> 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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