Audio Amplifier

[The Master]

Luciano, the TDA1558Q looks like it would be a good choice. At first glance it looks like it doesnt need any external components either. It is a little more expensive but the main thing is that Rapid doesnt seem to stock it. Ill keep it in mind as a backup plan but i think im going to stick with the LM386. Thanx anyway

skimask, no i dont know what those things mean. I do have a few soundcards from old PCs just laying around doing nothing so i guess you could call them expendable. I will still go with your idea and add the volume control in to start with though. Ill be making it all up on a breadboard first anyway and im sure i have some variable resistors spare too.

I kind of get what AC/DC coupling means but im not sure what i would go with. Arnt sound cards line-level (i believe that means 0V and below) so i would assume DC since the voltage should never cross 0V.

Do you know what the output impedance of your sound card is? Does it really matter?

Erm, I wouldnt have thought so but since you mention it i guess it might. I didnt think the sound card would matter because its inputting to the chip. I have heard that the impendance of the speaker matters though. These speakers are the type that only have a part number on them and no other usefull information. A quick google search says they are 4 ohms. One of the 2 (LM386 or the first one i was looking at) said it can be used for both 4 and 8 ohm speakers

[skimask]

I kind of get what AC/DC coupling means but im not sure what i would go with. Arnt sound cards line-level (i believe that means 0V and below) so i would assume DC since the voltage should never cross 0V.

AC coupling - basically thru a capacitor, output ends up swinging + to - around ZERO.
DC coupling - basically thru a resistor, output follows the input but with less 'driving' capability (ie. less current because it's going thru a resistor/current-limiter).

Impedance - Yes, come to think of it, all of these op-amps have very high input impedance, so you're right, for the most part, it doesn't matter.
Speaker impedance does matter though. Try to connect a 2-ohm woofer to an 8-ohm output and you probably won't be impressed.

[The Master]

Just to check, can the output impendance be less than the speaker impendance? I know it cant be more because it works the oposite way to watts (a 2W amp wouldnt work well with an 8W speaker etc).

Now im not so sure about the coupling. Is this actually something in the sound card or is it the way the circuit connects to it? If its part of the soundcard then how do i tell the difference?

[skimask]

Just to check, can the output impendance be less than the speaker impendance? I know it cant be more because it works the oposite way to watts (a 2W amp wouldnt work well with an 8W speaker etc).

Watts don't matter much... A 2W amp will drive an 8W speaker just fine, all other things being equal.

Impedance - Google it, Wiki it...
If the output impedance is LOW, then that means the output's load can draw MORE.

Now im not so sure about the coupling. Is this actually something in the sound card or is it the way the circuit connects to it? If its part of the soundcard then how do i tell the difference?

Both...

Just hook the thing up to something (mp3 player, whatever) and start playing around. Put a small resistor inline (to limit the current in case you accidentally short something with something else that wasn't meant to be shorted) with the inputs and start playing if you're that worried about it. Reduce the resistor value (parallel a few or something) until it starts working.

[The Master]

Sounds like a good idea. Ill order some of those chips with my next order from Rapid and start messing with them.

Thanx for your help

[Ioannis]

The LM386 is a low power chip (0,25w@8 ohm, 1w@32 ohm) and has many flavors according to the drive load impedance and power supply. Choose carefully, according to the speakers ohms. Do not choose an LM386 driving 32 ohms if your speakers are 8! You will loose many milliwatts.

If you finally select this one, provide adequate earth on the PCB as this is what cools the chip.

I believe it is not suited for the case... Choose a stronger chip as Luciano suggested.

Ioannis

[The Master]

Hmm, looks like this is about as difficult as finding the correct PIC chip :P

I went back to Rapid's site and found a TDA2030H 14W HI-FI POWER AMPLIFIER (RC). The datasheet says "12W on a 4W load" so im sure that would be enough. The datasheet even gives a PCB layout design (I can read those better than schematics).

Just incase you think theres something better heres the list i have to choose from Audio power ICs. There are more powerfull things on there but i dont want to waste money buying 75W amplifiers for 5W speakers. 20W is probably about right because im not sure exactly what the speakers are