Audio Amplifier

[The Master]

Hi, I plan to make a 4 chanel audio amplifier. Im not going too fancy, no volume control etc. I just want a PCB with 4 phono inputs and 4 speaker outputs. The inputs will be from a PC's soundcard and the speakers i have i think are about 5W. The speakers are for my pinball machine (yep, back on that project for a while).

Ive not really done anything with audio before. Google finds a lot of schematics but they are all different and im not sure what would be best so my question really is where do i start learning about these kind of circuits?

[skimask]

IMO - LM386 (or maybe LM383)...simple, capable of a few watts, popular, cheap...
I've also used NE5532, same deal, not quite as powerful.

[The Master]

Ive just been looking at the Rapid website and ive found something interesting. Aparently its a 20W audio amplifier inside what looks like a 5 pin triac. There are a few circuits in the datasheet. Could it really be as simple as the diagrams on pages 2 and 3? I hope the one on page 6 (labeled page 5) is whats inside this thing and not the circuit i would have to build.

[The Master]

Sorry, was replying at the same time as you.

Rapid actually have LM386M-1 and LM386N-1 on the same page as the one ive just been looking at and it seems to be pretty much the same thing but cheaper The diagrams actually look simpler too.

What exactly is the gain? Is that how many times more you get out than what you put in? Is it Volts or Amps or both?

Edit: It appears that the N and M determine the package type. Looks like i best get N. Ive already made that mistake once :P

[skimask]

There are a few circuits in the datasheet. Could it really be as simple as the diagrams on pages 2 and 3? I hope the one on page 6 (labeled page 5) is whats inside this thing and not the circuit i would have to build.

You'll notice the schematic on page 2 is a double ended supply (+v, -v, grnd) whereas the one on page 3 is a single ended supply (+v and grnd).

And yes, the one on page 6 is the internal schematic.

[The Master]

This suddenly seems a lot easier. Everything i found while searching google looked like that huge schematic and used a lot of transistors that Rapid doesnt stock.

I just read in the datasheet for the one you suggested that its "Voltage gain"

The one i was looking at before said you have to use a heatsink because it can overheat without even doing anything. I dont see any mention of heatsinks for this one at all though. Are they needed?

[skimask]

This suddenly seems a lot easier. Everything i found while searching google looked like that huge schematic and used a lot of transistors that Rapid doesnt stock.

I just read in the datasheet for the one you suggested that its "Voltage gain"

The one i was looking at before said you have to use a heatsink because it can overheat without even doing anything. I dont see any mention of heatsinks for this one at all though. Are they needed?

You'll find that these cheaper op-amp's aren't really brain surgery. You can beat them up quite a bit. They'll take it.
Don't worry too much about the gain. That's what the volume knob is for! When the speaker distorts, better back off.
And yes, heatsinks...Don't run without at least something on there. If I remember right, the chip has a thermal overload shutdown, but don't count on that saving the chip.

[The Master]

Ok good point, the first one i looked at had internal thermal cutout on it so this one probably does too. Ill make sure to get heatsinks just incase though.

Volume control isnt really a problem. I want the amp to be turned up as high as possible (without causing distortion) then turn the volume up and down on the PC that controls everything.

Are these chips safe to run directly from a PC? The diagrams for the LM386 show a variable resistor between the input and the chip. Since i dont want volume control can i just remove that completely or does there need to be some kind of resistor or protection device in place?