Class D amplifier system not working

Thread Starter

abuzar888

Joined Mar 6, 2024
2
Hello,
I hope you're all doing well. I'm putting together a sound system for my room. It has two power amps: one for two normal speakers and the other one for a subwoofer. I have put a pre-amp with the power amp that's gonna filter the sound going to the subwoofer. The whole system is powered by a 12v 10A AC to DC adapter. The source of audio for this system is an MP3 decoder that runs at 5v (via step down module). The audio comes from the decoder via three wires i.e., left, ground, and right. The preamp circuit receives audio from these wires as it has the same three terminals. However, it has two terminals on the output i.e., audio and ground. The audio goes from the preamp to the power amp which also has only two terminals (audio and ground). I'm running the subwoofer power amp with 24v (via step up module). Everything is connected to the 12v adapter in parallel. I'm using one wire to connect the ground terminals of all the circuits. The positive terminals are also connected by one wire but I have put switches in between.
Here are the problems:
1. When the whole system is hooked up to the power adapter, all the circuits are powered up but there's a constant ticking sound in all the speakers (two normal speakers and one subwoofer). There's no audio at all. I can hear the same ticking sound coming from the subwoofer power amp as well (yeah, the circuit itself can be heard making the sound).
2. When I take out the power amps and power each of them separately, they work. The subwoofer power amp has a constant buzz though. Powered separately, the other power amp give a good clear sound.
3. When I disconnect power, the capacitors in the circuits lose power gradually and this causes the speakers to make weird noises. I'm afraid it's gonna damage the speakers.
Questions:
1. How do I make this thing work and what am I doing wrong?
2. If I get this system to work, how do I get rid of the buzz in the subwoofer power amp?
3. Is there a way I can make the power to the speakers cut off immediately as soon as I disconnect the adapter?
Some more details:
I have tried changing the power source. The same issues persist with a 12v battery.
This is my first ever try at such a project so I don't know a lot. I have a multimeter and can do the basic checks with it. I'll be happy to give more details if needed.
I have attached a basic diagram of the whole system. InShot_20240306_233545691.jpg
I really appreciate your help. Thanks!
 

crutschow

Joined Mar 14, 2008
34,703
Some observations.

Your power supply can only deliver 12V *10A = 120W max., so it obviously can't power all the circuits.

The switching power supply modules you show are inherently noisy.
Better to use separate 120V to DC supplies for each voltage required (5V, 12V, and 24V).
You can then have each with the max power the circuits require.
Or use linear regulators, such as with an LM317, from a single 24V high power supply, to get the low power for the preamp and MP3 modules.

12V to the speaker amp will likely give a maximum of about 8W into each 8-ohm speaker.
24V will give about 35W max. to each speaker.
Don't see how you can get 80W unless it's with 4-ohm speakers.
 

Thread Starter

abuzar888

Joined Mar 6, 2024
2
Thank you for the reply. I'd like to mention that the wattage I have listed is of the power amps. The two speakers I'm using are 30 watts RMS each and have a rating of 50 watts max. Similarly, the subwoofer is rated at 60 watts RMS and can be powered with 120 watts max. From what I have read on this forum, I think I should get a decently loud output from the speakers. There's no audio even with the volume set to the lowest.
 

KeithWalker

Joined Jul 10, 2017
3,147
The problem may be caused by incompatible power supply modules and the common signal ground wiring.
It is usual to join the negative of the various supplies together to form a reference circuit common, which is at the same potential as the signal common.
The negative supply input is not always connected internally to the negative output on power supply modules. You should do a continuity check with an Ohm meter between the negative power input and output on the 5V and the 24V modules. If there is no continuity, you have a problem which can be solved by using seperate 120V powered supplies.
 

crutschow

Joined Mar 14, 2008
34,703
There's not enough information to determine the problem.

Try removing power to one unit at a time and power it with a separate supply to see if you can isolate the problem.
 

Dodgydave

Joined Jun 22, 2012
11,320
Start by powering the power amp on 12V first, see what happens, then add the mp3 decoder with the 5V supply, what happens then?

I bet its the step up converter..
 
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