Hiss in Bluetooth receiver when battery is removed.

[mraas]

Hi there,

I'm dealing with an issue.
For a project I bought a cheap BT audio receiver.
In this project I need it to power on when power is applied.


Originally, the BT receiver has a power switch, line out and a battery.
When there's no battery connected, the receiver powers on when power is applied, just as I want it, but there's a terrible hiss…

When the battery is connected, this his is gone, but the receiver stays powered on after my project is powered down due to the fact that the internal battery has been charged.

Charging voltage of this battery is ~ 4.2v
I've connected a couple of led's from a 4.5v application, the hiss is gone, but they burn out.
I've also connected a couple of resistors, the his is gone, but the resistors get very hot.


Do you happen to have some kind of idea what kind of load I need to apply or do you have other solutions to solve this his problem?


Thanks!

 

[Mooly]

Have you resolved this ?

I'm assuming you mean the 'hiss' is coming from the internal circuitry and not hiss on the audio output.

 

[mraas]

no, not resolved yet… I currently just leave the battery connected. then it's 'perfect' no his... but when battery is disconnected, the internals like to charge a battery which it can't so it starts hissing on the internals.

As long as it can 'waste' some power, I should be good, but as it's a wireless project I don't want it to 'suck' to much power.. yet I've to find the minimum value… and something which doesn't induct any interference, nor needs it to discharge in the bluetooth receiver, because when I switch the button to off, I'd like the complete project to be off... and not some bluetooth receiver still alive for a couple of hours…

 

[Mooly]

I wonder if adding a small cap would do anything. The battery will have a very low AC impedance whether charged or discharged. It might be worth trying. Perhaps a 10uF electrolytic for starters and if necessary in combination with a parallel resistor.