Preamplifiers:
A:
Ampsandsound Yellowstone: $25,000
This massive tubed preamp uses two 12AX7 (ECC83) twin triodes for line-input voltage gain; one 12BH7 as a driver; two 12AX7s for phono-input voltage gain; and one 12BH7 as a driver. There are also two 5AR4 rectifiers. The phono stage also uses 1:9 and 1:18 Cinemag step-up transformers. Listening to the phono input, Ken Micallef found that the Yellowstone was among the most neutral and transparent amplification machines he’d heard in-house. “It adds just a touch of warmth,” he wrote, “giving music a sweet liquidity and natural sonic flow I never grew tired of.” He noted that tonally, it played remarkably uniformly—“nothing tweaked, no frequency pushed, no agenda declared. It never called attention to itself; it let the music breathe and move. Pinning down its sonic character beyond that touch of warmth proved genuinely difficult.” In addition, the Yellowstone delivered a physical, sprinter-grade power and purpose. In the test lab, there was some high-end rolloff, the amount depending on the volume-knob position. With the control set to unity gain, the response rolled off by just 1dB at 100kHz. With it set to the maximum, the output was down by 2.2dB at 20kHz. (The manufacturer suspected that the early production review sample may have an out-of-spec capacitor.) The preamplifier could deliver high voltages into 100k ohms but clipped at just 453mV into 600 ohms. The distortion signature was predominantly second harmonic in nature but at a low level with the line input but higher in level with the phono input. Overall, the Yellowstone’s measured performance was typical of a purist tubed preamplifier. (Vol.49 No.8 WWW) Audio-GD Vacuum HE1 XLR balanced: $3999
This large, heavy, Chinese-made, tubed, all-balanced preamplifier doesn’t have a phono input, but it offers three balanced (XLR) and two single-ended (RCA) line inputs, balanced and single-ended outputs, and comes with a remote control. Tube complement is six 6H2N-EB twin triodes and four 6U4N-EB rectifiers, all Russian-made. Compared with the Lab 12 Herb Reichert, the Vacuum HE1 played slightly richer and thicker with more obvious three-dimensionality. Compared with the PrimaLuna EVO 400, the Vacuum HE1 XLR distinguished itself with quicker, sharper transients, more thoroughly exposed detail, harder-punching bass, and stronger pace, rhythm, and timing, Reichert noted. “Audio-GD’s Vacuum HE1 XLR line-level preamp allowed diverse audio sources to sound maximally diverse—and that, folks, is transparency,” Reichert concluded. In the test lab, John Atkinson found that the preamplifier’s top-octave output varied with the setting of the volume control. With it set to the maximum, the response was down by 5.5dB at 20kHz. With it set to “60,” the 20kHz output was down by 0.9dB. Harmonic distortion was fairly low and was dominated by the second and third harmonics. Atkinson warned that the HE-1 shouldn’t be used with power amplifiers that have an input impedance of 10k ohms or lower. (Vol.46 No.10 WWW) Ayre Acoustics KX-8: $6500; $11,000 as reviewed
This line preamplifier offers two pairs of balanced and three pairs of unbalanced inputs, one pair of balanced outputs, one pair of single-ended outputs, and balanced and single-ended headphone outputs. Three optional digital input modules are available: the X-8 DAC module adds $1500; the X-8 USB2 module adds $1000; the X-8 Net2 Ethernet module adds $1500. The KX-8’s zero-feedback, fully balanced analog circuitry features Ayre’s Equilock gain stage, which uses transistors operating primarily in current mode, Ayre’s Continuously Variable Gain Transimpedance (CVGT) volume control, and the company’s Diamond circuit for the outputs. Used as a line preamplifier, John Atkinson found that compared with a digital processor feeding the power amplifiers directly, the balance was a touch warmer with the KX-8 in the chain, but more significantly, there was an improved sense of what the late Art Dudley used to call “force.” This character was also present with headphones, coupled with superbly stable imaging—“the KX-8’s headphone amplifier is first-rate,” wrote Atkinson. The review sample had not yet been certified by Roon, so Atkinson auditioned the digital modules with the MConnect app installed on his iPad mini and network data sent to the KX-8’s Ethernet input. Image depth with the KX-8’s digital inputs was very similar to what he had experienced with the analog input, with voices projected a little forward in the soundstage. On the test bench, the KX-8’s measured performance as a line preamplifier and headphone amplifier was very good for a design that doesn’t use global feedback, especially at lower volume control settings, which, with the CVGT volume control, will maximize S/N ratio with the analog inputs and resolution with the digital inputs. (Vol.48 No.5 WWW)
Benchmark LA4: $2950; remote $100 extra $$$ ★
Benchmark’s usual approach to design is to out-spec the competition, and so it is here. Like other Benchmark equipment he has tested, the affordable LA4 challenged the resolution of John Atkinson’s test instruments, with “superb” channel separation, “extremely low noise, and virtually no power-supply-related spuriae.” Restricting his measurement to the audio band, Atkinson found an “astonishing” S/N ratio of 105.5dB for both channels; it remained extremely low across the audioband. He summed up: “Benchmark’s LA4 is the widest-bandwidth, widest-dynamic-range, lowest-noise, lowest-distortion preamplifier I have encountered.” In his listening room, Kalman Rubinson compared the LA4 to a cable—and couldn’t hear any difference. He concludes, “the LA4 is probably the most transparent and revealing audio component I’ve ever used. It does not seem to leave any fingerprints on the sound.” See also Herb Reichert’s review of Benchmark’s similar HPA4 headphone amplifier (see “Headphones”). Atkinson found that the LA4 had a more upfront presentation than the MBL N11 or Pass Labs XP-32, with less soundstage depth apparent on his own recordings. (Vol.43 Nos.1 & 11, Vol.44 No.3 WWW) Canor Hyperion P1: $13,500
This massive Slovakian preamp uses four 6922 tubes and two 6H30PI tubes. There are four pairs of balanced inputs and five pairs of single-ended inputs. (One pair can be set to fixed output.) Outputs include two balanced pairs and one single-ended pair. The circuit uses zero global feedback, and the 64-step balanced attenuator adjusts volume in 1dB increments. Jason Victor Serinus found that the Hyperion P1 distinguished itself with one of the airiest and widest soundstages that any preamp has delivered in his music room. Timbres were neutral and true, and the midrange was quite beautiful, albeit with colors less bold than with some gear. “Given that my room is prone to brightness,” he elaborated, “I enjoyed the fact that the P1 takes a soft and gentle approach to the top octaves. This treble reticence will prove a benefit in many systems.” His conclusion? “Highs were smooth, and music was graced with such a profound sense of air and spaciousness that it elicited smile after smile.” On John Atkinson’s test bench, the Hyperion P1 offered superb measured performance, with a wide frequency response and very low levels of noise and distortion. “However,” he cautioned, “this preamplifier does need to be used with power amplifiers that have a high input impedance.” This is due to the increase in source impedance at low frequencies: 6.6k ohms at 20Hz compared with 274 ohms at 1kHz and 20kHz for the balanced outputs. (Vol.48 No.7 WWW) CH Precision L10 Reference Line Preamp: $88,500
This modular, dual-chassis, dual-mono, direct-coupled, two-channel line-level preamplifier operates in current mode rather than voltage mode, which means that the gain comes after the volume control. The signal/noise ratio thus remains the same irrespective of gain. Unusually, the L10 offers a DC-offset calibration for each source component: the analog DC offset is measured, then converted to digital so that DSP can be used to drive current injectors in the signal path to provide the appropriate compensation. (The audio signal remains in the analog domain.) Jason Victor Serinus found that offset calibration resulted in sound that was “more intimate, natural, clear, present, sharply defined, detailed, and dynamic.” Serinus was impressed by the CH Precision, writing that it delivered a level of clarity and detail that rivaled the best preamps he’d ever heard, but without sounding cold and analytical. The L10’s output stage can be operated with local or global feedback. John Atkinson found that while distortion was higher with local feedback than it was with global feedback, it was still low in absolute terms. “Commendably,” he wrote. “there was no increase in the THD+N in the top audio octaves with either feedback setting, or with the load impedance reduced to the current-hungry 600 ohms.” Serinus summed up his time with the L10 by writing “I remain in awe of its clarity, transparency, and commitment to musical truth. It offers a stunningly detailed portal to musical art.” (Vol.49 No.2 WWW)
CH Precision L1: $34,500; optional X1 supply costs $21,500
This immaculately made, modular, solid state, Swiss line preamp is fully discrete, fully balanced, pure class-A, DC-coupled, fully symmetrical, and complementary. Unusually, the L1 monitors and counters DC offset at various points in the circuit and measures and compensates for DC offset on each input. The L1’s shunt-regulated power supply has two transformers and minimizes noise, but the preamp can also be powered by the optional X1 supply. This, according to CH, lowers the system noisefloor even further and increases “dynamic range, resolution and speed of response, transparency, detail, and above all, musicality.” Jim Austin auditioned the L1 both with its internal supply and with the X1. As much as he was impressed by the L1 alone, he noted that while the X1 improved the sound, so did the input DC calibration feature. “I found their sonic influence nearly identical,” he wrote. “Musical flow seemed improved; individual instruments had more drive.” He also found that the soundstage was more concretely laid out, easier to parse, and deeper. “Sonically, this could all be attributed to improved precision in the musical signal, both within and across channels, resulting most obviously in images within the soundstage being nailed in place and, as a result, seeming more palpable.” “Assuming you can pay the tab, it’s highly recommended,” Austin concluded about the combination. On the test bench, the CH Precision L1’s measurements were superb, some of the best John Atkinson had encountered, though he didn’t find any significant measured differences when he added the X1. (Vol.47 No.11 WWW) Dan D’Agostino Master Audio Systems Relentless: $165,000
The steampunk-styled Relentless places the power supply and control circuitry chassis between two mono preamplifier chassis. The Relentless utilizes four-layer circuit boards and hermetically sealed relays with gold-plated contacts and carefully segregates the analog circuitry, the digital circuitry, and the ground planes. The signal path is “fully complementary and balanced from the input to the output.” Each preamp’s discrete, differential FET input stage can handle 30V! The inputs and outputs are all balanced, and the Zone 1 and Zone 2 pairs of outputs can have volume adjusted independently either with the volume control rings around the meters or with the weighty, rechargeable, volume-knob–shaped remote control. (A new remote control is forthcoming.) Listening to a familiar recording of Mahler’s Symphony 5 performed by Rafael Payare conducting L’Orchestre symphonique de Montréal, Jason Victor Serinus was amazed to hear instruments and images that were larger, more tangible, and more emotionally impactful than he has grown accustomed to even with the outstanding preamps in his reference system. “The visceral impact of timpani, bass drum, and the lowest double bass lines increased. I’d long experienced lightning-fast attacks and credible leading edges on bass, but the center of bass tones occasionally lacked ultimate shape and color. Now, bass absolutely rang true, from first attack to final decay. Dynamic contrast between soft and loud passages increased. … The Relentless metamorphized organized sound into an expressive vehicle that impacted my heart and gut in revelatory new ways.” John Atkinson’s measurements found an input impedance close to 1M ohm, an output impedance of 2 ohms, a frequency response that was flat from 10Hz to 100kHz, and very low noise, harmonic distortion, and intermodulation distortion, even at high levels into the punishing 600 ohm load. An optional Digital Streaming Module costs $19,500. (Vol.47 No.9 WWW) EM/IA Autoformer: $4875 in copper, $8850 wound and wired with 0.999 silver.
This inscrutable-looking, remote-controllable black box with an LCD readout on the front panel replaces a conventional preamplifier. It offers inductive attenuation, in which separate autoformers, with Permalloy cores and multiple taps (one for each channel), allow the volume to be adjusted from +7dB to –54dB in 1dB steps. It has three inputs and two outputs, and balance can be adjusted with the remote. Alex Halberstadt compared the copper-wire version with PrimaLuna’s EVO 400 preamplifier and found that while music still sounded satisfyingly forceful (if not quite as fun as with the tubed preamp), John McLaughlin’s Extrapolation was disconcertingly clearer. What stayed with Halberstadt most during subsequent listening sessions was the remarkable coherence the EM/IA brought to his system. While there was a slight reduction in sheer grunt and propulsion, music sounded more natural, present, and intentional, “less like a collection of sounds and more like a real performance.” The EM/IA more consistently drew his attention to the music rather than the sound. When Halberstadt auditioned the silver version, he heard “sound that was even more detailed and clear, without any of the whitish, bleached cast that some silver components can impart. Recordings sounded bigger than through its copper sibling and created images that were even more uncannily free of the speakers. Most memorably, music became eerily holographic.” (Vol.47 No.4 WWW)
EMM Labs PREi: $28,900
The solid state PREi features discrete, dual-balanced signal paths, with ceramic circuit boards using pure gold traces, a class-A output stage, a 100-step precision analog volume control with intelligently calculated graduated steps, and a switch-mode power supply. It is supplied with a 15A Kimber Kable PK14 Base series power cord. Inputs and outputs are balanced and single-ended, and the selected input, volume level, and volume-preset choice are displayed on an OLED screen. A menu allows control of balance, display brightness, a screen saver, and factory reset. Jason Victor Serinus wrote that everything about the EMM Labs PREi felt so right. Comparing the presentation with the D/A processor connected directly to the power amplifiers, he noted that without the PREi, “colors were neither as rich nor as intense. The background wasn’t as black or transparent, and there was a subtle barrier between me and the sound. With the PREi, the veil was lifted. I heard more color and detail. The difference was not subtle.” Serinus concluded that no matter how you say it, slice it, or dice it, the EMM PREi was among the finest preamps he’s reviewed. In John Atkinson’s test lab, the PREi offered superb measured performance, with superbly low levels of noise, harmonic distortion, and intermodulation distortion. (Vol.49 No.6 WWW) HoloAudio Serene KTE: $3098 ★
Herb Reichert found that this “supertransparent” solid state line preamp enhanced the sound quality with every source he tried: “The Serene gave the May a dose of sunlight and a shot of adrenalin. [It added] grace and liquidity to the sound of the Mola Mola Tambaqui and punch and bass authority to the Denafrips Terminator Plus.” He also noted that it enhanced the spatial presentation of Sutherland Engineering’s Little Loco phono stage—“adding force and rhythmic nuance while peeling away a layer of shadow that had previously obscured the perimeters of the Loco’s projected soundscape.” (Vol.45 No.6; Vol.46 No.1 WWW) Lab12 Pre1: $2495
This line stage from Greece uses a single high-transconductance, twin-triode, E88CC tube per channel without any loop feedback to give a high maximum gain of 21dB. It offers five line-level (RCA) inputs and two outputs: one RCA, the other XLR. Herb Reichert found that compared to PrimaLuna’s tube-rectified EVO400, the Pre1 sounded turbocharged. “Could this be the difference between solid state and tube rectifiers?” he wondered. Compared with HoloAudio’s higher-priced KTE Serene, Reichert noted that the Pre1’s clarity/transparency/invisibility was equal to that of the Serene but the Pre1’s transparency was less stark than the Serene’s, “breathier and more vibrant with a slight, just-right aura of tube radiance.” He also found that the Pre1 couldn’t match the Serene “for low-end gut-punch, upper-bass detail, or dynamic swagger.” However, using the Pre1 to drive Genelec’s G Three active loudspeakers, Reichert realized that he was experiencing “a more refined, grainless, ‘invisible’ preamplifier than any I could recall using.” (Vol.46 No.1 WWW)
MBL Noble Line N11: $19,290 ★
This beautiful, multiple-input, multiple-output line preamplifier can be used in its Unity Gain mode for maximum sound quality or with a higher-gain setting. Jason Victor Serinus found that the N11 in its higher-gain mode “brought out the warm core of every note,” adding that it enabled him to hear “the subtle differences of interpretation, dynamics, and color that are the portals to the truth behind the notes.” He found that Unity Gain moved the soundstage farther back in his system with his D/A processors. While perspective was clarified, this mode made the sound less open with slightly reduced transparency and bass. Ultimately, he felt that the N11’s Unity Gain “toned down the noisy top ends of some recordings, making for easier listening.” The N11’s measurements revealed extraordinarily low noise and distortion, especially in Unity Gain mode. However, the CD input’s unbalanced impedance of 2.3k ohms will tax sources with a tubed output stage. Those can be used with the balanced inputs or the unbalanced Aux inputs, which have impedances of 10k ohms and 47k ohms, respectively. To his surprise, John Atkinson found that inserting the N11 between his DAC and power amplifiers resulted in a more palpable presentation, with a deeper soundstage. (Vol.43 Nos.7, 11 & 12; Vol.44 No.3 WWW) McIntosh C12000: $19,000
This massive, two-box preamplifier features separate tubed and solid state output stages. The signal circuitry is housed in one chassis; the control circuitry and power supply are in the second chassis. Tubes are 12AX7As and 12AT7s. There are six pairs of balanced line inputs, four pairs of single-ended line inputs, and two pairs of single-ended phono inputs, each of which can be set independently to moving magnet or moving coil. (The phono stage is tubed.) There is a headphone output as well as balanced and single-ended outputs. Stephen Mejias went back and forth between the tubed and solid state outputs, but listened mostly with tubes. However, listening to a percussive and impactful recording of Chabrier’s España, he “got a huge kick in the pants from the solid state presentation; the dynamics were more impressive compared to the tubed output.” Mejias decided that the genre of the music and the type of the recording will influence the choice between tubes and solid state. “It’s good to have access to both,” he concluded, adding that with the Decca 2022 reissue of Wagner’s Ring Cycle, “the quantity of musical information being launched at me was almost overwhelming.” The C12000 turned in an impressive performance on John Atkinson’s test bench, offering very low distortion and noise with both line and phono inputs and from both tubed and solid state outputs. “The McIntosh C12000’s measured performance is among the best I have encountered from a preamplifier,” he wrote. (Vol.46 No.11 WWW) Moon 891: $25,000
See Digital Processors. (Vol.48 Nos.1 & 3 WWW) NAD Masters Series M66: $7199
See Digital Processors. (Vol.47 No.11 WWW) Naim NSC 222: $8999
This full-function streaming preamplifier can be used with its internal power supply or with Naim’s NPX 300 external supply ($8999). “The fully loaded NSC 222 packs quite a punch in terms of facilities and features,” commented Martin Colloms, because as well as unbalanced line inputs, it includes a medium-sensitivity moving magnet phono preamplifier, a comprehensive streamer/DAC that can be controlled with the matching Naim app (for Android or iOS), and a dedicated headphone amplifier. Listening to the digital inputs, Colloms found that the NSC 222 showed high resolving power, revealing quite subtle differences between 16/44.1, 24/96, and 24/176.4 WAV files—and finally DSD64. The last was his favorite, revealing a marked degree of crisp precision and musical communication. While MC and his team of listeners liked what they’d heard with the internal supply, the sound was obviously better, in almost all aspects of sound quality, including the headphone output, with the NPX 300. Colloms summed up the NSC 222 by writing “All operational modes, analog disc, digital audio streaming and decoding, plus headphone and loudspeaker drive were consistent, distinguished by an innate sense of energy, imbued with transparency and microdetail. There was also a significantly open, wide-band character, somewhat different from the mildly ‘contained’ sense of some previous Naim iterations. And it is that satisfying, involving rhythmic quality that continues to entertain.” John Atkinson commented that Naim’s NSC 222 offered generally excellent measured performance via its digital inputs, with about 18-bit resolution and low jitter, and via its line and phono analog inputs. He did note that the ultrasonic response rolled off by 3dB at 41kHz with all these inputs, but this won’t have subjective consequences. (Vol.47 No.1 WWW)
Octave Audio Jubilee: $42,000
A zero-feedback, hybrid design with an outboard power supply and a tube-based “precision balancing stage,” the Jubilee combines four ECC82 tubes with a semiconductor-based, discrete, unity gain output stage. There are both RCA and XLR inputs, the latter equipped with unity-gain isolation transformers. Front panel buttons allow polarity to be inverted and gain switched between High and Low, the latter recommended for use with high-sensitivity speakers or very high-gain amplifiers. A switch allows the input and output XLR jacks’ grounds to be connected or lifted—Jason Victor Serinus found that the “Connect to Ground” setting delivered a fuller, richer, tighter, more profound bottom end, with weightier images and increased transparency, than he heard with the ground floated. “It was a total joy to listen to,” he wrote, adding that there was a seductive smoothness in the midrange. The soundstage was huge and deep “if not with ultimate transparency.” On the test bench the Jubilee’s noisefloor was higher in level and channel separation lower than with the best-measuring solid state preamplifiers, but the Octave preamp had no problem driving low impedances. Despite the lack of global negative feedback, distortion was low in level and primarily comprises the subjectively innocuous second harmonic. Price with optional stepped attenuator is $45,500. (Vol.48 No.10 WWW) Pass Laboratories XP-32: $20,212.50 in silver; $21,212.50 in black
Replacing the well-regarded XP-30, the three-box XP-32 looks almost identical. To minimize noise, each channel’s audio circuitry is housed in a separate chassis with the “dirty” control and power-supply circuitry in a third. Internal improvements include new transformers and DC-coupling of the balanced and single-ended inputs. The output stage runs a higher class-A bias with lower output impedance than the XP-30, and the volume control now operates in 0.5dB steps rather the earlier preamp’s 1dB steps. John Atkinson was enthralled by the XP-32’s transparency, hearing small details in his own recordings that he had not been fully aware of before. “A great preamplifier will allow through so much information, so much of the music, that the shortcomings of lesser speakers and amplifiers can be forgotten. The Pass Labs XP-32 satisfies that definition,” he concluded. In a follow-up, Jim Austin compared the XP-32 with the two-chassis XP-22. He was impressed with what he heard: “The XP-32 was just slightly more explicit than the XP-22. It was immediately noticeable on any music I played,” he wrote, concluding that he “thought the XP-22 preamplifier let through all the music, or all that mattered, but I guess it didn’t, because the XP-32 lets through just a little bit more.” (Vol.44 No.3, Vol.45 Nos.4 & 6 WWW) PS Audio PMG Signature: $8999
This solid state preamplifier features a fully balanced, pure class-A signal path using a “folded cascade” topology and zero-feedback diamond-buffer output stages. The power supply eschews electrolytic capacitors in favor of a large array of long-life film capacitors—a design choice intended to provide faster transient power and a lower noisefloor. There are two pairs of single-ended RCA inputs, four pairs of balanced XLR inputs, two pairs of RCA outputs, and two pairs of XLRs. Control is via a front-panel touchscreen or a remote control. Rogier van Bakel was skeptical about the benefit offered by a preamplifier when a source component equipped with a volume control could be connected directly to a power amplifier. Nevertheless, he found that with its high measured input impedance, low measured output impedance, and robust current drive, the PMG preamp let the source operate comfortably while feeding the amplifier a signal it can accept with minimal strain. The result in his system was “increased ease. I got cleaner leading edges and slightly firmer image outlines.” He summed up his review by writing “In a field crowded with embellishers and sweet talkers, PS Audio’s PMG Signature preamplifier speaks plain truths. I’d have no reservations about installing it as a reference.” John Atkinson summed up the PMG Signature’s performance by writing “the PS Audio PMG Signature is one of the best-measuring preamplifiers I have had in my test lab.” (Vol.49 No.5 WWW)
Soulution 727: $89,975; optional phono module costs $14,975
The solid state Swiss 727 uses a switched-mode power supply (SMPS). While it has an optional MC/MM phono section, Jason Victor Serinus auditioned it as a line preamplifier. A large rotary knob to the right of the central display handles volume, input selection, display brightness, and programming/configuration adjustment. (Settings and configuration choices include balance, phase, ground lift, start volume, maximum volume, and input selection/deactivation/naming.) Serinus loved what he heard, commenting that the midrange sounded gorgeous, the highs alive but not too bright, control was impeccable from the deepest bass to the most stratospheric highs, and timing was excellent. “This preamp really has no sound of its own. Rather than impose a distinct sonic signature, it gets out of the way of artists and engineers and lets music and the emotional truth it conveys speak for itself,” concluded Serinus, adding that the Soulution 727 deserved Stereophile’s highest possible recommendation. When John Atkinson measured the Soulution 727 he commented that it was the quietest preamplifier he had encountered. Overall, with both its line and phono inputs, the 727’s measured performance was superb, with extraordinarily low distortion and noise. (Vol.48 No.2 WWW) Treehaus Audiolab “The Preamplifier”: $24,000 incl. tubes
The A/Machines version of this retro-styled, two-chassis American tubed preamp, which was submitted for review, uses two 6CJ3 rectifier tubes and two 4P1L triode tubes, all new old stock. Because the 4P1L signal tubes can be microphonic, each one is fitted with three prominent tube-damping rings. Inputs and outputs are all single-ended. The simple signal path is transformer-coupled rather than the usual capacitor-coupled, and the volume control is also implemented with a transformer. The cores of these transformers are made from a nanocrystalline, soft magnetic metal, which is said to offer high permeability, hence efficiency, a smaller footprint, good temperature stability, and low hysteresis loss. There are two maximum gain settings: 6.75dB and 12.95dB. (John Atkinson found that the output impedance varied from 521 ohms at 20Hz to 677 ohms at 20kHz with the High setting and from 103 ohms at 20Hz to 147 ohms at 20kHz with the Low setting; all these values are sufficiently low.) Ken Micallef wrote that the Treehaus preamplifier “provided a largely neutral, silken, open conduit to the music.” Its neutral mien, allied to its low noisefloor and impressive information retrieval, unmasked both downstream and upstream components, allowing the system’s other components to define the sound’s color and tone. Nevertheless, it still delivered music with force and clarity Micallef had rarely heard from other preamplifiers. “The Treehaus Audiolab ‘The Preamplifier’ is a beast in velvet gloves, with a silken, soothing personality that doesn’t force itself on the music but rather invites it to bloom,” he concluded. Atkinson noted that the Treehaus Audiolab inverted polarity and concluded that its measured performance was considerably better than he was expecting from a circuit that uses a single triode as the active device. “It offers respectably low levels of distortion and noise at typical output voltages in both gain modes, provided the preamplifier is used with a power amplifier that has a high input impedance. That the distortion signature is primarily the subjectively benign second harmonic is a bonus.” (Vol.48 No.8 WWW) B: Quad 33: $1695 $$$
A reinvention of Quad’s bestselling solid state preamplifier from the 1960s, the 21st century 33 offers three pairs of single-ended line-level inputs, one balanced pair of inputs, and one pair of phono inputs, switchable between MM and MC. There are one pair of balanced line-level outputs, one single-ended pair, one fixed-gain Aux pair, and a ¼" headphone jack. The front panel features a small LCD display, backlit in orange, with user-variable brightness. Like the original 33, the new 33 offers Quad’s unique Tilt control, centered on 700Hz, which allows control of timbre and, to some degree, stereo image perspective. There is also a bass control that boosts or cuts the response below 50Hz by up to 3.5dB. Martin Colloms found that the sound of the 33, paired with the matching 303 power amplifier, had an impressive neutrality—“no fireworks but rather an easy refinement, everything in balance, almost (but not quite) self-effacing.” Bypassing the tone controls with the remote control made the presentation a little sweeter, more transparent and dynamic. There was some mild midrange bloom and loss of transparency with “tone” invoked. Colloms’s listening panel also noted slightly better stereo image clarity when the display was muted. With a Lyra Delos MC cartridge, the phono MC input was respectably quiet with no supply hum, just a little more, unobtrusive background shh than with the MM setting. The timbre was well balanced: a little bland, and reasonably spacious. Colloms fancied that the MM input was a tad clearer, more open and more dynamic than MC, so a higher-output moving coil might be favored. In John Atkinson’s test lab, the Quad 33 offered a wide frequency response, excellent channel separation, very low levels of noise and distortion, accurate RIAA equalization, and impressively high phono overload margins in both MM and MC modes. (Vol.48 No.7 WWW)
TEAC UD-701N: $4299.99
See Digital Processors. (Vol.47 No.12 WWW) Topping Pre90: $599 plus $249 for the Ext90 input extender $$$ ★
This affordable solid state preamplifier comes with a remote control and one pair each of balanced and unbalanced inputs and outputs. The optional $249 Ext90 adds one RCA and three XLR input pairs. Circuitry is all balanced. There’s no balance control, but the volume control operates in relay-controlled 0.5dB steps. “A transparent, noise-free sound,” decided Kalman Rubinson, who described the Pre90 as “a great bargain.” John Atkinson warned that the balanced input has very low impedance—1000 ohms—which will give a bass-light balance with source components that have a tubed output stage. But with its extraordinarily low levels of noise and distortion and very high channel separation, he concluded “the fact that that performance can be achieved in such a small chassis and for such a low price suggests that Topping has some serious audio engineering talent in-house.” Later brief, unpublished audition by Jim Austin found poor ergonomics and sub–Class A sound quality, so he demoted it to class B. Still, however, an exceptional value. (Vol.45 No.2 WWW) Deletions
Engström MONICA Mk3, not currently distributed in the US. PrimaLuna EVO 400 Preamplifier, Primare PRE35 Prisma, Schiit Freya+ F, not auditioned in a long time.
This massive tubed preamp uses two 12AX7 (ECC83) twin triodes for line-input voltage gain; one 12BH7 as a driver; two 12AX7s for phono-input voltage gain; and one 12BH7 as a driver. There are also two 5AR4 rectifiers. The phono stage also uses 1:9 and 1:18 Cinemag step-up transformers. Listening to the phono input, Ken Micallef found that the Yellowstone was among the most neutral and transparent amplification machines he’d heard in-house. “It adds just a touch of warmth,” he wrote, “giving music a sweet liquidity and natural sonic flow I never grew tired of.” He noted that tonally, it played remarkably uniformly—“nothing tweaked, no frequency pushed, no agenda declared. It never called attention to itself; it let the music breathe and move. Pinning down its sonic character beyond that touch of warmth proved genuinely difficult.” In addition, the Yellowstone delivered a physical, sprinter-grade power and purpose. In the test lab, there was some high-end rolloff, the amount depending on the volume-knob position. With the control set to unity gain, the response rolled off by just 1dB at 100kHz. With it set to the maximum, the output was down by 2.2dB at 20kHz. (The manufacturer suspected that the early production review sample may have an out-of-spec capacitor.) The preamplifier could deliver high voltages into 100k ohms but clipped at just 453mV into 600 ohms. The distortion signature was predominantly second harmonic in nature but at a low level with the line input but higher in level with the phono input. Overall, the Yellowstone’s measured performance was typical of a purist tubed preamplifier. (Vol.49 No.8 WWW) Audio-GD Vacuum HE1 XLR balanced: $3999
This large, heavy, Chinese-made, tubed, all-balanced preamplifier doesn’t have a phono input, but it offers three balanced (XLR) and two single-ended (RCA) line inputs, balanced and single-ended outputs, and comes with a remote control. Tube complement is six 6H2N-EB twin triodes and four 6U4N-EB rectifiers, all Russian-made. Compared with the Lab 12 Herb Reichert, the Vacuum HE1 played slightly richer and thicker with more obvious three-dimensionality. Compared with the PrimaLuna EVO 400, the Vacuum HE1 XLR distinguished itself with quicker, sharper transients, more thoroughly exposed detail, harder-punching bass, and stronger pace, rhythm, and timing, Reichert noted. “Audio-GD’s Vacuum HE1 XLR line-level preamp allowed diverse audio sources to sound maximally diverse—and that, folks, is transparency,” Reichert concluded. In the test lab, John Atkinson found that the preamplifier’s top-octave output varied with the setting of the volume control. With it set to the maximum, the response was down by 5.5dB at 20kHz. With it set to “60,” the 20kHz output was down by 0.9dB. Harmonic distortion was fairly low and was dominated by the second and third harmonics. Atkinson warned that the HE-1 shouldn’t be used with power amplifiers that have an input impedance of 10k ohms or lower. (Vol.46 No.10 WWW) Ayre Acoustics KX-8: $6500; $11,000 as reviewed
This line preamplifier offers two pairs of balanced and three pairs of unbalanced inputs, one pair of balanced outputs, one pair of single-ended outputs, and balanced and single-ended headphone outputs. Three optional digital input modules are available: the X-8 DAC module adds $1500; the X-8 USB2 module adds $1000; the X-8 Net2 Ethernet module adds $1500. The KX-8’s zero-feedback, fully balanced analog circuitry features Ayre’s Equilock gain stage, which uses transistors operating primarily in current mode, Ayre’s Continuously Variable Gain Transimpedance (CVGT) volume control, and the company’s Diamond circuit for the outputs. Used as a line preamplifier, John Atkinson found that compared with a digital processor feeding the power amplifiers directly, the balance was a touch warmer with the KX-8 in the chain, but more significantly, there was an improved sense of what the late Art Dudley used to call “force.” This character was also present with headphones, coupled with superbly stable imaging—“the KX-8’s headphone amplifier is first-rate,” wrote Atkinson. The review sample had not yet been certified by Roon, so Atkinson auditioned the digital modules with the MConnect app installed on his iPad mini and network data sent to the KX-8’s Ethernet input. Image depth with the KX-8’s digital inputs was very similar to what he had experienced with the analog input, with voices projected a little forward in the soundstage. On the test bench, the KX-8’s measured performance as a line preamplifier and headphone amplifier was very good for a design that doesn’t use global feedback, especially at lower volume control settings, which, with the CVGT volume control, will maximize S/N ratio with the analog inputs and resolution with the digital inputs. (Vol.48 No.5 WWW)
Benchmark’s usual approach to design is to out-spec the competition, and so it is here. Like other Benchmark equipment he has tested, the affordable LA4 challenged the resolution of John Atkinson’s test instruments, with “superb” channel separation, “extremely low noise, and virtually no power-supply-related spuriae.” Restricting his measurement to the audio band, Atkinson found an “astonishing” S/N ratio of 105.5dB for both channels; it remained extremely low across the audioband. He summed up: “Benchmark’s LA4 is the widest-bandwidth, widest-dynamic-range, lowest-noise, lowest-distortion preamplifier I have encountered.” In his listening room, Kalman Rubinson compared the LA4 to a cable—and couldn’t hear any difference. He concludes, “the LA4 is probably the most transparent and revealing audio component I’ve ever used. It does not seem to leave any fingerprints on the sound.” See also Herb Reichert’s review of Benchmark’s similar HPA4 headphone amplifier (see “Headphones”). Atkinson found that the LA4 had a more upfront presentation than the MBL N11 or Pass Labs XP-32, with less soundstage depth apparent on his own recordings. (Vol.43 Nos.1 & 11, Vol.44 No.3 WWW) Canor Hyperion P1: $13,500
This massive Slovakian preamp uses four 6922 tubes and two 6H30PI tubes. There are four pairs of balanced inputs and five pairs of single-ended inputs. (One pair can be set to fixed output.) Outputs include two balanced pairs and one single-ended pair. The circuit uses zero global feedback, and the 64-step balanced attenuator adjusts volume in 1dB increments. Jason Victor Serinus found that the Hyperion P1 distinguished itself with one of the airiest and widest soundstages that any preamp has delivered in his music room. Timbres were neutral and true, and the midrange was quite beautiful, albeit with colors less bold than with some gear. “Given that my room is prone to brightness,” he elaborated, “I enjoyed the fact that the P1 takes a soft and gentle approach to the top octaves. This treble reticence will prove a benefit in many systems.” His conclusion? “Highs were smooth, and music was graced with such a profound sense of air and spaciousness that it elicited smile after smile.” On John Atkinson’s test bench, the Hyperion P1 offered superb measured performance, with a wide frequency response and very low levels of noise and distortion. “However,” he cautioned, “this preamplifier does need to be used with power amplifiers that have a high input impedance.” This is due to the increase in source impedance at low frequencies: 6.6k ohms at 20Hz compared with 274 ohms at 1kHz and 20kHz for the balanced outputs. (Vol.48 No.7 WWW) CH Precision L10 Reference Line Preamp: $88,500
This modular, dual-chassis, dual-mono, direct-coupled, two-channel line-level preamplifier operates in current mode rather than voltage mode, which means that the gain comes after the volume control. The signal/noise ratio thus remains the same irrespective of gain. Unusually, the L10 offers a DC-offset calibration for each source component: the analog DC offset is measured, then converted to digital so that DSP can be used to drive current injectors in the signal path to provide the appropriate compensation. (The audio signal remains in the analog domain.) Jason Victor Serinus found that offset calibration resulted in sound that was “more intimate, natural, clear, present, sharply defined, detailed, and dynamic.” Serinus was impressed by the CH Precision, writing that it delivered a level of clarity and detail that rivaled the best preamps he’d ever heard, but without sounding cold and analytical. The L10’s output stage can be operated with local or global feedback. John Atkinson found that while distortion was higher with local feedback than it was with global feedback, it was still low in absolute terms. “Commendably,” he wrote. “there was no increase in the THD+N in the top audio octaves with either feedback setting, or with the load impedance reduced to the current-hungry 600 ohms.” Serinus summed up his time with the L10 by writing “I remain in awe of its clarity, transparency, and commitment to musical truth. It offers a stunningly detailed portal to musical art.” (Vol.49 No.2 WWW)
This immaculately made, modular, solid state, Swiss line preamp is fully discrete, fully balanced, pure class-A, DC-coupled, fully symmetrical, and complementary. Unusually, the L1 monitors and counters DC offset at various points in the circuit and measures and compensates for DC offset on each input. The L1’s shunt-regulated power supply has two transformers and minimizes noise, but the preamp can also be powered by the optional X1 supply. This, according to CH, lowers the system noisefloor even further and increases “dynamic range, resolution and speed of response, transparency, detail, and above all, musicality.” Jim Austin auditioned the L1 both with its internal supply and with the X1. As much as he was impressed by the L1 alone, he noted that while the X1 improved the sound, so did the input DC calibration feature. “I found their sonic influence nearly identical,” he wrote. “Musical flow seemed improved; individual instruments had more drive.” He also found that the soundstage was more concretely laid out, easier to parse, and deeper. “Sonically, this could all be attributed to improved precision in the musical signal, both within and across channels, resulting most obviously in images within the soundstage being nailed in place and, as a result, seeming more palpable.” “Assuming you can pay the tab, it’s highly recommended,” Austin concluded about the combination. On the test bench, the CH Precision L1’s measurements were superb, some of the best John Atkinson had encountered, though he didn’t find any significant measured differences when he added the X1. (Vol.47 No.11 WWW) Dan D’Agostino Master Audio Systems Relentless: $165,000
The steampunk-styled Relentless places the power supply and control circuitry chassis between two mono preamplifier chassis. The Relentless utilizes four-layer circuit boards and hermetically sealed relays with gold-plated contacts and carefully segregates the analog circuitry, the digital circuitry, and the ground planes. The signal path is “fully complementary and balanced from the input to the output.” Each preamp’s discrete, differential FET input stage can handle 30V! The inputs and outputs are all balanced, and the Zone 1 and Zone 2 pairs of outputs can have volume adjusted independently either with the volume control rings around the meters or with the weighty, rechargeable, volume-knob–shaped remote control. (A new remote control is forthcoming.) Listening to a familiar recording of Mahler’s Symphony 5 performed by Rafael Payare conducting L’Orchestre symphonique de Montréal, Jason Victor Serinus was amazed to hear instruments and images that were larger, more tangible, and more emotionally impactful than he has grown accustomed to even with the outstanding preamps in his reference system. “The visceral impact of timpani, bass drum, and the lowest double bass lines increased. I’d long experienced lightning-fast attacks and credible leading edges on bass, but the center of bass tones occasionally lacked ultimate shape and color. Now, bass absolutely rang true, from first attack to final decay. Dynamic contrast between soft and loud passages increased. … The Relentless metamorphized organized sound into an expressive vehicle that impacted my heart and gut in revelatory new ways.” John Atkinson’s measurements found an input impedance close to 1M ohm, an output impedance of 2 ohms, a frequency response that was flat from 10Hz to 100kHz, and very low noise, harmonic distortion, and intermodulation distortion, even at high levels into the punishing 600 ohm load. An optional Digital Streaming Module costs $19,500. (Vol.47 No.9 WWW) EM/IA Autoformer: $4875 in copper, $8850 wound and wired with 0.999 silver.
This inscrutable-looking, remote-controllable black box with an LCD readout on the front panel replaces a conventional preamplifier. It offers inductive attenuation, in which separate autoformers, with Permalloy cores and multiple taps (one for each channel), allow the volume to be adjusted from +7dB to –54dB in 1dB steps. It has three inputs and two outputs, and balance can be adjusted with the remote. Alex Halberstadt compared the copper-wire version with PrimaLuna’s EVO 400 preamplifier and found that while music still sounded satisfyingly forceful (if not quite as fun as with the tubed preamp), John McLaughlin’s Extrapolation was disconcertingly clearer. What stayed with Halberstadt most during subsequent listening sessions was the remarkable coherence the EM/IA brought to his system. While there was a slight reduction in sheer grunt and propulsion, music sounded more natural, present, and intentional, “less like a collection of sounds and more like a real performance.” The EM/IA more consistently drew his attention to the music rather than the sound. When Halberstadt auditioned the silver version, he heard “sound that was even more detailed and clear, without any of the whitish, bleached cast that some silver components can impart. Recordings sounded bigger than through its copper sibling and created images that were even more uncannily free of the speakers. Most memorably, music became eerily holographic.” (Vol.47 No.4 WWW)
The solid state PREi features discrete, dual-balanced signal paths, with ceramic circuit boards using pure gold traces, a class-A output stage, a 100-step precision analog volume control with intelligently calculated graduated steps, and a switch-mode power supply. It is supplied with a 15A Kimber Kable PK14 Base series power cord. Inputs and outputs are balanced and single-ended, and the selected input, volume level, and volume-preset choice are displayed on an OLED screen. A menu allows control of balance, display brightness, a screen saver, and factory reset. Jason Victor Serinus wrote that everything about the EMM Labs PREi felt so right. Comparing the presentation with the D/A processor connected directly to the power amplifiers, he noted that without the PREi, “colors were neither as rich nor as intense. The background wasn’t as black or transparent, and there was a subtle barrier between me and the sound. With the PREi, the veil was lifted. I heard more color and detail. The difference was not subtle.” Serinus concluded that no matter how you say it, slice it, or dice it, the EMM PREi was among the finest preamps he’s reviewed. In John Atkinson’s test lab, the PREi offered superb measured performance, with superbly low levels of noise, harmonic distortion, and intermodulation distortion. (Vol.49 No.6 WWW) HoloAudio Serene KTE: $3098 ★
Herb Reichert found that this “supertransparent” solid state line preamp enhanced the sound quality with every source he tried: “The Serene gave the May a dose of sunlight and a shot of adrenalin. [It added] grace and liquidity to the sound of the Mola Mola Tambaqui and punch and bass authority to the Denafrips Terminator Plus.” He also noted that it enhanced the spatial presentation of Sutherland Engineering’s Little Loco phono stage—“adding force and rhythmic nuance while peeling away a layer of shadow that had previously obscured the perimeters of the Loco’s projected soundscape.” (Vol.45 No.6; Vol.46 No.1 WWW) Lab12 Pre1: $2495
This line stage from Greece uses a single high-transconductance, twin-triode, E88CC tube per channel without any loop feedback to give a high maximum gain of 21dB. It offers five line-level (RCA) inputs and two outputs: one RCA, the other XLR. Herb Reichert found that compared to PrimaLuna’s tube-rectified EVO400, the Pre1 sounded turbocharged. “Could this be the difference between solid state and tube rectifiers?” he wondered. Compared with HoloAudio’s higher-priced KTE Serene, Reichert noted that the Pre1’s clarity/transparency/invisibility was equal to that of the Serene but the Pre1’s transparency was less stark than the Serene’s, “breathier and more vibrant with a slight, just-right aura of tube radiance.” He also found that the Pre1 couldn’t match the Serene “for low-end gut-punch, upper-bass detail, or dynamic swagger.” However, using the Pre1 to drive Genelec’s G Three active loudspeakers, Reichert realized that he was experiencing “a more refined, grainless, ‘invisible’ preamplifier than any I could recall using.” (Vol.46 No.1 WWW)
This beautiful, multiple-input, multiple-output line preamplifier can be used in its Unity Gain mode for maximum sound quality or with a higher-gain setting. Jason Victor Serinus found that the N11 in its higher-gain mode “brought out the warm core of every note,” adding that it enabled him to hear “the subtle differences of interpretation, dynamics, and color that are the portals to the truth behind the notes.” He found that Unity Gain moved the soundstage farther back in his system with his D/A processors. While perspective was clarified, this mode made the sound less open with slightly reduced transparency and bass. Ultimately, he felt that the N11’s Unity Gain “toned down the noisy top ends of some recordings, making for easier listening.” The N11’s measurements revealed extraordinarily low noise and distortion, especially in Unity Gain mode. However, the CD input’s unbalanced impedance of 2.3k ohms will tax sources with a tubed output stage. Those can be used with the balanced inputs or the unbalanced Aux inputs, which have impedances of 10k ohms and 47k ohms, respectively. To his surprise, John Atkinson found that inserting the N11 between his DAC and power amplifiers resulted in a more palpable presentation, with a deeper soundstage. (Vol.43 Nos.7, 11 & 12; Vol.44 No.3 WWW) McIntosh C12000: $19,000
This massive, two-box preamplifier features separate tubed and solid state output stages. The signal circuitry is housed in one chassis; the control circuitry and power supply are in the second chassis. Tubes are 12AX7As and 12AT7s. There are six pairs of balanced line inputs, four pairs of single-ended line inputs, and two pairs of single-ended phono inputs, each of which can be set independently to moving magnet or moving coil. (The phono stage is tubed.) There is a headphone output as well as balanced and single-ended outputs. Stephen Mejias went back and forth between the tubed and solid state outputs, but listened mostly with tubes. However, listening to a percussive and impactful recording of Chabrier’s España, he “got a huge kick in the pants from the solid state presentation; the dynamics were more impressive compared to the tubed output.” Mejias decided that the genre of the music and the type of the recording will influence the choice between tubes and solid state. “It’s good to have access to both,” he concluded, adding that with the Decca 2022 reissue of Wagner’s Ring Cycle, “the quantity of musical information being launched at me was almost overwhelming.” The C12000 turned in an impressive performance on John Atkinson’s test bench, offering very low distortion and noise with both line and phono inputs and from both tubed and solid state outputs. “The McIntosh C12000’s measured performance is among the best I have encountered from a preamplifier,” he wrote. (Vol.46 No.11 WWW) Moon 891: $25,000
See Digital Processors. (Vol.48 Nos.1 & 3 WWW) NAD Masters Series M66: $7199
See Digital Processors. (Vol.47 No.11 WWW) Naim NSC 222: $8999
This full-function streaming preamplifier can be used with its internal power supply or with Naim’s NPX 300 external supply ($8999). “The fully loaded NSC 222 packs quite a punch in terms of facilities and features,” commented Martin Colloms, because as well as unbalanced line inputs, it includes a medium-sensitivity moving magnet phono preamplifier, a comprehensive streamer/DAC that can be controlled with the matching Naim app (for Android or iOS), and a dedicated headphone amplifier. Listening to the digital inputs, Colloms found that the NSC 222 showed high resolving power, revealing quite subtle differences between 16/44.1, 24/96, and 24/176.4 WAV files—and finally DSD64. The last was his favorite, revealing a marked degree of crisp precision and musical communication. While MC and his team of listeners liked what they’d heard with the internal supply, the sound was obviously better, in almost all aspects of sound quality, including the headphone output, with the NPX 300. Colloms summed up the NSC 222 by writing “All operational modes, analog disc, digital audio streaming and decoding, plus headphone and loudspeaker drive were consistent, distinguished by an innate sense of energy, imbued with transparency and microdetail. There was also a significantly open, wide-band character, somewhat different from the mildly ‘contained’ sense of some previous Naim iterations. And it is that satisfying, involving rhythmic quality that continues to entertain.” John Atkinson commented that Naim’s NSC 222 offered generally excellent measured performance via its digital inputs, with about 18-bit resolution and low jitter, and via its line and phono analog inputs. He did note that the ultrasonic response rolled off by 3dB at 41kHz with all these inputs, but this won’t have subjective consequences. (Vol.47 No.1 WWW)
A zero-feedback, hybrid design with an outboard power supply and a tube-based “precision balancing stage,” the Jubilee combines four ECC82 tubes with a semiconductor-based, discrete, unity gain output stage. There are both RCA and XLR inputs, the latter equipped with unity-gain isolation transformers. Front panel buttons allow polarity to be inverted and gain switched between High and Low, the latter recommended for use with high-sensitivity speakers or very high-gain amplifiers. A switch allows the input and output XLR jacks’ grounds to be connected or lifted—Jason Victor Serinus found that the “Connect to Ground” setting delivered a fuller, richer, tighter, more profound bottom end, with weightier images and increased transparency, than he heard with the ground floated. “It was a total joy to listen to,” he wrote, adding that there was a seductive smoothness in the midrange. The soundstage was huge and deep “if not with ultimate transparency.” On the test bench the Jubilee’s noisefloor was higher in level and channel separation lower than with the best-measuring solid state preamplifiers, but the Octave preamp had no problem driving low impedances. Despite the lack of global negative feedback, distortion was low in level and primarily comprises the subjectively innocuous second harmonic. Price with optional stepped attenuator is $45,500. (Vol.48 No.10 WWW) Pass Laboratories XP-32: $20,212.50 in silver; $21,212.50 in black
Replacing the well-regarded XP-30, the three-box XP-32 looks almost identical. To minimize noise, each channel’s audio circuitry is housed in a separate chassis with the “dirty” control and power-supply circuitry in a third. Internal improvements include new transformers and DC-coupling of the balanced and single-ended inputs. The output stage runs a higher class-A bias with lower output impedance than the XP-30, and the volume control now operates in 0.5dB steps rather the earlier preamp’s 1dB steps. John Atkinson was enthralled by the XP-32’s transparency, hearing small details in his own recordings that he had not been fully aware of before. “A great preamplifier will allow through so much information, so much of the music, that the shortcomings of lesser speakers and amplifiers can be forgotten. The Pass Labs XP-32 satisfies that definition,” he concluded. In a follow-up, Jim Austin compared the XP-32 with the two-chassis XP-22. He was impressed with what he heard: “The XP-32 was just slightly more explicit than the XP-22. It was immediately noticeable on any music I played,” he wrote, concluding that he “thought the XP-22 preamplifier let through all the music, or all that mattered, but I guess it didn’t, because the XP-32 lets through just a little bit more.” (Vol.44 No.3, Vol.45 Nos.4 & 6 WWW) PS Audio PMG Signature: $8999
This solid state preamplifier features a fully balanced, pure class-A signal path using a “folded cascade” topology and zero-feedback diamond-buffer output stages. The power supply eschews electrolytic capacitors in favor of a large array of long-life film capacitors—a design choice intended to provide faster transient power and a lower noisefloor. There are two pairs of single-ended RCA inputs, four pairs of balanced XLR inputs, two pairs of RCA outputs, and two pairs of XLRs. Control is via a front-panel touchscreen or a remote control. Rogier van Bakel was skeptical about the benefit offered by a preamplifier when a source component equipped with a volume control could be connected directly to a power amplifier. Nevertheless, he found that with its high measured input impedance, low measured output impedance, and robust current drive, the PMG preamp let the source operate comfortably while feeding the amplifier a signal it can accept with minimal strain. The result in his system was “increased ease. I got cleaner leading edges and slightly firmer image outlines.” He summed up his review by writing “In a field crowded with embellishers and sweet talkers, PS Audio’s PMG Signature preamplifier speaks plain truths. I’d have no reservations about installing it as a reference.” John Atkinson summed up the PMG Signature’s performance by writing “the PS Audio PMG Signature is one of the best-measuring preamplifiers I have had in my test lab.” (Vol.49 No.5 WWW)
The solid state Swiss 727 uses a switched-mode power supply (SMPS). While it has an optional MC/MM phono section, Jason Victor Serinus auditioned it as a line preamplifier. A large rotary knob to the right of the central display handles volume, input selection, display brightness, and programming/configuration adjustment. (Settings and configuration choices include balance, phase, ground lift, start volume, maximum volume, and input selection/deactivation/naming.) Serinus loved what he heard, commenting that the midrange sounded gorgeous, the highs alive but not too bright, control was impeccable from the deepest bass to the most stratospheric highs, and timing was excellent. “This preamp really has no sound of its own. Rather than impose a distinct sonic signature, it gets out of the way of artists and engineers and lets music and the emotional truth it conveys speak for itself,” concluded Serinus, adding that the Soulution 727 deserved Stereophile’s highest possible recommendation. When John Atkinson measured the Soulution 727 he commented that it was the quietest preamplifier he had encountered. Overall, with both its line and phono inputs, the 727’s measured performance was superb, with extraordinarily low distortion and noise. (Vol.48 No.2 WWW) Treehaus Audiolab “The Preamplifier”: $24,000 incl. tubes
The A/Machines version of this retro-styled, two-chassis American tubed preamp, which was submitted for review, uses two 6CJ3 rectifier tubes and two 4P1L triode tubes, all new old stock. Because the 4P1L signal tubes can be microphonic, each one is fitted with three prominent tube-damping rings. Inputs and outputs are all single-ended. The simple signal path is transformer-coupled rather than the usual capacitor-coupled, and the volume control is also implemented with a transformer. The cores of these transformers are made from a nanocrystalline, soft magnetic metal, which is said to offer high permeability, hence efficiency, a smaller footprint, good temperature stability, and low hysteresis loss. There are two maximum gain settings: 6.75dB and 12.95dB. (John Atkinson found that the output impedance varied from 521 ohms at 20Hz to 677 ohms at 20kHz with the High setting and from 103 ohms at 20Hz to 147 ohms at 20kHz with the Low setting; all these values are sufficiently low.) Ken Micallef wrote that the Treehaus preamplifier “provided a largely neutral, silken, open conduit to the music.” Its neutral mien, allied to its low noisefloor and impressive information retrieval, unmasked both downstream and upstream components, allowing the system’s other components to define the sound’s color and tone. Nevertheless, it still delivered music with force and clarity Micallef had rarely heard from other preamplifiers. “The Treehaus Audiolab ‘The Preamplifier’ is a beast in velvet gloves, with a silken, soothing personality that doesn’t force itself on the music but rather invites it to bloom,” he concluded. Atkinson noted that the Treehaus Audiolab inverted polarity and concluded that its measured performance was considerably better than he was expecting from a circuit that uses a single triode as the active device. “It offers respectably low levels of distortion and noise at typical output voltages in both gain modes, provided the preamplifier is used with a power amplifier that has a high input impedance. That the distortion signature is primarily the subjectively benign second harmonic is a bonus.” (Vol.48 No.8 WWW) B: Quad 33: $1695 $$$
A reinvention of Quad’s bestselling solid state preamplifier from the 1960s, the 21st century 33 offers three pairs of single-ended line-level inputs, one balanced pair of inputs, and one pair of phono inputs, switchable between MM and MC. There are one pair of balanced line-level outputs, one single-ended pair, one fixed-gain Aux pair, and a ¼" headphone jack. The front panel features a small LCD display, backlit in orange, with user-variable brightness. Like the original 33, the new 33 offers Quad’s unique Tilt control, centered on 700Hz, which allows control of timbre and, to some degree, stereo image perspective. There is also a bass control that boosts or cuts the response below 50Hz by up to 3.5dB. Martin Colloms found that the sound of the 33, paired with the matching 303 power amplifier, had an impressive neutrality—“no fireworks but rather an easy refinement, everything in balance, almost (but not quite) self-effacing.” Bypassing the tone controls with the remote control made the presentation a little sweeter, more transparent and dynamic. There was some mild midrange bloom and loss of transparency with “tone” invoked. Colloms’s listening panel also noted slightly better stereo image clarity when the display was muted. With a Lyra Delos MC cartridge, the phono MC input was respectably quiet with no supply hum, just a little more, unobtrusive background shh than with the MM setting. The timbre was well balanced: a little bland, and reasonably spacious. Colloms fancied that the MM input was a tad clearer, more open and more dynamic than MC, so a higher-output moving coil might be favored. In John Atkinson’s test lab, the Quad 33 offered a wide frequency response, excellent channel separation, very low levels of noise and distortion, accurate RIAA equalization, and impressively high phono overload margins in both MM and MC modes. (Vol.48 No.7 WWW)
See Digital Processors. (Vol.47 No.12 WWW) Topping Pre90: $599 plus $249 for the Ext90 input extender $$$ ★
This affordable solid state preamplifier comes with a remote control and one pair each of balanced and unbalanced inputs and outputs. The optional $249 Ext90 adds one RCA and three XLR input pairs. Circuitry is all balanced. There’s no balance control, but the volume control operates in relay-controlled 0.5dB steps. “A transparent, noise-free sound,” decided Kalman Rubinson, who described the Pre90 as “a great bargain.” John Atkinson warned that the balanced input has very low impedance—1000 ohms—which will give a bass-light balance with source components that have a tubed output stage. But with its extraordinarily low levels of noise and distortion and very high channel separation, he concluded “the fact that that performance can be achieved in such a small chassis and for such a low price suggests that Topping has some serious audio engineering talent in-house.” Later brief, unpublished audition by Jim Austin found poor ergonomics and sub–Class A sound quality, so he demoted it to class B. Still, however, an exceptional value. (Vol.45 No.2 WWW) Deletions
Engström MONICA Mk3, not currently distributed in the US. PrimaLuna EVO 400 Preamplifier, Primare PRE35 Prisma, Schiit Freya+ F, not auditioned in a long time.
