The supply voltage is 48 V DC. This voltage is used to convert it to a suitable RING level with a ring generator. Once you pick up the phone this level is remarkably lower, so that it can be handled with semiconductors. Old telephones are still supposed to work at these lower levels to transport speech. Modern telephones however produce this ring or similar tones internally when a Ring Tone is detected.
Telepone line voltage
Re: Telepone line voltage
