What is the purpose of the amplifier? Impedance-matching? Current amplification? Voltage amplification?Impedance matching and current amplification is the save thing so a bit of all of them.Is the ringing around the rise and fall expected? Could it be improved somehow?It is due to the inductance of the speaker, it can be improved by a better transistor or amplifierAre there any "gotchas" in there? Like, drawing too much current through the transistor, or something?Yes it is quite a simple amplifier. I would include a 0.1uF cap between the pin input and the amplifier input.If I wanted to implement a volume control, what would be the recommended way of doing that?Put a pot directly on the output and connect the wiper through a cap to the input.Is the purpose of the 100K resistors to bias the transistor base?YesWhat is the purpose of the 10 ohm resistor? To limit current?YesIs the purpose of the 2.2K resistor for impedance-matching?No, it is isolating the bias circuit from the DC effects you get from the input pin, that is why I would use a cap because that removes it compleatly
The BC337 is a transistor that can handle 800mA.
The BC546 can do 100mA, and this circuits requires 278mA.
I built up the audio amplifier from the Arduino Basic Connections thread (http://arduino.cc/forum/index.php/topic,154549.0.html) in particular this:
But there is a much more serious problem with this design, namely that there will be a constant dc-bias on the speaker and a non-trivial amount of dc-current continually running through it.
Thanks for the comments everyone!Quote from: oric_dan on Apr 01, 2013, 08:30 pmBut there is a much more serious problem with this design, namely that there will be a constant dc-bias on the speaker and a non-trivial amount of dc-current continually running through it. Why is there that current (which incidentally the scope trace appears to agree with)?If the transistor is "off" it shouldn't be conducting, should it? Or does the biasing keep it on? I guess it must be that, because on the scope it looks like when the input signal is off, the output signal is around 2.2V.