Peavey Century 120 Distortion?

Sep 20, 2018
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I got a Peavey Century 120 today and I'm kind of confused about the distortion. When I turn up the distortion I can still hear the clean sound blended in. It's very obvious and annoying especially because I also like using this head for guitar. Is this just how the amp is or is something wrong? Also I heard that the distortion knob at 0 isn't the same as turning the distortion off with a footswitch. Can I use any footswitch for this?