Bluetooth speaker project - need help with amp input voltage (TPA3110, MAX9736A)

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Hello everyone, this is my first post here :) I've been wanting to do a DIY audio project for a long time and it's finally coming to life!

I'm building two portable, 18650 battery-powered bluetooth speakers - a small one and a slightly bigger one.

After doing a lot of research, I bought the parts and sketched out the circuit (based on readily available online plans). However, not having much experience with electronics, I'd like someone to have a look at my plans.

The circuit plans are attached. My biggest problem are the voltage step up/down converters. I don't know how to wire them correctly and I don't know what exact voltages I should set. The amplifiers I chose have pretty broad input voltage ranges (Sure Electronics 2x8W TPA3110 amp and 2x15W MAX9736A amp). It seems like the amp's behavior will depend on the voltage to some extent - I'm attaching the manufacturer's data.

I'm also not sure if I wired the charging port and the power switch correctly.

Any help will be appreciated!

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Can see you put quite some time and effort in research.

Your schematics looks fine to me. Only thing I would add is a fuse.

About the voltages; always should be lower than maximum voltage. I personally always set my voltages slightly higher than typical voltage.

Remember; the higher the voltage the higher the output power. But don't get to close to the maximum rated voltage, you'll risk burning your amplifier.
 
Thank you for your answers!

Sorry if this is a stupid question, but should I add the fuse between the battery protection circuit and the power switch?

doctormord, you're right, Sure does offer all-in one solutions. I wish I had known it earlier. I based my design off of readily available online plans and I had no idea Sure offered BT amps.
However, for the smaller speaker, the amp I bought will still be fine as it has a considerably smaller footprint than any of the BT amps. For the bigger project, I will consider buying the all-in one BT amp.
 
Is the battery protection circuit a simple one or does it has a real voltage cut-off when the required voltage is reached? Does it really switch of the battery when the undervoltage protection should kick in? In fact you do not only want protection but also some kind of charge management. Does the protection board balances the individual cells?

Problem with some cheap as chinese boards is that they don't doe it properly so you should verify or have a board from a reputable supplier.

Of course this doesn't matter (or matters less) if the battery's are only charged for a couple of hours but when you want the power supply to be always on or long time on and do so unattended it might make a difference.

Get good batteries like panasonic/LG/Sanyo etc. I got some issues with el cheapo chinese fantasy name ones and I know others did too.

edit: I made something like this except that I used a 12V BT board from sure (the advanced version with AptX) and an TA2024 amp. Therefore I didn't need step up or step down converters. I used 3 cells (max 12,6 volt en 11 and a bit nominal) I used an extensive protection board (not as extensive as I would liked) but still take proper care when charging.
 
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