"Dave Plowman (News)" wrote in
:

In article ,
Alan S. wrote:
Is anyone here still using AKG C451 mics, or remembers using them?

Hi Alan ;-) Yes indeedy - I also have a few.

Hello Dave.


I've had my 4 for some time but am becoming more and more aware of a
low level hum on the output. The hum gets worse the more of them that
are plugged in to the mixer. If only one is faded up, the hum gets
worse as others are plugged in. At first I thought the phantom power
supply was giving trouble but I have now tried them on two different
mixers and a, stereo, standalone mic pre-amp (M-Audio) with similar
results. I wondered if one of them was drawing too much current and
dragging the PS down but it doesn't seem to matter which combination
of mics I use.

Properly designed phantom should be immune to a dead short since
standoff resistors are used at each mic input. That's not to say all
mixers have properly designed phantom.


I think the hum is
100 hertz, which still suggests PS but on three differant i/ps?

Both mixers and the standalone are fine when used with dynamic mics.

The C451s are long in the tooth so are they prone to draw high
current as they age? Or am I barking up the wrong tree altogether?

Not one I've come across.

Any suggestions, polite ones, would be appreciated.

It does sound like a PS fault to me - have you tried other phantom
powered mics? Have you access to a scope to look at the DC?


My Heathkit scope went the way of all flesh many moons ago! But my gut
instinct says PS. I just couldn't believe 2 mixers and one standalone
all had a problem. A careful cable check has been suggested, just in
case there's a rogue. Ah, memories of those aweful _tails_ on the booms
at TVC.

Alan S.