While many users of Nikko components say their preamps are nothing special and their amps are better built, I have observed the contrary. I think that they had their best preamp on their Beta 1, followed by Beta 20 with nothing close to being a third best. Their amps side probably was the same, Alpha I being their best, and the second best, this side of the gear category, being a far Beta VI.
My gears of Nikko are :
Beta 600 preamp (all Mitsubishi opamp inside)
Beta 20 preamp (mostly discreet circuitry, with tone circuit being on two opamps, MM and MC)
Beta 1 (only MM and line, but all FET and transistors inside. Also, best built pcb among their Beta line)
Alpha 220 X 3, 230 X 1, 440 X 1 (the 220 had best components incl wires inside, otherwise the 230 is the same. The 440 had big output but all these amps have discontinued drivers and outputs. So pray these won't smoke at start up!!)
I think I like their Beta 1 the best. It sounds so so not like all the other gears listed up here. It has body in its delivery and low distortion, Also the stage depth is the best, almost holographic if you close your eyes and attentively listen. I opened it and found 6 FET pairs with 6 other transistor pairs in its phono, line and tone stages, respectively. I pray they won't go bad or, I may not be able to repair it coz they do not exist as of now, not even on eBay.
My .2 cents
Terence