ISU Audio and Arduino Clubs

Altoids amp project - FAQ

Some questions and answers

• Is the Altoids tin necessary?
  Nope. It is just for fun. The PCB should be put into some kind of case to protect it from possible damage or accidental short circuits, but any kind of enclosure will do.
• Are 9-V batteries essential? Those things are expensive and don't last very long.
  Nine-volt batteries are not essential. Any sort of bipolar supply that provides ±5 V or more should work. The batteries are convenient and provide easy portability. I strongly recommend using rechargeable batteries. They are not terribly expensive and will last forever (probably).
• Can this amp drive a set of speakers?
  No. If you connect a pair of external speakers, some sound will come out. But standard op amps cannot provide enough output-current drive to produce very loud sound without serious distortion. The output current for a standard op amp is purposely limited to about 20 mA or so, which might produce 3 mW of electical power into the speaker and a lot less acoustic power coming out. Pushing the op-amp current beyond the limit will make for a very distorted signal and very bad sound. To drive a set of speakers, the amp will need an output-current stage, as done with the little GTDT amp.
• Are the LEDs essential?
  No. Almost all of our Audio- and Arduino-Club projects include "power on" LEDs to indicate that the batteries are sufficiently charged or the power supply is plugged in. They do use a small amount of power. They can certainly be omitted if you don't care about having power indication — the rest of the circuit will work just fine.