Bose QuietComfort 15 upgrade, battery noise

Thread Starter

vicinator

Joined Apr 4, 2021
2
Hi everyone

I'm doing a little project at home and came across an issue. So I'm trying to convert my old Bose QuietComfort 15 to wireless headphones. The stock version uses a AAA alkaline battery and only has an AUX connector for the audio. I'm integrating a rechargeable battery and bluethooth module. For the battery, I ordered a AAA lithium battery from Aliexpress which is essentially a 3.7V lithium cell with a DC-DC converter to 1.5V. The 1.5V is needed for the headphone to still work correctly. For the bluetooth module I use a cheap module also from Aliexpress.

My plan was to desolder the internal lithium battery of the bluetooth module and connect it to the lithium cell of the AAA lithium battery, so that the whole system works from one battery. The USB-C charging port would be extended using a USB-C connector (listed below). The bluetooth audio output would be directly connected to the aux input of the headphones.

After having done this, I noticed a lot of noise and cracking sounds coming out of the speakers. I fiddled around trying to find the source and I should have located it to the lithium battery cell powering the bluetooth module. When I don't power the bluetooth module from the AAA lithium cell but use its original battery instead, the noise is gone. I assume that there is noise coming from either the DC-DC converter or the headphone PCB coupling back to the lithium battery, which passes through the bluetooth module towards the audio output.

I now have two possible solutions in mind.

1) I could try to just use the original battery for the bluetooth module. I would then route the USB-C charging connector to both the AAA lithium battery and bluetooth module, to charge them in parallel. The downside to this is that I would then have two batteries in the system which could be depleted asynchronously.

2) I tried placing a large capacitor (470uF) between the + and - battery supply terminals of the bluetooth module to basically filter out the noise. The noise reduced but was not gone. I'm not sure if I would have to try and use an even bigger capacitance (which I don't have atm) or implement another type of filter.

Any remarks? Other propositions are always welcome!


Links to the used components:

Bose QuietComfort 15:

https://www.bosebelgium.be/nl_be/su.../bose_around_ear_headphones_support/qc15.html

Bluetooth adapter:
https://www.aliexpress.com/item/400...sea!BE!2347445641!&curPageLogUid=pw98ayltR7Ka

Lithium battery:
https://www.aliexpress.com/item/100....order_list.order_list_main.35.70e51802EbljAm

USB-C connector:
https://www.aliexpress.com/item/100....order_list.order_list_main.30.70e51802EbljAm
 

MrChips

Joined Oct 2, 2009
30,467
Batteries are not usually the source of noise.
I suspect that the noise is coming from the DC-DC converter.
Try a different converter or a different battery.
 
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