Channel A is relatively tame - on its own, it's a nice up-front sounding light overdrive. Perfect for driving Ch B for a lead boost. Compared to other overdrives, it has a slightly extended low end and high end, and the clipping characteristic is slightly uneven, but not fully asymmetrical.
Channel B is a more crisp and transparent overdrive with full low end and lots of available gain. Compared to other overdrives, it has a more extended high end and low end, and the clipping is perfectly symmetrical. Channel B also passes through the voicing circuit, so any blanket description of it's tone is really invalid once you start turning the voicing knobs.
The idea of Channel A is to give a light overdrive sound on it's own, and to cascade into B for added gain. The idea of Channel B is to act as a more aggressive and cleaner sounding overdrive, providing the voicing circuit with the best frequency range to work with. Once you cascade the channels and the voicing circuit gets a hold of it... forget about it - you're in the ZIM ZONE.
When you look at ZIM, what you're really looking at is a modular, dual channel true-bypass mainframe with a voicing circuit on Channel B. Since all of the overdrive circuitry is located on the ZIMcards, the operation and entire sound of ZIM can be changed by swapping out the cards.
ZIM with Bottom Removed:
ZIM with Both ZIMcards Removed:
ZIMcards Outside of the ZIM:
ZIMcard Being Installed: