As a general rule, the D-104 element likes to see 10 megohms as an input
impedance, typical of tube circuits. The input impedance of the Omni and
Paragon series has a 1 meg input shunted by a 0.01 uF cap at the MIC input
and again at the AUD input on the rear panel. Based on the combined network
in the first stage, the true input Z is somewhere near 50K ohms.
Traditionally, the D-104 is loaded by the lower Z input. With the
introduction of solid state audio stages some years ago, Astatic produced
the amplified G stand. This is really more of a impedance converter to
allow the D-104 element to see something like 10 meg while being able to
drive lower impedance inputs. Heavy loading of the D-104 element has been
shown to cause excessive HF loss and a generally unpleasant or muffled
sound.
As to transformers, unless carefully used and shielded, they typically are a
source of humm being introduced into the audio if they are in the proximity
of power transformers. Good quality well shielded transformers are
expensive. On the other hand, several have reported good results with those
"in-line" units sold by RS.
73
Bob, K4TAX
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