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I am working on a "device" based on a CSR8645 Bluetooth Receiver module from eBay. Photo of the module here.

My current issue is the fact that each audio channel has its own ground, and if I connect both grounds together to the jack, the sound coming out is distorted. Granted, this may be an imperfect connection on my part or the PCB is faulty.

This gentleman here also has a similar issue. Granted he's getting mono output and wants to output to speakers (with each speaker having its own ground).

Looking at his post, maybe my board is using the same bridge amplifier technique. If that's the case, how can I properly drive a pair of headphones (Left, Right, Ground) with my module which has L+, L-, R+, R-.

Also a bit off topic, I would like to connect the microphone output as well but that's not the main issue and purpose of this question (granted if I want to connect my microphone which also has its own ground...

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    \$\begingroup\$ You need a balun to convert from the balanced (differential) audio output, so unbalanced (single-ended) used by your headphones. \$\endgroup\$ – Tom Carpenter Dec 21 '20 at 12:19
  • \$\begingroup\$ Questions on the use of electronic devices are off-topic as this site is intended specifically for questions on electronics design. - any bought item that you wish to have help with requires a schematic or it's just plain guesswork. In addition, items from ebay (or amazon et al) are not guaranteed to any level of consistency so, even if you did have a believable schematic today, there's absolutely no reason why it will remain believable by the end of next week or next year hence, modification answers given become naturally useless. It's off-topic in my opinion. \$\endgroup\$ – Andy aka Dec 21 '20 at 12:19
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    \$\begingroup\$ How can I... Simple answer: you can't. I've seen this being asked before and noticed this module has a "balanced class D" output stage which is almost ideal for driving speakers (which share no connections) but impossible to use with headphones via a 3.5 mm jack as then the ground connections of the speakers are shared. \$\endgroup\$ – Bimpelrekkie Dec 21 '20 at 12:23
  • \$\begingroup\$ Since the module clearly has a H bridge amp chip to drive speakers which can't be used for simple TRS headphones, and you seem to be determined getting this work by hacking stuff, simply take the audio from between the amp chip and bluetooth chip. Rwmove the amp chip and wire in your own headphone amp chip. \$\endgroup\$ – Justme Dec 21 '20 at 12:34
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You may well find that using L+, R+ (via AC coupling, e.g. 100uF capacitors) and GND works.

Depending on the internal details of the module, L+/R+ are likely to be accurate copies of L,R referenced to GND (but with a Vcc/2 bias) while L-,R- are inverted copies.

In that case, there is no harm in leaving L-,R- disconnected.

Quality may depend on how clean the Vcc supply to that device is; you may need to add decoupling to the supply you are giving the module.

Some more info here regarding a similar device :
Cost Effective Solution to using PAM8403 as a headphone amp

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The old fashion way. Safe. Works. As far as the amplifier is concerned, there are two separate, unconnected loads. But this may not be worth it due to price, weight, or bulk. It may be easier, cheaper, lighter etc. to just get an amplifier that can handle having a 3-wire stereo load, than to adapt an existing amplifier with transformers.

schematic

simulate this circuit – Schematic created using CircuitLab

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  • \$\begingroup\$ what is XFMR 1 and 2 supposed to mean? Transformers? Why is it safe and it works but it may not be worth it? \$\endgroup\$ – TermoZour Dec 22 '20 at 7:16
  • \$\begingroup\$ Yes, those are transformers. They provide "galvanic isolation", so on the secondary side, two of the leads may be electrically connected forming a "common" or "ground", while the corresponding leads on the primary side remain isolated. It is safe because it doesn't rely on the circuit driving the primary sides "allowing" a connection between the signals. As far as that circuit is concerned, it has two separate loads. It may not be worth it because the weight and cost of the transformers may exceed the weight/cost of the little circuit board. Might be easier to just get a different amplifier. \$\endgroup\$ – Math Keeps Me Busy Dec 22 '20 at 14:21

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