[Elecraft] Appropriate Mic for K3 (new)

[Joe Subich, W4TV]

 > That system applies a positive voltage in the
 > range of 18 - 48VDC through close-tolerance, equal value resistors to
 > the two sides of the balanced signal circuit (pins 2 and 3 of the
 > XL-connector) with return for DC going to the cable shield (Pin 1).

While modern professional condenser mics use phantom power applied
through high value resistors, the *original* connection was between
the *center tap* of the audio console input transformer and shield
of the cable.  In those days a much higher current was required to
power *tube preamplifiers*.

73,

    ... Joe, W4TV


On 12/5/2016 12:32 AM, Jim Brown wrote:
> On Sun,12/4/2016 8:36 PM, Don Wilhelm wrote:
>> Ham microphones are the Electret type, pro-audio Condenser microphones
>> are different.
>
> Yes, they are POWERED differently, but the vast majority (I'd guess 90%)
> of pro mics that are called condenser mics are electrets. BUT -- that
> powering system REQUIRES that they feed a balanced input and have
> "balanced phantom power." That system applies a positive voltage in the
> range of 18 - 48VDC through close-tolerance, equal value resistors to
> the two sides of the balanced signal circuit (pins 2 and 3 of the
> XL-connector) with return for DC going to the cable shield (Pin 1).
>
> The unbalanced electret mics we use in ham radio only require a positive
> voltage as bias for a FET-follower stage that transforms the very high
> output impedance of the capsule to an impedance low enough to drive mic
> inputs. The balanced outputs of pro electrets have an additional gain
> stage with an output impedance low enough to drive a long mic cable.
>
> 48V phantom is applied through 6.8K resistors; 18V phantom is applied
> through resistors of lower value. Virtually all pro mics will work with
> 48V, and most will work with 18V, but most non-electret condensers
> require 48V.
>
> 73, Jim K9YC
>
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