"Alan S."

Is anyone here still using AKG C451 mics, or remembers using them?


** The C451 is not a mic - but a pre-amp / handle for the CK series of
capsules.


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.

** That can only mean the phantom power has hum.


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

** Your story indicates that it is all 3.


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


** Naturally.


The C451s are long in the tooth so are they prone to draw high current as
they age?

** C451s draw about 6mA from a 48 volt phantom supply - many other mics
draw less than this.

The design is such that they work fine from as little as 9 volts of phantom
at the mic signal pins, with a much lower current draw than when that
voltage is 48.

From recollection, C451s are not particularly immune from hum on the phantom
supply ( there should NOT be any of course ) so your probelm as decribed is
not likely due to any fault in the mics.


...... Phil