Audio ResearchSP-9usedAudio Research SP-9Audio Research SP-9trade in --sounds great and looks great Audio Research SP9 preamplifier J. Gordon Holt, Various | Nov 29, 1995 | First Published: Nov 29, 1987 Following the introduc...995.00

Audio Research SP-9

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Ships fromBensalem, PA, 19020
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Audio Research SP-9

trade in --sounds great and looks great

Audio Research SP9 preamplifier

J. Gordon HoltVarious  |  Nov 29, 1995  |  First Published: Nov 29, 1987 Following the introduction of their very expensive, tube/FET hybrid SP11 preamplifier, there were rumors that Audio Research was working on a hybrid tube/transistor preamplifier targeted to cost less than $2000. The rumors were confirmed when ARC showed a black-and-white photo of the SP9 at the 1987 Winter CES. Obviously, like all magazines, we were impatient to receive a review sample, but the first review of the SP9 actually appeared in the summer '87 issue of Peter Moncrieff's IAR Hotline. Peter's review was almost intemperately enthusiastic, comparing the SP9 positively with early samples of the SP11 and suggesting that its sound quality was considerably better than would be expected from its $1695 asking price. Naturally, we were anticipating good things when our review sample arrived in Santa Fe in late July.

image: https://www.stereophile.com/images/archivesart/ardp91.jpg

Like most other ARC watchers, I had assumed the SP9 would be a stripped-down version of the highly regarded $5000 SP11. And in the sense that it is rather more restrained in concept than the '11, it is just that. The one-piece unit (no separate power supply) has four knobs and four toggle switches vs the SP11's six and eight, respectively. There is only one volume control (vs the '11's two), but since it is located in the circuit right after the high-level inputs, there's no possibility of input-signal overload regardless of how strong the signal. ARC, however, denies that the 9 is a "stripped-down SP11," preferring to describe it as "an adaptation of some of the SP11's patented hybrid technology."

Well, it is and it isn't. Both are hybrid units, in that both have tubes and transistors in the signal path, but those components are combined rather differently in the two preamps.

In the SP11, each signal "stage" consists of a FET and a tube in a cascode configuration. This arrangement plays off the operating characteristics of both devices against each other, resulting in a combined performance better than either the FET or the tube on their own. The characteristic curve of an amplifying device is a graph which plots its through-current against the input voltage applied to its control gate (or grid). Ideally, through-current should be an exact function of input voltage, producing a characteristic "curve" that is a straight, diagonal line. In actuality, though, this "line" is more like a curve, with its ends fairly sharply curved and its middle section approaching but never quite becoming a straight line. Classic design practice has been to place the device's operating parameters on that mid-part of the line that has the least curvature, as this yields the lowest distortion. But because the line is never completely straight, the distortion is never zero.

The characteristic curves for a tube and a FET are interesting in that they are almost exact mirror images of each other: while one tends to curve in one direction, the other tends to curve in the other direction. Combining both devices into what is essentially a single amplifying stage has the effect of cancelling the curvatures of both, resulting in an almost perfectly straight transfer characteristic and, of course, vanishingly low distortion (footnote 1). Also worth noting is that the tubes in this kind of hybrid circuit are run in what's sometimes called "trickle mode." That is, their plate current is much lower than is usual for a tube, resulting in a product whose top panel, even after four hours' use, is barely warm to the touch. This means you don't have to give an SP11 (or the '9) as much ventilation space as is necessary with conventional tube preamps. It also means you can expect unusually extended tube life—ARC claims up to 10,000 hours of service life will be possible from the SP9 tubes!

By critical consensus, the SP11 is the best-sounding tube preamp Audio Research has ever made; certainly it has few, if any, peers. This is not that surprising, given that ARC has never made a less-than-excellent tube product, and that the hybrid cascode design should, in theory, be better than one with tubes alone. The SP9, however, features a rather different circuit topology. Almost identical gain blocks are used for both phono and line stages, the latter being less complicated, however, as it doesn't need as much gain, nor does it apply RIAA equalization. According to the supplied schematic, the circuitry is single-ended, operating from a single high-voltage rail. The input signal is applied to the gate of an n-channel FET, the drain of which is connected in a classic cascade manner to the grid of half of a 6dJ8 (ECC88) dual triode, biased by a resistive divider. In the phono stage, the plate (anode) of this tube feeds a pair of MOSFETS for additional gain, followed, like the line stage, by a MOSFET output driver, this AC-coupled to the volume control (phono) or main output (line). The output stage has a total of 20dB gain (a wire link on the board can be easily desoldered to lower the gain to 14dB, for use with more sensitive power amplifiers) with a single feedback loop around the FETs and tube. The phono stage has two overall loops, one AC, one DC, to provide the RIAA equalization. Components used are very high quality.

As with all ARC amplifiers, the power supply is sophisticated, with separately regulated supplies feeding the phono stage, the output stage, and the timing and muting circuitry. Power MOSFETs are used as the series pass elements. The transformer itself is a high-quality, electrostatically shielded toroidal type, fixed to the rear of the LH sidewall as far away from the phono circuitry as possible.

All the input and output sockets are gold-plated Tiffanys and the SP9 has inputs for four line-level inputs—Video sound, CD, tuner, and spare—in addition to inputs and outputs for two tape recorders. The phono input is nominally moving-magnet compatible; its very low noise makes it suitable for MCs with not too low an output and an internal resistor can be changed to lower the loading for MC cartridges. Input capacitance can also be changed appropriately. Upon turn-on, a timing circuit mutes the output for 45s, allowing the operating points to stabilize; the muting is performed with a relay which pulls the output to ground—the signal only flows through the potentially sound-degrading relay contacts when there is no sound!—a series resistor prevents excessive current flow through the output MOSFET when muted.

System
Before auditioning, I allowed the SP9 to warm up for a day or so, something I have found to be absolutely necessary before any new product will perform up to snuff. Other components used for my tests were the SOTA Star Sapphire turntable (with Electronic Flywheel), the Well-Tempered Arm, an Ortofon MC-2000 cartridge with its X-2000 step-up transformer, Threshold SA-1 power amplifiers, and Sound Lab A-3 full-range electrostatic speakers. Interconnects were the new Monster M-1000 Laboratory Reference series, and the speaker cables were by Straight Wire. Signal sources were from original 15ips tapes, CDs (from the Sony CDP-650ESD/DAS-703ES combo), and analog discs from Sheffield, Reference Recordings, Wilson Audio, and Opus 3 (the Depth of Image test record).


Footnote 1: This hybridizing technique was first used in a similar but patented circuit by David Berning ten years ago in his TF-10 preamplifier. (You can guess what the T and the F stood for.)—J. Gordon Holt

Sound Quality
On first listen, using high-level sources only, I am saddened to report that the sound was not good. In fact, it was hard, rough, thin, and both spatially and dynamically compressed. The phono preamp added more of the same of everything. The adjectives I used above—and I gave considerable thought to their choice—do not reflect merely personal value judgments on my part, but are descriptive of the changes wrought by the SP9 on signals passing through it. That is, they were audible on simple bypass tests, in which the preamp under test is compared with the signal being fed to it.

My system, straight-through from high-level source to speakers, is, if anything, a bit on the warm side, so my complaints about the SP9 are actually giving the preamp some benefit of what doubt there may be. With a more neutral system than mine, the SP9's irritations would be exacerbated, not mitigated. In addition, confirming what David Prakel had said in his review of the SP9 in the September 1987 issue of Hi-Fi Answers, crosstalk between line-level inputs was higher than I would have liked. If a tuner is operating while a disc is being played, its signal will be faintly heard in the background.

In their literature, ARC warns that the SP9 needs to see quite a high amplifier load impedance: 60k ohms in parallel with 100pF is recommended, the capacitance being very low, equivalent to no more than 2 meters or so of a typical audiophile interconnect. The worst-case loading is 20k in parallel with 1000pF, this still not unusual with many solid-state power amplifiers connected via reasonably long interconnects. Worried that I might have been mistreating the preamp's output stages, I checked my cabling: the 1m length of Monster M1000 had a total capacitance of 175pF, while the 75k input impedance of the Threshold SA-1 should not have presented the SP9 with any problems.

I was then told that according to Ken Kessler, who was reviewing the SP9 for HFN/RR, the SP9 needed "at least 72 hours of warmup before its sound reached its best." JA took our sample SP9 home and tried that (see below), then suggested I go forth and do likewise.

After four days of continuous warmup (96 hours), I was prepared to modify my initial response to the SP9's sound, but only to the extent of putting the word "somewhat" ahead of each of the adjectives I had used previously. I still found the preamp to be one of the least ingratiating I had heard in years. But why, I wondered, did it sound so completely different from the SP11, in which ARC's "patented hybrid technology" had worked such sonic wonders?

The answer may lie in the fact that the SP9 combines its tubes and FETs in a cascade, rather than cascode, configuration. The difference is that, whereas the latter allows both devices to act as a single stage, the former normally makes them behave like two separate series-connected stages. Thus, instead of canceling their inherent distortion characteristics, the two sets of distortions would be added. That still wouldn't explain why the '9 sounded mediocre; ARC used cascading in its all-tube preamps, and they sounded warm and sweet rather than thin and rough. But it might explain the differences between ARC's two hybrid designs. (If, in fact, there is some other provision in the SP9's circuitry that would make it behave differently from the way I think it does, I would be interested to learn about it.)

Comparisons
The SP9—my sample, anyway—is not what I would call a bad preamp. Its problems are really only moderate in degree. But most are errors of commission rather than omission, and are of a kind I personally find very hard to tolerate. But what's a better preamp, for the price? Or even as good? Well, $1700 is a popular price range for preamps, and solid-state design and available materials (like active devices) have reached a point where some transistor designs are comparable in performance to tubed units costing several times as much. Unfortunately, I haven't heard any of the current solid-state models in this price range. But I am very familiar with a $1500 tube preamp from a competing firm: the Conrad-Johnson PV-5.

A three-year-old design (although probably improved since the one we have on hand was loaned by the manufacturer), this has long been almost a cult favorite with audiophiles who dote on the classic "tube sound." To refresh my memory of it, I brought home our PV-5 from the office and gave it three days to warm up before listening to it.

The sound was much as I had remembered, but the increasing accuracy of other, more recent, preamplifier designs has rendered its previously "slight" colorations more conspicuous by comparison. Through any high-level input, its sound is warm and rich, with a soft but subtly grainy high end, a slightly forward upper midrange, an almost fat and somewhat ill-defined midbass region, and a marked lack of really deep low end. Its soundstage is wide, its rendition of depth so marked as to seem almost exaggerated. Phono-stage performance is relatively free from coloration, adding only a trace more midbass bloom and a slight high-end roughness to what was heard through the high-level section, but, of course, it will not handle MC cartridges with insufficiently low noise.

In other words, the PV-5 is a far cry from the idealized straight wire with gain. It's not a very accurate preamp—probably not as accurate as the SP9—but the nature of its imperfections is completely different. Whereas I had been actively irritated by the SP9, I had the opposite reaction to the PV-5. Yes, the PV-5 was drying up highs and losing deep bottom and making everything sound fat and rich, but these were faults I could have lived with even while acknowledging their existence.

Given the choice between these, there is no question which I would buy. A more intriguing question, though, is why my sample SP9 was apparently so different from the samples reviewed by Peter Moncrieff, and by David Prakel and Ken Kessler in the UK. I would like to think that the Stereophile sample was, in fact, not typical of average off-the-line production, although I find it hard to believe a firm as conscientious as Audio Research would allow anything sounding like this to leave the factory, let alone go to a high-end magazine for testing. The fact that they did, though, is reason enough for us to publish this review: to alert Audio Research SP9 buyers that at least some samples in stores may not be up to ARC's usual quality standards.—J. Gordon Holt


Read more at https://www.stereophile.com/content/audio-research-sp9-preamplifier-page-2#CrfJUrbWqFv55hzm.99
Quest For Sound
2307-R Bristol Pike
Bensalem Pa
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Questions for the seller
Sir: Why don't you sell it to me for 700.00 plus shipping and I'll call tomorrow and give you a credit card number or a pay-pal or cash or three gold double eagles....Let me know Will
Will Give me a call after 12 noon ..I’ll b in till 4 pm Stephen
Sir: Did you ever get paid on this SP-9.............Will
Hi Will Did not get check and he won’t respond ..

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