Audio Research SP-11 (1985)
A two-box hybrid preamplifier from the midpoint of Audio Research's shift toward neutral, transparent sound.
Overview
The Audio Research SP-11 is a high-end preamplifier that appeared in 1985. It sits between the fully tube-driven SP-10 and the more solid-state SP-9 and SP-14. It is a hybrid, with vacuum tubes and transistors in the same circuit, and the aim was clarity and depth without the listener fatigue often blamed on solid-state gear. At the time it was considered one of the most complex preamplifiers ever released. It won over many new audiophiles. Some traditionalists criticized the global feedback and the high parts count.
Design
The SP-11 is a two-box preamplifier, with the main power supply in a separate chassis. The supplies are triple-regulated. Each amplifying stage uses a hybrid gain block built around a 6DJ8 triode, a power MOSFET, and one or two JFETs. The triode acts as the load for a P-channel JFET in a cascode-like arrangement. A MOSFET source follower comes after that to lower the output impedance. The valve provides all the voltage gain, and the transistors run at unity gain. Feedback from the output to the valve grid through a voltage divider sets the stage gain. The line section adds an N-channel JFET ahead of the gain block and wraps the whole circuit in a global feedback loop. The phono stage has four active stages with its own global feedback. Options include variable gain and an inverted output.
Context
The SP-11 appeared in 1985, at the midpoint of Audio Research's experiments with hybrid topologies. It sat between the traditional tube-based SP-10 and the more solid-state SP-9 and SP-14. It marked a move away from the "warm and cuddly" valve sound toward a more neutral, detailed presentation. The SP-15 later replaced the SP-11 at the top of the range, with MOSFETs instead of valves in the line stage and balanced outputs added. The SP-9 and SP-14 were less ambitious single-box designs with similar hybrid circuitry. The SP-9 used one valve per stage, and the SP-14 used a single dual triode in the phono input.
Market Value
┌──────────────────────────────────────────────────────────────────────────┐ │ AUDIO RESEARCH SP-11 Jul 2026 │ ├──────────────────────────────────────────────────────────────────────────┤ │ High $43 Latest $43 │ │ Median $38 Trend — │ │ Low $25 Volume ~2/mo │ ├──────────────────────────────────────────────────────────────────────────┤ │ $50 ┤ │ │ │ .│ │ │. │ │ $29 ┤ │ │ │ . │ │ │ │ │ │ │ │ $0 ┤ │ │ ├─────────────────────────────────────────────────────────────────│ │ vol │█ █ █│ │ └─────────────────────────────────────────────────────────────────│ │ 2026-04 2026-05 2026-06│ └──────────────────────────────────────────────────────────────────────────┘
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