Issues With Stereo Audio(Pi3+PAM8403+ Kedei HDMI)

[DeRock89]

I was discussing this in one of my own solved threads for something unrelated to this audio issue. veteran was really helping me out in that tread, but I feel it needs its own thread.

In short, when Volume on my builds audio circuit is turned up past a certain threshold, the screen starts turning off and on over and over. This does not seem effect the Pi Or any other components, just audio and the screen.

I'm using a Pi 3 connected to a Kedei HDMI screen version 1.1 via FPV ribbon cable. I'm attempting to achive stereo sound with a PAM8403 amp connected to the screens audio jack with two small 1W speakers.

I'm using a 24 pin FPC ribbon cable because I wanted to eliminate as much wires and crap spanning between the two halves as possible. The audio amp is powered through Pin holes 19 and 20 which come out the other side of the cable and connect to the power rail PCB.

I followed veterans diagram for wiring up the Audio.


I am not using a headphone jack at all and had to improvise for it not being present. I've been pretty confused about the grounding. I kind of guess based on very little that it could have something to do with this.

Here is my initial wiring


Veteran suggested that I move the pot to after the amp instead of before. The result from this was no sound at all.
Here is my wiring with trying my best to follow the diagram and move the pot.


I had this other variation to the audio amp with a pot built into it. I used this to rule out malfunctioning with my pot wiring or the regular amp. It produced the same results and the screen would start cycling on and off. The game I used for testing remained on and running as normal while the screen flashed on and off. This is the wiring for this test.


I've also tried just connecting the speakers directly to the audio jack. This resulted in Barely audiable sound. I'm at a loss. This build has been one problem after another and not went smoothly at all...

[DeRock89]

I believe I made a breakthrough figuring this out myself BUT there's bad news with that and more issues.

I got an idea to make a separate power supply to power the PAM8403 separately from the build. I took a USB cord, stripped it and wired it to the Amp. I plugged that cord into a 5V 1A phone power supply. This worked! I got sound going and the screen remained on without cycling on and off.

The bad news....
obviously there's an issue with my power system or it's unable to handle powering everything I guess.. I'm using an Adafruit 1000c. Although I don't have the battery installed. I'm just plugging the powerboost in with a canakit 5V 2.5amp raspberry pi power supply. This may be relevant but I have no idea.

The rest of the bad news....
I turned the volume all the way up to make sure the screen wouldn't cycle on and off and I blew my little speakers...

I searched forever for these speakers and waited weeks for them to arrive to the US from China. I wanted to have speakers small enough to fit two into the space where the original speaker goes, and potentially locating the other speaker to left to have actual stereo sound. The speakers were rated for 1 watt. I figured this would not be an issue considering that I see a lot of people using the pam8403 and 0.5 to 1 watt speakers.
If anyone knows of any other oval shaped speakers that are less then 30MM(1 and 3/16 inches) in length that would be awesome.

[VeteranGamer]

its good you narrowed the issue down....

i was seriously consider changing the wiring points on the screen, it may improve power the power going to the screen

1UP has his builds wired like this....




its worth a try....


.

[DeRock89]

its good you narrowed the issue down....

i was seriously consider changing the wiring points on the screen, it may improve power the power going to the screen

1UP has his builds wired like this....




its worth a try....


.

What in the world does on those copper wires do?!

[VeteranGamer]

its good you narrowed the issue down....

i was seriously consider changing the wiring points on the screen, it may improve power the power going to the screen

1UP has his builds wired like this....




its worth a try....


.

What in the world does on those copper wires do?!

Ignore the copper wires, they are only necessary if you chopped your board the way he does for his builds....

It's where the 5v (red +) and Gnd (black -) are that relevant....

.

[DeRock89]

its good you narrowed the issue down....

i was seriously consider changing the wiring points on the screen, it may improve power the power going to the screen

1UP has his builds wired like this....




its worth a try....


.

What in the world does on those copper wires do?!

Ignore the copper wires, they are only necessary if you chopped your board the way he does for his builds....

It's where the 5v (red +) and Gnd (black -) are that relevant....

.

What about the copper wire going from the positive point of contact on that yellow component up to where the swich used to be? That's where the power is connected now on my screen.

[VeteranGamer]

What about the copper wire going from the positive point of contact on that yellow component up to where the swich used to be? That's where the power is connected now on my screen.

Ignore the copper wires, they are there because of the board modifications done to the bottom left of the board and the right....

Soldering at the points I've suggested, may give you a better power connection

Especially the ground

.

[vnman]

You might take a look at this - http://chromo.cc/crate/crate-sound-headphone-amplifier. From what I gathered all are saying NOT to connect L- & R- together. Since it is a 3W amp it is no wonder that the 1W speaker would blow if the volume at max.

As for powering the screen, I would think power from the battery via the power strip is the way to go. I wired the screen excatly as shown above and have no problem.

Almost finish with my build, this is black / red build, this is delayed due to me ordered 20cm FPV HDMI cable and the order never arrived. So I ordered new one should arrive in 2 weeks. In the mean time it gives me a chance to finish the back part of the case.

[DeRock89]

You might take a look at this - http://chromo.cc/crate/crate-sound-headphone-amplifier. From what I gathered all are saying NOT to connect L- & R- together. Since it is a 3W amp it is no wonder that the 1W speaker would blow if the volume at max.

As for powering the screen, I would think power from the battery via the power strip is the way to go. I wired the screen excatly as shown above and have no problem.

Almost finish with my build, this is black / red build, this is delayed due to me ordered 20cm FPV HDMI cable and the order never arrived. So I ordered new one should arrive in 2 weeks. In the mean time it gives me a chance to finish the back part of the case.

Do you mean left and right shouldn't be grounded together? I ordered several 3W 20mm Veco speakers and some other 3W 19.5mm speakers from mouser electronics to try to solve the problem of the speakers blowing

You wired yours like I did above or like veteran is saying with the 1up build?

Power from the battery from the power strip? I have everything that's drawing power ultimately connected to the power strip. There are 3 components on my power strip now; the Pi3, screen, and audio amp.

Look at lololos build here.
viewtopic.php?f=43&t=4418&p=50094#p50094

He's using capacitors because he was having a power issue and it sounds like it solved his power issue BUT created another issue of it draining the battery really fast...

If I would have known you needed an FPV cable before you ordered, I could have sent you a spare one I have.

[vnman]

I prefer NOT to draw power from the PI. Remember that the 5V pin supply on the Pi 3 is ~750mA (source https://raspberrypi.stackexchange.com/q ... imitations).

I see that you now use power strip for the three components, that would help. As for the capacitors you only need it if the supply is unstable (that is whay it is called "smoothing" capacitor). You would need to wire the capacitor on the powerstrip, checkout this build viewtopic.php?f=43&t=1615&hilit=sota&start=20.

As for the FPV cable if you have a spare..I'll have it. I will pay full price plus postage as this will save me the waiting time...

Sorry for all the links