4 X 40Watt Computer Audio Amplifier

This project started when I finally got fed up with having to turn on my 2 X 200Watt NAD amplifier every time I wanted to listen to some music or play a game..

I should mention that 200Watts with an efficient speaker setup is a little overkill.. 10Watts would probably be sufficient, but 40 sounded better :). In actuality you can only achieve about 18W with this setup before distortion becomes severe, that should still be plenty for most everyone, and is for me.

Basically this is a car audio amplifier running off the internal computer power supply and connected internally to my sound blaster audigy ZS sound card.

I should also mention that the design for this amplifier was inspired by this web page: http://ludens.cl/Electron/audioamps/ta8215.html

TDA7386 Datasheet PDF (643KB)

Schematic Link

Note: PCB design does not have component part numbers, please use the schematic to find what part goes where.

PCB All Layers in Color : Blue = Top Copper, Green = Bottom Copper, Red = Top Silkscreen, Yellow = Bottom Silkscreen

PCB Top Copper in B/W

PCB Bottom Copper in B/W

PCB Top Silkscreen in RED

PCB Bottom Silkscreen in RED

In order to produce a two layer printed circuit board in the way I do using the toner transfer method you will need a copy of the PCB design with the top layer mirrored and the bottom layer un mirrored.
Here I provide two PDF files that should print to the correct size so that anyone can duplicate my PCB provided they have a laser printer, an iron, and of course some blank PCB material and etchant.

PCB Top Copper Mirrored in PDF

PCB Bottom Copper in PDF

Construction Photos:

Top Side 0

Added some small wires to act as Via's.

Bottom Side 0

Here you can see an error I had to fix in the PCB because the toner didn't stick that well in a few spots.. Right in the middle that long straight wire is bridging a gap in one of the input signal traces.

Top Side 1

Added the surface mount components and a few others..

Bottom Side 1

Added surface mount components.

Top Side 2

Added another resistor.

The jumper you see on the top left corner by pin 1 is incorrect, ignore it.

The Flexiwatt25 package that the TDA7386 comes in is designed to be mounted vertically as you can see in the data sheet. I didn't see any easy way to attach a heat sink to it and decided to mount it flat in the same plane as the PCB.. the bottom layer pins don't have to be bent at all. the top layer must first be straightened and then bent, I found it easy to first solder the bottom pins on and then bend down each top pin one at a time with the soldering iron, having the PCB pads and chip pins pre-tinned.

Bottom Side 2

Here you can see the cut I had to make on the trace from the IC TAB pin (1) to the signal ground, it should have gone to the power ground. The cut is on the lower left hand side of the PCB.

* This design error has been fixed in both the schematic and PCB designs at the top of this page.

Bottom Side 2.1

Nothing new, just a different view.

Top Side 3

Completed Board

Showing large 1000uf filter caps and terminal blocks installed. The terminal blocks were a pain to solder on the top side because you have to leave space between them and the PCB in order to get the soldering iron between them. If I had a professional PCB with plated through holes this wouldn't be a problem.

Bottom Side 3

Completed Board

This picture shows the installation of the stand by pin resistor on the top right.

Pin 25 has a pad for it on my PCB designs, this pin can provide clipping information, I didn't need that so its left unconnected.. The data sheet has more info.

 

Back Panel Connector

This is how I get the speaker connections to the back of the computer. The wire is recycled from a broken computer PS.

The RCA jacks have special beveled insulating washers to isolate them from the case. This is needed because neither of the audio outputs is referenced to ground, both float at half the supply voltage with no output signal.

DO NOT CONNECT THE OUTPUTS TO GROUND

Okay the chip is supposed to have output short protection, but id rather not test it.

Box 1

Another view with more of the connections done.

You only want to use one ground wire from the sound card to avoid ground loops

The standby pin can be shorted to ground to turn off the amplifier. Because of the input filter it even has a nice turn on transition.

Box 2

Ready to be mounted in the computer. Almost.

Case Side

Here you can sort of see the wires leading from and to the amp. I should organize my cables better..

Sound card Connections

Unless you have the same exact sound card as me the connections will be different. I used a 3.5mm jack with open leads and an multi meter to find out which pins on the back of the plugs I needed to connect to.

The white cable with plug hanging off is from my front panel headphone and mic jack.

Case Front

This shows the toggle switch used to turn the amp on and off.. Its the one on the left.. The two on the right control the speed of my fans.

Case Front Open

Kinda messy with everything open..

Case in Rack 0

Case in Rack 1

Fits perfectly (its not touching any metal).

Hard Drive Caddy

This came with my Antec Solo computer case for mounting hard drives on rubber grommets.

It just so happens to work perfectly to insulate my box electrically from the computer case and provide easy removal.

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