Purrin from Headfi first introduced this idea of modding m-stage's opamp by biasing it into Class A. Michael from Headfonia took it into actions and confirmed the amazing performance of this mod.
This is a very simple mod you can do it yourself at home with some basic DIY tools and common parts follwing the guide below.
However, some people may not have the time or proper tools to make this little magic thing. So I sourced some high quality parts and made some finished adapaters. You can mod your m-stage simply "plug and play", as easy as switching an opamp.
You can also purchase this adapter together with your m-stage amp and request a free installation. I will be happy to send you a modded version of m-stage that you can enjoy the "next level" sound of it out of the box.
3.9K is the recommended value for the resistors. You can also choose other values if you know how it works in this mod. Otherwise, just go with the default.
OPA627BP (DIP) performs better than OPA627AU (SOIC).
This unit is plug-and-play and can replace any dual opamp.
High Quality Materials
Nextron OpAmp sockets from Taiwan
OPA627BP (DIP) x 2 on a class A biasing adapter
Matrix m-stage Class A Biasing | Headfonia
Biasing Op-Amps into Class A | Audiologica