Rode NT2A circuit - identify SMD

[ghiatorino]

Hi guys,
i have 2 Rode NT2A experiencing the same problems (wind noise, random pops-crackles). One started last year and the second some days ago.
I changed the capsule, 2 different brand new capsules, and the problem is still there.
So i tried to get into the SMD circuit and change the 470 pF input coupling cap (marked in green on the attached picture) with a through hole WIMA soldered on the circuit tabs. No result.
I am searching the issue on the high-Z part of the circuit, since AFAIK this problems are related to the input section (capsule and related JFET input circuitry).
No schematic around the web, so working on the SMD's is very difficult. Can you help me identify the 2 components marked in Red? They could be some high value resistors, i am expecting 2* 1 Gohm resistors around there (one is joined to FET's gate ).
I would also try to change the FET, marked in blue, do you know which one is used?
I would appreciate comments or hints (or schematic !?!), thanks in advance

 

[RuudNL]

Did you check the capacitors in the filter for the polarisation voltage?
(I had this problem a couple of times.)

 

[ghiatorino]

if you mean the 2 big ones above the capsule leads yes, changed on the other mike, no results.
If no, please help me identify where they are on the board...
many thanks!

 

[OPR]

I had the same problem with an Nt2A and fixed it by reheating the solder connections. It was a while ago but I think it was one of the capacitors  capacitors circled in  my pic.

 

[rubiks202]

Hi i know this was some time ago. I am experiencing The same problem. Can anyone suggest me capacitance values? Im basically just gonna replace most of them that see a higher voltage

 

[Khron]

Have you tried to measure anything at all?

 

[dima_k85]

Capacitors circled in green - about 2.2nF x 100V, red - 100nF x 100V. C0G (NP0).
JFET - IF4500.

 

[ZHAOMENG]

风或不规则的爆炸，但很可能是胶囊两层之间的水分导致绝缘层下降

 

[M V]

Hi guys,
i have 2 Rode NT2A experiencing the same problems (wind noise, random pops-crackles). One started last year and the second some days ago.
I changed the capsule, 2 different brand new capsules, and the problem is still there.
So i tried to get into the SMD circuit and change the 470 pF input coupling cap (marked in green on the attached picture) with a through hole WIMA soldered on the circuit tabs. No result.
I am searching the issue on the high-Z part of the circuit, since AFAIK this problems are related to the input section (capsule and related JFET input circuitry).
No schematic around the web, so working on the SMD's is very difficult. Can you help me identify the 2 components marked in Red? They could be some high value resistors, i am expecting 2* 1 Gohm resistors around there (one is joined to FET's gate ).
I would also try to change the FET, marked in blue, do you know which one is used?
I would appreciate comments or hints (or schematic !?!), thanks in advance

I worked at RODE for quite some time. This was a common issue with a few mics. You'll wanna change the White SMD 100nf caps to WIMA 100nf film caps. Eliminates the problem completely.

 

[MetroStudios]

I worked at RODE for quite some time. This was a common issue with a few mics. You'll wanna change the White SMD 100nf caps to WIMA 100nf film caps. Eliminates the problem completely.

Hey MV! I'm having a similar issue. Can you outline which caps were to be replaced? Maybe use ghiatorino's pic as a guide?

 

[Khron]

Hey MV! I'm having a similar issue. Can you outline which caps were to be replaced? Maybe use ghiatorino's pic as a guide?

OPR already pointed them out. I had an issue with the one on the positive bias rail, from the pair in the lower-right in that photo (plenty of noise and nearly no signal in cardioid or omni, only in fig-8)

I had the same problem with an Nt2A and fixed it by reheating the solder connections. It was a while ago but I think it was one of the capacitors capacitors circled in my pic.

 

[jp8]

If changing the caps does not help and you suspect the JFET is broken: JFET is InterFET type IF4500.

Jan

 

[MetroStudios]

Thank for all the info everyone! Will start by re-eating the caps, and then go from there.....

 

[Khron]

Thank for all the info everyone! Will start by re-eating the caps, and then go from there.....

Just don't melt'em - those big silver ones are film capacitors, and plastic melts more readily than solder...

That, and they HAVE been known to fail (almost ironically enough, rather than the ceramics) in these mics.

 

[MetroStudios]

Just don't melt'em - those big silver ones are film capacitors, and plastic melts more readily than solder...

That, and they HAVE been known to fail (almost ironically enough, rather than the ceramics) in these mics.

Thanks for the heads up! I have zero experience with SMD's, so this'll be a challenge....

 

[MetroStudios]

SOLVED! Update:...I reseated two little caps where the leads from the capsule connect to the PCB and voila! Thanks for everyone's help! Man this mic sounds good.....