I don't understand how the effects balance knob works. It seems that only in dual send/return modus I'm able to adjust the balance. In serial mode turning the effects balance knob either left or right seems to kill all effects. Why does this happen?
The effects balance knob adjusts the balance between the Effects Engine and the Reverb Engine. Maximum effect from both Engines is achieved at 12 o’clock position.
When using the M300 in serial routing mode, you should therefore leave the effect balance knob at 12 o clock. It is important that you leave the mix knob in the middle. Turning the FX balance knob either left or right will either decrease the output volume or cut the output entirely.
In dual/send return routing, you can use the FX balance knob to adjust the balance between the effect and reverb engine. That way you can choose how much signal from each engine you want to return to your mixer.