The T-Rex Engineering Compnova Compressor is a pedal designed for use with electric guitar, but can be used with any electronic instrument.  It has 1/4 inch connections and is powered by the power supply that comes with it.  The pedal is quite easy to use as it only has three different parameters - one for compression level, one for attack, and one for overall output level.  I've used a lot of different compression pedals out there that have been designed for electric guitar, and the T-Rex Engineering Compnova Compressor is one of my favorite ones because of its ease of use and top notch sound quality.  You can get a bunch of different types of compression tones with this pedal including more subtle compression and really heavy and crunchy compression.  Over the last year or two I've become a big fan of T-Rex Engineering because they offer great sounding pedals that are put together well and are always reliable.  The T-Rex Engineering Compnova Compressor is no exception to this rule as it has a great sound to it and I can't imagine this thing breaking unless you were to throw it at a wall or something.  When compared to other guitar compression pedals like the Boss CS-3 and the MXR Dyna Comp, the T-Rex Engineering Compnova Compressor sounds just as good if not better and definitely offers more tone control when compared to the Dyna Comp.  The price of the T-Rex Engineering Compnova Compressor is more expensive than those pedals, but with good reason as it is made better than those.  If you are looking for a compression pedal for your guitar, the T-Rex Engineering Compnova Compressor is more than adequate but I would encourage those interested to check out all of the pedals I mentioned as they all have a time and place and you need to determine what will work best for you and your sound.