Rode NT1A schematic?

[abbey road d enfer]

The zener noise should be pretty well filtered out by the 100r and 220uF. In addition, it is shared equally on both legs of the output, so any mic preamp with decent CMRR should attenuate it significantly.
The cold leg is referenced to ground, so there is no noise, except for the Brownian noise of the 50r resistor. The hot leg is referenced with an identical 50r to the discretete opamp, which has a sub-1 ohm impedance. The onluy possible explanation is that the opamp is noisy.
But, you say that with the opamp disconnected, noise is still there...
OK, what is the actual noise level?

 

[saint gillis]

The oscilloscope shows something like 10-20mV pp
On a breadboard, I've put two 4K7 resistors, a 100r + a zener to the ground, and when I put a 47r resistor between ground and cold leg, I have the same amount of noise, maybe my preamp is faulty then, but this is why I thought it could be something normal.

 

[Strider0007]

What kind of noise are you getting?

 

[saint gillis]

kind of white

 

[Tubetec]

Could the capsule have become damaged by the fall? or has that been ruled out?

 

[abbey road d enfer]

The oscilloscope shows something like 10-20mV pp
On a breadboard, I've put two 4K7 resistors, a 100r + a zener to the ground, and when I put a 47r resistor between ground and cold leg, I have the same amount of noise, maybe my preamp is faulty then, but this is why I thought it could be something normal.

This is somewhat normal because you are ruining CMRR in doing that.
Same when you disconnect the opamp, which leaves the hot leg unloaded, when teh cold leg is loaded passively.

 

[saint gillis]

Could the capsule have become damaged by the fall? or has that been ruled out?

No, capsule seems ok

 

[saint gillis]

This is somewhat normal because you are ruining CMRR in doing that.
Same when you disconnect the opamp, which leaves the hot leg unloaded, when teh cold leg is loaded passively.

Thank you, this is a welcome clarification

 

[Austral]

Since the mic was dropped, I am guessing that there might be a bad connection to the capsule, which can cause white noise. (Could be in the form of a broken PCB track as someone else suggested, or simply a loose wiring connection.) If you disconnect the capsule, do you get the normal hum without white noise? Just a thought...

Seems like you've replaced all the likely components! (It is at this stage in debugging that I start to believe in black magic, and give up...)

 

[saint gillis]

Since the mic was dropped, I am guessing that there might be a bad connection to the capsule, which can cause white noise. (Could be in the form of a broken PCB track as someone else suggested, or simply a loose wiring connection.) If you disconnect the capsule, do you get the normal hum without white noise? Just a thought...

Seems like you've replaced all the likely components! (It is at this stage in debugging that I start to believe in black magic, and give up...)

Yes same thing with the capsule disconnected or replaced by a capacitor, I wouldn t give up if it was not smd...

 

[slipperyflax]

saint gillis: Did you ever get this sorted?

 

[saint gillis]

No, I had the project to do new replacement pcbs, but never had the time to do it

 

[MidnightArrakis]

No, I had the project to do new replacement pcbs, but never had the time to do it

1) What are the dimensions of the PCB?

2) Can you provide a clear, very close-up and well-lit photo of the PCB? This will show me the components placement.

3) The schematic shown has several capacitors without any value. Can those values be provided?

4) The schematic shown shows its filename with a -- .dsn -- extension. Is this an OrCAD schematic? Can you send it to me?

That's it for now!!!

/

 

[Strider0007]

Yes same thing with the capsule disconnected or replaced by a capacitor, I wouldn t give up if it was not smd...

Try removing the cap between the capsule wires. I had a faulty SMD film cap causing the noise problem. I used a 0.1uf 100v film cap to replace it and it worked fine after.

 

[slipperyflax]

The reason I ask is because I've got one on the shelf for a long time. I bought it very cheap as a project (thought I could use it as a donor in worst case). FInally got it out and I've got this sound coming from it, sounds almost like it's constantly windy. Thought it was the capsule because it looked like hell but after a swap (had a capsule lying around) it still produces that noise.

Try removing the cap between the capsule wires. I had a faulty SMD film cap causing the noise problem. I used a 0.1uf 100v film cap to replace it and it worked fine after.

That might be it! Fiddled around that cap and if I put gentle sidewards pressure on that cap the noise goes away. Thank you very much!

 

[slipperyflax]

Swapping that capacitor did the trick for me. Now I can move on to the capsule-upgrade. Maaaan that felt nice, thanks!

 

[Strider0007]

Glad to hear that did it.