Google nest mini speaker linkage

[BAM_075]

Hi,
recently I have bought a Nest Mini with the purpose of adding a rca cable to it. I wanted to do this so that I could add it to my stereo installation. I opened the mini up with, and stripped ass well as the speaker wires as the wires of the rca cable. After that I held the red wire together with the rca positive wires and the black one with the grounding. At this moment I started testing it before drilling a hole for the rca cable in the housing, but with music I heard a loud machine gun-isch sound on my stereo, and only some bass. The Nest mini had just normal music playing , and when it gave spoken feedback the MG-sound was less than with music.

Has anyone any idea on why this occurs or what I can do about it, so that I can just add it to my stereo as a bluetooth receiver/smart device?

 

[kellys_eye]

The output from the nest (speaker connection) is too high and overloading your amplifier. You can fix this by adding a potentiometer or a resistor divider to reduce the signal level.

 

[BAM_075]

Okay, thanks! Do you have any idea on what the speaker's voltage is on the nest mini? I can't find it anywhere.

 

[kellys_eye]

It's not a 'voltage' as such. Most amplifiers require an input signal level that doesn't exceed around 750mV (0.75V) - this could be more or less, I'd need to see the spec on the amplifier to be certain. The signal used to drive a loudspeaker can be 10's of volts (again, depends on the device) so you need to attenuate the voltage.

Check out this link for a technique that will work https://www.epanorama.net/circuits/speaker_to_line.html/

 

[BAM_075]

Okay, I think I found the resistance of my stereo amp. So, when I find the resistance of the Nest Mini's speaker, I can compensate the differences in resistance with a potentiometer?

 

[kellys_eye]

Nope - you need the amplifiers input sensitivity. What you show is the amplifier OUTPUT power. If it's 'standard' (should be) then the input sensitivity could be 200mV.

You won't find out the Nest output voltage listed anywhere - it's not something any manufacturer lists. This is why you should use a potentiometer to reduce the level as you an set it to whatever is required rather than having to calculate or sort through a gazzilion individual resistor combinations to get the right one.

 

[BAM_075]

Ah, so I just have to experiment with a potentiometer with a range of around 1kΩ, or is this a to high resistance?

 

[Audioguru]

A Google Nest Mini is modern so it probably uses a bridged amplifier that drives BOTH speaker wires without a "ground' connection.
You might convert its output to an aux "RCA" signal if you add a capacitor in series with one speaker wire being the signal wire of a shielded audio cable with the shield wire as the 0V of the Google Nest Mini.

 

[BAM_075]

In this video at 3:30, the man just adds some resistances before he adds the aux jack. Isn't it possible to do the same, but instead of using a jack, using a rca cable? (For him it's the Home Mini, for me the Nest Mini). Just like @kellys_eye says.