I have had one of these units for about two years now in my system. I've had a lot of gear come and go since then. As an avid tinkerer and someone who repairs and modifies and has designed circuits I'm fairly blown away by the transparency and musicality of this circuit. I have no problem hanging this unit onto the end of a fairly highly resolving DAC but I have run into problems with the 10k input loading on tube output stages whose impedance doesn't like to be loaded that heavily. In most applications it's not a problem like a DAC or CD player with low Z output. It tends to breathe life into some drier sounding circuits without reducing a shred of transparency. I have replaced caps, resistors and tubes but that's because I can't help myself. The GE 5670 JAN version is a no-brainer and is readily available cheap. WE 396A is even better but good luck finding them and to be honest the improvement of the GE over the Chinese is night and day and very close to the Western Electric. I get the problems pointed out in an earlier comment with the feedback loading with the output volume being hung on the second gain stage plate but I don't use the unit as a pre-amp (it isn't a buffer either since technically it's the opposite) so I have the output fixed. I think it's the simplicity of the circuit that doesn't take away much, it's quiet, doesn't intrude on dynamics (actually creates a sence of punchier dynamics with tighter bass, doen't rob the high end air and adds sparkle to cymbals and fills out vocals with a sprinkle of richness commonly associated with much higher end preamps. It's realy quite a marvel when implemented correctly.
