Yet another question about an 8ohm speaker and volume

What is wrong with this particular setup here?

Dozens of things. For a start, the person who drew that has put the transistor on the wrong side of the speaker (you need a PNP where he put it). That’s probably the only thing saving him from dumping 600mA through the speaker and making it a race to see which dies first…his USB port or the speaker.

Hi, Crossroads, the two hand drawn diagrams you posted. The one on the left with the cap in series with the speaker to supply, how is it going to discharge each time the transistor turns off? All the circuit will do is charge up the cap, so current will flow through the speaker at first, then with no place for it to discharge, no current will flow, no speaker current, no noise. Second diagram has a charge and discharge path so current will flow through the speaker in both directions.

Tom..... :)


synic: I think I just need to get some sort of electronics bible. Every time I think I might be getting somewhere, there's so much more I wouldn't even consider.

I will find a book to buy, read it, and come back if I have more questions.

It won't help.

I agree. It seems electronics is one of those fields you could spend the rest of your life learning, and still feel like you're only just beginning to understand. ;)

My approach: Just dive in. Keep it simple and add new things as you start to understand them. Once you have a little practical experience, you'll get more out of the things you're told and read about. It starts to stick eventually.



synic: I will find a book to buy, read it, and come back if I have more questions.

It won't help.

I agree.

The idea that there's a magic book out there that will suddenly make everything clear is a myth.

Take it one project at a time and use the Internet a lot.

@TomGeorge, Hmm, you may be right, I'd have to wire it up & try it. The 2nd one on the lower right I know works, I use that but with a MOSFET from a 12V source to drive a speaker in my fencing scoring machines.

synic: Ah, I've actually seen your diagram, but someone told me "no base resistor is a bit meh". I have no idea what he meant.

No base resistor is fine for a Class AB push-pull amplifier, since the emitters are connected to the load which will limit the current. It's just when using a transistor as a low-side (NPN) or high-side (PNP) switch, with the emitters connected straight to ground or power, that you need a base resistor to limit current.