I thought I’d write a quick post on this in case some of you experience a similar problem, it may save you hassle and expense.
I have a pair of AKG C414B mics, they are real workhorses and as the cliche goes, the studio Swiss army knife. On top of that they are solidly built and very reliable. But sometimes things go wrong. I recently did a bit of drum recording for myself and was listening back when I noticed a faint but distinct mains frequency hum on the overheads (my 414s). I had them running through my home made Neve preamps and then into a pair of line-level inputs on my UA Apollo interface. I automatically assumed the hum was coming from my home-made preamps rather than the solid, Austrian-engineered AKG mics. I duly set out to test, swapping cables, microphones and trying various configs of phantom power on / off on each channel, until it was clear that the problem lie with one of the 414s.
Faced with an expensive repair, I thought, well, let’s open it up and see if anything obvious was up with it.
Hmmm, lots of surface mount components and no obvious signs of trouble. A quick Google search led me to this post. Not exactly the same problem but similar, so I read on. Turns out that the grill / mesh of the mic connected to ground via pin 1 of the XLR forms a Faraday Cage, which helps shield the high-impedance capsule from EMI noise in the room. The mesh makes contact mechanically and if this connection is a little dodgy, it won’t work and there will be noise. I tested the resistance between pin 1 on the XLR and the mesh, it was a variable which immediately suggests a problem. I went about gently squeezing the base of the mesh in an attempt to improve the mechanical connection. Checking again, the resistance was now consistently minimal, so time to test. I put the body back on and plugged it in, powered it up and hey presto, no noise. Phew!…. So if you’re having this kind of issue, try this first, the mic is easy enough to open , just remove the 2 screws on the base (star driver or a flat head screw driver will do) and the smaller cross head screw in the XLR connector base and then slide the body off.
Wij Productions 
I’m Catalin Popescu and I have an identical microphone. I use this microphone very often to record voices for commercials. One day, I noticed that my microphone has a buzz. Now, I solved this problem, because I found the information you wrote. Thanks buddy! Success in everything you d
Hey Catalin, Thanks, I’m glad my post helped you…
Hi, many thanks for your post. I’ve bought a pair of XLII (I think two of the last few “made in austria” specimens). I’ve discovered that both of them have slight hum in certain scenarios depending on the configuration I use them in. E.g. when connected to a Scarlett 2i4: no hum; when connected to a battery or PC powered Zoom H6: no hum but when the Zoom is powered from a USB power adapter (i.e. phone charger) there is a slight hum, which worsens a lot when I touch the back of the mic, especially the two buttons on the back. However, the hum disappeared when I also touched the body of the mic or the grill. Also hum when used with the mains powered Studio Projects VTB1 preamp.
So, following your advice, I opened up the mics but it was not clear, how to bend the grills in order to make better connection with what other parts of the mics. However, I tried to move the grills a bit. Then when the mics have been reassembled, the hum is away.
I reserve the right to be wrong but let me share my suspicion with you: I guess, the screws did not make good electrical contacts between the different parts of the mic body due to the paint on that parts and probably that was the reason why the high impedance parts cannot be effectively shielded against EM interference.
Anyhow, thank you again for encouraging me to open up the mics.
I was scared but your post was very helpful. I could say that it is not necessary to disassemble it, applying a little pressure on the grill is enough to know if the hum noise is coming from it. THANKS A LOT!!
For a more durable solution: solder a (thin) wire to the inner mesh layer and connect the other end to a point inside the microphone that is connected to pin 1 of the XLR insert. Preferable do this on both sides of the microphone.
This will cure the ‘hum problem’ forever!