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

[vnman]

Sorry didn't realise that you don't intend to use headphones. I was thinking of using the headphones with switch such that you can cut out the output to speakers when headphones plugged in.

Anyhow, the diagram above will reduced the output of the amp then you can connect the speakers to where it says left/right/sleeve(GND).

This won't solve the power supply issue...

[DeRock89]

Sorry didn't realise that you don't intend to use headphones. I was thinking of using the headphones with switch such that you can cut out the output to speakers when headphones plugged in.

Anyhow, the diagram above will reduced the output of the amp then you can connect the speakers to where it says left/right/sleeve(GND).

This won't solve the power supply issue...

I'm not sure I comprehend... it looks like the diagram is explicitly for headphones. Also it looks kind of like it's bridging the grounds. I was doing some reading and it sounds like because the amp is bridge-tied that it's very important that the grounds for he left and right remain separated and are not made common or it will overload the amp.

I also got a 50uF cap to put on the power rail. Do you know how this doesn't manage to draw a lot more power? I'm just reasoning that the power and ground rails are sort of being bridged with the cap. I realize tha cap has resistance in it I assume and that it's not bidirectional so I assume it won't nessesarily short but would cause more power draw. I don't actually have any knowledge to base this off of, I'm just reasoning; "cap is electical connection and connecting between ground and power, power will draw current accross connection to the limit that resistance will permit"

Im sorry for being so inquisitive, I'm just simply tying to understand everything. I'm not the type of person to just do something, but the type of person that feels a nessesity to understand as much as possible everything I can to my abilities anything before I commit to action. Im the type of person to research the crap out of a product before I buy it because I want to understand exactly what I'm buying first.

[codeman0624]

I also got a 50uF cap to put on the power rail. Do you know how this doesn't manage to draw a lot more power? I'm just reasoning that the power and ground rails are sort of being bridged with the cap. I realize tha cap has resistance in it I assume and that it's not bidirectional so I assume it won't nessesarily short but would cause more power draw. I don't actually have any knowledge to base this off of, I'm just reasoning; "cap is electical connection and connecting between ground and power, power will draw current accross connection to the limit that resistance will permit"

Capacitors between power and ground do not draw any power. Resistors burn power, not capacitors. Capacitors are actually energy storage devices, they are put on power rails to help stabilize the voltage.

https://learn.sparkfun.com/tutorials/ca ... n-examples

[DeRock89]

I also got a 50uF cap to put on the power rail. Do you know how this doesn't manage to draw a lot more power? I'm just reasoning that the power and ground rails are sort of being bridged with the cap. I realize tha cap has resistance in it I assume and that it's not bidirectional so I assume it won't nessesarily short but would cause more power draw. I don't actually have any knowledge to base this off of, I'm just reasoning; "cap is electical connection and connecting between ground and power, power will draw current accross connection to the limit that resistance will permit"

Capacitors between power and ground do not draw any power. Resistors burn power, not capacitors. Capacitors are actually energy storage devices, they are put on power rails to help stabilize the voltage.

https://learn.sparkfun.com/tutorials/ca ... n-examples

Yeah I knew that caps store power, I've been shocked by them lol. I just didn't realize that they don't cause some sort of current draw too...

[vnman]

I think you are the first to use pi 3 and HDMI.
did you try the config.txt example to see if it helps with the power problem?

I read somewhere in this forum that composite screen draws 430mA, which would means the HDMI screen draws much more. In your case you need to source a more powerful power boost.

Maybe this will do the job? https://www.aliexpress.com/item/5V1A-2A ... 0.0.yfQF0d

The AMP can be supplied with 3.3V, you might want to try that too.

[VeteranGamer]

I think you are the first to use pi 3 and HDMI.
did you try the config.txt example to see if it helps with the power problem?

I read somewhere in this forum that composite screen draws 430mA, which would means the HDMI screen draws much more. In your case you need to source a more powerful power boost.

Maybe this will do the job? https://www.aliexpress.com/item/5V1A-2A ... 0.0.yfQF0d

The AMP can be supplied with 3.3V, you might want to try that too.

The kedei screen is paired with a Pi3 in all the 1UP HD builds....

Have a look how he powers it up...
I think he has the generic/banggood boards....

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[DeRock89]

I've done several experiments and found some interesting things.

First I used a multimeter to test how much the Kedei HDMI screen is drawing. It appears to draw around 380 to 400mA.

Next I tested how much the PAM8403 is pulling with the two 3W 4 ohm speakers and it jumps all over the place depending on the audio signal but it seems to average anywhere from 500-700mA and sometimes briefly peaking to an 1 amp when there was a loud noise. The volume output was WAY too loud for a game boy when turned up.

I tried both one and two speakers and this didn't seem to effect currant draw.

I'm waiting for a massive variety of resistors but I happen to have some 1K and 10k resistors so I tried them in various locations in the audio circuit.

First I tried both resistor values in line with the amp power supply and just got poping noises like a metronome.

Next I used only one input and tried differnet combinations of resistors on that single input.
One 10k resistor reduced mA to around 200-300 volume was still very loud at max volume.
Three 10k resistors in series reduced power to 50-100mA with still pretty loud volume.
Five 10k resistors reduced power to 30-50mA and in my opinion still had loud enough max volume.

What's concerning to me is there are points when the power has a very brief and high peak when there is a loud noise produced in the audio such as an explosion.

Based on these experiments and my rudimentary knowledge, I would say that the audio signal from the Kedei screen already has a very high output, the amp is able to amplify a signal a LOT or I'm just an idiot stumbling around in the dark.

MAYBE I can dial in the correct resistor configuration to be within tolerable parameters of what the powerboost can handle. The power draw at a volume level I would actually play at seemed to be around 16-20mA. I ASSUME that enough available power has to be accounted for to deal with surges and/or peaks in draw. I used a separate external power supply to power the amp during these tests. The audio signal I used for all these tests was emulating crash bandicoot warped and letting the intro and demo video music play from that game. Just like Veteran was saying about the 1up build. He's pulling it all off somehow... It was the 1up build that gave me the confidence to try this kind of build in the first place....

[DeRock89]

Does anyone know why putting resistors on the amp input worked, and which mA I should aim for reducing it to if this was a good fix? I was wanting some feedback from you guys before I consider this a solution and go through with it. My shipment of 1/4 watt resistors at 1% with 100 varieties of values came in the other day so I have pretty much any value to use. It's like 1000 resistors for 15 bucks!

[DeRock89]

I think you are the first to use pi 3 and HDMI.
did you try the config.txt example to see if it helps with the power problem?

I read somewhere in this forum that composite screen draws 430mA, which would means the HDMI screen draws much more. In your case you need to source a more powerful power boost.

Maybe this will do the job? https://www.aliexpress.com/item/5V1A-2A ... 0.0.yfQF0d

The AMP can be supplied with 3.3V, you might want to try that too.

I tested the screens draw with a multimeter and it appears to draw 380-400mA. The amp by itself was drawing 500-700mA by itself, possibly more, I was nervous about turning it up too loud...

I've done some experimenting with resistors in various places and it seems I can reduce the draw by placing resistors in line between the amp and audio jack on the screen. I don't know what the safe level I should aim for though... it seems to be loud enough at max volume with a high enough resistor value in this location to reduce the currant to about 60mA. I got a ton of resistor 1/4 watt resistors with 1% value in the mail the other day to try and find the right values and locations for them. I have no idea if what I'm doing is actually a good idea or not...

Also I'm wondering if it would be a good idea to put the resistors in this location and in line between the amp and speakers.

[VeteranGamer]

I think you are the first to use pi 3 and HDMI.
did you try the config.txt example to see if it helps with the power problem?

I read somewhere in this forum that composite screen draws 430mA, which would means the HDMI screen draws much more. In your case you need to source a more powerful power boost.

Maybe this will do the job? https://www.aliexpress.com/item/5V1A-2A ... 0.0.yfQF0d

The AMP can be supplied with 3.3V, you might want to try that too.

I tested the screens draw with a multimeter and it appears to draw 380-400mA. The amp by itself was drawing 500-700mA by itself, possibly more, I was nervous about turning it up too loud...

I've done some experimenting with resistors in various places and it seems I can reduce the draw by placing resistors in line between the amp and audio jack on the screen. I don't know what the safe level I should aim for though... it seems to be loud enough at max volume with a high enough resistor value in this location to reduce the currant to about 60mA. I got a ton of resistor 1/4 watt resistors with 1% value in the mail the other day to try and find the right values and locations for them. I have no idea if what I'm doing is actually a good idea or not...

Also I'm wondering if it would be a good idea to put the resistors in this location and in line between the amp and speakers.

I really find it hard to believe that you have a major power issue, and that you haven't been able to sort it out yet....

the setup you've got is pretty much identical to the 1UP HD Game Boy kits



now your issue might actually be the powerboost, but i personally wouldnt start getting power supplies that havent been tried and tested in builds....

i would try the generic/banggod psu, and if you havent already done so connect a battery to the setup (having a battery hooked up can also make a difference)


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