When you need to amplify, filter, add, or otherwise manipulate analog signals you'll certainly want an operational amplifier at your side. This is our favorite hobby op-amp, which we use in our kits! Great for amplifying audio, conditioning sensors, buffering analog signals, etc.
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It's DIP package so very easy to work with on a breadboard or perfboard. It has two amplifiers inside. It can run from voltages as low as 2.7V and up to 6V. It has rail to rail input and output, which is a common problem for beginners who don't know how to bias op amps (cheaper op-amps such as the LM358 can't handle a full range of input voltage!) 6 MHz gain bandwidth & 1.6 V/us slew so you can drive fairly fast signals. Best of all it has a beefy output that can push up to 80mA, so you can drive small speakers and headphones directly.