AKG C414 XLII strange noises

[phaldini]

Hello,

My C414 emits a 50Hz signal! I will have to send it back under warranty for repair but I wondered if anyone on the forum would have an idea of what it might be. I have a stereo pair so I know it's the mic as the other one is fine.

Any ideas?

Thanks,

Alex

[Hugh Robjohns]

Either a poor body earth, or a faulty power supply circuit. Probably the former.

hugh

[phaldini]

Thanks for that, Hugh. I was wondering though that as I'm in Spain would it not be emitting a 60Hz signal if it were a grounding problem?

Is it then more likely to be a fault with the power supply as you suggested? How would this work? All the harmonics of the 50Hz fundamental are present all the way up the spectrum. I'm just curious to know how this signal could be generated?

Alex.

[Hugh Robjohns]

Thanks for that, Hugh. I was wondering though that as I'm in Spain would it not be emitting a 60Hz signal if it were a grounding problem?

Not unless they've moved Spain to South America when no one was looking! Since January 2004, the mains supply of ALL European countries is nominally 230V (-6%, +10%), and 50 Hz (±1%).

I'm just curious to know how this signal could be generated?

My money is on a defective case earth, reducing the effective screening of the mic capsule and its high-impednace electronics. It is picking up the stray EM radiation from mains wiring and any mains powered equipment in the vicinity.

Send it back for repair!

hugh

[phaldini]

Thanks Hugh.

I obviously got a bit muddled over mains supply standards. All makes sense now.

cheers!

[Persuazion]

What about an dodgy/out of phase XLR cable? Had a couple quite recently(Neutrik too!) with the pins swapped and this caused earthy hums.

[Hugh Robjohns]

Yes, a miswired or broken cable (with the screen shorted to to pin 2 or 3 in error) could cause similar problems, or a faulty mic preamp.... but the OP said his other mic is fine on the same input channel and cables.. which would imply that it is the mic itself that is faulty.

Hugh