Thread: Dead SM-48s
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Phil Allison[_4_] Phil Allison[_4_] is offline
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Default Dead SM-48s

Ron C wrote:

Phil Allison wrote:


Have you checked whether there's a break in the inteqrnal wiring?

Peace,
Paul


Yes, I've checked .. no problems there.


** Hang on - you say the internal wiring is all OK ( not corroded) and the mics are both dead ? Have you checked the voice coil with a DMM ?? A reading at the XLR of about 250 ohms shows it is intact.


Heck, the mic's are 20++ years old,



** Still within the useful lifespan for Shure vocal mics that get low usage.


so I guess
I've gotten my money's worth out of them.


** I disagree and think the foam wind sock disintegration is a separate issue to the mics going silent.


I understand that electrets can become depolorized
but never thought dynamics would/could go bad just
sitting in a box. Live and learn.



** Fine copper wire, as normally used for voice coils on mic diaphragms, corrodes under damp conditions and develops opens.

However, Shure mics like the SM57 & SM58 use much thicker wire for the voice coils followed by a step up transformer which goes a long way to extending these mics lives.



... Phil


Damn, I hadn't thought to check for an open voice coil.


** Not a lot else makes a dynamic mic go silent.


Yep, they both measure as open. Corrosion of the super
fine wire is quite the logical explanation.


** I think Klay Anderson's advice is worth taking.

" Send them back to Shure. Theyll give you new ones for the price of repair or better. "

Shure may just send you two new SM-48s.



.... Phil