Phantom Power Issues with Mbox 3 and CAD m179 condensers?

[kcrimi]

I've been recording on my mbox in protools 10 and have run into some issues with using my matched pair of CAD m179 condensers.

When turning on the phantom power with both mics attached, I get the squeals and pops and eventually it finds equilibrium but at a very low signal level. I'm verifying this signal level both aurally through the headphones and looking at the signals on Pro Tools and in the Mbox control panel. I have to basically bring the gain knobs all the way JUST before the huge jump at the final position of the pot and still only get to about -20dB with loud singing or acoustic guitars. Of course the noise floor is pretty bad at this point.

I had thought it was just the mbox until I unplugged one mic by accident. This caused the same popping sound that occurs when turning on the +48v and then finally a MUCH louder usable signal afterward. I can then plug the mic back in, repeat the process with the other cable and bring the 2nd mic's level up. This seems like the proper signal and I'm able to record in the yellow with a good noise floor at a reasonable gain level. Unfortunately, this eventually deteriorates and the level goes back down with time.

Things I've tried:

• switching xlr cables
• using only 1 m179 (levels are normal)
• using 1 m179 and sm57 (levels remain normal)
• using a powered usb hub (Sabrent 4-Port USB 3.0) - (no help)
• trying the above with and without the computer power supply (no help)
• plugging mbox into both USB ports (no difference)
• trying with and without external HD plugged into the other USB (no difference)
• plugging in to a mac book pro instead of my air and monitoring levels in mbox control panel (no difference)

It seems pretty definitive to me that the mbox just can't feed both m179s at once my questions are:

1. Can I do anything to fix this?
2. Is this an issue with my unit or will I have this issue with all mboxes?
3. Is this an issue with the mbox or will I have this issue with any USB powered interface?

Thanks

mbox (3rd generation)
Pro Tools 10
mac book air
1.3 GHz Intel Core i5
4 GB RAM

[mesaone]

I have a CAD M179, which I had modded by Michael Joly.

This mic does transmit a squeal when engaging and disengaging phantom power. That much is not unique to the MBOX, I first noticed it on an SSL-9000 J-series console. Duplicated on everything else I plug into.

Video here. Is that what you hear/see? If so, I'm given to understand that it's normal for this mic. Note: I do say "it's never done that before" in the video, but that may not be true - I never had the channel feeding monitors when engaging phantom before.

I sent it to Michael to check, and there were no problems. His advice was to avoid monitoring the channel when engaging and disengaging phantom power. Which is normally what I do, the problem was just brought to my attention by the unusual meter activity - obviously I should have noticed this prior to the session, but I don't feel bad about spending 2 minutes testing it live because we were doing pro bono.

So there's no problem I can see with your mic or your audio interface, as long as the squealing noises happen only when engaging and disengaging +48 V. Be aware that this mic is very thirsty when it comes to phantom power, so there are interfaces that just don't supply enough juice for two (and sometimes even one) of them.

If the level continuously dies (or decreases) during use, then that is a problem. Does it happen only when using two M179 mics connected to the mbox? If so, I recommend buying an external phantom power supply (http://www.amazon.com/rolls-PB223-Ph.../dp/B0002BEO5O). Two thirsty M179 microphones may require more than the bus-powered MBOX3 is able to supply.

[kcrimi]

Thanks for the response. I'm not really that worried about the squealing. I am worried that I will never have a truly portable way to use these microphones. So is there no way to get these to work properly with a USB powered interface (whether mbox or some other brand)?

[mesaone]

I've not had a problem, but I only have one of these mics and the portable interfaces I've used with it are a few steps up from the MBOX.

Check out the 2-channel phantom power supply I provided a link to. Better yet, try these mics on a mixing console or some other device that is known to supply ample power. If you have a friend with a mixer or audio interface that has an AC adapter, then give it a shot. If everything works with no problem, then your MBOX is the culprit.