How to convert RJ11 to RCA

Question

We have a Marantz sound system. We also have an Asterisk PBX. Now, I want to have Asterisk play a bell tone for a schedule over the sound system.

So I've set up a Cisco SPA112 Port Adapter (basically a Digital-to-Analog convertor) and assigned it an ipaddress on the network. I've also set up Asterisk to know what to do. So I am able to send the sounds to the Port Adapter, but I need now to get the sound from the Adapter box into the Marantz.

We have done something similar with our PA system. Asterisk broadcasts to a Port Adapter which in turn allows the signal to pass as analog to our Viking ZPI-4 Paging Interface. Asterisk plays the "5" tone and the Viking allows the sound to play.

But the trick here is to do the same thing through the sound system attached to the Marantz.

The Adapter has an RJ11 output, and the Marantz has an RCA input.

The circuit is only one-way. We would only send FROM the Port Adapter TO the RCA input.

So it looks like I need an RJ11 to RCA convertor. But I would like to make one instead of buy one, which means I need to know how the wires should map to the pins. I can't find the answer in a google search, so I was hoping some of the knoweledgeable folks here might be able to help me out.

[conclusions]

The wiring diagram is actually what I was looking for here, and Spiff supplied exactly the solution I sought, so I am marking the answer.

However, I realize I haven't solved the underlying issue. Another solution I am looking at (in case anyone is following this) is [sending the sound transmission directly to the Marantz]3. Another approach to the underlying issue is to see whether Asterisk can transmit to the line without waiting for an answer.

Answer 1

[This doesn't solve all of @BGM's unique requirements, but if someone comes here with simpler requirements, this might be an answer for them, so I'm going to post it anyway.]

If it weren't for the problem of dealing with the ring signal (90VAC 20Hz with enough power to physically ring metal bells on old-school telephones), and dealing with auto-answer (can't send audio down a phone line unless someone completes the circuit by going off-hook), it's actually pretty simple to electrically connect a phone line to a line-level audio cable. You just need a transformer of the kind that were always built into analog modems. So if you have an old analog modem lying around unused, you can just unsolder the transformer from it, and connect it between a phone line and an RCA connector like this:

Telco                         Phone
T---------------------------------T
                                         <-- phone line
R----------+      +---------------R
           |      |
           uuuuuuuu
           ========    <-- Transformer from analog dial-up modem
           nnnnnnnn        (Do you like my ASCII-art transformer symbol? ;-)
           |      |
Center ----+      |
                  |    <-- RCA connector
Shield -----------+
/Ground

See also: Telephone line audio tap (YouTube link)

Answer 2

Telephone lines carry power to drive the telephone. RCA is a low voltage, unamplified signal. You can't just wire one into the other. In addition, telephones have the concept of on/off hook, and ringing. You have to present the correct impedance to convince the adapter that the "phone" is on or off the hook, and it's going to want to see it on the hook, then deliver a high power ( 48v ) ring signal to ring the bell until you take the phone off hook. That would blow out any RCA gear.