Only one mic doesn't work on the SD 664 [solved]

[Michiel]

Today I experienced the weirdest mic problem so far.

I connected a Rode NT1 to the Sound Devices 664, which went fine for a couple of days until today.

Now there's soft static noise around 500Hz and some crackle that fades away if you re-connect it, that should not happen.

 

The WEIRD thing is, is that this NT1 still works fine on the Mixpre-3 II and a DBX preamp. No noise, no crackle.

Other microphones (Schoeps, Sanken, Rode) all still work fine on the 664.

It is only this specific mic-mixer combo that now suddenly is failing...

I changed cables, tried internal AA cell power and other input.

 

Audio (warning, loud pops from disconnecting):

 

 

I thought perhaps the NT1 might have started to produce an ultrasonic signal that the 664 translates to noise. However, a 192kHz recording on the Mixpre reveals nothing unusual.

If anybody has an idea I'd love to hear it

[The Documentary Sound Guy]

Only thing I can think of is maybe the NT1 is more sensitive to P48 voltage than others (or requires more current).  First thing I'd do is use a multimeter to check what voltage your phantom power is out of the 664 and see if it's in spec.  If it's possible to measure while under load, that would be ideal, but will probably take building a special pass-through that will let you tap the appropriate wires.

Other than that ... could be that something has failed (most likely a capacitor) in the NT1 that is making it sensitive to impedance differences, and the 664 is the odd machine out.

Either way, fixing something like that is probably going to take some knowledge of electronics ... I'd send one or both in for factory maintenance and request that things are checked to make sure they are in spec.

Also,

I'd listen closely to noise floor with other mics on the 664, or other recorders with the NT1.  If you find noise floor isn't what you expect in one of those combinations, that might give a hint as to which piece of hardware is out of spec.  Go looking for subtle problems ... don't just assume things are working 100% just because your gear is passing signal and there's no obvious issues.

[Michiel]

Thanks! Now a similar thing happens on the Mixpre that didn't happen before. Still, the type of noise on the 644 is very different from the Mixpre which is still strange. Looks like indeed some component in the NT1 is slowly failing as it still sounds fine on the DBX, for now... Perhaps it gives more phantom power as you suggest.

 

Turns out these NT1's are quite unreliable as this is the second one failing. NT1's have 4.5dB self noise, until they don't... 

[Tim Norris]

Quote

Turns out these NT1's are quite unreliable...

 

You get what you pay for?

 

Cheers,

Tim