[ProAudio] Western Electric 111C transformers

Kevin P. Mostyn lists at mostyn.com
Tue Feb 1 07:56:08 PST 2022

They were 15 kHz circuits. AT&T offered them in the late 1930s onwards, IIRC. They also offered, starting later, but definitely in the early 1960s, matched stereo pairs of 15 kHz circuits. They had to pass a strict test summed to mono. The paths were designed to match arrival time and phase. I used many of these in my career.


On Feb 1, 2022, at 7:44 AM, Scott Dorsey via ProAudio <proaudio at bach.pgm.com> wrote:o off

Yes, you could order a 16kc loop line from the phone company as a studio
to transmitter link, or as a link from a local club or used car lot for 
live remotes.  Needless to say the tariff on a 16kc loop line was higher
than for an 8kc loop.

But it wasn't just that.... there were lines carrying FDM multiplexed voice
and data traffic which required wideband circuits, and these were used for
that service too.  

The phone company made millions of these things; they were often available
for the asking if you knew your phone installer well.

Part of the key to these is the core material used, which required a very
large core to prevent saturation at low frequencies but also provided very
low distortion.
ProAudio mailing list
ProAudio at bach.pgm.com

More information about the ProAudio mailing list