How can I build a simple sound system for my laptop?

Well.. you have a typo, it sounds like nothing is wrong to begin with

Do you want a battery powered solution, USB powered, or wall powered?
How many parts do you want to re-use?

 

You're right, I should have picked up on that right away.
USB standard output would only be about 2.5W, but could approach 10W depending on the current standard and wiring used.
Even then... far too low for those.

Measuring the speakers will not do you any good with a multimeter. The speakers are an inductive load, and the 6Ω load rating is a value that represents the impedance at a range of frequencies. So... unless you have some other method of testing the impedance, all you'll end up measuring is the resistance of the speaker at rest

Now... as far as the project is concerned...
You can do the following:
-Repair the unit as a whole, and simply send the laptop audio to the input of the repaired.
-Ditch the main unit, and buy/build your own amplifier for the speakers. (Buying will be easier, and you can buy them as a circuit board)
*Scour the main board for parts to build your own amplifier from scratch.

The third option is more difficult, so I would, hands-down advise you choosing one of the first two.
If you want to repair the main unit, pop it apart and look for some physical damage:
-Burn marks
-Broken leads, wires, or jumpers
-Bulged/Blown capacitors
-Dry/Cracked solder joints (harder to spot... wiggle some of the bigger parts to make sure the solder connection is solid)

Providing pictures will help recommend where you should poke and prod with a multi-meter to get it working again.

Now if you want to buy an amplifier, you will need to create/buy a power supply, connect it to the amp, and run audio from the laptop to the amp.
All-in-all not too difficult, you just need to shop for some of the parts. This solution would require that you build or modify some kind of enclosure for the parts... it is not safe to leave exposed circuit board laying around on the floor

 

http://www.aliexpress.com/item/700W...key=6vYvMRFf&gclid=CP_Jz_rx9sECFUiTfgodipAAtA
I just did a google search for "Amplifier Board"
This is the kind of thing you need, but this one may be a bit of a stretch for your first one.

 

I don't think those speakers are up for 700W!

Something like this should be more than sufficient:

http://www.ebay.com/itm/Amplifier-B...mplifier_Parts_Components&hash=item3f3481744f

Bob

 

Thank you bob, I just linked one of the first ones I found... was in a bit of a hurry.
Just dug through the manual for the old stereo, looks like the speakers are rated on paper to handle 100W. (50W each if I read correctly... the other similar models have 150W amplifiers built-in)

In any case, this should give the op a good idea of the device he is after.

 

You could.. but your donor system has a total power consumption of 155W... so it's not 100W per speaker, it's most likely 50W per speaker and 100W for the pair.

The schematic you linked requires a split rail power supply to provide positive and negative 45V, and the schematic is of an A-B class push/pull amplifier which is not very efficient.

Ultimately, it's your call, but I think you should look for a pair of 50W amplifier boards, or a stereo 100W board. Keep your eyes open for 'Class-D' as it will be more efficient and run cooler.

If you want to build your own from scratch, let us know. That circuit should be something you work up to though, as you could be dealing with up to 90V on your circuit itself...

 

I can guarantee you that if you put 150W into those speakers, they will be torn to shreds.

The 100W (music power) is a bogus rating used to make cheap equipment look good.

I maintain my position that 15W per channel would be about right.

If the system is drawing 155W, and a typical AB amplifier is 33% efficient, and there is also a loss in the power supply, and the electronics before the output stage, lets say 100W is used for the output stages making it 33W total going to the 2 speakers.

If you want to go 25W per channel, I am sure you can drive the speakers to distortion.

Bob

 

I agree with Bob. Even normally reputable companies like Panasonic will use creative exaggeration when specifying speaker power ratings, because they too have to compete with BS specifications from less reputable companies. If you can have a look inside, you may find the truth marked on the speaker drivers themselves. I'd say 25W per channel would be more than you need.

 

Sneaky crap... I don't have much experience with those types of stereos. Mainly automotive audio.

 

That looks OK. It's 18W/channel into 4Ω. Power into 6Ω will be somewhat less. But that's probably a reasonable match.