AUDIO RESEARCH PH1 PHONO PREAMPLIFIER (review) (Nov. 1992)

by Robert H.

Audio Research PH1 phono preamplifier

Frequency response: ±0.25dB of R1AA curve, 10Hz-60kHz, -3dB points below 0.5Hz and above 150kHz. Distortion: <0.005% at 0.25VRMS at 1-khz. Gain: 48dB at 1-khz (MM and MC compatible). Input impedance: 47k ohms (provisions for any value below 47k ohms, or added input capacitance for matching certain cartridges). Output impedance: 350 ohms. Recommended load impedance: 50k-100k ohms and 100pF (10k ohms minimum and 2000pF maximum). Input overload: 160mV RMS at 1-khz (800mV RMS at 10kHz). Rated output: 250mV RMS, 10Hz-60kHz driving 100k ohm load (output capability is 50V RMS at 0.5% THD at 1-khz). Noise: 0.12p.V EIN (equivalent input noise), IHF weighted, shorted input (78dB below 1-mV input). Power consumption: 35W. Dimensions: 19" W by 5 1/4 " H by 10 1/4 " D (handles extend 1 5/8" forward of front panel, rear chassis fittings extend 7/8 "). Weight: 10 lbs net, 19 lbs shipping. Price: $1495. Approximate number of dealers: 62. Manufacturer Audio Research Corporation, 5740 Green Circle Drive, Minnetonka, MN 55343-4424. Tel: (612) 939-0600. Fax: (612) 939-0604.

In a recent article criticizing audiophiles, the author used as an example of audiophile dementia the continued assertion that LP play back was superior to Compact Disc. In the author's mind, the CD was truly an advance in the science of music reproduction, and the vinyl record was a primitive reminder of just how far audio technology has evolved since the advent of digital audio. The author's shock that there could be any debate on the issue was genuine My reading of this article coincided with a switch to LPs after three weeks of hearing nothing but CD playback. I'd just finished reviewing four inexpensive digital processors (which consumed all my listening time), and had returned to vinyl.

Upon hearing LP playback again after this long digital dry spell, I was bowled over by how much more musically involving records are. Although I hadn't doubted the superiority of LP playback, the preceding three weeks' all-digital diet threw into sharp relief just how much better vinyl was than poly carbonate and aluminum. Playing LPs produced a much stronger compulsion to put on record after record, without regard for time's passage or duties' calls. What really drove the point home was playing records of music I'd been using the CD versions of to audition the digital processors. There was a lifelike quality, a realism, a sense of taking one step doser to the music's expression from the LP not even approached by CD. It isn't that the LP medium is so great--it's not. Rather, LP's superiority comes, I believe, from the fact that the signal in its grooves has, on most LPs, never been digitized.

When, shortly after this experience, I read the amide expressing shock that anyone would even consider the LP to have merit in the face of the technological achievement of the CD, I wondered how the author could reach such a conclusion. Had he never heard an LP played back correctly? Was his value system so different from mine that he valued lack of surface noise above all else? Or did he just assume that, because CD is vastly more sophisticated technically, it must be musically superior? I haven't a clue Sorry for the diatribe I'll move on to what this piece is all about--the $1495 Audio Research PH1 phono preamplifier.

TECHNICAL DESCRIPTION

The PH1 shares its build and cosmetics with other Audio Research products, particularly the DAC1 digital processor and LS2 line stage preamplifier. A brushed-aluminum panel is flanked by a pair of curved black handles; a narrow rectangular cutout houses two toggle switches, one to turn the PH1 on and off one to mute the output. A green LED lights up when the unit is on, dimming when the out put is muted by the front-panel switch or automatic turn-on timer. The muting circuit and LED function identically to ARC's LS2 line-stage preamp. Also like the LS2, the PH1 is minimalistic, designed to give the best possible sound for the least money, and eschewing features and controls. As with other ARC products, the PH1 is available with a black front panel.

The rear panel holds a pair of high-quality RCA input jacks, identical output jacks, and a ground terminal. A line fuse and captive AC cord finish off the unit. Chassis construction is typical Audio Research, with perforated top and bottom panels for ventilation. The PH1 is attractive and nicely built.

Inside, a dual-secondary toroidal trans former is mounted vertically to the left-hand chassis edge, well away from the analog circuitry. Physically isolating the power trans former from the audio circuit is especially critical in a phono stage; the input signals are very tiny, and the circuit has lots of gain--a recipe for hum.

The power supply and audio circuit share a large printed circuit board suspended in the chassis. The power supply, which occupies about a third of the real estate, reflects ARC's philosophy about building audio components: very simple signal path, very sophisticated power supply. Discrete regulation is employed on the audio circuit's +285V rail, this reportedly providing an excellent 0.01% level of regulation. Running the audio circuit on such a high voltage rail is said to improve the PH1's sonics, particularly dynamics. The +285V power supply employs ARC's patented DEC (Decoupling Electrolytic Capacitor) scheme which bypasses electrolytics with a high-quality film cap and allows the electrolytic to perform at its best.

The other transformer secondary winding supplies a more conventional power-supply stage this powering such PH1 housekeeping functions as the turn-on muting timer and muting relays.

The audio circuit's front end consists of a direct-coupled, very low noise very high input impedance JFET. The left- and right channel JFETs are gain-matched, and enclosed in separate clear-plastic housings for thermal isolation. These housings prevent air currents from changing the device's temperature.

According to ARC, air currents can cause significant drifts in this device's operating point.

Out of the box, the PH1's input impedance was 47k ohms in parallel with 600pF of capacitance. The input impedance can be adjusted, however, by soldering a pair of resistors to turret terminals on the underside of the pcb. Five resistor values-and high quality solder-are supplied with the PH1, allowing the user to match the PH1's input impedance to his or her phono cartridge.

Removing the 560pF capacitors reduces the input capacitance to 40pF. Additional capacitors (not supplied) can be soldered to the turret terminals for exact matching, or the stock capacitors can be completely replaced.

The standard capacitance of 600pF, however, is suitable for most moving-coil cartridges.

ARC believes this method of changing fixed value parts is both sonically superior and more economical than pots or a switched resistor network. I left the unit with 47k ohms input impedance, ideal for the Audio Quest AQ7000 phono cartridge used during the auditioning.

The input stage is followed by a gain stage, a buffer, the main gain stage, and an output follower for low output impedance. Each of these stages uses a single FET (j- or MOS-), augmented with additional active devices that are not in the signal path (constant-current sources, gate protection, etc.). The entire circuit is direct-coupled, except for a single coupling capacitor at the output.

While the final high-frequency rolloff portion of the RIAA EQ appears to take place after the output capacitor, the main RIAA equalization is implemented in the feedback loop, with paths to the source of the input FET taken from both sides of the output coupling capacitor. This technique reportedly improves the sonic performance of that cap.

As with other ARC products, the Ft Is are graded, sorted, and matched within each product. At least half the PH1's development time was spent listening to different iterations of the circuit or various parts. In addition, each production PH1 is listened to in a temperature-controlled listening room before leaving the factory. The PH1's parts quality, build, and overall execution are what I've come to expect from Audio Research: first-rate.

PLAYBACK SYSTEM & REVIEW CONTEXT

The LP front end used with the PH1 included the Well-Tempered Turntable fitted with a WT Tonearm and AudioQuest AQ7000 cartridge.

The WTT has been heavily modified with Larry Pederson's arm tweaks' and Marigo's Well Damped Clamp, isolation system, and platter mat (see "Follow-Up:' next issue). The whole rig was mounted on a spiked and lead shot-filled Merrill Stable Table. Interconnects in the phono chain were Expressive Technologies superb new IC-2 cable. I also experimented with Expressive Technologies' SU-1 step-up transformer in the signal path.

The PH1 fed Audio Research's LS2 line stage preamplifier, presumably the ideal match for the PH1. I've found the LS2 to be a superb preamplifier, with very little editorial influence on the signal passing through it.

The LS2 drove the Muse Model 18 sub woofer through 20' runs of IC-2, with the Muse's HF output feeding a Mark Levinson No.23.5 power amplifier via a lm run of AudioQuest Diamond. The No.23.5 drove the usual Hales System Two Signatures via 8' runs of bi-wired AudioQuest Sterling/Midnight.

AC power to the system (except that to the Model 18 and No.23.5) was conditioned by a Tice Power Block and Titan, running off the listening room's dedicated AC supply.

The built-from-scratch listening room has optimum dimensional ratios for room-mode distribution.

My reference in phono preamplifiers is the superb Vendetta Research SCP2B, designed and manufactured by John Curl. This $2500 unit, purchased by Audiophile after JGH's glowing review in Vo1.11 No.6 (June 1988), has been an integral part of my LP chain for the past year. Everyone who has heard the SCP2B has been captivated by its musicality.

The Vendetta is vastly superior to other phono stages I've had in the listening room, including the Audio Research SP-11 Mk.II, SP-14, and Classé DR-5. The Vendetta thus stands as a benchmark against which other phono stages can be judged? But on to the music.

LISTENING

The PH1's sonic signature made itself known I See Vol.15 No.1 for a "Follow-Up" on the arm mods. Lary Pederson can be reached at The LP Lab, 208 Pepperwood, Hercules, CA 94547. Tel: (510) 799-3858, 11 am to 2pm PST 2 I should point out that I don't have the latest iteration of the Vendetta, the SCP2C. on the first LP, with extended auditioning largely confirming first impressions. My immediate reaction was that the PH1 was a little on the hot side of reality-forward, incisive, and bordering on the analytical. It was also remarkably transparent, tightly focused, and produced a feeling of palpable images in the listening room.

The PH1's most salient characteristic was its immediacy. Hearing music through the PH1 was like moving from Row T to Row B. The sound became drier, more forward, and had greater focus through the PH1. With this type of presentation came a remarkable clarity and transparency, but at the expense of a diminished sense of bloom and air around instrumental and vocal outlines. On the Robert Lucas LP Usin' Man Blues (Audio Quest AQ-LP1001), for example, the impression of space surrounding the guitar and vocal shrank slightly. It was as though the microphones were moved closer to the instruments, decreasing the ratio between direct and reflected sound.

There was a concomitant increase in detail, much the same as when sitting closer to an instrument. I first felt that the PH1 was resolving more information than the Vendetta, but quickly realized that the more laid-back Vendetta was actually revealing more detail in the recording, but was doing so with greater subtlety. The PH1 tended to hype detail- particularly transient information-at the expense of conveying the music's innermost nuances. Conversely, the Vendetta was more suave and delicate, allowing the listener to move into the music and explore the finely woven fabric of instrumental tortures. I found the latter a more satisfying experience.

Nevertheless, the PH1's clarity and transparency provided a huge, clear picture window on the music.

In its ability to present dynamic contrast, I have nothing but praise for the PH1. It superbly conveyed the music's dynamic structure, both in terms of absolute difference between loud and soft, and portraying the gradations in between. There was an effortlessness during crescendos and musical peaks that opened up the music. Moreover, the PH1 didn't become thick or congested during loud, complex passages. Instead, it retained its excellent clarity, focus, and delineation of individual instruments within the soundstage.

Transients were razor-sharp and precisely executed; The PH1 was the antithesis of slow and rolled-off The LP Cascades, by the Brazilian trio Azymuth (Milestone M-9109), is particularly revealing ola component's speed: there are layers and layers of complex rhythms played on Latin percussion. Some products tend to take the edge off the rhythmic intensity, dulling the interaction between instruments. Not the PH1: it faithfully conveyed the sharp leading edge of transients, allowing each instrument to be resolved firm the whole As I noted above, however, the PH1 was a little dry and analytical for my tastes. Al though there was a clarity and sense of high resolution, music became fatiguing more quiddy through the PH1 than the Vendetta. I didn't feel the sense of relaxation and ease that characterizes the Vendetta. Adding to this impression, the PH1 had a slight hardness and glare in the upper mids. The attack of the strings on John McLaughlin's acoustic guitar on his Belo Horizonte LP (Warner Bros. BSK 3619) was a little edgy. Similarly, the leading edge of piano transients lacked the Vendetta's smoothness and liquidity. On Bill Evans's Quintessence LP (Fantasy F9529), for example, there was just a trace of stridency in the upper registers. Violins also had a harder and slightly steely texture through the PH1, in contrast to the Vendetta's lush, velvety rendering. This is one area in which the Vendetta is unparalleled; its portrayal of instrumental textures can only be described as gorgeous. The contrast between the two phono stages was particularly evident on the superb Harmonia Munch recording of Han del's Water Music (HMU 7010). The violins took on a very slightly steely sheen through the PH1, making the LP sound a little closer to the CD version of this recording. Similarly, on the Sheffield direct-to-disc Tower of Power Direct (Lab 17), the horns were a little on the chromium side of reality, rather than having a burnished brass sound.

In the ability to throw a sense of space and depth before the listener, the PH1 was excel lent, while not being in the same league as the Vendetta. The PH1 was drier, less spacious, and lacked the Vendetta's degree of three-dimensional layering. On one track of the Cascades LP, the percussion instruments at the extreme left and right of the soundstage have the least reverb; each successive pair of percussion tracks is panned a little closer to center and has a greater sense of distance, with one instrument dead center in the soundstage, seemingly miles away. The Vendetta better resolved the spatial cues that allow the listener to hear the three-dimensional effect of this technique. There was also greater spatial separation between instruments, with the farthest instruments appearing to be even farther away? The Vendetta also had a greater sense of air surrounding instrumental out lines. Stage width, however, was comparable, with each phono preamp throwing a very wide soundstage.

I should add that the PH1 was remarkable in its sense of focus, delineation of individual instruments within the soundstage, and transparency. Its sound was far from the colored, thick, and congested presentations one hears from lesser phono preamps, such as those found in inexpensive full-function preamps.

Bass presentation through the PH1 tended to be lean and tight rather than generous and weighty. Again, the nod goes to the Vendetta.

Although the PH1's bass was precise and controlled, the Vendetta had a greater warmth, roundness, and power. Bass guitar lines reproduced by the PH1 had less of the "purr" quality that produces a feeling of weight and warmth in the music. Consequently, the PH1's sense of pace was ameliorated. On "Cruise Control," from the Dixie Dregs' Unsung Heroes (Arista AL-9548), Andy West's powerful, driving bass line-the tune's foundation-lacked the propulsion and energy it had when heard through the Vendetta.

There was also less sense of "bounce" in the bass through the PH1. I must point out that my playback system's sonic signature-particularly the Audio Quest AQ7000 cartridge feeding the two phono stages-may unduly favor the Vendetta. The 7000 tends to be slightly analytical, very fast but somewhat etched, a tad forward in the upper mids and treble, and lean in the bass--all characteristics of the PH1. It's very likely that the 7000's sonic signature is not an ideal match for the PHL The traits of each are acceptable individually, but exacerbate one another when combined. Moreover, the Hales System Two Signature loudspeakers couldn't be described as having a weighty bass, a laid-back upper midrange and treble,

[3 All this was, of course, artificially created, but is nevertheless convincing. I once tried to duplicate this effect but ran out of reverbs.]

or a slow transient response. Add to this the Well-Tempered Turntable's penchant for a lightish, detailed rendering, and it all adds up to a less than ideal system for allowing the PH1 to achieve its potential.

It came to mind that the ideal cartridge for the PH1 may be the Benz-Micro MC3- on a VPI turntable. In the short time I had the Benz (for comparison with the AQ7000), I appreciated its laid-back sense of ease, subtle presentation of detail and transient information, and tube-like portrayal of instrumental textures-just what the PH1 needs. Its slightly higher output level (035 mV) is also a benefit.

Given the PH1's sonic signature, I cannot stress strongly enough the need for careful system matching. The choices of turntable, cartridge, electronics, cables, and loudspeakers are crucial if the PH1 is to satisfy musically.

Systems that are already forward and analytical would be better served by another choice in phono stages, in my opinion. I can, however, think of several systems in which the PH1's transient speed, transparency, and superb dynamic abilities would bring life and vitality to the music.

Despite the system bias toward the Vendetta, I have no doubt it is the better phono stage. I found myself enjoying music more through the Vendetta. It seemed to convey more of the music's expression and emotion, making it easier to get lost in the music and forget about the sound. Although the PH1 was good, it didn't produce the same level of involvement as the Vendetta.

MEASUREMENTS

The PH1 had a measured input impedance of 53k ohms at 20Hz, 49k ohms at 1-khz, dropping to 12k ohms at 20kHz, with the standard 47k ohm input resistor. Output impedance was 1200 ohms at 20Hz, drop ping to 320 ohms at 20kHz. Although this fairly low output impedance would suggest the PH1 could drive a power amplifier directly through a passive level control, ARC strongly discourages using the PH1 without an active line amplifier.

Measured gain at 11khz was 47.64dB, enough for most moving-coils, but better suited to the "high-output" variety. The moderate gain figure suggests that the lowest-output cartridges-the ScanTech--manufactured variety with an output voltage of 0.18mV--should be avoided. The AudioQuest AQ7000, also made by ScanTech but with an output of 03mV, would seem to be the lower limit with which the PH1 will work comfortably. I found I set the LS2's volume control about three-fourths of the way up for moderate listening levels. Despite needing so much gain, the AQ7000/PH1 combination was very quiet.

Commendably, gain was perfectly matched (0.016dB!) between channels at 1-kHz.

The PH1 accepted very high input levels before clipping: 17mV at 20Hz, 158mV at 1-kHz, and 1.154V at 20kHz, equivalent to moving-magnet overload margins of 44.6, 30, and 273dB. These are generous headroom margins; the PH1 is unlikely to be overloaded by even the highest-output moving-magnet cartridges playing the highest levels on any LP. These input levels produced a whopping 38.3V output.

Fig.1 Audio Research PH1, RIAA error (right channel dashed, 0.5dB/vertical div.).

Fig.2 Audio Research PH1, crosstalk: R-L, top L-R, bottom (5dB/vertical div.).

Fig.3 Audio Research PH1, THD+noise vs frequency at 5mV at 1-khz (right channel dashed).

Fig.1 shows the PH1's RIAA accuracy.

Although the curve looks less flat than those of digital processors or line stages, it is actually excellent. The right channel had a very slight (0.2dB) upward shelving spanning the top four octaves, and the left channel had a mild 0.15dB dip through most of the bass and lower midrange. This is excellent performance: it exceeds ARC's specification of ± 0.25dB, and is better than the RIAA accuracy measured in ARC's SP-9 and SP-14.

Inter-charnel separation, shown in fig.2, was unusual in that it improved with frequency. The lower trace (R-L) indicates 88dB of channel separation, increasing to 97dB at 20kHz. This is superb performance The PH1's THD + Noise plot at a typical input level is shown in fig3. The distortion and noise are below 0.05% across the band, a low figure, though an average of 7-8mV of very low frequency noise was present on the outputs.

The PH1 does not invert absolute polarity.

CONCLUSION

At $1495, the Audio Research PH1 has many qualities of much more expensive phono stages. The unit had a remarkable clarity, focus, and superb dynamic expression. The presentation through the PH1 was the antithesis of thick, compressed, congested, colored, and slow. In these qualities, it rivaled the best phono stages I've heard.

For my tastes, however, the PH1 was a little too forward and incisive. The music tended to be forced on the listener, rather than presented in a way that encouraged the listener to lean into the music. This description was true of the entire presentation, but particularly appropriate to the PH1's portrayal of transient detail. Although quick and clean, musical detail tended to be slightly etched and analytical.

It's very likely that the playback system used to evaluate the PH1-especially the AudioQuest AQ7000 cartridge (see my review in Vol.14 No.6)-did not form a synergistic match that would allow the PH1 to reveal its full musical potential. The need for careful system matching cannot be stressed too strongly. The PH1's sonic signature may bring a newfound clarity, resolution, and dynamics to many systems, yet could push other systems over the brink into analytical un-musicality.

In short, the PH1 is a very good, but not superlative, phono preamplifier. It was clearly a notch below the state-of-the-art Vendetta Research SCP2B, both in specific performance attributes and ability to involve the listener in the music. The Vendetta, however, is substantially more expensive than the PH1 ($2500 vs $1495), is only manufactured in extremely low numbers since John Curl's home was destroyed in the 1991 Oakland fire, and, with four boxes, is much more cumbersome.

The PH1 has earned a Class B Audiophile recommendation, but with the strong caveat that system matching is crucial, and an audition in one's own system mandatory. I suspect that, given the right support of ancillary components, the PH1 could offer superb performance for its price.

Manuf Comments

AUDIO RESEARCH PH1

Editor: First of all, it is evident that, in spite of Mr. H.'s obvious personal preference for the higher-priced "competitive" unit that is a part of his reference system, he made a fair-minded and serious effort to factually appraise the PH1. We appreciate that.

I would simply like to observe that, of obvious necessity, there should be some correlation between price and performance, all other things being equal. (Except in very rare instances, it is not normally possible for a given unit to have the better construction quality, the better sound

quality, and the lower price. Any two of the three, yes.) Systems employing equipment commensurate in quality with products such as our SP9, SP14, and, of course, most earlier units, should find the PH1 a satisfying improvement in sound quality at an affordable price.

For those needing a unit of greater resolution, we have a more expensive unit, the PH2, priced at $2495.

WILLIAM Z. JOHNSON; President, Audio Research

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[adapted from Nov-1992 issue]

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