Speakers & amplifiers

[Swiz1611]

Maybe somebody here can help me out with this so whatever tips or advice you can give me will help a lot so here it goes.

I acquired two small amplified speakers from an old computer. I can't find who makes these speakers at all. The name on them is (EP-280/Amplified Speaker System). No serial number, model or anything.

The speakers had a bad hum so I decided to take it apart and fix the hum but became intrigued and wanted to know how to build the small amplifier attached to the circuit board. I can read and figure out schematics and componets which I have already. The problem I have now is I don't know the size amplifier schematic to build to test with the small speakers. There is no impedance or wattage printed any where on the speakers. I want to build the entire amp circuit board from scratch and hook them up to the speakers. I tried figureing out the circuit board that was already in it but lost track of the componets hook ups, became ****ed and soldered everything off of it.

Does anybody have any ideas or advice on how I can start this out? I want to build the amp but I don't know the size amp to build because I can't figure out the wattage of my small speakers or the ohm load. They are real small speakers so this is not a lot of power here. The speaker size is approx. 3 in. I also took the transformer out (assuming a step down transformer) and don't know how to measure the voltage coming out of the transformer. any tips on that also?

Any help or suggestions would be great Thanks

-Justin

[Alex R]

It's going to be like one watt or something. Look up the ratings of the output device(s).

To find out about the transformer you will have to feed some AC into the primary. I don't advise using the mains for this. A little low-freq signal out of a signal generator will do. Then you can see how far it steps down the AC volts by measuring it on the secondaries, get the ratio that way and do the sum. If it's too small a voltage to measure, put the small input signal on the secondaries and read off the primary vAC which will be much higher, the ratio will be the same, just in reverse.

But the max voltage on the main filter caps will probably give you a rough idea. Or check the max voltage of the output device(s), to give you an upper parameter.

[Swiz1611]

It's going to be like one watt or something. Look up the ratings of the output device(s).

To find out about the transformer you will have to feed some AC into the primary. I don't advise using the mains for this. A little low-freq signal out of a signal generator will do. Then you can see how far it steps down the AC volts by measuring it on the secondaries, get the ratio that way and do the sum. If it's too small a voltage to measure, put the small input signal on the secondaries and read off the primary vAC which will be much higher, the ratio will be the same, just in reverse.

But the max voltage on the main filter caps will probably give you a rough idea. Or check the max voltage of the output device(s), to give you an upper parameter.

thanks...I will try that out. I think the hum came from the transformer anyway so I might just by a new transformer. do you have a good website on how to property measure the output voltage on a small (step-down) transformer?

[Alex R]

Whaddaya mean, properly?!

[Swiz1611]

Whaddaya mean, properly?!

haha...sorry about that. I meant properly......

[Alex R]

no, what I meant was, I already told you how to do it properly!