Background noise with DPA 4088, DAD6001BC and Motu traveler

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waigy

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I recently treated myself to a DPA 4088 and the DAD6001BC microdot to XLR adapter.

I noticed this background noise (recorded at maximum trim and gain) when it's plugged into my Motu traveler using the Motu's phantom power.
The noise in question is the sort of buzzing, not the hiss, it's at a low level, but may be noticeable in recordings.
I get the same noise using my AKG C1000S, but only when the AKG is switched off, as soon as I switch it on the noise disappears.
The DPA doesn't have an on/off switch.

I tried the DPA in my behringer PA using it's phantom power and that noise isn't there.

Is this noise a possible fault of the DAD6001BC or the traveler?
 
Sounds like it might be digital noise from your computer. There are several possible ways to fix this. The first thing I'd try is using an external power supply to power the Traveler.

If that doesn't help, then the next thing I'd try is adding a heavy-gauge grounding lead from the signal ground on one of the Traveler's inputs or outputs to the ground pin on an electrical outlet. That's fixes most noise problems, in my experience.
 
Do you have a multimeter that can read VAC in the microvolt range? Or even tenths of a mV? If so, with phantom on, measure from pin 2 or 3 to pin 1 of the MOTU's mic inputs. It should be a very, very small figure, much less than 100uV ideally.

If it's more than that, I would suspect that the DPA adaptor doesn't have well matched impedance on each pin to ground, causing a loss of common mode rejection, which will cause noise on the phantom supply to leak into the audio signal. That would be odd, because DPA makes well engineered stuff, and they claim 60dB of CMRR, but stranger things have happened . . .
 
Does the buzzing change with the location of the mic? I get a buzz like you described if I'm near the electrical box on the outside of the trailer. Keeping the mics further away and closer to the ground helps. Not all of my mics suffer that, so it could be mic specific.
 
Thanks for the replies guys, I'm going to try each suggestion, should suss the problem eventually.

Dgatwood, it's not pc related as I still get the noise with the traveler nowhere near the pc and not plugged into it.
I'm going to try the earth cable thing you suggested soon, my brother is an electrician and should be able to get the proper wire for the job.

Mshilarious, I'm going to have to find the manual for my multimeter to see if I can measure the way you suggested, if not my brother has a better multimeter than me.

Shadow7, I've only tested it so far at 2 ends of my livingroom, connected and not connected to my PC, the sound stayed the same.

I also tried powering it using a portable battery supply that I made myself (which bypasses any mains related problems) while disconnected from the pc, still the same noise.
 
After a few checks on this noise problem, I’ve came to the conclusion that the fault is the traveler’s phantom power supply.
If I have my headmike plugged into channel one on the traveller and I switch on the phantom power for channels 2,3 and 4, the noise changes pitch getting lower as each extra channel is switched on.
It sounds like the phantom power supply is struggling to supply power.

I contacted Motu, but they only repeatedly told me to send the unit for repair and, as it’s out of warranty, I can’t afford the £150 to do that.

I was wondering if there’s anything I could do myself to fix this problem, I’m ok with soldering and taking electronic components to bits.
If I knew what to look for I could maybe replace any needed components/capacitors etc.
I’m assuming that the traveller uses an inverter as it can supply 48v power when it is powered by 18v or even 5v via firewire.
 
what's the voltage of the phantom power supplied (is that pin 2 to 3?)? On my traveler I think it was as low as 41 volts when I checked. I haven't noticed a noise problem like this, but I do have some mics (such as 414s) that sound like crap with the sub 48v supply. For those mics, I just use a separate in-line phantom supply if I'm using the traveler pres. Kind of a lame answer I know, but maybe something you hadn't thought of.
 
Hi antichef

This is far from being a lame answer, I just measured my traveler's phantom voltage at 41.7v, the same as yours.
DPA recommends 48v +/- 4v for full performance, but I reckon with 41v it should still work ok maybe with less sensitivity.
I doubt if the buzzing noise I'm getting is caused by insufficient voltage.

I'm considering an inline phantom power supply as a workaround (behringer ps400), but I would prefer the traveler to be fixed.
The traveler wasn't cheap so surely it should have quality phantom power.
 
Probably a design problem with the unit's DC converter circuit rather than a repair issue. Could be anything from inadequate filtration to improper ground plane design. Not easy to troubleshoot . . .
 
I've just found out on motunation that the problem I'm having is very common with motu travelers, not just the MK1.
Lots of people complaining about noisy preamps when using phantom power.
I feel a bit let down after spending what I think is a lot of money to get a decent bit of gear that would do me for a lot of years.
I also think that motu should fix this for free if it's an inherent fault, even out of warranty.
I've hardly used my traveler, I always look after it and it's in my living room 99% of the time.

Seems that the seperate inline phantom power supply is going to have to be the solution.

I always liked the thought of being able to go to the top of a mountain and recording my geet at very high quality with my traveler and laptop.
I'll still be able to do that, but I'll just have to carry a few car batteries with me.

Does anyone make a 4 car battery belt for wearing round your waist?
Gap in the market?
 
Updating this in case anyone has the same problem as me.

Just got a behringer micropower PS400 portable phantom power supply to power the mike, problem solved, no buzzing noise.

So the noise was definitely caused by the traveler's phantom power supply.
 
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