Audio Research SP8 Vintage Tube Preamplifier - Serviced
This is the first SP-8 to come through our shop. Unlike the LS series, the SP has a desirable built-in phono section perfect for those vinyl lovers that want to keep things simple.
We took our time and got this beauty up to spec by doing a bunch of work listed below.
We also have several matching ARC tube amps that would go nicely with this pre.
Condition is very good with light signs of use. Super clean faceplate and featuring a good rust-free chassis.
Working perfectly and ready to go for another decade.
• This preamp was fitted with a mix of balanced Sovtek and RAM branded tubes.
• Select power supply axial capacitors replaced
• Line and Phono stage circuit JFET's replaced
• Power on timer IC replaced and power on delay timer increased from approximately 60 seconds to 120 seconds.
• Power switch replaced
ARC Service Note 5 Performed: R27 removed from both channels which reduces the overall gain by 10 dB, offering better volume granularity when using systems with high efficiency speakers.
If you would like the 0 dB factory gain level restored please contact us before making your purchase.
Vintage Equipment Power On/Off considerations:
• This preamp has a power-on "thump" that occurs after the turn-on delay. This can be easily avoided by starting the unit with mute/operate control in the mute position. Wait 2-3 minutes before turning on your power amplifier, then flip the SP-8 into operate mode.
• Likewise, at power off, it is best to follow the practice of turning off your power amplifier first, and then the SP-8 preamp. Setting the unit from operate to mute before power off is also suggested.
• The turn on / off "thumps" are especially apparent when using solid state amplifiers with direct coupled (DC) designs. This preamp is best suited for use with tube based power amplifiers.
Click below to add our recommended matching cables from Kimber Kable, all brand new as SkyFi is an official Kimber dealer.
Kimber Kable - RCA Interconnects - Better
The SkyFi Testing Process for Preamplifiers:
We start with a visual inspection of all internal components to make sure there are no signs of stress or aging. Capacitors are checked for telltale sings of bulging or leaking, resistors are checked for signs of overheating or cracking, and transistors are checked for signs of stress or damage. Special attention is paid to the power supply which is the most common source of failure for preamps. We then power up the unit and run a simple 1k sine wave while monitoring the low voltage output on an oscilloscope for signs of distortion or noise to get a baseline.
At this point we will lubricate and clean all switches and potentiometers (that are not sealed) with a high quality contact cleaner, and then re-test all functions for any signs of noise or scratching.
Final testing involves putting actual music through the preamplifier. We have learned over time that some issues are only noticeable to a trained ear while listening to a familiar source material. Our test bench has reference vintage KEF speakers that we are super familiar with which will quickly reveal any discrepancies. Some preamps will then move into the listening room where they will be tested with our in-house reference system.
High level section: ±.25dB, 5Hz to 30kHz. -3dB points below 1Hz and above 100kHz Magnetic phono: ±.25dB of RIAA, 30Hz to 40kHz
Harmonic distortion: Less than .01% at 2V RMS output, 20Hz to 20kHz (Typically less than .0005% in midband) Intermodulation distortion: Less than .002% at 2V RMS output
NOISE & HUM
High level: (1) 250µV RMS maximum residual unweighted wideband noise at main output with gain control minimum (86dB below 5V RMS output) (2) More than 90dB below 1V RMS input (less than 20µV equivalent input noise)
Magnetic phono: 5µV equivalent input noise, wideband RMS (-66dB reference 10mV input) (Approximately 1µV above 200Hz or -80dB reference 10mV input)
Magnetic phono input to tape output: 34dB
Magnetic phono input to main output: 60dB
High level inputs to tape output: 0dB
High level inputs to main output: 26dB.
50K ohms, all inputs (Magnetic phono may have any value from 10 ohms to 100K ohms substituted. Also has provision to add to the 40pF input capacitance for matching certain magnetic cartridges.)
1000 ohms main output and tape output. Recommended minimum load for maximum audio quality 20K ohms and .001µF maximum capacitance.
Magnetic phono, 900mV at 1kHz. (3.5V RMS, 10kHz)
High level inputs essentially overload-proof
2V RMS 5Hz to 30kHz, all outputs; 60K ohm load (main output capability is 60V RMS output at ½% THD at 1kHz into 100K ohm load with 3V RMS high level input)
Electronically-regulated supplies utilizing both vacuum tube and solid state elements. Line regulation better than .01%
SP-8 MKII: (2) 12AX7, (2) 12AX7, (2) 6922, (1) 12AT7, (1) 12BH7
100-125VAC 60Hz (190-240VAC 50Hz) 60 Watts
19" (48 cm) W
5-1/4" (13.4 cm) H (standard rack panel)
10-1/4" (26 cm) D
Handles extend 1-5/8" (4.1 cm) forward of front panel.
Rear chassis fittings extend 7/8" (2.3 cm).
22 lbs. (10 kg)
Net: 30 lbs. (13.75 kg) Shipping
Yes - Power Only
7 / 10
10 / 10