Stessa fonte:
The four-pin preamps need a power supply with only +25VDC.
(80-watt Peterson, four-pin connector (early square, later round), FR-7054 Amp. Production ending in 1977.)
The five-pin preamps need a power supply with +15VDC and -15VDC.
(100-watt Hagler, five-pin XLR connector, FR-7710 Amp. Production starting in 1977.)
(Before 1969 they had the Jordan preamp that got +24VDC power via the ring of a tip-ring-sleeve 1/4" jack.)
Ti interessa l'ultimo.
ciao