Monday, July 15, 2013


      A low-impedance/high-impedance microphone matching transformer:
     This example arrived with some barbaric ham-radio mic connector on the low-impedance side, a three-pin, threaded-shell item.  ETA: I found the mating connector in my collection!  This is why you save 'em.

       The transformer is a Shure Brothers A86A.
      "Model A86A is a  high-quality cable-type transformer which offers additional versatility when used in conjunction with Shure Models 55,556, and 51 Dynamic Microphones, which employ the impedance matching switch. It solves the frequent problem of installations requiring long  lengths of microphone cables  without the loss of high-frequency response. Model A86A matches 35 to 50 and 150 to 250 ohm microphones to high impedance amplifier input.  Compact, sturdy.
Case diameter 1-5/8", length 2-7/8",  7 foot cable.  Shipping weight 1-1/2 pounds.
Model A86A. Code: RUDEB.  List Price $13.10"

    (Link to a Shure catalog listing it at Preservation Sound.)

     That was pretty a high price, back when this was new.  Frequency response is cited as "within 1 dB, 20 to 20,000 cps," which is darned good.  The various low impedances are selected by removing three screws on the low-Z side, opening the case up and moving a jumper.

     Does this one work?  I don't know yet.  It was priced to move at $3.00 and for that kind of money, worth finding out.

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