Two audio amplifiers in series (IKEA symfonisk into powered speakers)

Question

I am hacking an IKEA symfonisk into being a cheap, Sonos connected amp, but the speakers I would like to wire it into are not passive, but active.

I am just wondering if the fact that there is an amplifier in the sonos speaker, which is sending amplified signal to the amplifier in the powered speaker, will cause issues for the speaker and potentially result in damage.

Each Sonos speaker actually has two channels (high and low frequencies) so I would also like to sum those into one signal for each speaker.

Would something like the diagram below work?

Answer 1

Just build an attenuator.

^{simulate this circuit – Schematic created using CircuitLab}

If the sourcing amplifier is bridge mode, use spkr OUT+ and GND, and ignore spkr OUT-

Attenuator component values are fairly non-critical, values shown are a reasonable starting point. If it's too quiet, double R1.

Answer 2

There are a few potential problems:

• The output of the Sonos will be several volts. The input to your powered speaker will be < 1 V max and exceeding this will result in clipping distortion.
• Turning down the volume of the Sonos will prevent the clipping but since the volume control will precede the power amplifier the hum and noise from the Sonos amplifier stage will not be attenuated. i.e., the signal (music) to noise ratio will decrease.

Figure 1. A bridge-mode amplifier configuration. Note that neither side of the speaker is grounded. (Ignore the 160 W reference.) Image source lost in the mists of time.

• The Sonos might be using a bridge-mode output which means that neither end of its speaker is grounded. That means that you have a problem with the COM / GND connection between the two systems. For more see my answer to Single-supply amplifier design without output capacitor?.

Figure out the details of the Sonos, have a look at the power amplifier chips, read the datasheets and post the details in your question.