[SML] Telephone line simulator

Bruce Purdy bpurdy at rochester.rr.com
Sat Apr 11 18:29:08 UTC 2020

I THOUGHT I had something along these lines in my files - I found it:


Bruce Purdy
Central New York Magic Theatre Co.

> On 11Apr, 2020, at 1:57 AM, Jerry Durand via Stagecraft <stagecraft at theatrical.net> wrote:
> For the low of budget people, if you just need to generate ring you can do so with bits you might have laying around.
> You'll need:
> An audio source for 20Hz sine wave, pulsed in whatever cadence you want.
> An audio amplifier, I used a Radio Shack PA amplifier for one setup.  Doesn't need to be quality, just function.
> If the amplifier has 70 volt line out, you can skip the transformer in the next line.
> An 8 ohm to 70 volt PA transformer.
> A blocking capacitor, steal a RUN capacitor from an induction motor you're not using.
> The capacitor isn't strictly needed, but does limit current.
> Circuit is audio source > amplifier > 8-transformer-70 > capacitor in series with one lead > telephone.
> Be sure and cut the audio when the actor picks up, you don't want to blast his ear with the ring signal.  Maybe remove the speaker from the phone.
> Experiment to find what works well with your phone and gear.
> ---
> Jerry Durand, Durand Interstellar, Inc. +1 408 356-3886
>  <http://www.durandinterstellar.com/>www.DurandInterstellar.com <http://www.durandinterstellar.com/> &  <http://www.durandinterstellar.ru/>www.DurandInterstellar.ru <http://www.durandinterstellar.ru/>
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