Audio Amplifier

[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?

[Luciano]

Hi,

(Philips Semiconductors)

TDA1558Q
2 x 22 W or 4 x 11 W single-ended car radio power amplifier

Datasheet: (See page 9).
http://www.nxp.com/acrobat_download/...558Q_CNV_2.pdf

Digi-key price: USD 5.50
Quantity Available: 552

http://search.digikey.com/scripts/Dk...=568-3508-5-ND

* * *

UK RS Components Ltd

RS Stock No. 182-7834
RS price: £3.76

Best regards,

Luciano

[skimask]

Do you know what the output impedance of your sound card is? Does it really matter?
Are you going to use AC coupling or DC coupling?
If you don't know what any of the above, you might want to get to some researching before you blow something else up! (ie. sound card outputs, amp inputs, etc).
Other than that, put the volume controls in there, play with them, get it all working, play with it after that, make it work good for you, remove what you think you don't need and go with it. You really can't go wrong starting small and working your way up.

[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?