2019 Issue-4
I need to put the speaker-level output from a PA system on a POTS telephone line. I don’t need dialing capability, as I can connect a POTS phone to make the call, but once the call is established, I need a circuit that will:
If a reasonably-priced product with good sound quality (i.e., no hum, etc) is already available to do this, suggestions are welcome. I’ve found many products for recording phone conversations or putting them into a PA, but only quite expensive ones with way more features than I need that will do the simple job I want.
Thanks for any help/suggestions.
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All you really need is a “wet” 600 to 600 ohm transformer. The “wet” designation is for a transformer that will work properly at audio frequencies with up to about 100 mA of DC flowing through the POTS side winding.
Connect it directly across the telephone line through a switch. Then apply the audio attenuated down to a low level to the other side of the transformer. Make sure that you don’t apply very much audio, as there are FCC regulations regarding the maximum audio levels. See FCC part 68 for the particulars.
You can find music on hold adapters that will do exactly what you want, like the On-Hold MOH 150 for about $15 on ebay. You can plug the PA line into the device and it will play on the phone by putting it on hold from the device.
