Extending Inputs

Because SD cards can die on you at any time, or because you might want to change the speaker software, the memory card of the Raspberry Pi should be accessible from the outside. To do this, use an extension that lets you insert an SD card at the back of the housing. You can also extend one of the USB ports, which opens up the possibility of connecting peripherals, such as a USB Ethernet adapter.

On the front of the Symfonisk speaker is a row of small control buttons. You need to keep them. Therefore, you have to redirect the key connections to the Raspberry pins. For this operation, you need an FFC/FPC 10-pin adapter with 0.5mm pin spacing. On the adapter are the 10 flat cable wires. Connect the adapter with the original Sonos cable and use a multimeter to measure which wire provides which function. The Sonos cable has small fuse tabs at the left and right ends. If you are using an FPC adapter on which these are not provided, the extensions can be removed carefully with a sharp knife.

To simplify your work, use the information in Table 2 to map the wires. Even after various Sonos conversions, the manufacturer does not appear to have changed the assignments. Play/Pause and GND are assigned twice. It is totally okay to use just one of the two wires on the adapter.

Rewired

The adapter is soldered to the Amp2 pins with the switch wires according to the mapping in Table 2, which are selected so as not to interfere with the Amp2 functions. You need to solder and not use connectors; otherwise, speaker vibrations could easily loosen the connections. Because the pins are so close together, it is advisable to insulate the individual soldered pins with heat-shrink tubing.

Now use the original Sonos cables to connect the speakers. You can simply unplug the connector to the main board of the Sonos speakers. When connecting, it is essential to observe polarity: Sonos cables have the positive terminal on the larger plugs. Connecting each speaker to a stereo channel of the Amp2 (Figure 3) eliminates the need to build a crossover, which is done digitally with software later on.

Figure 3: The complete wiring of the rebuilt Sonos player, with no speakers plugged in.

You have now connected all the components, but you need to test the system before you put the components back into the housing. To do this, you have to set up the Raspberry Pi system and prepare the software.

Software

You can discover a number of other software solutions for multiroom streaming, and you are free to try them out. I decided to use SlimServer [5] (formerly known as Logitech Media Server) because the software is initially the easiest to set up.

Again the focus is on free (i.e., open source) software. Furthermore, you will want a centralized server with simple clients as playback devices, with multiroom and speaker synchronization support, expandability with plugins (e.g., for Internet radio), and of course support for streaming services.

SlimServer provides most functions. I used a server installed in a Docker container on a NAS system. The server itself is very easy to set up; you can find numerous instructions and how-tos on the web [6]. The speaker can optionally be operated as a SlimServer, but to do this, you would have to configure the function in the web front end (see the "First Start" section). I will not be looking into setting up the server, but instead cover setting up the speakers.

For the loudspeakers, I decided to go for the piCorePlayer [7]. The software is simple to set up, is easy to expand, and runs entirely in Rasp Pi memory; in this way, you cannot damage the SD card in case of power loss. Additionally, the piCorePlayer requires very little space: A simple memory card with 1GB capacity is fine.