maki wrote:it is near pump, externally. as I installed it for testing the idea - it works. do I need it? not sure, as I am not a big fan of light roast.

Which model of needle valve did you use, this one? I love light roast when brewed as V60 and similar methods, but seldom use it for espresso at home due to excessive acidity. If a Slayer-style needle valve bypass circuit could help with that, I'd probably buy a whole lot more light roasts...

i'm using this, because it was easy to source it locally. i would suggest asking someone who's in your region for an easily available part.

So I've thought up another interesting option: Keep the GS/3 3d5, but replace the current AV firmware with the MP version instead (assuming the boards themselves are identical). Hmm, what to do...