G9 micpre working fine , except with akg 414eb

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nashkato

Well-known member
Joined
May 3, 2007
Messages
872
Location
Europe/Austria
hello everbody.
finished my first G9 some time ago , quite a bit i a hurry. did no real final checking , it worked fine in the first place.

lended it a friend for some time now , and getting it back , trying to do some recordings i experienced some hum on my akg 414eb´s. one with the old one with a newer capsule.

every other condenser mic sounds nice and quiet, also the line and dynamic input.

sure it gotta have to do something with the 414´s , despite they work without hum on every other pre or mixer.and surprisingly both do the same.
so don´t know where to locate the hum (btw : sounds like an earthing hum to me) is it the pre or the mics.

ps: haven´t tried to run it with groundlifted cable , and yes i connect at only one point to earth at the xlr-inputs.

nice regards
 
You can't run it ground lifted, as the ground line is required for P48 powering.

One thing that's a little different than many other condensers is that the C414EB sources phantom power through the middle tap of the output transformer. (I'm talking about the later black C414EB P48 version, but it probably applies to the earlier one as well). Maybe that's a hint as to where the problem is located. But it could also be something else.

Maybe you have hum on your P48 line? Perhaps your C414s cannot suppress that hum as well as your other mics. It could also be a problem with your C414s that isn't as apparent with other preamps. I'd check the filter caps for instance.
 
It's not uncommon in these mics to lose the ground connection to the grilles in the headbasket. That's the first place I'd look.
 
Hey I havent checked the phantomsupply capacity of the G9 but I know that these 414EB
runs on quiet high current. In the region of 3-4 mA. An U87/KM84 runs at about 0,5 mA. I think the hum comes from that high current load.
Cheers Bo
 
The only way a 414 uses that much current is if you have one set for 12Volts and plug it into a 48V line... -They positively SIP current, not guzzle.

Scope for ripple on the 48V line coming out of the G9. There's nothing else that can be the problem, and a ground lifted cable will probably get rid of the hum, but (unfortunately for you) it will also get rid of the signal.

Keith
 

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