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prontold
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#1
10th November 2012
Old 10th November 2012
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AT4050 making farting noises

I've had a second hand Audio Technica AT4050 for the past year or so. I've noticed the few times that I've taken it out recently that it has picked up some weird behaviors. For a while, it would let out periodic bursts of low frequency noise. Haven't noticed that recently, but take a listen to what it did as I was recording some awfully pitchy Radiohead cover for a personal mic shootout. Anybody know what could cause this to happen? Was it just razzing my awful performance?
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10th November 2012
Old 10th November 2012
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Anybody experienced something like this before?
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10th November 2012
Old 10th November 2012
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Quote:
Originally Posted by prontold View Post
Anybody experienced something like this before?
sounds like a damaged capsule that got sensitive to moisture.. At least that was the issue i had once.. was ok when the session started and as more the singer was in a hot mood as sooner the problem started..

but might be something else like a dying cap maybe? that would occur more on a random base and might get better as longer the mic is powered...
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10th November 2012
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Just a guess as I know nothing,but maybe it's a power supply problem? It sounds like an intermittent starving of power discharging a capacitor and then the pop/fart is it powering up again? You may have heard something similar when powering down studio monitors while a signal is still being applied.

Got another phantom power source to try? I would start there first.
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11th November 2012
Old 11th November 2012
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Thanks for the suggestions. I've tried plugging in to my 3 different preamps as different phantom power sources, and the problem seems pretty continuous regardless. It does seem to die down the longer it is plugged in. I've also noticed that I often get a hiss as phantom power dies away if I turn it off with the mic plugged in. Maybe it's a faulty capacitor? I'll probably just send it in to Audio Technica pretty soon.
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11th November 2012
Old 11th November 2012
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I suppose that confirms it's the Mic then. Bad cap or crappy solder inside. It's a good idea to get someone knowledgeable to look at it if your not sure about repairing it yourself. There's nothing worse than making it worse.
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11th November 2012
Old 11th November 2012
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If is an AT4050 CM5 version, I think that is an old mic with non SMD components. Can you open and check components ? and put images ?
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11th November 2012
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Humm, it is a /CM5. I had assumed it would have surface mount components, but it turns out it just has really, really small through-hole components. Score? This is probably the most complicated mic circuit I've looked at. Lot's of transistors and diodes and a couple of things that look like boogers. These were the best pictures I could snag without having to get out the soldering iron. There's an output board and a main board. I think I can see why nobody has offered modifications for these mics (not that they need them).

Can't really see anything obvious. Not sure I would know where to start with troubleshooting this with a multimeter.
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AT4050 making farting noises-p1000698.jpg   AT4050 making farting noises-p1000703.jpg   AT4050 making farting noises-p1000704.jpg   AT4050 making farting noises-p1000707.jpg   AT4050 making farting noises-p1000708.jpg  

AT4050 making farting noises-p1000709.jpg  
#9
12th November 2012
Old 12th November 2012
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Have you tried running the mic in the different directional patterns? That may give a clue as to which of the diaphragm circuits is creating the noise.

I have a couple of 4050-CM5s that make that noise (did since new) for a second or so when they are being powered-up, but it stops immediately once they reach full phantom voltage.

Without a complete schematic, you're completely in the dark as far as even beginning to troubleshoot the circuits. As you've noticed, there is nothing obvious in the photos of the circuit boards, no externally leaking caps or cold solder joints.

Remember, that mic has a very high impedance FET input stage that can be easily damaged by applying even a small electrostatic charge. You should have the mic on a conductive surface, and have a grounding strap attached to your wrist before touching anything inside the mic with your fingers or any external probe.
#10
12th November 2012
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My 4050 has the same issue. I spoke with A/T and they said it sounds like a bad element/capsule. Said it would be $250 max to make it new again. Just haven't sent it in yet, been too busy.
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12th November 2012
Old 12th November 2012
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Looking at picture nr 4 I would suggest examining the soldering on that board.
Take a magnifying glass and look for bad soldering joints.
I already saw a few on the photograph I would check.
If you know how to solder you may spot bad contacts and you may be able to re-solder these.
If this already puzzles you: Leave it to a maintenance guy or repair shop that is familiar with professional recording gear.
From the many times I repaired microphines 9 out of ten it was not the capsule.
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12th November 2012
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+1

And inspect bottom-left cap (big green), it's seems little puffed on top.

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12th November 2012
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Wow, SP2016, there is actually at least one possible cold solder, now that I look more closely. I see what you mean, Manzini, about the capacitor being puffed up as well, so I will check that out again. I kind of expect that the problem wouldn't be a cold solder joint, as the mic was not making these noises 4 months ago. That would lead me to believe a capacitor or (hopefully not) the capsule has developed a problem.

Thanks Lotus 7 for the reminder on being safe with static discharge. I wasn't being too cautious while I was taking the pictures. The problem happens in cardioid, so I believe that means that it will happen in every other pattern as well, since both capsules are engaged in omni and fig 8. Could be one or both of the capsule sides that has the problem.

Thanks everybody for the help and advice, and for sharing your experiences if you have had similar issues with your AT4050
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12th November 2012
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Hmm, just recorded 30 minutes of guitar without any problems. The pieces here are very small, and it would be risky/a huge pain to do work on the mic. I think for now I will keep my fingers crossed and defer any repairs. If it acts up a whole lot, I'll take another look at that capacitor.
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12th November 2012
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It could be something that's a little loose and you taking it apart has temporarily fixed it, or the farting is coming from somewhere else? I know I have this problem.
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12th November 2012
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I have a pair of AT2050s that have done the same thing in the past. I found that flicking the switches back and fourth resolved it (I tried all of them but I believe the polar pattern switch is what fixed it). It hasn't happened to me in awhile but it may have been oxidation that caused it in my case. Maybe the same sort of issue with the 4050 since it's also a MP mic?

I've also worked with a few musicians that have sworn that they weren't making the noises, and blame the chair or the mic (or the drummer). You can never be too sure sometimes !

Cheers,
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#17
12th November 2012
Old 12th November 2012
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Quote:
Originally Posted by prontold View Post
I kind of expect that the problem wouldn't be a cold solder joint, as the mic was not making these noises 4 months ago.
A cold solder joint may be there for a long time without causing any problem.
But is is like rusting: Corrosion may make the joint "colder" and making real bad contact then.
That may explain why four months ago there was no problem (yet...).
Also check the soldering of the switch contacts for bad joints.

Have fun !
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12th November 2012
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Quote:
Originally Posted by apprenticemart2 View Post
It could be something that's a little loose and you taking it apart has temporarily fixed it, or the farting is coming from somewhere else? I know I have this problem.

Quote:
Originally Posted by JustMastering View Post

I've also worked with a few musicians that have sworn that they weren't making the noises, and blame the chair or the mic (or the drummer). You can never be too sure sometimes !
Oh youse guys... You got me. I swear I'll never eat a black bean and corn quesadilla again
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12th November 2012
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Quote:
Originally Posted by SP2016 View Post
A cold solder joint may be there for a long time without causing any problem.
But is is like rusting: Corrosion may make the joint "colder" and making real bad contact then.
That may explain why four months ago there was no problem (yet...).
Also check the soldering of the switch contacts for bad joints.

Have fun !
Hmmm, interesting. Did not know that!
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13th December 2012
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#prontold, do you have any progress about ?
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18th December 2012
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My M-Audio Delta 44 audio interface does the SAME thing when I power down the computer without first turning off the monitors and mixer. I've always suspected a cap, but never had the breakout box apart to be sure. More than 10 years later the soundcard is still working so I never cared to look into it more.

Would be curious to hear more about the AT mic.
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25th December 2012
Old 25th December 2012
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I've only heard that sounds (caused by microphones) when the phantom voltage sags or bad grounds. replace cable first, if that doesn't fix it, disconnect all other mics cords (remove loading effect).If this fixes it, add mics with the same cords one at a time to see when it comes back (change cable if it does). If it doesn't, recap the mic.
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25th December 2012
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Quote:
Originally Posted by SP2016 View Post
A cold solder joint may be there for a long time without causing any problem.
But is is like rusting: Corrosion may make the joint "colder" and making real bad contact then.
That may explain why four months ago there was no problem (yet...).
Also check the soldering of the switch contacts for bad joints.

Have fun !
This is true. I think what's happening in that case is that the component lead is making enough contact with the circuit board to make a connection when the unit is tested. This could be a mechanical connection or friction fit from the lead bending process etc. Over time the lead and the traces / holes/ vias/ get oxidized from airborne contamination and essentially become insulated from each other by the oxide coating. I have seen MANY cold solder joints, and even NO solder joints in equipment that has been in use for a long, long time. I have had a Neve 33609 make several visits to my shop over the last eight years or so. Each time I have re-done numerous suspect looking joints and had it working perfectly. A few years down the road, it comes back and some OTHER joint has gone bad.
Best,
Ike
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25th December 2012
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I have a 4050/CM5 and have also come here to get some help. Mine is making a spluttering noise more than a farting... Thinking first thing to replace the electrolytic caps on the board.

I'd be interested to follow along on this and see if you discover anything to solve your problem.
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26th December 2012
Old 26th December 2012
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Haven't really done anything with the mic. It works well enough as long as I use a decent cable, though it still occasionally sputters a bit. Not sure I trust myself to work on it. I've done some DIY stuff before, but these boards are particularly packed and the components are tiny. If I do decide to try to do some work on it, I'll try to remember to post here about the results.
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31st January 2013
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I made contact with AT in Australia and was quoted about $350 for a new capsule for my CM5, and at minimum $110 labour...

Eeeek!
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31st January 2013
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Take a magnifying glass and look closer for bad soldering contacts/cold joints.
Much cheaper than a new capsule and you can do it yourself.
Or have an experienced tech to check the soldering if you are not comfortable with that.
I really doubt it is the capsule.
Reason for that is that i have serviced many AT4050's and 9 out of 10 the problem was bad soldering or corroded soldering causing cold joints.
Are you sure your phantom power is 48VDC ?

Last edited by SP2016; 1st February 2013 at 07:11 AM.. Reason: typing error
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