1, What's different between NFB-2.1 and NFB-3.1?
The main differences are as follow:
1, The NFB-3.1 applies 2 groups of class A parallel connection PSU supplied for analog output stage, (the analog output stage power supply is very important, so we keep the 2 groups of class A parallel connection PSU here). Another 5 groups of linear PSU's supplied for other parts.
The NFB-2.1 applies 6 groups class A parallel connection PSU for the whole gear, and 1 linear PSU for the control parts.
2, The NFB-3.1 applies a toroidal transformer, the NFB-2.1 applies an R-core transformer.
3, The NFB-3.1 applies mostly 1% SMD resistors and caps, the NFB-2.1 applies mostly DALE resistors and WIMA caps.