Rode NT-2000 rumble

[Ike Zimbel]

Hi All,
I have an NT-2000 on the bench with LF rumble on the o/p. So far, I have subbed a pair of 82pf caps for the capsules and dialed up the HPF and neither get rid of the VLF noise on the o/p (it's around 10Hz). I looked in the tech docs and I didn't find a schematic, and mics are not my long suit so any info and ideas would be appreciated.
Thanks!

 

[kingkorg]

Is it constant? How loud is it?

 

[Ike Zimbel]

Yes, constant but random (IOW, not one fixed frequency), like LF "rocks". I'll have to pop down to the bench in a bit and measure the level and report back.

 

[Ike Zimbel]

So the noise floor, with capsules out of the picture is around -57.00 dBu. On the FFT, there's two "haystacks", the first from around 0-125 Hz and the 2nd from around 250-500 Hz and these are about 42 dBu higher than silence, albeit fluctuating. Adjusting the attenuation pot causes the noise floor to go up right across the spectrum, but it will settle back to the same levels afterwards so I'm guessing that pot has some DC on it.

 

[kingkorg]

Well i presume you've checked the shielding, and ground. The grille has good contact? There aren't any layers missing? There should be two or three layers of wire.

Other than that i'd go through the caps, i had a bad cap once that filters the pol.voltage on NT-2a. I guess the good part of the circuit is similar to NT1-a, for which we have schematic. The pattern selection is obviously non existent on NT1, but voltage multiplier circuit should be similar.