🚀 go-pugleaf

Its quite simple!
We use telephone audio in our studio all the time. 
And yes  it's an off the shelf design. I designed and built such a device
with scrap droor components.  I used an audio coupling transformer and a 
capacitor. The primary windings add in series to 500 ohms. Instead of 
connecting them directly together i added a cap between them. I think it 
was somthing like 0.047 micro farads with a 600vlt rating. And the 
secondary which is 500 ohms runs into the control room mixer.



           Tip   >------------/ II
                              / II /------------<
      (primary winding 1)     / II /
                              / II /
                 >-----X------/ II /
                       I        II /
         0.047 uF      =        II / -----------CT   (secondary winding)
      		       I        II /	
                >------X------/ II /                      Output Side 
                              / II /                        to Mixer
      (primary winding 2)     / II /
                              / II /-------------<
        Ring    >-------------/ II



Sorry 'bout the art work..... 

Try this circuit it works great for us in the studio. Just make sure you 
use properly rated components.

					Tom Pappas