Vintage SM58 impedance change and crumbling foam

FAQ #3688 Updated October 26, 2017


I have an SM58 "made in U.S.A." "Dual impedance 38 & 150 ohms" and does NOT say "Unidyne III".


1) In what instance would I use the 38 ohm impedance and how do I change it from 150? I don't see any references to dual impedance on this site. 

2) Could you tell me the aproximate vintage? 

3) The foam on the top of the capsule is crumbling. What should I do?


1) Remove the XLR connector. The impedance is changed at the back of the XLR connector. Red wire is 150 ohms/Orange wire is 38 ohms. In 2010, the 38 ohm setting has little use. You would notice a decrease in the output level if changed to 38 ohms.

2) 1966 to 1983.

3) No need to be concerned. The amount of P-pop protection provided is minimal. Add an external windscreen to compensate if P-pop is a problem.

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