🚀 go-pugleaf

Mike Diack <mike-d@staff.tc.umn.edu> writes:
>Bill Jaeger, jaegerwl@wckn.dorm.clarkson.edu writes:
>>At my university's cable TV station we're working on putting together
>>a program that involves a viewer call-in.  
>>
>What you need here is a Hybrid. 
>This consists of a pair of transformers
>each having a single primary and a split secondary, cross wired to

>PS you may need a resistor to hold the phone "off hook" depends on
>your setup.

Good suggestions. Also, keep in mind that you want to block
the phone line's DC from flowing in the core of the transformers
with capacitors; that would lead to saturation distortion and 
make the sound worse than it has to be.

Experiment with values between 0.05uF and 1.0uF. Depending on
your setup, you might want to minimize the amount of low
frequencies you pull off the phone line so that you don't
drive your limiter crazy and end up with cruddy sound and
pumping of the compressor, if you use one. For an otherwise
high-grade outfit, C-SPAN's phone line audio is awful, for example. 
It can be done right.

For a holding bridge to keep the phone line busy (off-hook)
you can use something as simple as a 1K-1.5K resistor, depending
on your distance from the central office. Farther distance =
greater wire resistance = less holding resistance.

If you want to get really fancy, you can design a solid-state
current sink, but that sounds a lot fancier than what you want.


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