Audio Research SP9 MKIII Tube Preamp with Phono

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These ARC preamps are our best sellers.

This particular sample was upgraded to MKIII status at the factory receiving the last round of improvements and upgrades. Cosmetically it benefits with the later designed faceplate featuring rounded corners and removed rack mount holes.

The SP series, as opposed to the LS series, features a built-in phono preamp section for convenient connection to your turntable.

Legendary warm tones, mostly due to tube harmonics, is the signature for these preamps.

In perfect working and great overall cosmetic condition. We've only rated this a 7 for "Physical Condition" due to its age and the fact that we're super conservative.

This SP9 MKIII was also upgraded with an IEC power socket so you can choose your own power cord (stock power cord will be included).

SkyFi Tube Notes:

• This unit was fitted with (2) very well balanced vintage Philips ECG USA marked 6922 tubes.

SkyFi Input Notes:

• The CD player input is fitted with alternate input resistors which decrease its level with reference to the other inputs.
• The phono stage was returned to its stock loading of 500pF 47K

Recommended Cables:

Kimber Kable - RCA Interconnects - Better

Kimber Kable - RCA Interconnects - Best

Kimber Kable - Phono Interconnects - Better

Kimber Kable - Flagship Tonearm Interconnects - Best

Kimber Kable - Power Cords - Better

Kimber Kable - Power Cords - Best

The SkyFi Testing Process for Preamplifiers:

We start with a visual inspection of all internal components to make sure that there are no signs of heat stress or damage. Capacitors are checked for telltale signs of predictive failure including bulging, shrunken wrappers, or physical leakage. We also inspect the PCBs for discoloration from resistors or transistors that may have been running hot. On vintage units we often spot check select capacitors for value and ESR.

When we first power on a preamplifier we connect its RCA output to a Sencore PA81 Power Analyzer which simulates real world loading conditions and gives us an oscilloscope interface. The first order of business is checking that the volume control works smoothly throughout its entire range with acceptable channel balance. This is accomplished by feeding a 1KHz sine wave into one of the preamp’s line level inputs while monitoring the preamp’s output on an oscilloscope. We then switch to a 1KHz square wave to test the tone controls, loudness function, and filters where applicable. During this step we are watching for equal alteration of the test signal by both channels. This also helps us identify dirty controls that will need treatment. Once the basic line stage functions are verified, we test each input individually. This is especially important for devices that use relays to select their sources. If the preamp is equipped with a phono stage we test that as well. We use an inverse RIAA filter which allows us to feed a reference test signal into the phono input with the proper RIAA equalization and level. A square wave or sine sweep is used to verify that the device’s phono stage is faithfully reproducing the RIAA curve. If the preamp under test has balanced inputs and/or outputs these are tested as well.

We finish up our bench testing with a listening test with our bench amplifier and reference speakers. During this test we check for hum or hiss that may not have shown up in earlier testing. We also check that all of the tone controls and filters perform as expected. If the preamplifier has remote control functions these are also tested. Preamps with tube circuits or complicated power supply topologies are connected at our long term test rig for extended stress testing under real world conditions.

Owner's Manual:

https://www.arcdb.ws/Database/SP9/ARC_SP9MKIII_manual.pdf

Details and Specifications:

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)

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 1V RMS input (less than 7µV equivalent input noise). 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: 66dB. High level inputs to tape output: 0dB. High level inputs to main output: 20dB.

INPUT IMPEDANCE

50K ohms line inputs. 40K phono (Phono provisions for any value below 47K ohms or added input capacitance for matching certain magnetic cartridges). 

OUTPUT IMPEDANCE

500 ohms main output. 850 ohms recorder output. Recommended load 60K ohms and 100pF. (20K ohms minimum and 1000pF maximum).

MAXIMUM INPUTS

Phono, 200mV at 1kHz (1000 mV RMS, 10kHz). High level inputs essentially overload proof.

RATED OUTPUTS

2V RMS 5Hz to 50kHz, all outputs; 60K ohm load (main output capability is 50 V RMS output at 1/2% THD at 1kHz 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) 6DJ8/ECC88.

POWER REQUIREMENTS

100-135 VAC 60 Hz (200-270 VAC 50/60Hz) 50 watts max.

DIMENSIONS

19” (48 cm) W x 5 1/4” (13.4 cm) H (standard rack panel) x 10 1/4” (26 cm) D. Handles extend 1 5/8” (4.1 cm) forward of the front panel. Rear chassis fittings extend 7/8” (2.3 cm). 

WEIGHT

13 lbs. (5.9 kg) Net; 22 lbs. (10 kg) Shipping. 

The SkyFi Testing Process for Preamplifiers:

We start with a visual inspection of all internal components to make sure that there are no signs of heat stress or damage. Capacitors are checked for telltale signs of predictive failure including bulging, shrunken wrappers, or physical leakage. We also inspect the PCBs for discoloration from resistors or transistors that may have been running hot. On vintage units we often spot check select capacitors for value and ESR.

When we first power on a preamplifier we connect its RCA output to a Sencore PA81 Power Analyzer which simulates real world loading conditions and gives us an oscilloscope interface. The first order of business is checking that the volume control works smoothly throughout its entire range with acceptable channel balance. This is accomplished by feeding a 1KHz sine wave into one of the preamp’s line level inputs while monitoring the preamp’s output on an oscilloscope. We then switch to a 1KHz square wave to test the tone controls, loudness function, and filters where applicable. During this step we are watching for equal alteration of the test signal by both channels. This also helps us identify dirty controls that will need treatment. Once the basic line stage functions are verified, we test each input individually. This is especially important for devices that use relays to select their sources. If the preamp is equipped with a phono stage we test that as well. We use an inverse RIAA filter which allows us to feed a reference test signal into the phono input with the proper RIAA equalization and level. A square wave or sine sweep is used to verify that the device’s phono stage is faithfully reproducing the RIAA curve. If the preamp under test has balanced inputs and/or outputs these are tested as well.

We finish up our bench testing with a listening test with our bench amplifier and reference speakers. During this test we check for hum or hiss that may not have shown up in earlier testing. We also check that all of the tone controls and filters perform as expected. If the preamplifier has remote control functions these are also tested. Preamps with tube circuits or complicated power supply topologies are connected at our long term test rig for extended stress testing under real world conditions.