Topic: M-Audio's response to 48v phantom power bug

[nic]

didnt you read , they did check some" esoterics"
might work , probably not :-)

yeah. I'm holding my breath (right!) since my esoteric QTC1 and SR-77 mics aren't owned by a single person other than a handful of people in NH who make them and me. 

Actually if they would simply fix the digital input problem I would buy one simply so I could do a rough down and dirty two-track mix in the field from the Deva IV ... Of course this also assumes that it will handle a real AES signal.

Wayne

I think ToddR said he fed his Microtrack from the AES2(pro) line on his V3...

[oleg]

didnt you read , they did check some" esoterics"
might work , probably not :-)

Actually if they would simply fix the digital input problem I would buy one simply so I could do a rough down and dirty two-track mix in the field from the Deva IV ... Of course this also assumes that it will handle a real AES signal.

Wayne

it would make your deva, deva 5 :-)

[Jonny Durango]

Here's another one fired off today:

-------

As posted to rec.audio.pro by David Satz

<<
Pawel, please do not try to use the Schoeps CMC 6-- amplifier (whether
it is the xt version or not) with a power supply that offers neither
standard 12 Volt phantom powering nor standard 48 Volt phantom
powering. What will very likely occur with a 30-Volt supply is that the
voltage received by the microphone's circuitry will be in the 20s or
lower (because of the 6.8 kOhm supply resistors), and the microphone
will switch over to its 12 Volt mode.

In that mode, however, the microphone draws about 10 mA and that will
very likely bring down the power supply regulator in the recording
device, quite possibly causing damage to the MicroTrack if its circuit
is not protected. I have personally seen that occur with another
lightweight, portable preamp/ADC in which the "phantom power" supply
was not up to standard.

M Audio should certainly know about this issue; they experienced it in
the design of the DMP3 preamp, since its predecessor the DMP2 could not
properly power a pair of modern condenser microphones--not even
Neumanns at 2 - 3 mA apiece, let alone a Schoeps (4 - 4.5 mA) or any of
the types that require more current, such as the Shure KSM series (5 -
6 mA), the original AKG C 451 (6 mA), the CAD Equiteks (8 mA) or
Earthworks (10 mA). I had an email exchange with the designers, and the
eventual model DMP3 was a definite improvement (also in regard to its
input overload margins).

>>

Also posted to sci.electronics

<<

Actually a repair problem for a low noise microphone pre-amp but seems to be
a general design flaw.
Pre-amp uses a Burr Brown INA103 very low noise instrumentation op-amp.
In this M-Audio Omni i/o preamp and an outline design application in the
Burr Brown book show much the same circuitry.
The 48Volt phantom supply to the mike is protected by 6.8K limiter
resistors.
But to block the 48V DC to the op-amp there is a 10uF/100V electrolytic in
each line directly to the inv & non-inv i/p of the op-amp .

If , as seems in this case, a balanced line microphone with a short to
ground is connected to such a system
then the +48V / 0V across the elecrolytic will instantneously go to 0V
/ -48V with -48V
directly connected to the op-amp i/p powered from +-15V rails and according
to the databook
can be taken to only +-12V.

Blown input to this op-amp due to just the owner connecting a microphone.
Anyone familiar with this, adding limiting diode pair at each input ?
I see no point in replacing this 15 GBP/ 25 USD IC until this design flaw
is attended to or it will happen again should a fault to ground develop in a
mike or lead while the 48V power is on.

>>


I hope this is helpful in troubleshooting this problem. Please let me know when/if you plan to address this issue in a later revision of the Microtrack. Thanks!

--

Jonny Durango

www.jdurango.com

"If the key of C is the people's key, what is the key of the bourgeoisie?"

[oleg]

http://www.m-audio.com/index.php?do=products.list&ID=microphones
check the power requirement for m-audio mikes , isn't it strange :-)

[F.O.Bean]

this problem is minimal in my uses w/ it anyway

whats up w/ the damn auto-split

[rdvdijk]

whats up w/ the damn auto-split

M-Audio said they would look at it, but they have other bugs to fix / requests to grant which have a higher priority (for them). Let's wait and see how first firmware turns out..

Roel

[Jonny Durango]

Here's one of the initially released pics of the MT. Anybody notice anything strange?



Thanks cmoorevt!

Jonny Durango

[John R]

based on the photos and lit presented by m-audio, this could possibly become a very expensive glitch for them.  there are a lot more people out there receiving this thing than frequent this or any geek board.  what's going to happen when joe newsroom of bill homerecorder plugs his 48v mics into it and things need ot be replaced/repaired?

jr

[Colin Liston]

So if I plugged in my DPA 4023's did I screw them up?   

[it-goes-to-eleven]

You might want to contact DPA and ask them about powering at 30v.

[keepongoin]

i don't think you are going to fuck up your mics with less than 48 v.  some mics won't work.  others won't put out levels like they would normally.  that is what jon (jklabs) told a year ago after i plugged in my battery to my ps-2 with the polarity reversed and it would only put out 36 v.

[eric.B]

as long as this thing will sucessfully record bit perfect 16 44,48 and 24 44,48,96(when the firmware is updated) over spidiff..  this box is a winner..  I dont much care if this thing even takes a line in/mic in signal or has phantom power.. 

[Ed.]

as long as this thing will sucessfully record bit perfect 16 44,48 and 24 44,48,96(when the firmware is updated) over spidiff..  this box is a winner..  I dont much care if this thing even takes a line in/mic in signal or has phantom power.. 

i'm with ya on that one.

[BayTaynt3d]

I just got a B&H Pro Audio catalog in the mail last night. It had the MT in it, and right there in your face was "48v Phantom" listed as a feature...

[wbrisette]

you know just because they removed 48V from their claim of Phantom Power, that doesn't mean they are off the hook. If they followed the spec, then they are either at 12V, 24V, or 48V @ 10mA. They aren't going to be able to provide that amount of current at 30v, so they really are still in trouble.

Wayne