Re: The things you see when ya go lookin'......


"Jim Lesurf" <jcgl@xxxxxxxxxxxxxxxxxx> wrote in message
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In article <dtk9bp$7lt$1@xxxxxxxxxxxxxxxxxxxxxx>, Iain Churches
<taelNOSPAM@xxxxxxxxxxx> wrote:

"Serge Auckland" <serge.auckland@xxxxxxxxxxxxx> wrote in message
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Interesting! Did you wind your own transformer? What secondary load
are you driving? I presume it's 10k bridging rather than 600 ohm
terminating.



Wound for me at a local broadcast engineering workshop. (I have friends
in low places:-)

Nominal impedance 10k. 48dB attentuation in 2dB steps. Inductance 80H.

Since I am unfamiliar with the use of such transformers for audio, I'll
risk asking a few simple questions. :-)

Can you explain what you mean by "10k bridging" in the above? Does it
refer
to the input load/arrangement?

For many years now, pro-audio has abandoned the old 600 ohms terminating
(that is, 600 ohms sending impedance, 600 ohms receiving) for the more
modern very low sending impedance (typically less than 50 ohms) into a high
receiving impedance (typically 10kohms) The 10k impedance is referred to as
"bridging" as it can be put across (bridge) a 600 ohm load without
materially affecting the level. The use of the terms is now something of an
anachronism, but is still retained to indicate a high load impedance, and to
distinguish it from the now rarely used 600 ohm terminating imedance. Before
I get lots of replies from professionals pointing out that 600 ohms is still
used, I agree, it is still used, but exceptionally, when terminating very
long lines. In studio use, it is never (almost never?) used.


Under what conditions of use does the system present (?) 10kOhms?

If a transformer is designed for 10k use, it needs to be presented with a
high load impedance on the secondary. A 10k transformer presented with a
600ohm load will distort at a much lower level than with a 10k load, as the
core saturates.

Conversely, if a transformer is designed for 600 ohm use is used with a 10k
load, it won't saturate or distort, but it could have an undesirable peak in
the treble response, although with a well-designed transformer, this won't
be too serious a problem. Nevertheless, the cousel of perfection is to
terminate transforers with their design impedance.


What would be the levels of series resistances, shunt capacitances, etc,
for the above device? You quote '80H' for an inductance, but don't
distinguish the coupled (mutual) value from the uncoupled values.

This will depend on the specific transformer, so I can't answer this....
Iain?

S.


.

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