Hi guys. I'm building a bluetooth speaker and need some advice on volume control. This is a single-speaker amp, so I chose THIS mono TPA3118 based amp. The bluetooth module i'm using is THIS ONE. I'm planning to power them both with a 12v (ish) li-ion pack, or a 12.6v power supply when the unit is plugged in for charging. I'm currently using a 4ohm 5" full-range speaker... but I have a question about that as well that i'll ask later.
When testing last night, the volume seems very high. That is, with my phone connected via bluetooth (or wire) and on its lowest possible volume setting, the volume is higher than i would want my minimum volume to be. Going past half-way on my phone's volume results in the amp being way too loud and beginning to distort.
So i'm thinking i should wire up a potentiometer. I know I need a logarithmic pot, but i don't know how to choose the pot's value. Can someone tell me what value pot would appropriate for this project?
Also, the pot should go between the bluetooth's output and the amp's input, right? Like this:
And finally, concerning the speaker: If battery life is a concern, would an 8 ohm speaker be a better choice?
Thank you for your time and advice!
When testing last night, the volume seems very high. That is, with my phone connected via bluetooth (or wire) and on its lowest possible volume setting, the volume is higher than i would want my minimum volume to be. Going past half-way on my phone's volume results in the amp being way too loud and beginning to distort.
So i'm thinking i should wire up a potentiometer. I know I need a logarithmic pot, but i don't know how to choose the pot's value. Can someone tell me what value pot would appropriate for this project?
Also, the pot should go between the bluetooth's output and the amp's input, right? Like this:
An externally hosted image should be here but it was not working when we last tested it.
And finally, concerning the speaker: If battery life is a concern, would an 8 ohm speaker be a better choice?
Thank you for your time and advice!
I would use a line level pot of anything between 10 and 50k. Lin/log; your choice but no preference as it doesn't matter.
Loosely speaking, an 8R speaker needs more voltage for the same output as a 4R speaker. A 4R speaker will draw twice the current than an 8R speaker for the same sound output but the power is the same for the same volume.
Loosely speaking, an 8R speaker needs more voltage for the same output as a 4R speaker. A 4R speaker will draw twice the current than an 8R speaker for the same sound output but the power is the same for the same volume.
According to my understanding the Bluetooth module is the source (of sound) and the amplifier is the "consumer" for the signal. As I see it, your diagram is not the way it is normally done. The upper-most pin on the potentiometer (left-most seen from the front) is the GND pin that has to be connected to ground on the Bluetooth module and ground of the amplifier input.
Then, as you apparently want to turn a Bluetooth stereo signal into mono, you connect two 4K7 resistors from each of the Bluetooth outputs (stereo) to the lower-most pin on the potentiometer (opposite of the GND pin). The middle pin of the potentiometer has to be connected to the input (signal input) of the amplifier.
Use a 10K potentiometer with the two 4K7 resistors.
Just summing two stereo outputs by a short circuit (as you indicate) may distort the signal (use resistive summing instead).
Good luck with it!
Then, as you apparently want to turn a Bluetooth stereo signal into mono, you connect two 4K7 resistors from each of the Bluetooth outputs (stereo) to the lower-most pin on the potentiometer (opposite of the GND pin). The middle pin of the potentiometer has to be connected to the input (signal input) of the amplifier.
Use a 10K potentiometer with the two 4K7 resistors.
Just summing two stereo outputs by a short circuit (as you indicate) may distort the signal (use resistive summing instead).
Good luck with it!
What a nonsense! Ofcourse does it matter! That's an audio signal, not a DC voltage! If you use a linear pot, you'll end up with 90% of the way it doing next to nothing and the whole range of the rest of the volume is within 2mm and extremely fiddly to adjust. And if it was a DC voltage, you'd have the same problem with a log pot!
@jackstraw: You need a log pot, 50k is usually a good choice, everything from 10k-100k will work though. FauxFrench already said, it's better to limit the influence of the mono-'short' from the BT audio output since it got a low output impedance (<600 Ohm). 4,7k is fine, if you don't have these at hand, you can go up to 10 or 15k if you got a pot of 20k or 50k Ohm. Just keep the resistor values below ca. 1/2 of the resistance of the potentiometer.
Bluetooth outputs (stereo) to the lower-most pin on the potentiometer (opposite of the GND pin). The middle pin of the potentiometer has to be connected to the input (signal input) of the amplifier.
Use a 10K potentiometer with the two 4K7 resistors.
Thanks Faux. I will add the resisters as you say. If i read that correctly, you are saying i need to reverse the 2nd and 3rd pins (the non-grounds) in my diagram?
Hello,
I am interesting in a similar project. I have this board but when in starts the volume is really loud and and a woman voice shouts bluetooth pairing commands. Any advice on how I cant solve it ? I tried to "short" the little vol+ pins out (delivering 3,3v) but it does seems do to do anything.
Thanks in advance for your help
I am interesting in a similar project. I have this board but when in starts the volume is really loud and and a woman voice shouts bluetooth pairing commands. Any advice on how I cant solve it ? I tried to "short" the little vol+ pins out (delivering 3,3v) but it does seems do to do anything.
Thanks in advance for your help
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