SP-9 MKII (1991)
Technically, the Mark II version of the SP9 preamplifier includes a group of 14 different improvements, utilizing 61 component and wire changes. These combine to provide enhanced reliability and flexibility, in addition to the sonic improvements.
– In the CD unit the gain has been reduced by 12 dB, allowing operation of the gain control in its mid rotation or high positions, while still leaving all other inputs with normal gain for lower input program sources.
– Low-level hum in the line section is reduced 10-20 dB, which is noticeable primarily in systems with high-efficiency speakers, small “live” rooms, high-gain power amps, or low-noise CD program sources.
– The power supply and phono sections are “beefed up” to prevent accidental damage if a CD source is mistakenly connected to the MC phono inputs and is played at a high level, even with the mute on.
SP-9 MKIII (1993)
The technical improvements are numerous, and include the liberal use of M.I.T. capacitors in critical input and output locations; additional filter and bypass capacitors for the power supply; a new input circuit board that reduces point-to-point wiring and improves overall grounding; new gold-sleeved tube sockets for better corrosion resistance and lower noise; new 6922 dual triode tubes; and improved high voltage regulation. New units also have the new, thicker front panel and handles, while these are optional on updated units. Note that only MK II units can be upgraded to the MK III standard; earlier units must first be upgrade to the MK II level.