry100]

If you're recording from a laptop, you might try recording on battery power and see if the noise goes away. If it does, you have a power / groundling loop type issue.

Try moving the mic around the room while recording and see if that influences the noise. Might be time to turn off the A/C, cell phone, police scanner, washer, dryer, and other devices if location influences the noise / noise level. There's some interference going on.

Try the mic on other interfaces and preamps and see if it's the mic that way.

If you're using florescent lighting you might turn it off and see if the noise goes away. Some light types tend to influence guitar strings and other like instruments. It might have an affect on other gear as well.

Beyond that you might have a cable or phantom power issue.

Thanks Shadow 7.

I've already tried some of the suggestions you make. What I haven't tried or thought about is recording on battery power. I'll try it later and get back to you.

 

[Perry100]

...Does that Focusrite unit have a three-prong power supply? Does your computer have a three-prong power supply?

Are you referring to the look of the power supply? They look different here in Sweden. I have attached to this message two photos (not mine - copied from Wikipedia) on how it can look here. One is grounded (similar to the one on my laptop), the other is not grounded (similar to the one on the Focusrite). On the Focusrite however, there is an AC-adapter connected on the electrical cord between the soundcard and the outlet. That's the way they come here.

 

[mshilarious]

Hmm. Interesting. I'm going to have to think about that one. My first inclination would be induced noise caused by a poor signal ground. Does that Focusrite unit have a three-prong power supply? Does your computer have a three-prong power supply?

If it's a noisy phantom supply, it might not have any effect without a condenser mic attached. The noise will be common-mode when the input is unterminated, or terminated with a dynamic mic. But when you hook up a condenser, the DC path of the two legs gets merged back together, and many mics aren't designed with a high degree of power supply rejection. Thus, the noise leaks into the mic signal before it is balanced for output.

 

[dgatwood]

If it's a noisy phantom supply, it might not have any effect without a condenser mic attached. The noise will be common-mode when the input is unterminated, or terminated with a dynamic mic. But when you hook up a condenser, the DC path of the two legs gets merged back together, and many mics aren't designed with a high degree of power supply rejection. Thus, the noise leaks into the mic signal before it is balanced for output.

I'd have assumed that the CMRR on what is probably a pretty inexpensive preamp circuit probably wouldn't be good enough to reject phantom noise even without anything hooked up. Maybe I'm just being too cynical.

Still, the answer to my question about grounds was pretty much what I expected---the audio interface is using the computer's ground as its reference ground, which can be prone to all sorts of noise issues if the computer and/or interface isn't designed properly. So it could easily be either of these problems.

The only way I know of to really nail down whether the problem is the phantom circuit or noise on the ground bus is to build a grounding pigtail. Make yourself a short male-to-female cable of any type and plug it into a seldom-used jack on the interface. Solder a heavy gauge wire to the ground pin on the audio plug that plugs into the interface. Fasten the other end to the ground pin (or hole) on a 3-prong (or two-prong and hole) power connector. Tape up both of the hot contacts inside the plug to make sure that if the wire jumps off, it doesn't come into contact with the hot or neutral wires. (I assume this is single-phase 220/240V and not split-phase.) If the noise goes away, the problem is the crap ground. If it doesn't, check the filter caps in the phantom power circuit.