Condensor mic noise?

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mjbphotos

mjbphotos

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This came up a couple of times recently - my AKG P220 (7+ years old now) all of a sudden starts getting static-type noise, and a lot of background noise. It's not all the time - I left it on all day yesterday and there was no noise until late. At first I only heard it late at night (using it on skype). This morning, it's happening again.
Verified its not the cable (and no movement happening), nor the interface, as I have another condensor plugged in and its fine - I've swapped channels and cables. Sometimes the noise is fairly low level - have to crank the input gain way up to hear it, other times, its noticeable at normal gain level.

Can a mic pick up noise through the power system (the interface has a wallwart power supply)? Can it pick up RFI somehow?
 
Humidity? Damp capsule can act up in that way. Place it in a Ziplock bag with some desiccant packs for a day or so and see if that clears it up. I've had a couple mics (Lauten LA-220 and a CAD M179) exhibit noise on humid days.
 

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We have had some humidity here recently, for sure, as you know.

Add: noise completely disappears when I turn off the low pass switch
 
One of my 414's started doing this - and I got the bag with desiccant solution here. I was sceptical but with nothing to lose and a minim £100 repair bill, I popped the mic into a bag with a few packets of silica gel and left it in my central heating boiler cupboard for a few days. It went away!
 
Wish I had some silica gel... Its drier out today, maybe put it out in the sun?
 
Lacking silica gel packets, you could try dry rice. Put the rice (maybe 1/4 to 1/2 cup) in a nylon stocking and tie it closed so any small bits of rice husk don't get into the mic. Place in Ziplock bag with mic. While it might work putting it out in the sun, I'd be cautious as to not get it too hot.

This is the silica packets I bought from Amazon. They can be baked out so they can be reused.
Amazon.com: Dry & Dry 10 Gram [25 Packets] Premium Silica Gel Orange Indicating(Orange to Dark Green) Silica Gel Packets Desiccant Dehumidifier - Silica Packets for Moisture Absorber Silica Gel Packs: Kitchen & Dining
 
I have some older Sony condensers that get this way. My solution is to power them up and let them hover a few inches above a low-watt incandescent lightbulb until the moisture bakes off.
 
RRuskin said:
I have some older Sony condensers that get this way. My solution is to power them up and let them hover a few inches above a low-watt incandescent lightbulb until the moisture bakes off.
Click to expand...

I was actually thinking of that!
About an hour (total, not at once) in the sunlight seemed to do the trick when I plugged it in, but now, 2 hours later, its making noise again when the low cut is on..
 
Possible ghosty capacitor or solder joint? De-oxit the switch?
 
I've used AKG mics for years and I really like them. The condensor mics are great for vocals. On an unrelated note, I'm a new user and need help in navigating this site. How do you find a particular forum? (presonus studio 1 professional) How do you post a question?
 
albertadude said:
I've used AKG mics for years and I really like them. The condensor mics are great for vocals. On an unrelated note, I'm a new user and need help in navigating this site. How do you find a particular forum? (presonus studio 1 professional) How do you post a question?
Click to expand...

Welcome to the site.

You can got to the top of the page and click on the Homerecording.com banner. That will take you to the main page. It is divided into sections. There is no forum for the Presonus, so you can post a new thread in the Digital Recording and Computers forum. When you open that section, near the top is a button called Post New Thread. Click away....
 
So I am hoping its moisture, interesting that the hum problem only seemed to happen when the low cut was off, and the static when it was on... And since some sunlight, seems to be ok, at least for a while. Got some desiccant packs on order.
 
mjbphotos said:
So I am hoping its moisture, interesting that the hum problem only seemed to happen when the low cut was off, and the static when it was on... And since some sunlight, seems to be ok, at least for a while. Got some desiccant packs on order.
Click to expand...

Doubt if it is moisture Mike. You would expect that to get better with use not worse. and after all, it is the same capsule whether HPF is on or off. I am with whoever said "bad joint" (we old techs call 'em "dry" joints)
So, do you get into it? If it was a £100 mic then I would say "have a go" but personally I would send it for professional repair. If you DO decide to dabble be very careful not to touch the circuits around the capsule. They are at G'Ohm resistance and smear of sweat could wreck things. I would also not use any sprays in there. Maybe GREAT care with a solder iron around the HPF area?

Rethink! Just realized, that mic WAS only ~£120 new so after seven years maybe have a look and if you can't fix it put the ton toward something else. There are some very well received capacitor mics around at the moment.

Dave.
 
you mention walwart noise, this is more noticeable in a desktop situation probably.

I often wave my mic around like a "noise detector", up close to walwarts a huge hum is heard, moving it around to the powersupplys in the rack gear etc.. the hum can get really loud. I think some days its worse than others? Maybe the ac lines are noisy that day? Sounds simple but in a desktop setup the distance doesn't get very big so the hum is there. My house I find ceiling fans being on can create low rumble, all kinds of noises coming and going. (its basically a closet/vocal booth/desktop setup)

Sounds like your process of elimination is working. interesting drying out the mic works, Ive never done that. Seems making a "sock cover with dessicants" to leave on your mics when not in use would be a good practice then. Like a Velcro pouche for dessicant bags, sewn to a velvet pouch like Shure sells with the KSM mics...
Desiccant covers.... do dynamics suffer this issue or only phantom powered mics?
 
Cool Cat. Re chasing hum and noise in the 'Compact and Beejew' studio? Worth making a reference test recording. Set things up for say mic on acoustic guitar then get a standard level and note the gain setting of the knob. Now unplug the mic from the AI. (best to replace it with a screened short 2&3, or 200R termination R but I have found it only makes a couple of dBs diff') then record a minute of 'nothing'.

You can now put the recording through your DAW's Real Time Analyser or better, download RightMark Analyser. Save the graph.
Periodically run the test to see if low level noises are creeping up on you.

Dave.
 
I picked up the mic used for US$90, so got my money's worth. The static was back last night, but no hum when the lo-cut was turned off. I have noticed that the static seems to (mostly) only being heard when a neighbor's bathroom exhaust fan is running - I can hear it running in my bathroom, which is next to my studio room. I do have another condensor mic to use, if needed. Not sure how to disassemble the mic, there are no obvious set screws, so I'm guessing from the connector base somehow.
 
FWIW it took about 3 days with desiccant to totally dry out my CAD M179 and the desiccant pack did change color. I now store it in a plastic bag with a small desiccant pack. I have an AKG Perception 200 I got for about $40 and it's a decent sounding mic.

If you do want to take a peek inside and if it's like my P200, there is a ring on the bottom that takes a spanner type wrench to unscrew it. Needle nose type pliers can be used to grip the two slots on the ring to turn CCW. This will drop the lower case. Not sure about access to the capsule area. Image below looks like my P200.
http://cdn.recordinghacks.com/images//mic_extras/akg/P220-circuit.jpg
 
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