audio research

Hybrid tube/FET stereo preamplifier.



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.

Remote control $500 (1994)

MSRP (US new retail)
$1,795 (SP-9 MKII)
$2,495 (SP-9 MKIII)



Frequency response High Level Section: ±.5dB, 5 Hz to 50 kHz, - 3dB points below 1 Hz and above 200kHz.
Phono: ±.3dB of RIAA, 30Hz to 40kHz.
Distortion (THD) Less than 0.1% at 2V RMS output. (Typically less than 0.005% in midband)
(SP-9: < .01% @ 2V RMS output 10Hz to 30kHz )
Noise & hum High Level: (1) 70 µV RMS maximum residual unweighted wideband noise at main output with gain control minimum (98 dB below 5V RMS output). (2) More than 100dB below 1 V RMS input (less than 7µV equivalent input noise)
(SP-9: Phono IHF weighted 72 dB below 1 mV input)
  Phono: 0.12 µV equivalent input noise; IHF weighted, shorted input (78dB below 1 mV input).
Gain Phono input to tape output: 46dB
Phono input to main output: 67dB (SP-9: Phono 66dB (RIAA ±.25 dB)
High level inputs to tape output: 0dB
  High level inputs to main output: 21dB
  CD input to main output: 9 dB
Input impedance 50 k ohms line inputs
  47 K phono (Phono provisions for any value below 47K ohms or added input capacitance for matching certain magnetic cartridges)
Output impedance 250 ohms main output
  850 ohms recorder output
  Recommended load 60K ohms and 100pF. (20K ohms minimum)
Output polarity  
Maximum inputs Phono, 200 mv at 1kHz (1000 mv RMS, 10kHz)
High level inputs essentially overload proof
Rated outputs 2 V RMS 5 kHz to 50 kHz, all out-puts; 60k ohm load (main output capability is 50 V RMS output at 0.5% THD at 1 kHz into a 100K ohm load with 5V RMS high level input)
Power supplies Electronically–regulated low and high voltage supplies and electronic decoupling. Shielded toroid transformer. Line Regulation better than .01%.
Tube complement (2) 6922
Power requirements 100-135 VAC 60 Hz (200-270 VAC 50/60Hz) 55 watts max
Dimensions 19” (48 cm) W x 5 1/4” (13.4 cm) H (standard rack panel) x 10 ¼” (26 cm) D. Handles extend 1 ½” (3.8 cm) forward of the front panel. Rear chassis fittings extend 7/8” (2.3 cm).
Weight 12 lbs. (5.5 kg) Net; 21 lbs. (9.5 kg) Shipping


Issue 50 (SP-9: Full Review), Issue 52 (SP-9: Further Thoughts)
Vol. 10 No. 8 (SP-9), Vol. 13 No. 11 (SP-9 MKII), Vol. 14 No. 6 (SP-9 MKII)