Power Isolator preventing audio from passing through bluetooth

Thread Starter

Invisigram

Joined Sep 26, 2018
2
Hi there,

This is my first post, so I hope that it is O.K.

I've been following along with a tutorial to build a bluetooth portable speaker.
Everything works as expected, until I introduce a 5v dc to 5v dc isolator between the regulated 5v and the bluetooth module.

The isolator is required in the circuit to eliminate a noisy ground-loop signal, which is audible.
With the bluetooth powered straight off the regulator, the audio signal comes through strong and clear, but so does ground loop interference noise.
with the isolator between the two, the ground loop noise is eliminated... but so is the audio! With a multi-meter, the isolator is receiving 5v and also supplying 5v, so it isn't faulty as far as I can tell. Even so, it reduces the audio output to the faintest whisper, only audible at all at full volume on the pot and broadcasting device. For reference, without the isolator, that volume position would be too loud for comfortable listening.

I can find no other mention of anyone experiencing this issue. All I can find is advocates of the isolator as a great solution to eliminating ground-loop interference, but no-one seems to have hit the problem that I have, as far as I can tell.

Attached is a sketch of the circuit, apologies if it is hard to read, i'm quite new to all this, and also the program it was created with, which is great but not so user friendly :)
circuit_layout.jpg


Anyway, Hopefully one of the great minds amongst yourselves will identify some foolish error in my ways, and be kind enough to let me know about it.

If any further info is needed then please let me know :)

Thanks,

Invisigram
 

ArakelTheDragon

Joined Nov 18, 2016
1,327
Ground loops are my weak spot.

Try this:
1. Measure the voltage, frequency, and current of the ground loop. It must not be close to the audio signal characteristics.
2. Try reversing the isolator (switch the output and input "-","+").
3. Is a second ground and option for you?
 

Thread Starter

Invisigram

Joined Sep 26, 2018
2
Ground loops are my weak spot.

Try this:
1. Measure the voltage, frequency, and current of the ground loop. It must not be close to the audio signal characteristics.
2. Try reversing the isolator (switch the output and input "-","+").
3. Is a second ground and option for you?
Hi,
Thanks for the quick reply!

I've tried the isolator in every concievable pinout combination, just in case that was the issue, but the only one that actually powers the device is the one in the drawing.

I also tried putting a load resistor across the bluetooth device in case there wasn't enough power draw, but that also had no effect. Also I tried with some capacitors across the source and load of the isolator, in case ripple was creating the issue, but still that had no effect. These ideas came from the data sheet of the isolator.

The ground loop is eliminated, but so unfortunately is the functionality. I'm really stumped! :)

I'm not sure where to begin with directly measuring the ground loop or finding a different ground source, sorry!

Thanks,
Invisigram
 
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