Thank you both for your advices, I know how it will sound, i tried a volume pedal in the loop. It's not the best master volume but it's an easy tonal option (clean phase invertor and lower volume). I'll chek and different pots.
I'm not an electronician, so to mod my amp i'll ask to a technician in my town.
My amp is a reissue not collectible so why not mod it. I tought about a switchable post phase invertor master volume. HamishR advice a 2203 MV that i don't understand the difference with the fx loop placed before phase invertor (i'm not electronician...
). Maybe could you explain me how it works.
I tried the marshall 20W (JCM800 and plexi) and they are really cool but 20w at max is loud too. To be perfect the plexi needs (IMO) a way to manage the output volume, the JCM800 sounds as my 2203 reissue 100w.