[ProAudio] Western Electric 111C transformers

[Dave Collins]

IMO, the 111C is not a good candidate for a ‘color’ transformer.  In fact, it’s *the* lowest distortion transformer at LF I’ve ever measured.  You can try increasing the source Z, but I doubt it will  decrease the performance by much - same by adding DC.  

The technique I have used is to take a really lousy transformer, and apply mixed-feedback (Lundahl data sheet is a good start).  This allows easy adjustment of the amount of “correction,” and works surprisingly well.


DC
> On Feb 1, 2022, at 7:56 AM, Kevin P. Mostyn via ProAudio <proaudio at bach.pgm.com> wrote:
> 
> 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.
> 
> Kevin
> 
> 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.
> --scott
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