SDC capsule noise

[Icantthinkofaname]

Just got a used SDC from eBay, it's an electret and it's definitely the capsule that's the problem because another capsule works just fine on that body and the noisy capsule sounds the same on another body. I've already contacted the seller because the listing said the mics were in "good working condition". The noise is a very loud hiss (I'd say like a waterfall or the ocean) and the capsule has lower output than the working capsule (both mics are the same model). Could it be humidy or moisture on the capsule, or maybe dirt? Or some issue with the charge of the capsule since it's electret?

 

[neowalla]

Possibly the FET assuming it has a built in one. I recently bought a SCM-1 stereo mic directly from Ningbo in China and the top capsule sounded like a waterfall. This mic has LDC, externally polarized, but it is a FET mic and it turned out to be a bad FET on the PCB that serves the top capsule. I replaced it and all is quiet and serene
In the case of built in FETs in SDC capsules, unfortunately I don't think replacing the FET is an option!

 

[mhelin]

I've too got an old Oktava SDC electret (MKE-2 capsule I think) that was noisy and quiet even after replacing the FET (used K596, S to gnd), and it is still after phantom power bias (via 1G resistor) to the electret capsule. I'm wondering how the polarity of the electret affects after all as the bias voltage and electret charge are summed. The MKE-2 capsule afaik has the electret in the diaphragm so it might have correct (positive) bias.

 

[neowalla]

When researching the issue with my SCM-1 mic, the two most likely culprits were either a bad capsule or a bad FET. Needless to say Googling "waterfall" sound from mic capsule is a pretty difficult thing to get good search results for. The manufacturer was even less helpful what with the language barrier and all, but at least they supplied me with the schematic. Fortunately in my case replacing the FET was easy and it worked like a charm.
I would contact the seller and ask for a refund on that capsule. If they won't, then try to file a claim with ebay.

 

[Icantthinkofaname]

Possibly the FET assuming it has a built in one. I recently bought a SCM-1 stereo mic directly from Ningbo in China and the top capsule sounded like a waterfall. This mic has LDC, externally polarized, but it is a FET mic and it turned out to be a bad FET on the PCB that serves the top capsule. I replaced it and all is quiet and serene
In the case of built in FETs in SDC capsules, unfortunately I don't think replacing the FET is an option!

I don't know if it has a built in FET, since I don't know much about the AKG Blueline mics, but it definitely seems like a likely explanation. I left the mic in a bag with a rechargeable dessicant and no improvement. I also tried leaving it powered on for a little while because some people have had success with some noisy mics that way, but the preamp is fine. The problematic capsule has 6-8 dB less output, so it's definitely not functioning correctly.

 

[k brown]

Each B. L. capsule has a small circular PCB in it containing SMD FET and biasing parts.

Have you cleaned the capsule contacts with DeOxit?

 

[Icantthinkofaname]

Each B. L. capsule has a small circular PCB in it containing SMD FET and biasing parts.

Have you cleaned the capsule contacts with DeOxit?

I haven't. I think I'm just gonna send them back. If I can't improve the capsule I'll have to replace it, and then I'd be spending almost what I paid for the pair of mics (I paid $300 for the pair, a new cardioid cap is $200), and I find the CK93 hypercardioid sounds like ass compared to my MK-012s, AT4053bs, and MKH 8050.

A Line Audio CM4 would be cheaper and give me similar performance (slightly less sensitivity at 8mV/Pa but also only 16dB A self noise).