True Wireless Stereo (TWS) Bluetooth for Speakers

[sven_nilsson]

Does anyone know how high signal level the BLenhance preamp can output?

I assume because it runs on 5V, probably less than that.

Anyway I'm planning to put an isolation transformer on the bass channel because I still have some noise issues, and the one I'm looking at (TY-250p) is rated for 4.2Vrms 7mA 20mW.

 

[xrk971]

Murata and other brands make nice PCB isolated DCDC converters so that you can take the 12v(or whatever powers your main amp) and make 5vdc for the BT circuit. There is a 5kv isolation transformer in the DCDC. This usually stops ground loop noise.

 

[sven_nilsson]

I have a 36V battery for the power amps and a 5V battery for the BLenhance.
Since it is 100% battery powered the DC supply signals should be clean.

My issue occurs only when I connect two power amps to the BLenhance.

If I connect only the bass channel amp, all is fine, no noise at all.
If I connect only the L/R channel amp, all is fine, no noise at all.
When I connect them both, I hear significant noise in both the bass and L/R channels.
If I unhook the ground lead on the bass channel input, the noise disappears from the L/R channel but instead gets stronger in the bass channel.
If I unhook the ground lead on the L/R channel input, the noise disappears from the bass channel but instead gets stronger in the L/R channel.

Is this consistent with a ground loop?

All wires are very short, less than 10cm... and the longest possible ground loop would be less than 30cm.

 

[xrk971]

Yes, that’s a ground loop when you connect two channels and there is noise that was otherwise not there before. BT is very sensitive to ground loop noise and usually an isolator is needed in between their supplies.