Hi friends,
I had never audio project experiance before. I've jdy62 Bluetooth module and tda7850 4x50watt amplifier module. I want this module to work at 80 percent of its maximum power. That is, it will give 45 watts of power instead of 50 watts. By the way, I am thinking of doing this so that the system will have a longer life.
How would this be done without compromising the sound quality? Is it a bad idea to put resistors on the L R inputs? If not, how many ohms should be used?
No.
Use a voltage divider to reduce the input level by 0.8.
4.99K and 20K will work
Why not simply adjust the level control? Reducing the output power by 20% can significantly improve sound quality. It's an easy and effective solution to consider.
Why do you think this will increase the system life? How long do you need it to last?
Lowering the power supply voltage will limit power output (which also depends on load impedance). There is a graph on the datasheet for the chip.
But if this is a car amplifier, that's not practical.
That doesn't lower the gain. It limits the maximum power output. If you've got the volume cranked-up with peaks at 50W (and just below clipping) and then you lower the voltage the output will clip (distort).
If the peaks are hitting 45W and you lower the voltage, nothing will happen.
Higher speaker impedance also lowers power but you won't find a speaker to lower it by 80%. Double the impedance is half the wattage, but that's only 3dB quieter.
That won't work unless the output of the Bluetooth module is exactly matched to the gain of the power amplifier so they both max-out at the same time. That's rarely the case. Usually audio line-level is higher than the sensitivity of the power amplifier, so usually there is "extra" gain and if turn-up the volume control (usually a pot at the amplifier's input) you can usually get clipping.
The extra gain also allows you to get full power with songs (or other program material) that's quieter than "average".
Also check the "Protections" section of the datasheet. Typically these things are fairly electrically rugged. You probably won't burn it out unless you make a BIG mistake.
In your code, at the output multiply it by 0.8. That doesnt work?
As you stated, this will improve lifetime of the device, but it might be unnoticeable. For this to work you should limit to 0.5 (3 dB).
Or use a 90 W amplifier.
The same goes for the speakers, and power source.
A schematic of your setup should be attached to the OP.
How can i adjust level control? If you talking about phone's level, my guests can put the full their volume level when they connected.
@cedarlakeinstruments there will be less heat basically.
@DVDdoug Much thanks for your very detailed answer. 12v car battery is used in this project I forgot to mention 
The project will be on our garden, not in a car . According to datasheet when supply voltage is 12volts, for 4 ohm speakers my system is about 35 watts. but if we change it to 2 ohms speaker then it will go up to 60 watts. Kindly I want to see your ideas about jim-p's voltage divider solution ?
@jim-p I will try this tomorrow, thanks.
@maikarg Phone --> JDY62 Bluetooth module --> TDA7850 amplifier module.
TDA7850 directly powered on 12v battery. JDY 62 powered from 12v to 5v lm2596. L R and gnd connected to amplifier module's music inputs.
I’ll take a SWAG and assume that the drawing I’m posting matches your circuit. You can adjust the value of Rfx to change the gain as needed.
All that information is missing on the original post.
Check bluetooth module datasheet (even the IC datasheet). Adding a voltage divider at the output of the AudioL and AudioR should do the work. Or the input of the amplifier for each channel.
What I'm really getting at is are you trying to solve a problem that doesn't exist? i.e., as it stands now, why do you think the product won't last as long as you need it to?
