Frank Stearns wrote:
I need to cobble together a single-channel two-way mic splitter -- one
output "flow through" and the other transformer isolated.

I've got an ancient Triad line-to-line audio transformer: each side has
600 ohms with taps for 250 and 50 ohms. (Model number is rubbed off, but
it's a metal can, 3/8" stud mount, roughly the size of a shot glass with
leads coming out through the stud,)

This is not the right sort of transformer for a bridging splitter. For
a bridging splitter you want a high-Z-to-low-Z transformer, so that the
bridging load does not much affect the load that the microphone sees.

Since you don't have one, the best you can do is probably to strap it as
a 600:600 transformer and bridge the 600 ohm input across the first console's
input. This will mean the mike will see somewhat lower impedance than it
is used to.

If it has dual primaries and secondaries instead of just taps, you could
probably strap the primary for 600 ohms and then use the two secondary
windings for two isolated outputs. This gives you a full isolation splitter
rather than a bridging splitter.

1. I figured on using the 250 ohm taps on both sides. For the transformer
output side, should I continue with that 220 ohm resister across the
output? (I assume "yes" given most modern preamps.)

This is way, way too low impedance. Leave the load resistors off and let
the preamp input do the loading.

2. On the input side to the transformer, should I "bridge" the
flow-through mic line with some resistive value, or just make a hard-wired
"Y"? (The flow-through line will be carrying phantom power.)

No, make a hard-wired Y.

3. I'm assuming I should float the 50 ohm legs on both sides of the
transformer... or should I terminate them in some way?

Anything that isn't used on the transformer should be floating.
--scott
--
"C'est un Nagra. C'est suisse, et tres, tres precis."