Andy wrote:
I want to use an audio transformer to see if it helps to reduce the
ffect of an earth loop.

An old audio transformer I have come across is marked as "LT44" and I
that that LT44 is sometimes used to indicate a 1:1 (or
600-ohm:600-ohm) transformer.

However when I measure the resistence of the tarnsformer I get
650-ohms on the primary and 80-ohmns on the secondary which has a tap
at 40-ohms.

That doesn't feel right.

A slip of paper with the transformer says LT.44 transistor driver
transformer and says "impediance ratio is 20K ohm to 1K ohm C.T.".

(1) Why is my measurement of DC resistemce so very different from the
impendence on the specifications?

(2) Is this LT44 useless as an audio transformer? I seem to remember
something about number of turns in the windings being important for an
audio coupling transformer as well as the impedences.

(3) Is it wrong to use "LT44" as an accepted shorthand for a 600-
ohm:600-ohm audio coupling transformer?

It is probably from an old microphone amplifier.
I think it will be quite suitable for the test you want to do. It will also
work the other way round, connect the 20k to your input and the 1k side with
a 3.3k to 10k resistor in series to the output of your setup. The resistor
will attenuate the signal and thus compensate for the gain of the
transformer.
--
ciao Ban
Apricale, Italy