MOTUnation.com

In reading over my earlier post I realize I may have confused some folks. So let me try again.

A condenser (capacitor) microphone basically consists of two plates one of which is charged (biased) with 48 volts (in most instances). The purpose of the phantom supply is to deliver that 48 volts. It is simply a static charge.

It appears that some newer microphones (I suspect Chinese in origin) may actually have pre-amps built into them. They are taking power dynamically from the phantom supply. So the current draw varies at an audio rate. That means there needs to be some filtering or isolation at the microphone and this apparently is not happening. Of course, this is a misuse of the supply, too, as it is not meant to provide current.

This should not be confused with microphones like the AKG C414 which uses an FET as an impedance converter. There is essentially no current involved.

The immediate solution may be to increase the value of the filter capacitor (impedance) on the regulator to keep it from generating noise. And this is what I'll check when I return next week.

This should not be confused with microphones like the AKG C414 which uses an FET as an impedance converter. There is essentially no current involved.

I use AKG C451 B and got lot of noise... The preamp are just crap... gonna kill myself

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have you tried to use an external phantom supply ? i have the impression pre-amps are ok, not the phantom power supply.

w.

We tried a fix which was to increase the value of the filter capacitor to 47 MFD and it helped considerably but did not cure the problem. If the value of the cap is increased too much the high frequency response of the regulator suffers and thus, regulation suffers. The problem does not exist in the old Traveler or the 896 MKIII. The preamps themselves are fine, in fact excellent, but let us look at this a little further and I'll post the results here. Give me a couple or three weeks as I have to get unpacked and caught up but will work it in as I can.

this is great news!
thanks for doing so much research.
do you have more info ( photo's ?) of your experiments ?
w.

Confirmed here:
Traveller MkIII
Sennheiser ME66/K6
Horrible and constant white noise (but restricted to frequencies mentioned in earlier posts).
Turning Phantom off and using the mics battery power solves the issue, however, is still a major design fault. I really don't want t waste batteries on the mic, I'd rather reserve them for my wireless packs.


MacBook Pro 15"
Traveller MkIII

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do you have 2 ( or more ) ME's ?
try next
connect 1 to input 1
the second to input 2, don't switch its phantom power
listen only to channel 1
you hear the typical noise
switch on the second mic phantom power
the pitch will change higher

yes ... pity for the mk3

w.

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i did some looped recordings by the principle of alvin lucier.
http://ubu.artmob.ca/sound/source/Lucie ... itting.mp3
this way the noise become looped also and very audible
i had to use my external phantom supply to avoid it.



hope soon for a solution



thx,

w.

...

again ...
used my traveler mk III yesterday for some "silence" recordings, used 2 DPA 4060 and heard clearly the phantom noise again ...
i had to use my external phantom power supply to get rid of it.

you can hear is at:
http://dl.getdropbox.com/u/137991/DPA%20%26%20MOTU.mp3

the mic amp was in +30 db. ( i added 12 db extra to make it audioble without the need to turn the volume up )
first you hear for 5 seconds the internal supply, the last 5 seconds is the extrenal one.

i agree is isn't much, when you record rock or other heavy music you don't hear it ... but i like more the silent stuff. when recording classical music it sounds as you heard some airco in the background.

have someone a better solution than using an external supply ?

w.

Hey folks! I am buying a Traveler MK3 in less than 3 hours, and I am quite a bit horrified in reading about this phantom noise issue!

Any news on the theme?... APADRecordings?... Am I going to waste 800 Euros?...

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yes, as far as i know motu didn't do any modification or upgrade.
i use it still in most occasions with my external phantom supply.
i understand from your login you are in classical music. i heard it the first time when i was recording in a chapel. i had the impression i heard the airco, or a plane high in the sky ... but it was the phantom supply instead.
it's really sad this fine unit ( i like it very much ) has this strange hardware design problem.
most sad is the reply of motu support: " not out of the ordinary " ... are we not talking about a 192/24 unit ?
my edirol UA25 sounds better !!!

i can only advice to use an external phantom supply.
I wait until my warranty is finished so I can open the box and have a look inside with some electronic wizard. I hope to find a solution …

Maybe someone else know already ???

w.

ps. i am very interested to hear your impression of the test ... hope you have something i don't have.

Hi planktone

I have decided to go on and see... You are right, I am interested in recording classical music only, mostly organ music: it's true that the kind of noise you encountered could easily be taken for the organ blowers' noise, but blowers are already so noisy... there is no reason to raise the noise floor even more!
Incidentally, I am an electronics designer, my skills and interest are mainly in ANALOG electronics. Since this problem with the noise is essentially an analog issue, I suppose I can work on it, provided that somebody hands me the schematics of the MK3...

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interested to hear you opinion.
what microphones do you use for organs ?
i did a lot myself once

don't hope to get any schematic from MOTU.

w.

APADRecordings wrote: It appears that some newer microphones (I suspect Chinese in origin) may actually have pre-amps built into them. They are taking power dynamically from the phantom supply. So the current draw varies at an audio rate. That means there needs to be some filtering or isolation at the microphone and this apparently is not happening. Of course, this is a misuse of the supply, too, as it is not meant to provide current.

This should not be confused with microphones like the AKG C414 which uses an FET as an impedance converter. There is essentially no current involved.

Uuups... wait a second. By mere chance, two of my 4 microphones are AKG C 414 XLS. Apart from the current drained by the preamplifier circuit itself, you must take into account the current drained by the THREE LEDS (pattern, pad and HP filter) and the digital logic which handles the LEDs and the buttons: AKG specifies a total current drain of 4 mA, that @ 48V means almost 200 mW...

planktone wrote:...

interested to hear you opinion.
what microphones do you use for organs ?
i did a lot myself once

don't hope to get any schematic from MOTU.

w.

I use a matched pair of AKG C 414 XLS and a pair of Røde K2 (tube preamp... they don't need phantom power! )
If MOTU doesn't want to give schematics around (...which at this point I hope to get from other sources...), better they listen to their customers complaining after spending hundreds of Euros in their gear, rather than replying "not out of the ordinary"