I'm still a relative beginner - I've just bought a Boss Katana 50 amp but still have a cheap guitar which was gifted to me (yamaha erg121). I've been trying to get better sustain for playing long sounding power chords for rock / metal. Despite turning both the gain & booster knobs up to high on the amp, I cannot get a decent level of sustain for power chords. Anyone got any ideas for best amp setting for good sustain? I suspect it might be just down to cheap pick ups on the Yamaha ( I am using the humbucker in the bridge position). I will be looking to upgrade the guitar in the near future (something like an Epiphone Plus Top Pro). Hopefully a better guitar will improve the sustain but very grateful for any advice in the meantime regarding amp settings on the Katana.

Thanks to anyone who can respond.