Clean Smile ZIMcard is a very transparent, tube-like overdrive that lets the sound of your pickups shine through. It produces a mild crunch with clean bass and treble and no mid hump. Also works well as a moderate gain clean boost. Cleans up well with your guitar's volume knob. Feel the thump of the low E string, and hear fingers rub against the high strings. All of your sound comes through. Very similar to VT, but with more inherent gain and a slightly different voicing. If you want a transparent overdrive and VT doesn't quite do it for you, you should try CS.
