BOATANCHORS Digest - 30 Aug 2003 to 31 Aug 2003 (#2003-209)

[Bob Bruner WB4TAJ]

The EV 664 is a dual impedance model.  Pin 1 is case ground, pin 2 is Hi-z
(50K).  Pins 3&4 are balanced low-Z out.  This same wiring applies to the 636
and all other EV mics of this era using the MC4 connector.
    Note, some people optionally re-wire the microphone so that a push to
talk feature is supplied.  In this case, pin 1 is still case ground, pin 2 is
still hi-z out, pin 3 is now low-z unbalanced out and pin 4 is PTT to ground.  To
make this latter scheme work, you have to rewire the DPDT switch inside mic.
    The switch is normally wired so that ground and pin 1 are wired to the
middle lug on one side of the switch, the hi-z wire is wired to the end of the
switch such that the two wires are shorted when the switch is in the off
position.  the two lo-z wire are wired to the corresponding pins on the other side
of the switch, which likewise shorts them in the "off" mode. The two lugs on
the other end of the switch, which are closed when the switch is "on," are not
used.
    There are several ways to make the PTT modification. Probably the
simplest is to connect the two center lugs of the switch together and remove the wire
that comes up from pin 4 of the connector and solder it to one of the
previously unused lugs at the other end of the switch. These two wiring changes
unbalance the low-z audio, connecting one side of it now to ground, and provide a
contact closure to ground when the switch is in the "ON" position.
    If the microphone has previously been in the hands of a ham, the
modification is likely already in place.  If it comes directly from PA service, it
will be wired the first way described above.
   The manual for the 664 is on the BAMA website, as well as a on number of
other classic microphone manual sites.   www.bama.sbc.edu

Bob Bruner, W9TAJ

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