Ericksquivel

Hello my name is erick and i have the same problem! My spider iv 75 doesnt work very great in less of 25% of the full master volume. When im playing the sound just goes down and doesnt come back till i move the knob up but it doesnt happens all the time, sometimes it just stays very low for a couple of minutes and when im playing live is very annoying cause the sound goes up suddenly. I dont know what to do i checked with the channel volume and with the master volume and its the same. I hope someone could help us soon.