Deja Vu ... again. Or, Twice bit, once shy. KSM27 issue.

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MicMaven

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Jun 4, 2022
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Good Day. I foolishly returned to the well and drank deep. Notwithstanding my recent struggle with a used KSM44 microphone, I recently purchased a used KSM27 from a reputable vendor.

On arrival, it sounded sort of OK on a very brief initial test, although it had decidedly lower output than similar microphones including commercial products and home-brewed project microphones. A couple of other mic mavens (including Jules Rikenbush) on the Mic Builder reflector said it was OK, just use higher GAIN on the mixer. So, I set it aside until today. Now it produces even lower output and a terrible random crackling noise. The attached sound clip is comprised of two separate clips - I speak in the first bit, and the microphone is just sitting on a stand in the later bit. It makes that much noise just resting on the stand.

OK, I can accept comparatively low output ... but this crackling thing is a deal breaker. I re-read Mr. Khron's 2015 thread about fixing his noisy KSM27 microphones, as well as the thread on my recent KSM44 debacle. I wonder whether this sounds like Mr. Khron's problem. I will review and retrace the suggested diagnostic routine from the previous discussion and see what gives. I wonder if the audio clip gives any clue to what is wrong. I plan to test the circuit with another capsule as soon as possible.

Any ideas in addition to those previously proffered in the earlier thread? I am not sure I will buy another used Shure ... / THANKS Loads. James


View attachment KSM27 alone test 5a.wav
 
I believe Shure had some service note or something, mentioning the rough date of production for the alleged bad batch of mics. No recollection whether mine was within that or not, but i can confirm that shotgunning all the little ceramic caps cured my issue.

But then again, i AM a stubborn cheapskate, so i utterly refused to give up when the cure only required a couple of bucks and a bit of elbow-grease 😁
 
PS. There was no mention of other models suffering of that issue, but the same treatment cured the noises in my KSM141 (which actually mostly shares the same circuit), so there's that too.
 
PS. There was no mention of other models suffering of that issue, but the same treatment cured the noises in my KSM141 (which actually mostly shares the same circuit), so there's that too.
You wouldn't happen to have that on hand would you? I'm interested in picking up KSM141s if I can find some cheap ones. I figure they're only a bit more than the 137 (or whatever the cardioid only is), and it's said to have a tight cardioid pattern, so I figure it'd be a great location mic (not necessarily for film, but concerts, and maybe as a back up for video projects).
 
Hiya James! That KSM 44 gets a 414 circuit this week. I think the PSU is fine, seems like the short circuit is on the main board. One thing I noticed was that the phantom voltage at the microphone plug was only a volt or two, though the maximum capsule voltage was slightly higher than that. Check your voltages. When I get this thing up and running, you're welcome to any parts I didn't use. I should also mention that the beta 27 had measured 30 volts from 48vdc supply @ microphone XLR output. Similar specs & body, I think, but the capsule on the beta is tuned higher and brighter.
 
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