Hissy SDC... what to check?

[clepsydrae]

Hi -- I got two CAD CM217's super cheap off craigslist. One works and actually sounds really good, the other has substantially more hiss and a bit less highs. It's just barely usable, but definitely seems out of range of natural variation between mics.

I managed to tear the bad one apart, with minimal collateral damage, cleaned off the board with some isopropyl, looked for anything obvious and didn't find anything. I jiggled everything around looking for bad solder joints/etc while monitoring the output. Moved the switches back and forth a bunch of times, etc. (I also ruled out cables and the audio interface/etc.)

Is this kind of symptom something that may just come from a bad capsule, or is there something to look at in the circuit? E.g. replace the large capacitor, etc? It's mostly tiny SMD stuff, but I'm not afraid to attempt some microsurgery if there's something to try. Happy to post pics of the board/etc if it would be useful. I just wanted to see if I should even bother going down that road, but it seemed to my naive brain like it was more likely the circuit...

Thanks for any ideas!

 

[pucho812]

sounds to me like there is condensation trapped in the capsule...

 

[clepsydrae]

Thanks! -- I would note that compared to it's better-functioning brother, the mic exhibits increased hiss at identical gain levels, so its not a loss of overall sensitivity... does that change your suspicion at all?

I just pulled the two mics up again, and now the bad one isn't working at all, and making "cloudy" low-freq noise when I wiggle the XLR... interesting. Maybe condensation as well?

I'll put it on a warm radiator for a day and see what happens.

 

[clepsydrae]

Well, a few hours in a hot dehydrator and overnight on a warm radiator, and it's still the same.

When I first plugged it in, it was in the same almost-no-signal/cloudy noise state it was in from the end of the day before. I checked the capsule wires and it seemed like one was perhaps folded over onto the other, possibly shorting the capsule connection, and once I had the capsule dangling off the end everything sounded normal again, so that may have been what that was about. So it's working normally again.

But "normally" means back to the hissy/bit-less-highs state it was in before.

It got me wondering if the wires to the capsule could cause the hiss/dullness if there was a partial break in there somewhere? I'd expect it to be intermittent though, if so, eh? Or maybe the solder joints on the capsule: the blobs look pretty close to each other... could that contribute?

I'm just trying to narrow it down... I'll post audio samples too, soon, in case it's helpful.

If I basically just bought a project mic body, I'm OK with that, I just want to know if there's something I can try to resurrect it...

 

[clepsydrae]

Heard back from the CAD service department, who kindly replied to my email:

"Sounds like a noisy FET internal to the capsule can! It was probably born that way."

Seems like the specs of electret capsules are broad enough that pretty much any one would work in place of the original?

Ideally I'd like another cardioid but it seems like all the "good" ones are omni (Primo EM172, Panasonic WM-61A). Presuming those would even work.

Any cardiod recommendations?

Thanks!