How to improve quality of basic 2.0 PC speakers

[SuperDuty]

Hello,

I have a set of typical late 90's basic PC speakers (Juster AC-691N, made around 1997), they do their job, no problem with them but not very powerful but that doesn't matter much.



Now I want to experiment things a little, is there a way to improve the sound quality and remove the buzzing sound that can be heard when something is plugged to the jack, or even when I just touch the jack (bad grounding maybe ? Lack of shield between the transformer and the amp ?) ?

A sticker on the back says "The unit is double insulated an earth connection is not required".

Will replacing caps with newer good caps change things (caps are CrapXons, and two small unknown brand ones) ?

Speakers themselves are small rectangular shaped, branded WSI FE5090 4, they are 4 ohms and output 2W to 3W max. Very small indeed, can I replace them with more powerful ones with damaging the amp ?

That's only a matter of learning and experimenting things.

Thanks !

[mariushm]

Re: How to improve quality of basic 2.0 PC speakers

What audio amplifier chip is it using?

Cheap audio speakers have class AB amplifier chips which aren't efficient, they need a lot of power to output something on speakers.

In your case, for 2-3 watts of power per channel, (6 watts in total) ... the power should be 9-12v at around 1-2 A at least. I suspect the transformer inside isn't capable of more than 9v at 0.5-0.75A

This also isn't helped by the small capacitors usually used after voltage from transformer is rectified... it makes the voltage seen by the amplifier go up and down all the time. Larger capacitor would help smooth the voltage, but a larger transformer would do much more.

Post some pictures of the insides or at least write whats on the ICs and the transformer.

ps...
http://www.atacom.com/html_print/SPE...UST_06_93.html
3.2 watts total .. so even though the speakers are 2-3w each, probably the amp chip can only do 1.5w per channel with the transformer included..

later edit :

buzzing also happens when the cable going to the computer isn't shielded properly from interferences. Sometimes it helps to do something as simple as wrapping the cable going to the pc with aluminum foil (or some metal, but aluminum foil is simple to get, cooking foil will do, or cut coke cans/beers in worst case) and connecting that foil to the ground of the computer (anywhere on the metal case)

[SuperDuty]

Re: How to improve quality of basic 2.0 PC speakers

Here are the pictures, I had to remove the ridiculous steel heat shield from the chip : ST TEA2025B :


Not sure if the markings are of any help :


Size comparison (CR2032 battery) :

[budm]

Re: How to improve quality of basic 2.0 PC speakers

that is the heat sink for the IC. Not much you can really do, you may be able to upgrade the speakers with that is more sensitivity.

[mariushm]

Re: How to improve quality of basic 2.0 PC speakers

Well, the transformer is decent, 8.6 vac @ 0.6a is about 12v @ around 0.45a ..

https://cdn.badcaps-static.com/pdfs/...2dcb7a17ec.pdf

The amp chip is designed to work between 3 and 12v so it's certainly powered well. Other than that, by design the chip can't do more than 1-1.5 w per channel without huge distortions so there's no point changing the transformer or putting bigger capacitors, you won't gain much quality.
The plastic shell of those speakers would ruin whatever improvements you make anyway.

[lti]

Re: How to improve quality of basic 2.0 PC speakers

That amp chip isn't bad. It is one of the best low-end amplifier chips you can get. The specs don't look very good, but the actual sound quality is very good. You can try to reduce noise by using a bigger filter cap or changing the SVR cap (connected to pin 8 of the chip). The "heat shield" is really a heat sink and should not be removed.

What do the speakers look like? If they are the same 1.5"x3" 4 ohm speakers used in most cheap speakers (like these or these), you can't do much. Actually, the second set of speakers I linked to might be the USB powered version of the speakers you have.

[SuperDuty]

Re: How to improve quality of basic 2.0 PC speakers

Yes it looks very similar to the second set. The speakers are indeed, those small rectangular ones. And yeah, I meant heat sink not heat shield. I did put it back after removing it.
Is it possible to replace the amp chip with another more powerful one that would be pin compatible ?

[budm]

Re: How to improve quality of basic 2.0 PC speakers

To get more power with stronger IC, you will need more voltage. At 12V power supply, the max voltage at best across the voice coil will be about 11v peak to peak, so new IC is not going to change anything much. Your transformer is also only putting out about 12v at 1/2A. You want more power, you will need bigger power supply and IC to drive the speakers. More efficient speakers will help.

[lti]

Re: How to improve quality of basic 2.0 PC speakers

The only thing you can do to improve sound quality is to use better speakers and a better enclosure. Any modification to the amp wouldn't help.

[SuperDuty]

Re: How to improve quality of basic 2.0 PC speakers

Allright, thank for the answers guys ! Exactly what I needed