I plugged my Shure SM91 direct into phantom power, not using a pre-amp, with the 3 pin XLR. Can't find the pre-amp, so cannot check if the mic still works. But it certainly didn't then!

What is likely to have happened, and is it retrievable? It's a condenser boundary mic.

  • 1
    There's only half a tale here. I can't actually figure out what you did & what doesn't work. Bit of stream-of-consciousness going on ;))
    – Tetsujin
    Mar 19, 2023 at 9:54
  • @Tetsujin - quite simple - without the pre-amp available, I plugged the SM91 into a recording desk, with phantom power, and got no sound.. Wonder if the mic got fried, or whether it would still work when I find/buy a pre-amp.
    – Tim
    Mar 19, 2023 at 10:14
  • Did you use some kind of adapter cable? I don’t think the SM91 will work at all without the preamp. Mar 19, 2023 at 11:32
  • Sorry, I hadn't realised how integral the pre was to the setup. It also doesn't have a standard XLR interface, so you'd have to have used a mickey mouse cable to connect it to regular phantom. Shure just says 'you must have one' - service.shure.com/s/article/… GearSpace says you'll fry it if you connect it direct, but provides no citation - gearspace.com/board/so-much-gear-so-little-time/…
    – Tetsujin
    Mar 19, 2023 at 11:59
  • @Tetsujin - no, the cable is mini XLR into the mic, with standard 3 pin male XLR on the other, which obviously fits nicely into the input on a desk.
    – Tim
    Mar 19, 2023 at 12:05

1 Answer 1


You say "with the 3 pin XLR". WHAT 3 pin XLR?

If you made up a special cable converting the supplied "miniature Switchcraft connectors" to XLR, and plugged it to a mic input with phantom power, here's at least one opinion that you will have "toasted the FET".


  • Thanks. Since posting, I did some homework, and read that blog already. Doesn't sound too promising. I never used the SM91 with its supplied lead (2nd hand) maybe because the XLR didn't fit the pre-amp. Should have smelled a rat...
    – Tim
    Mar 19, 2023 at 18:12
  • Conclusion is : frying a FET smells like rat.
    – Tom
    Mar 19, 2023 at 19:39

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