 However, the loop was placed between two critical gain stages, and tended to overdrive some instrument level effects, and also caused volume pedals to act as remote gain controls for the lead mode.Mesa later implemented a mod that caused the effects loop to become more transparent, and smoothed out the lead channel, similar to the IIC+'s lead channel.More importantly, it marked the introduction of Mesa/Boogie's "Simul-Class" system, where two of the power tubes (always 6L6s) run in class AB pentode while the other two tubes (either 6L6s or EL34s) run in class A triode.