The Java Boost is a germanium based Treble Booster designed to give you classic tones from the 60's and 70's. It is not a clean boost.
It must be used with a cranked amp that is overdriven or distorting a bit already. Cranking the amp and pedal will result in more creamy, beautiful, sustaining distortion with the Java Boost.
The Java Boost is most widely used with a tube amp set to a bit of overdrive or clipping which is the key to getting a great sound from this pedal. Setting the java boost in front of a very clean amp with the volume on 1-2 will surely result in a fairly weak guitar tone! Set the amp for some breakup, then click the Java on. There, you'll have a fantastic sound and see why people rave about the Java Boost.