PC Speaker electronics to amplifier conversion

[BasicHIFI1]

Low watt amplifiers are capable of driving large speakers. Experiments with a PC speaker amp connected to 6" woofers showed acceptable volume. Distortion and component damage is a concern, though.

My project is to re-use the electronics from a used PC speaker that would probably be thrown away. I will be using an external power adapter instead of the AC in which is for 110 volts. A suitable enclosure will complete the project.

Something along these lines here:

[maillard]

Thank You for the link, a very good blog.

[BasicHIFI1]

You are most welcome.

[BasicHIFI1]

First step is to open up the set of speakers. The set I tried was difficult to open up, so I tried another pair that I used for testing earlier.

I originally thought of connecting an external power supply to supply dc current to the amplifier circuit. Like it says in the article I quoted, this is for safety. I did not feel safe allowing 220 Volts AC current into the unit I was going to be working on. On opening up the unit, however, I saw that the transformer was connected to the board and marked "AC" : there were four electronic components just next to the AC input : I guessed they were diodes to rectify the AC current to DC.

Looks like I will stay with the original amplified speaker enclosure this time.

[picowallspeaker]

Originally Posted by BasicHIFI1

First step is to open up the set of speakers. The set I tried was difficult to open up, so I tried another pair that I used for testing earlier.

The only way for doin' it

however, I saw that the transformer was connected to the board and marked "AC"

Yap! The secondary ( winding) of the transformer provides the necessary low voltage ISOLATED from the mains ( GAlvanic isolation )

If you play with electronics, you'll often encounter one

[BasicHIFI1]

Here is a picture of the board. If I can find the output from the rectifiers then I can connect a DC adapter to this. Otherwise stick with the original AC input and enclosure.

My low cost Amp I bought is butting out a hum and heating up the speaker drivers - at high volumes and high bass control settings, I think. Why take a chance though?

So PC speaker conversion is the plan/

[picowallspeaker]

Classic TEA 2025 design, outputs about 1 W / channel
Better to not exceed with +Vs...as often it will drive 4Ω load, so 8/10 V AC transformer, bringing a rectified & levelled 12/13 V to the chip

[BasicHIFI1]

Tested with 8 Ohm speakers - with 8 ohm woofer and 8 ohm tweeter in parallel, and a cap for the tweeter, will it be equavalent to 4 ohms impedence? The theory says it does. The original speaker was marked 4 ohms and 2 watts.

So to the point - how will it be possible to damage this amp and /or the speakers? Once I know that I can avoid it.

Very similar thread:

http://www.diyaudio.com/forums/power...p-project.html

[picowallspeaker]

Theory says that loudspeakers are complex loads and therefore cannot be assimilated to resistances.

The fact is that low power chip amps ( low is < 10 W ) show an increase of distortion above their average power which is rather unacceptable.

The fact that they are so diffused is because often there's a more powerful subwoofer ( often the same chip but in BTL mode ) that provides the so-called ooomph

Music contains peaks which are the most demanding in terms of current and driving for the speakers, so those are where the limits of the system is shown.

*music* is not sitting in front of the computer listening to YT from 1/2 m with speakers placed on the desk

[BasicHIFI1]

As a test, I connected the wires to the unpowered speaker to my set of Radio Shack speakers shown here in this project. The small powered speaker deowned out the sound of the 40-1011, so I snipped the wires to the powered speaker inside the case, and connected the wire to the said Radio Shack woofer unit.

Music, or program material was the following jazz cd: Diana Krall Live in Paris, tracks 2 and 3

What did it sound like?

Firstly it was huge improvement on the little pc speakers. It was pleasant to listen to. I could here the bass clearly in the background, something that the smaller speaker would not highlight. Guitar was full and clear, and vocals were well represented but with a boxiness that surprised me. Piano was coloured, again, seeming to be played from inside a box.

The point is that the same amp will play a better set of speakers very well, and with listenable sound quality. Remember I was testing one speaker, one woofer unit without the tweeter connected. To make things worse, the woofer in question had a damaged dome and a crack in in where a careless screwdriver pierced it a few days ago.

There is a funny tendency to cut out in the middle of the music - is it because the wires are not soldered or could this be clipping? No smoking yet though.

Volume is 50% and I get an average 80dB at 1 metre from the speaker.