Audio Research SP-10 (1982)
At 31 pounds and split across two chassis, this preamp doesn’t just demand space—it commands attention.
Overview
The Audio Research SP-10 Stereo Tube Preamplifier isn’t just another high-end tube preamp from the early '80s—it’s the one that redefined what Audio Research stood for. Introduced in 1982, it was positioned as the company’s most-evolved, top-of-the-line preamplifier, a dual-chassis statement piece built for those who refused to compromise. Its two-box design—separating the signal stage from the power supply—wasn’t just about aesthetics; it was a deliberate engineering choice to minimize noise and maximize regulation, setting a benchmark for clean, dynamic tube performance. At $3,450 when new, it was a serious investment, squarely aimed at the upper echelon of audiophiles who valued transparency, holographic imaging, and a soundstage that could fill a room with precision.
Owners report it delivers exactly that: an "amazingly holographic 3-D soundstage and images" that few contemporaries could match. The phono stage, in particular, earns near-reverent praise—after 22 years of use, one owner claimed to have only heard two or three preamps (Hovland and CAT) they’d prefer for vinyl playback. That said, the line stage is considered by some to be less exceptional, with the suggestion that it "can be improved upon," especially when paired with modern sources. Still, when mated with an Audio Research power amplifier—tube or solid-state—the synergy is reportedly transformative.
But this is no plug-and-play relic. The SP-10 is known to be finicky, especially in its phono stage, where tube selection becomes a near-obsessive pursuit. Finding 7308 tubes (a premium variant of the 6DJ8/6922) that are quiet, non-microphonic, and durable enough to handle the circuit’s demands has proven so difficult that one Vice-President of Gold Aero reportedly went through 80 tubes to find two acceptable ones. A well-selected EH6922, however, is said to be a viable and sonically satisfying alternative—quiet and robust enough to survive long-term use.
Specifications
| Manufacturer | Audio Research |
| Product type | Stereo Tube Preamplifier (Two-piece design) |
| Original price | $3,450.00 |
| Frequency Response | 5 Hz to 30 kHz, ±0.25 dB; -3 dB below 1 Hz and above 100 kHz |
| Maximum Output | 60 V (into high impedance) |
| Harmonic Distortion | 0.01% at 2 V rms output, 20 Hz to 20 kHz; mid band, typically 0.002% |
| SMPTE and IHF IM | 0.002% at 2 V rms equivalent |
| Input Sensitivity | Phono (MM or MC), 0.125 mV; high level, 35 mV |
| Phono Overload | 300 mV at 1 kHz; 1V at 10kHz |
| S/N Ratio | Phono (MM or MC), 86 dBA; high level, 90 dB below 1-V in |
| MM Phono Input | Capacitance, 40 pF; impedance, selectable, 10, 30, 100 ohms, 10 or 47 kilohms |
| Dimensions | Two pieces, each 19 in. (48.3 cm) W x 5 1/4 in. (13.3 cm) H x 10 1/4 in. (26 cm) D, plus 15/8 in. (4.1 cm) forward extension for handles and 7/8 in. (2.2 cm) projection for rear fittings |
| Weight | 31 lbs. (13.9 kg) |
Key Features
Two-Box Design with Dedicated Power Supply
The SP-10’s dual-chassis architecture is central to its performance. The preamp and its separate power supply both occupy standard 19-inch rack widths, connected by a 1-meter cable fitted with gold-plated "aircraft type" connectors. This physical separation isn’t just about heat management—it’s a strategy to isolate sensitive signal paths from power supply noise. The interconnect cable ensures a robust, low-resistance link, preserving signal integrity across the divide.
6DJ8-Based Signal Circuitry with Cascode Stages
A significant departure from earlier Audio Research models, the SP-10 abandons the 12AX7 in favor of 6DJ8 dual triodes (marketed as 6922 or 7308 in premium forms). The signal path is divided into two main blocks: the phono preamp/equalizer and the output amplifier. The phono stage uses both elements of each 6DJ8 in parallel, increasing headroom and lowering noise. The second stage employs a cascode configuration—combining a grounded-cathode amplifier below with a grounded-grid amplifier above—for exceptional bandwidth and linearity. This stage feeds directly into a cathode-follower third stage, minimizing phase shift and capacitive loading.
Elaborate Power-Supply Regulation
Power-supply design in the SP-10 is described as more elaborate than any other preamp of its time. The high-voltage supply begins with a full-wave bridge-rectified 550 V d.c., filtered through 100 µF capacitance. A hybrid high-voltage regulator then delivers a stable 305 V d.c. using two triode-connected 6L6 tubes in parallel as the series-pass element, backed by a 12AT7 for control. For the tube heaters, two dedicated transformer windings feed individual bridge rectifiers and filter capacitors, regulated by six three-terminal TO-3 power regulators to ensure low-noise, stable 6.3 V operation.
"Wonder Cap" Polypropylene Capacitors
Signal path integrity is further ensured by the use of "Wonder Cap" polypropylene coupling and bypass capacitors. These components, known for their low dielectric absorption and superior sonic performance, were a hallmark of high-end Audio Research designs. Their inclusion in the SP-10 contributes to the preamp’s reputation for clarity, transient speed, and absence of coloration.
Phono Input with Selectable Impedance
The MM phono input offers selectable impedance settings—10, 30, or 100 ohms, and 10 or 47 kilohms—allowing users to fine-tune cartridge matching. Capacitance is fixed at 40 pF, a value chosen to work well with most moving-magnet cartridges of the era. The phono stage’s overload margin is generous: 300 mV at 1 kHz and 1 V at 10 kHz, suggesting robust handling of dynamic transients.
Historical Context
In 1982, the SP-10 arrived as Audio Research’s flagship, representing the culmination of their tube preamp development. By 1984, it was directly competing with high-end rivals like the Convergent Audio Technology MC-7. Reviewers at the time noted the SP-10 had "a faster and more dynamic way with music," though with slightly less extended bass. It was praised for superior ergonomics and styling compared to its competition. In 1987, Audio Research's preamp lineup included the SP8/II, SP9/I, SP11/I, and SP10/II, with the SP-10 having been the flagship model introduced earlier. It was reviewed in both Stereophile and The Absolute Sound, cementing its status among the elite.
Collectibility & Value
The SP-10 is widely regarded as a classic, even described as "THE HOLY GRAIL" in some listings. Current market prices vary wildly: one listing shows $4,895, while another—possibly reflecting condition or modification—is marked down from $1,279.99 to $399.99. These discrepancies suggest that condition, tube complement, and service history heavily influence value. Given its age, potential buyers are cautioned: one user on Audio Asylum was advised against purchasing an SP-10 because it was "nearly 30" years old at the time. Maintenance is non-trivial—finding quiet, reliable tubes for the phono stage remains a challenge, and repairs should be entrusted only to technicians with "Special Audio Research experence," as one owner urgently sought. Modifications exist, and DIY clones have been attempted, but the original remains a sought-after benchmark.
eBay Listings
As an eBay Partner, we earn from qualifying purchases. This helps support our independent vintage technology research.