patch phone call into PA system

[Othello]

I had hoped not having to ask this here, believing that there would be a commercial product, but maybe I am wrong.

I need to patch an incoming phone call into a PA system.

The scenario is we have book reading at libraries (we could take our small PA system) and every now and then the author calls in for Q&A. The libraries vary and I can't take their phone system apart.

 

[MikeMl]

How about one of the old suction cup inductive pickups that you attach to the backside of the phone earpiece (if it is mini speaker)?

If not one of those, find a 500Ω:500Ω audio isolation transformer, a couple of blocking capacitors so that the dc resistance of the transformer primary doesn't short the phone line, hook the secondary to one of the Mic inputs on the PA amp.

Go to a ham radio site and look up "phone patch"

 

[audioguru]

Don't libraries have an "office phone system" with many telephone lines, not a single telephone line like at home?
Then you will not be able to connect a transformer and capacitors to the phone line.

How will you feed the questions into a phone line anyway?

 

[MikeMl]

Don't libraries have an "office phone system" with many telephone lines, not a single telephone line like at home?
Then you will not be able to connect a transformer and capacitors to the phone line...

By the time the call is routed through a PBX to some desk telephone, the line selection is done, even if it is a digital PBX.

 

[Ross Craney]

The Bosch PA amps have such a facility for telephone paging over the PA

 

[audioguru]

Are PBX telephone systems with single-line phones used in libraries today? I think they use digital key telephones instead.

 

[MikeMl]

...I think they use digital key telephones instead.

Even a digital key 'phone converts the incoming call to an analog signal at the earpiece

 

[crutschow]

Even a digital key 'phone converts the incoming call to an analog signal at the earpiece

The problem, I believe, is that many modern phones do not radiate a sufficient magnetic field to be detected by an inductive pickup.

 

[MikeMl]

The problem, I believe, is that many modern phones do not radiate a sufficient magnetic field to be detected by an inductive pickup.

A couple of clip leads will fix that.

 

[audioguru]

A telephone handset injects "sidetone" so that you can hear the volume level of your own voice. The 4-wire to 2-wire converter also causes similar feedback. Then if you feed a telephone's earphone signal to a PA amplifier your microphone signal will come out of your PA speakers and cause severe acoustic feedback howling.

Speakerphones and tele-conference systems use simple cheap "voice-switching" which frequently cuts-off a lot of speech or a complicated digital echo-canceller circuit to avoid feedback.