"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.

"Dave Plowman (News)" wrote in
:

In article ,
Alan S. wrote:
It has been apparent at two different locations in particular, both
of them CofE churches as it happens. It was, however, with the same
mic cables. Can I assume that the phantom power supply would not work
if one leg or ground is missing on the cable? They were each
approximately 25metres.

Seem to remember a one legged cable just results in a low output from
a 451. Which may well give hum if you increase the gain for a distant
mic. Do you not have a 'bright eyes' phantom tester? Basically two
leds built into an XLR. If not contact me - I'm sure I've got a spare.

If you lose the screen you'll get no audio at all, IIRC.


Thanks for the offer, Dave. I have got one somewhere, buried in the goodie
box. It's a long time since I used it - more than eight years since
retiring from TVC and Parkinson's means my days carting gear around are
probably numbered!

Now, where's the goodie box?

Thanks to all for your thoughts.

Alan S.

If you lose the screen you will probably get radio Moscow instead..grin.

Brian

--
Brian Gaff -
Note:- In order to reduce spam, any email without 'Brian Gaff'
in the display name may be lost.
Blind user, so no pictures please!
"Dave Plowman (News)" wrote in message
...
In article ,
Alan S. wrote:
It has been apparent at two different locations in particular, both of
them CofE churches as it happens. It was, however, with the same mic
cables. Can I assume that the phantom power supply would not work if
one leg or ground is missing on the cable? They were each approximately
25metres.

Seem to remember a one legged cable just results in a low output from a
451. Which may well give hum if you increase the gain for a distant mic.
Do you not have a 'bright eyes' phantom tester? Basically two leds built
into an XLR. If not contact me - I'm sure I've got a spare.

If you lose the screen you'll get no audio at all, IIRC.

--
*42.7% of statistics are made up. Sorry, that should read 47.2% *

Dave Plowman London SW
To e-mail, change noise into sound.

On Sat, 30 May 2009 11:21:17 GMT, "Brian Gaff"
wrote:

If you lose the screen you will probably get radio Moscow instead..grin.

Brian

At least that might be interesting. It's always minicabs.

d

In article ,
Brian Gaff wrote:
If you lose the screen you will probably get radio Moscow instead..grin.


You'd be surprised. Some time ago I made up 100v line XLR cables using
ordinary mains 2 core flex. Cheaper than screened cable. And found one in
use with a dynamic hand mic - because it was a nice shiny white, rather
than the more usual mic cable grey or black. And apparently worked just
fine. In other words it's the balancing that gives the majority of the
rejection of spurious stuff.

--
*Time is the best teacher; unfortunately it kills all its students.

Dave Plowman London SW
To e-mail, change noise into sound.

"Alan S."

It has been apparent at two different locations in particular, both of
them
CofE churches as it happens. It was, however, with the same mic cables.
Can
I assume that the phantom power supply would not work if one leg or ground
is missing on the cable? They were each approximately 25metres.

** All 3 with the same fault??

Yawnnnnnnnnnnnnnnnnnnnnnn



..... Phil

"David Loser"


With a one-legged cable the audio must pass through the phantom power
supply,


** The OP is a ****wit TROLL

you ass.

"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 think most epeople referred to them as C451 mics but for the record,
it was C451 bodies with CK1 capsules.

** CK1 = basic cardiod capsule.

Got a nice CK2 omni myself I use for response testing.



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.

My first reaction but I couldn't couldn't believe 3 different PSs were
_faulty_.


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.



If I have three phantom supplies which are unable to deliver the
required current, which appears to be the case, then,


** Nope.

The actual case is your story is 100% total ********.




......... Phil

In article ,
Phil Allison wrote:
I think most epeople referred to them as C451 mics but for the record,
it was C451 bodies with CK1 capsules.

** CK1 = basic cardiod capsule.

By far and away the most common combination was a 451 with CK1 capsule -
in Alan's and my side of the industry anyway - so there was no need to
call it anything other than a 451. The handmic version was called a 421
omni. The gun mic varieties weren't used - the Sennheisers were so much
better.

Got a nice CK2 omni myself I use for response testing.

I've got a couple of what was known as the TV omni with a built in
windshield. IIRC, CK22. Quite a rarity.

--
*Why do we say something is out of whack? What is a whack? *

Dave Plowman London SW
To e-mail, change noise into sound.

Phil Allison wrote:
"David Loser"


With a one-legged cable the audio must pass through the phantom power
supply,


** The OP is a ****wit TROLL

you ass.


That is strange...how did you manage to climb out of my killfile ????

Ahh well, not to worry......plonk !