Hi Everyone,
I think this problem with the Spider IV 75-150 Watt series has been reported before. I recently upgraded the firmware on my Spider IV head (2015 model) with the Spider FX infusion 2.0 update. The added effects are great ! Many come from the new Spider V. But I can't say that the problem I've encountered is due to the update.
I use my Spider IV 150 Watt head, FBV Shortboard MK II, and classic Line 6 4x12 cabinet at home at relatively low volumes, rather than a performance situation.
Occasionally, with some presets that I have created or downloaded, if I turn the gain/auto/pitch knob to off (FX1), and then turn it back on (the light will go from yellow back to green), the amplifier volume and/or gain will become uncontrolled and "pinned" to a very high volume level. I can't clear the condition, except by powering down the head, waiting for 15 or so seconds and then powering back up. This is a very dangerous (potentially ear-splitting !) situation. On stage it would be a disaster.
For electrical/audio engineers, its akin to the feedback loop on a high gain amplifier going "open-loop", that is, uncontrolled and pinned at the maximum gain. I can't tell whether this is a mechanical problem, like a "noisy" potentiometer, or a code problem with the firmware or operating system in the Spider IV series.
Anyway, be aware, have the power strip close to your foot if you are experiencing this problem.
Thanks,
Mark