Is this the right one https://www.musikding.de/Stage-3-Booster-kit
Ok, if this is the one, I don’t get it which switch is for phase correction because SW1 is intended for bass guitar if I understand right.
<div>This in instructions: SW1 is a bass ready switch which allows you to add more bass frequencies. If you don’t wish to play bass, don’t install C3 or SW1.</div>
<div>I would like to have simple SPDT switch for turning boost off or on, not 3PDT…</div>