My custom audio amplifier

[Aurelio]

Hello guys, I'd like to give you some infos about a project I've worked on for the last few days.
It is a custom audio amplifier with some neat features:

• 2.5W/channel of output power for a 4 ohm load
• Integrated headphone jack with plug sense
• Selectable analog or I2S input
• Digital controls for audio volume
• The volume can be set indipendently for the headphones and for the speakers
• 8 IO ports of which 2 are used for the volume switches and 1 to set the input (I2S or analog). The remaining 5 might be used in the future, I'm still unsure how

This is still a work in progress, I've just finished designing the PCB layout. I will double check it and then I will order some of them from OSHPark. Here is a sneak preview of how the board will look like (click on the image to see a high resolution one):

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The board is 2.86x0.93 inches (72.69x23.49 mm).

Let me know what you think about it!

UPDATE (3rd of February 2016):
I double-checked the PCB design and I fixed some minor mistakes. I've just ordered 3 boards from OSHPark, I should get them in a month (heh, I should find a cheap PCB manufacturer in Europe).
I'll update you as soon as I receive the boards

In the mean time I'm also looking for a simpler and cheaper solution that will allow me to build a smaller pcb

PS: This was done because I want to implement it in a GCp, since it has I2S input, so that's why I wrote this post here, but please mods move it to another section if you think this is not the right place.

 

[gman]

Nice, what is the size of the pcb?

 

[Aurelio]

Nice, what is the size of the pcb?

Right, I forgot to specify it. It is 2.86x0.93 inches (72.69x23.49 mm). I'll add it to the first post

 

[Hermaphroditus]

Interesting, I didn't know the GC had an i2s line. I've had to deal with the i2s protocol some (as well as the i2c protocol) in terms of state machines to control them, etc. What ICs are you using? Also, with the PIC is that just to control the IO to give input to the amplifier IC, or are you doing any digital filtering as well? I don't think that's the case, though, since I don't see any data from the audio side to the PIC.

 

[Aurelio]

Yes, the GC sends i2s audio signal over the digital port .
The IC that I'm using is a LM49450 from Texas Instruments which is controlled (input settings, i2s parameters, volume) through i2c, so that's why I'm using the PIC (which is actually overpowered for this, but I already have some of them).
There is no digital filtering done by the PIC, all the audio handling is done by the LM49450 itself; the PIC is there just to handle user inputs and to configure the amplifier.

 

[Diminuendo]

ooh, seems interesting. would be cool to use digital sterio in a portable

 

[Hermaphroditus]

Ahh, I see. Makes sense. If you need any help with the I2S/I2C I could maybe help some. Though in terms of I2C control I actually only used a hardware implementation, not software, to control it (using a FPGA, which would be waaaaay overkill for this unless you wanted to do digital filtering), but I understand the concept of I2C enough lool.

 

[Aurelio]

Ahh, I see. Makes sense. If you need any help with the I2S/I2C I could maybe help some. Though in terms of I2C control I actually only used a hardware implementation, not software, to control it (using a FPGA, which would be waaaaay overkill for this unless you wanted to do digital filtering), but I understand the concept of I2C enough lool.

Thanks, but hopefully I shouldn't run in any problem with i2c, I know it quite well, while for the i2s side it should be completely driven from the amplifier (besides some minor settings done by the PIC).

Anyway, I double-checked the PCB design and I fixed some minor mistakes. I've just ordered 3 boards from OSHPark, I should get them in a month (heh, I should find a cheap PCB manufacturer in Europe).
I'll update you as soon as I receive the boards

In the mean time I'm also looking for a simpler and cheaper solution that will allow me to build a smaller pcb

 

[Aurelio]

I've made another amplifier board. Take a look at it here: http://forums.modretro.com/viewtopic.php?f=9&t=14727

 

[Mooper]

Does the digital volume remember it's position after being powered off? And what's the advantage of l2S in a portable?

 

[Aurelio]

Does the digital volume remember it's position after being powered off? And what's the advantage of l2S in a portable?

Yes, the position can be stored in the internal memory of the microcontroller.
About i2s actually I'm not sure if there will be any noticeable difference, but I wanted to try it.

 

[Hermaphroditus]

Does the digital volume remember it's position after being powered off? And what's the advantage of l2S in a portable?

I feel with the I2S in a GC Portable it's less of a "why" and more of a "why not."