Hey y'all, I'm new here so I hope this question hasn't been asked too many times already.

I am currently working on a little bluetooth speaker projet in which I aim to reuse an old driver I have lying around and so far I managed to mostly understand how to wire this up and for what I have to look out for, but my problem is the potentiometer I'm planning to use as volume control as well as on/off switch for the whole system.
As a little warning: As of the time I'm writing this, most of the parts haven't arrived yet so I currently can't test anything. However I want to make sure I understand the concept before I start soldering things.

The components:
- speaker: 3W and 8 Ohm
- VHM-314 bluetooth receiver: runs on 5V and outputs up to 5W on left and right channel
- PAM8403 Amplifier: runs on 5V and outputs 3W on left and right channel, also is rated for 4 Ohms so I think it should work with my speaker
- Potentiometer with switch: 50k Ohm? (haven't decided yet what I need), logarithmic
- bog-standard USB powerbank: output 5V

The plan:
I want to connect the receiver and amp to 5V and ground. The receiver output (left and right) will be combined into a mono signal by adding a 1k resistor to each line and combinig them into one cable. This mono signal will go to the pot and from the pots middle pin to the amp input. I've heard you are not supposed to put volume control right before the speaker which is why I'm using an amp at all. The left pin on the pot will be ground but I'm not sure how to wire all of these ground cables together in order to avoid a ground loop. The potentiometer has a switch because I want to be able to turn the whole speaker on and off just by turning the knob without any extra buttons.
The power cables will just go to a usb c breakout board into which I can plug any USB c powerbank.

Any help would really be greatly appreciated!
Oh and as an extra question: While writing this I noticed that my bluetooth receiver outputs 5W and the amp outputs only 3W (because the speaker has 3W) is it fine to use these components or do the wattages have to match?

 

Schematics are the language of electronics (that's why AI is so bad at electronics- it's not TEXT)
Your words are a bit ambiguous and confusing, draw a diagram of the system and you will get more action here.

 

Schematics are the language of electronics (that's why AI is so bad at electronics- it's not TEXT)
Your words are a bit ambiguous and confusing, draw a diagram of the system and you will get more action here.

That makes sense.... not sure if I can edit the post so I'll just put the picture below:

This is how I planned to wire every thing up. I'm not sure if it would work this way at all but I know that this won't enable the pot to turn the whole system on and off (I've senn that you can buy potentiometers with integrated switches).

The black module on the right is the bluetooth receiver and the green one on the left is the amp. 5V and GND will be soldered to a USB connector into which I'll plug the powerbank.

I've seen DIY perks on YouTube build a similar system like this and he mentioned that he wired every thing in a way that the whole system turns off when he turns the pot to essentially 0 volume. Sadly he didn't explain how he wired this and I can't find any resources online that helped me.

 

That makes sense.... not sure if I can edit the post so I'll just put the picture below:

So as it turns out I'm an idiot and the only potentiometers with switch I could find are WH-138 which have seperate pins for their switching ability. I've edited my schematic as follows. Do you think this could work? And does this introduce too much noise to the audio signal?
Also how important is it to use logarithmic pots? Because this one is linear only.

 

I wouldn't switch the ground, don't you want to turn OFF the power from the 5 volt source using the switch?
Why mono output?
Link to this BT receiver? The one pictured in post #4 does not have a power amp on board.
Logarithmic pots are generally used for audio giving better control of the sound level at the lower end of the setting.

 

how important is it to use logarithmic pots? Because this one is linear only.

Why are you switching ground rather than the 5V connection to control the power?
Switching the ground could conceivably damage the IC's.

Because the ear has a log response to sound intensity, a log pot makes the perceived loudness change to the ear approximately proportional to pot rotation.
Its output is typically no more that 10-20% of full scale at the 50% wiper position.
A linear pot will give a very non-linear loudness change, with the loudness increasing rapidly at the start of the rotation.

But you can effectively approximate a log pot output by adding a resistor from the wiper output to ground of a linear pot with value about 1/10th the pot resistance.
Thus for a 100kΩ pot you would use a 10kΩ resistor.
The (unknown) input resistance of the amp module would be part of this resistance value (and could be the only resistance if it's close to the desired value).
You can experiment with the resistor value to get the desired loudness change versus pot rotation.

 

Link to this BT receiver?

https://www.roboter-bausatz.de/p/vhm-314-bluetooth-5.0-audio-decoder-verstaerker-micro-usb - this is from a german website so hopefully everything translates correctly.
I actually didn't know you were supposed to put the switch on the positve cable. I think I heard somewhere that I should always switch the ground on or off and so if been doing it ever since but putting it on the positive cable might make the installation easier anyways - I'll try that thanks!

I'm doing mono because this is supposed to be a small "test project" where I'm reusing an old speaker driver I have lying around from an old Google Home Mini I believe. This is more of a proof of concept before I start building bigger and more expensive Speakers and so I didn't want to buy a set of drivers in order to keep costs low.
If I had a second Home Mini I'd probably cannibalize it to make the speaker stereo but for now I think mono is good enough for this project.

 

Why are you switching ground rather than the 5V connection to control the power?

I thought switching the ground on and off was better and didn't know any better. Honestly I also never thought about it and just took someones word for it but it makes sense. One quick google search revealed that I should start getting used to putting my switches on the power wire.

As for your advice with the pot, that's actually really helpful because I could not find a potentiometer with switch that was also logarithmic. I don't want to add a seperate switch for power because, if things work out the way I planned, the powerbank will be hidden inside the speaker and no control interface should be visible to make for a really clean looking little speaker.
Once the parts get delivered (hopefully next week) I'll experiment with a few resistors and see if I can't get a smoth volume control working. Thanks for the tip!!

 

But you can effectively approximate a log pot output by adding a resistor from the wiper output to ground of a linear pot with value about 1/10th the pot resistance.

I've updated the circuit with the correct power switch and added the resistor as you mentioned.
On the left is a close up of the pot because things were getting growded...
Is this the correct implementation for the diy logarithmic pot, assuming the pot is a 10k?
Also which resistance would you recommend?

 

I think I heard somewhere that I should always switch the ground on or off

Whoever said that is totally wrong.
Only under unusual circumstances should you ever switch the ground.

Is this the correct implementation for the diy logarithmic pot, assuming the pot is a 10k?
Also which resistance would you recommend?

Yes, you would use about a 1kΩ resistor for a 10kΩ pot, but you can experiment with the value to get the control response you want.
That will make the minimum load on the Bluetooth output 1kΩ at the maximum loudness, but since the module has a low impedance output that can deliver 1W of power, that shouldn't be a problem.

 

Yes, you would use about a 1kΩ resistor for a 10kΩ pot, but you can experiment with the value to get the control response you want.

Thank you very much! This was extremely helpful. I can't wait for my components to come in and start laying everything out on a bread board - that'll be the true test for my design. I'll also use this opportunity to test the difference between the linear and logarithmic potentiometer.

I think I can handle the rest from here on out and I'll try and remeber to post a picture of the finished product I'f anyone is interested. Thanks again! And take care.