Tech: Condenser Mic/Phantom power problem ?

Subject: Tech: Condenser Mic/Phantom power problem ?
From: GUEST,Not Shure
Date: 21 Aug 08 - 05:12 PM

Hi..Ok.. I'm not a very technicaly minded musician..
I'm testing a new budget price Studio Condenser Mic..
[same spec model and factory production line as a popular OEM badged product]..

Tried it on 2 different mixers, with phantom power switched on,
[with brand new XLR-XLR mic cable, on sturdy mic stand]
and it sounds far too noisy even at the lowest audible channel gain
and level settings..
very hissy and constant low frequency crackle and pops..

Don't have any other equipment that operates on phantom power
that I can compare it to in order to eliminate any other variables..

So.. if this mic is faulty as I suspect,
is there any possible way it could be shorting out
and cause damage
to any components in the mixers ????..

Thats what I'm most concerned about..
[apart from the aggro of returning it back to the ebay shop
and proving it don't work right]

OR.. might there be something I'm not doing correctly with it ?

Thanks

Subject: RE: Tech: Condenser Mic/Phantom power problem ?
From: GUEST,Not Shure
Date: 21 Aug 08 - 05:20 PM

..and it is attached to mic stand suspended in a shock cradle..
so I think I've covered all the standard user operations
to eliminate handling noise..

Subject: RE: Tech: Condenser Mic/Phantom power problem ?
From: GUEST,Not Shure
Date: 21 Aug 08 - 05:46 PM

Also, if I can ask a suplementary question:

whats the correct procedure to minimise potential for problems,
plug in mic, then switch on phantom power..
or switch on phantom power, then plug in mic ?

thanks

Subject: RE: Tech: Condenser Mic/Phantom power problem ?
From: GUEST,Not Shure
Date: 21 Aug 08 - 05:50 PM

and one more bit of context info to add..

A pop shield is not relevant at the moment
because I'm not recording vocals.
I'm concentrating on mic-ing dulcimer
about 9" away from the sweet spot on the fingerboard

Subject: RE: Tech: Condenser Mic/Phantom power problem ?
From: treewind
Date: 21 Aug 08 - 06:14 PM

Looks like you're doing everything right. Take the mic back and either test it in the place where you bought it or swap it for another one. Check the cable too...

Generally best to plug in first, then switch on phantom power. Don't forget to mute the channel or at least turn it down, or you'll get loud noises from your monitor speakers as the phantom power comes up.

Anahata

Subject: RE: Tech: Condenser Mic/Phantom power problem ?
From: pasher
Date: 21 Aug 08 - 06:18 PM

"Budget Price", "ebay", - sounds to me that you got what you paid for ;-)
From what you say, it sounds like a faulty mic.
How budget was it?
These days you can get studio condensor mics from you local music shop for £50 or so - I have a couple and they're fine for home recording, and they are easy to take back if there is a problem with them.
hth

Subject: RE: Tech: Condenser Mic/Phantom power problem ?
From: John J
Date: 21 Aug 08 - 06:27 PM

I rather sounds (geddit?) like an impedance mismatch, perhaps you have a high impedance input with a low impedance microphone. The mismatch would have to be quite extreme, but it would certainly have a detrimental effect.

Try sending a PM to Bernard, he's something of an expert - and being the splendid sort of chap he is I'm sure he'd be delighted to advise.

John

Subject: RE: Tech: Condenser Mic/Phantom power problem ?
From: Bernard
Date: 21 Aug 08 - 08:12 PM

It sounds like a dry solder joint to me - either in the cable or in the microphone.

I have four Behringer B2 Pro microphones, excellent value for money, large diaphragm studio condensers loosely based on the Neumann U87 (which costs over 10 times as much!).

One of them became noisy, so I opened it up and got lucky - found a loose wire, soldered it up and it's perfect. Easier than sending it back...!

I doubt that it's an impedance mismatch, because phantom power is only provided on the appropriate input for the microphone.

The way Phantom works is to send the +ve DC up the signal pair, with the -ve DC on the shield/ground wire. As the microphone signal is AC, the two co-exist quite happily until something goes wonky.

Subject: RE: Tech: Condenser Mic/Phantom power problem ?
From: Bernard
Date: 22 Aug 08 - 09:10 AM

Forgot to answer the main question...! Sorry!

It's unlikely that having it connected to any equipment will cause damage as such, but pops from phantom being disconnected and reconnected can damage tweeters.

So if the problem is a dry joint - most likely on the shield/ground - then yes, damage could possibly result to loudspeakers, which is why Anahata (Treewind) advised muting the input. I'd go one step further and recommend that microphones are connected and phantom switched on BEFORE the amplifier is powered up, and that the amplifier is powered down before disconnecting, etc. That way the speakers are protected from pops.

It is standard practice with a system to switch the amp on last at power-up and off first on power-down. It doesn't much matter what you do with everything else... though maybe you should take care if you're using headphones!

Subject: RE: Tech: Condenser Mic/Phantom power problem ?
From: GUEST,iancarterb
Date: 23 Aug 08 - 12:58 AM

Pretty much the only damage you can do with phantom power is apply it to a piece of non-powered gear without a DC block at its input. Some old Lectrosonics VHF wireless mic receivers had a resistor effectively right at the connector and if +48 from a camcorder or mixer were inappropriately switched on it would actually see something (that pesky resistor) to draw current and sometimes turn into a noise source. I agree it sounds like a questionable mic if the cable works with a dynamic mic.
carter

Subject: RE: Tech: Condenser Mic/Phantom power problem ?
From: GUEST,Al no cookie
Date: 23 Aug 08 - 01:15 AM

Find out what voltage phantom power the mic needs, and what you are feeding it. Some want around 15 volts, others (most) want 48 volts. If you apply 48 volts to a 15 volt mic, you might have problems. How about you just post the name of the mic, and a link to online information about it.
Al

Subject: RE: Tech: Condenser Mic/Phantom power problem ?
From: Bernard
Date: 23 Aug 08 - 12:52 PM

A dynamic mic can work perfectly well with a cable having a dodgy screen/ground, but a condenser mic will have problems... it's because the -ve DC phantom uses the screen, but a dynamic only needs the twisted pair and will work okay with the screen completely disconnected!

Subject: RE: Tech: Condenser Mic/Phantom power problem ?
From: ConcertinaChap
Date: 23 Aug 08 - 02:46 PM

If you still can't crack it despite the (very good) advice above, try the forums here at Sound on Sound. They have a Newbies subforum for newbies (oddly) where the assembled centuries of studio knowledge is deployed very helpfully.

I think you need to see if you have the problem with a different condenser mic. Do you have a friend who can lend you one? If that mic has the same problems then it's your mixer/cable. If not, it's the mic.

Chris

Subject: RE: Tech: Condenser Mic/Phantom power problem ?
From: GUEST,iancarterb
Date: 23 Aug 08 - 04:24 PM

Quite right, Bernard, and the shield is the most likely culprit for a break. I sit corrected. Well, 33% corrected. :) Carter

Subject: RE: Tech: Condenser Mic/Phantom power problem ?
From: pdq
Date: 23 Aug 08 - 06:52 PM

Is this an electret design or a large capsule type? Both require bias voltage but the electret version can be very low. A definite suspect is the amplifying device, assumed to be an FET. Quality control on mics in the $100 to $150 range (made in China) is not always good. Borrow a known good specimen and try it.