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Positive Feedback ISSUE 66
Phono Stage - The New Kid on the Block
as reviewed by Myles B. Astor
High-end audio is often a giant—not to mention often frustrating—conundrum. Take for example those crème de la crème moving coil cartridges blessed with miniscule 0.1 to 0.3 mV outputs that test the mettle of all but the best phono stage designs. Sadly, audiophiles weren't until the most recent generation (or two) of phono stages (especially with those using "pure" tube phono sections, because of noise, dynamic and frequency response constriction and loading considerations) able to harness the inherent potential of these moving coil cartridge designs. So as a devout analog lover, my mission for the past year or so, was to audition the newest breed of phono sections capable of amplifying the lowest output MC cartridges beginning with the Avid Audio Pulsare and now continuing with the new reference quality Doshi Audio phono stage.
Can't Get No Satisfaction
Doshi Audio, a relative newcomer to the high-end audio scene, put themselves squarely on the map with some extremely impressive demonstrations at Rocky Mountain Audio Fest. Indeed, it was hearing the Doshi electronics (phono, tape preamplifier and amplifiers) paired with Wilson Audio Sashas at a recent RMAF that prompted me to further investigate this company's new phono section.
Nick (short for Nishith) Doshi, the brains (and brawn) behind the operations, holds both a Bachelor's Degree in Physics and a Master's Degree in Electrical Engineering from FDU. Post-baccalaureate, Nick spent the next 25 years of his life working at various radio and TV stations developing an inquisitiveness into how the equipment worked and is put together. During this period, Nick, like so many of us [audiophiles], observed that, "while solid-state equipment measured better than tubes, solid-state was bested by the simplest tube designs especially when it came to dynamics." Nick concluded "that if musical satisfaction, not measurements, was the ultimate goal, he needed to simplify the circuit." This led to his experimenting with tube based electronic circuitry that, "offers greater gain per stage and can be operated without feedback."
Exploiting An Old Technology
The Doshi phono stage is a two piece affair consisting of a large (and rather heavy at that) outboard power supply connected to via a specially made, Silver-plated Copper/Teflon dielectric umbilical cord (the same wire is also used inside the phono stage) a second unit housing the more sensitive electronics section. Nick opted for an outboard power supply in order to reduce the phono stage's noise floor—not to mention he couldn't shoe horn his dual choke regulation design into one box.
Four switches located on the front panel of the electronics section allow for quick and easy selection of cartridge loading, phono input and muting function. The far right knob switches between one MC and two MM inputs (the Doshi can also be custom ordered with two MC inputs). MC1 allows for 12 loading values while MM1 and MM2 are preset for 12 and 47 K loading, respectively. (Although the unit comes with two outputs, the owners' manual cautions against loading them down to much if both are used.) The far left knob allows for easy muting when turning the phono stage on/off, changing LPs or swapping phono cables. Finally, the two middle knobs allow for dual mono loading with twelve values including 20, 45, 70, 100, 180, 400, 600, 900, 1200, 1800, 2700 and 6000 ohms. Phono stages equipped with a second (optional) MC section use one control per section; thus the left and the right loading knob controls MC 1 and MC 2, respectively. Located on the rear of the unit are three sets of single-ended inputs along with two single-ended outputs.
One of Nick's primary objectives when designing his phono stage was separating the MM from MC sections in order to prevent mixing of the ground current return paths. The phono MM section comprises the first gain stage and uses four paralleled JJ/Tesla 12AX7s to drive a passive equalization section; the output is then fed into a pair of paralleled Canadian/GE 12AT7s. While this approach might seem at first blush like overkill, the paralleled triode sections Nick points out, "are an elegant way to decrease output impedance of the first MM amplification stage while at the same time improving the S/N ratio." In this case, paralleling the 12AT7s drops the phono section's output impedance to around 1K. Coincidentally, it turns out that operating the 12AX7s in pull and the 12AT7s in push mode results in the same load/drain to the power supply, no change in current draw and eliminates much of the current modulation at the power supply. In short, better dynamic response.
Nick also devoted a great deal of thought to optimizing the design of the moving coil phono section. For all intents and purposes, cartridges are a balanced drive device and because of that, Nick opted for a JFET input a la John Curl and a custom designed interstage coupling transformer (made by Brian Sowter (UK) wound with PCOCC wire) to convert from balanced to single-ended operation. In addition, the interstage coupling transformer also optimally loads the FETs and optimizes the power transfer function, avoids signal compression and provides isolation between the two stages.
Nor did Nick skimp when it came to parts quality. Both custom-made Clarity ICW MR (Clarity's all-out effort) and ESA series (Clarity's mid-priced series) capacitors are found inside the Doshi phono stage. Clarity's MR series capacitors consist of an ultra pure Al metallization along with a "non-standard" polypropylene film housed in a colored acrylic tube. This tube is then encapsulated in epoxy resin to further control the capacitor's internal resonance, dielectric absorption and overall sonic performance. According to Nick, the MR series is audibly clearer than any other cap he auditioned—including interestingly enough the highly regarded Teflon dielectrics—without smearing. The list of the parts used inside the Doshi goes on and includes Takman vapor deposited carbon film resistors, Audionote plate load inductors and Shalcro switches.
Revisiting Cartridge Loading
To load, or not to load, that is the question? For much of my audiophile life, I was a made member of the unloaded, 47K crew. After all, loading—especially with pure tube phono sections—sadly meant throwing away ever so precious gain with the concomitant loss of dynamics, frequency response and added noise and hiss levels. In short, the music had all the qualities of Mississippi Delta mud.
The arrival of the Doshi phono stage, however, forced me to reconsider many of my preconceptions about the importance of cartridge loading. Interestingly the Doshi, unlike many other phono stages, doesn't allow for cartridge loading north of 6000 ohms. Nick explained that the rationale behind that choice is directly traceable to both, "the issue of Johnson noise (noise intrinsic to semiconductor devices such as transistors and resistors) that may affect the performance of high output impedance cartridges and that 47K doesn't because of the combination of electrical (loading) and mechanical damping (cartridge resonance), provide optimal loading for moving coil cartridges." Nick adds, "the elastomeric damping of the cantilever is designed to optimally control the mechanical resonance while the electrical loading acts to damp the coil's electrical resonance. When the electrical loading is as in a 47K load, 'very light,' the inductance of the coil produces a transient overshoot." Nick continues, "listeners perceive this [resonance] as enhanced dynamics or leading edge detail but it is not quite what is on the vinyl. Too much of this phenomenon masks low level detail." In other words, "right source, right load equals better power transfer." In Nick's experience, "many moving coil cartridges prefer 'seeing' a 30 ohm load, although he always suggests experimenting with values from 300 ohm to 1K-ohm (note some MC cartridges such as the Benz's or high output MC cartridges sport internal impedances as high as 70 ohms). Nick also notes, "a law of diminishing returns when one starts approaching 30:1 load to cartridge output impedance ratios."
Now that the issue of whether "to load, or not to load" is settled, the next question is whether the Doshi—or for that matter any phono stage—allows for optimal cartridge loading? Perhaps the only phono stage that fits the bill was John Curl's old Vendetta Research phono stage that allowed for, in conjunction with a DVM (under a value of 200 ohms), ultra-precise loading down to the ohm. To paraphrase John, "cartridge loading and proper cartridge VTA/SRA affect the sound in similar ways."
Each of the low output moving coil cartridges in house (ZYX Omega Au, Haniwa, Ikeda 9TT or the Lyra Atlas or Titan i) preferred seeing loads between 75 and 180 ohms with the Doshi. For instance, my current reference Lyra Atlas sounded too dead and muddy at 75 ohms and too bright, shouty and two-dimensional at 6000 ohms. With the Atlas loaded at 100 ohms, Joe Gordon's trumpet displayed a good balance between instrumental timbre and the proper energy without crossing over into forbidden territory where the instrument sounded too hard and two-dimensional on that wonderful 1960 live recording of Shelly Manne at the Blackhawk, Vol. 3 (Contemporary S 7579—original B/G). Advancing the twin loading knobs to 180 ohms bought some additional "air" but unfortunately, at the expense of three dimensionality and low frequency tautness. Turning the knob fully clockwise to 6000 ohms collapsed the soundstage and in particular, front-to-back depth and instrumental layering. Thus in an admittedly imperfect world, intermediate loading values between 100 and 180 ohms (especially if the 1:10 ratio holds up) would allow for greater experimentation and possibly even better sound from these cartridges. In defense of his phono stage, Nick also pointed out that once an optimal range has been determined, finer loading selections are available upon request.
After all is said and done, the Doshi's 72 dB of total gain (the MC and MM sections possess 26 and 46 dB of gain, respectively) allows the phono stage to handle without any extraneous noise any cartridge thrown at it ranging from the miniscule 0.15 mV output of the Ikeda 9TT to the rather generous by comparison 0.55 mV output of the Lyra Atlas cartridge. Other ancillary gear used with the Doshi included the outstanding Kubala-Sosna Elation and Emotion power cords, Transparent, MIT, Kubala-Sosna and Audience phono cables and the Silver Circle 5se power line conditioner.
Walking the Walk
The Doshi phono stage rekindled long forgotten memories of HP's seminal Goldmund Reference turntable review. Here for the very first time in HP's experience was a turntable that allowed him to clearly differentiate the cartridge's sonic signature from that of the playback deck. Today's current crop of turntables, arms and cartridges possess coloration levels undreamt of years ago (thanks to materials science and vibration isolation, less resonant tonearms, improved platter drive systems and last but not least better designed cartridges) often making the phono stage now the weakest link in the analog playback chain. The latest generation of phono stages such as the Doshi has once again leveled the playing field—bringing the sonic signature of the table, arm, cartridge and not to be forgotten phono cable—once again to the forefront. As should be the case with any top flight phono stage, the Doshi allows each cartridge's trademark sonic signatures to emerge unscathed. The Titan i's resolution, low frequency impact and slight edge on strings. The ZYX Omega Au's ability to engage the listener on top of a touch of warmth and smoothing in the lower registers. The Ikeda 9TT's ultra-precision and neutrality. And last but not least, the Atlas' tremendous sonic balance from top to bottom of the frequency spectrum and transparency.
So what does the Doshi sound like? In a nutshell, this phono stage's sonic signature is eerily reminiscent of the best of reel-to-reel tape. As with the best of that original high-rez format, the Doshi is extremely capable of recreating wide dynamic swings, capturing that ever so important low level, subtle "inner" detail as well as dynamic accents and plumbing the lowest octaves with aplomb. Initially, the Doshi's mid-bass reproduction appeared slightly rounded; then the mega-wattage Matthew-James Cello Encore solid-state amplifiers replaced the cj ARTs and magically, the Doshi's (and system's) bottom octave performance became faster, tighter and more detailed. (Yes, the quality of the "main" amplifier driving the self-powered Summit-X woofers is very important!) No, the phono stage still doesn't have that ultimate sense of dynamic ease, timbral completeness, three-dimensional palpability of instruments or that sense of space of a good 15 ips tape played back on a deck with reworked electronics; on the other hand, both analog mediums are clearly cut from the same sonic cloth.
Of the Doshi's many virtues, it's perhaps the piece's neutrality, transparency, openness and resolution that stand out the most. Far too often neutrality is synonymous with sterility, thinness, coldness, analytical, etc. Not in this case! Nor does the Doshi phono stage sound "solid-state" and imbue a mechanical quality or "tubey" and add a romantic quality to the music. The Doshi nimbly walks a very fine line between the two camps and if anything falls ever so slightly to the Yin side of neutrality. Two tracks that particularly illustrate the Doshi's exceptional speed, transparency and resolution are the "Nagasaki" or "Minor Mood" cuts off the amazing Analogue Productions 45 rpm reissue of The Poll Winners: Barney Kessell with Shelly Manne and Ray Brown (Analogue Productions/Contemporary S7010, 45 rpm). Now the Martin-Logan Summit-Xs—more than almost any other speaker—are capable of in combination with the Doshi (and Atlas or Ikeda cartridges) of unraveling the complexity, solidity, cleanliness and speed of Kessell's guitar playing. The rendering of the shifting dynamics and the stopping and starting of Kessell's guitar on a dime. With other phono stages, Brown's bass comes across as being a bit boomy and at its worst, even a little bit out of control at times; through the Doshi, Brown's bass sounds much tighter without compromising the instrument's rich tone.
Another superlative, but sadly now next to impossible LP reissue to find (and you don't want the original pre-distorted, Dynagroove mess either!), is the classic George Avakian produced recording Sonny Meets Hawk (Classic Records/RCA LSP-2712). The tracks "Summertime" or "Lover Man!" from this pair of jazz giant's first recorded effort together serve very nicely to illustrate the Doshi's ability to not only recreate each tenor sax's distinctive tonality but also the instrument's finer textures and nuances. These instrumental textures are especially apparent on the Hawk's remarkable solo as well as when Rollins is improving alongside Hawk on "Lover Man." (Oh and yes, Paul Bley on piano isn't exactly chopped liver on this recording either.) Through the cj ART amplifier, the harmonic envelope of Hawk's and Rollins' saxophones is highlighted; conversely with the Matthew-James/Cello amplifier, there's a greater emphasis of the nuances of Hawk's and Rollins' instruments.
Then again, there's nothing like a Rudy van Gelder recording to test musical reality and they don't come much better than the outstanding Analogue Productions 45 rpm reissue of Shakey Jake: Mouth Harp Blues (Analogue Productions/Prestige/Bluesville 1027) featuring the late, great blues guitarist Jimmie Lee Robinson on the title track. There's with the Doshi/Atlas combination, a striking naturalness to Shakey Jake's vocals along with a remarkable sense of inner detailing and lack of blurring of Robinson's guitar. Jakes's closely miked harmonica retains its characteristic sharpness and vibrato without crossing over into strident territory. All that is coupled with a crystal clear window through which to see Bank's piano in the mid-right side and Blackmon's drums in the back of the stage.
Or take my reference cut "The Worried Drummer" from Mallets, Melody and Mayhem (Columbia CS 8333). The Doshi digs down deep and captures both the size of the recording's soundfield and sense of airiness (especially after cleaning the record with the Audio Deske record cleaning machine) enveloping the piano. At the same time, the tiniest nuances of the shaken sleigh bells and of the tambourine zils, is revealed without any sense of exaggeration or blurring. Another acid test here—that the Doshi passes with flying colors—is a component's (or cartridges) ability to render the triangle's initial strike, ringing and decay. The Doshi largely avoids much of the distortion and hardness so often heard with lesser phono stages while at the same time recreating the triangle's slow decay (or in one case, damping of the ringing). At the other end of the frequency spectrum, there's a marked reduction in that characteristic "Columbia" fatness on drums.
The Doshi's also excels at recreating the recording's micro and particularly macrodynamic range. Take the relatively unknown Decca recording of Bartok's Bluebeards Castle (Decca Set 311) featuring Istvan Kertesz conducting the London Symphony Orchestra and the wonderful singing of the husband and wife team of German born mezzosoprano Christa Ludwig and Austrian born bass-baritone Walter Berry. This recording is particularly noteworthy for not only its large dynamic swings but an incredibly realistic midrange presence and sense of the recording space. Both singers have an uncanny vocal presence as they enter from offstage right and then proceed to move across and around the stage. At the same time, the low end driven by the Matthew-James Cello Encore monoblocks provided simply immense and stunning, drum thwacks.
Finally, the Doshi's soundstage is largely determined by the individual cartridge eg. Ikeda 9TT, Lyra Titan i or Atlas, ZYX Omega Au or Haniwa and doesn't take a back seat to any other phono stage that has passed through this system. At its best with the Atlas/VPI Classic 3 arm combination, the Doshi does a phenomenal job of throwing a sometimes greater than wall-to-wall soundstage. At the same time, albums such as Michael Oldfield's Tubular Bells (Classic Records/Virgin VS 2001) or Jean Michel Jarre's Oxygene (Polydor PD-1-6112) are awash in a sea of 'visual sonic' effects happening with machine gun rapidity. On Tubular Bells, there's a virtual kaleidoscope of layered sounds and effects occurring in all dimensions along with an uncanny ability to separate out individual tracks in this densely orchestrated composition.
Truth be told though, most tube equipment manufacturers are forced to ship their gear not with necessarily the best sounding but the best currently available tube (s) that is/are available in large quantities and will be for the foreseeable future. Sadly, the sound quality, quality control and lifespan of these new Russian and Chinese tubes leave much to be desired. Those lucky enough to find truly genuine and quiet NOS tubes are at a distinct advantage. So in the case of the Doshi review, I violated my unwritten rule of reviewing tube equipment with the stock tube complement in large part because Nick intentionally designed his phono stage with an open architecture to facilitate tube rolling. So without any further ado is the Reader's Digest version of my tube rolling sessions.
JJ/Tesla ECC83, ECC83S or ECC803Ss (reissue). Toss the stock tubes immediately, if not sooner, into the nearest recycling container. Any sonic resemblance between the new JJ "version" of the Tesla ECC83, ECC83S or ECC803S and the original tubes is purely coincidental. These tubes are as much of an insult to the sound of the original Tesla tubes as Clarence Thomas is to the memory of Thurgood Marshall. The JJs are hyperdetailed, thin, edgy and lacking in low level resolution and finesse. Not to mention that JJ's quality control absolutely stinks as four tubes either went microphonic, noisy or simply gave up the gas within 100 to 200 hours of operation. The ECC83S and 803S are a small but not enough of a sonic improvement over the ECC83.
Gold Lion ECC83 (reissue). Place this tube in the acceptable but definitely colored category. Like the classic British tubes of yore, a little thick in the lows, big, bold and beautiful in the midrange, but troublingly closed-in sounding on top. Nor does this tube possess a lot of finesse or is it the last word in transparency. Overall, the Gold Lion impressed me as a tube for listeners wanting all their music to sound pretty, but not truthful to the source. The Gold Lions remained quiet for as long as ran them but as with many new tubes, one really doesn't know how these reissues will hold up with a couple of hundred hours under their belts.
Tungsol ECC83 (reissue). Overall, the best sounding of the new reissues. The Tungsols proved extremely durable replacements for the Ei ECC83s used in my cj TEA1bc phono section and there's no reason to believe they won't perform the same way in the Doshi. These ECC83s are relatively neutral and balanced from top to bottom, exhibit good tonality and harmonic balance with just a little glint of edginess and sheen. Their opaque, slightly tarnished "aluminum" sound also doesn't make them the last word in transparency. Nor do the Tungsols begin to approach the resolution, dimensionality, clarity or transparency of the best NOS ECC83 tubes, particularly the Telefunken or Teslas.
EAT ECC803S. The "stock" EAT tubes, unfortunately, don't work in the Doshi. Strangely enough, this had nothing to do with anything electrical but simply that the EAT's tube damper hits the "open" top plate of the phono section; consequently, the tube pins can't reach the Doshi's tube sockets (unless you operate the unit with the top plate off (but then dirt can get into the exposed circuitry). The good news is that according to EAT importer Roy Hall, the ECC803S tubes are also available without tube dampers. Unfortunately, I didn't learn about this option until the recent CES and thus received the damperless EATs too late for the review. Fear not as there will be a short update on the sound of an EAT equipped Doshi.
Tesla (original) ECC83s Mid-70s vintage. Difficult but not impossible to track down. Primarily available nowadays from Eastern Europe tube dealers, a pair of these tubes will set you back in the neighborhood of $150/pair (and the Doshi uses 2 pairs). But these are the tubes to get if like me, you treasure that clean, transparent, low in distortion, resolving and extended Telefunken-like sound. An additional bonus is that more of these tubes are truly "NOS" rather than the mostly "tested pull NOS" Telefunkens sold on ePay and other sources. And there's no mistaking both the inward and outward signs and signs of a used tube. Outwardly, the tubes sound juicy and luscious but have zip, nada, zero get up or go.
Reportedly rated for 10,000 hours of usage (for what that means), one of the four Teslas did give up the ghost early on. These tubes, along with the Tungsol, proved my go to ECC83 for the purposes of this review.
"Pre-war" Ei 12AX7 "Pre-war" vintage: This tube proved a total mystery as they had sounded very good, if not a touch colored, closed-in and soft at the top end in my conrad-johnson TEA1bc phono stage. In the Doshi, however, it was a totally different tale and this particular quartet of Ei ECC83s simply lacked any semblance of bass whatsoever (perhaps they were a counterfeit?). The real issue with Yugoslavian Eis is, however, that their Q/C leaves much to be desired and thus require careful selection. Typically, the Ei ECC83s test all over the place and in more cases than not, one half of the dual triode is fine while the other section is microphonic. Plus many Ei ECC83s go noisy or microphonic relatively quickly. Caveat emptor.
NOS Canadian GE 12AT7/6201. The stock tubes supplied with the unit. A little less of that oh-so-typical GE burnished Aluminum, thin and edgy sound but these tubes are nowhere as transparent, grain free and resolving as either the Tele or Mullard tubes.
NOS Telefunken ECC81/12AT7. Little brother to the ECC801S, the Telfunken ECC81/12AT7 is another tube worth considering if you don't want to shell out the big bucks. Cut from the same Telefunken ECC801S "cloth," the ECC81 has just a little less of everything including transparency, resolution, quietness and effortlessness. The ECC81s will set you back more than the Mullard but they too can be found in NOS condition.
NOS Mullard CV4024. It took a little while for these vacuum bottles to settle-in—but when they did, wow. The Mullards are absolutely the tube steal of the century and at roughly 1/5 the typical cost of the Tele 801Ss (coincidentally, the Mullards also really improve the sound of the VTL 450 amplifiers too!). These British tubes possess wonderful imaging, low level resolution, transparency and an amazing midbass to lower midrange. While not embarrassed by the 801S, the CV4024 doesn't possess the lower or upper octave extension and impact, solidity and neutrality of the legendary Telefunken tube. Additionally, the Mullard also has bit more of an upper midrange edge or sheen compared to the Telefunken. Oh, and you get that famous Mullard "flash" every time you turn the phono stage on thrown in for free!
NOS Telefunken ECC801S (Ulm). The best of the best, the crème de la crème, the Holy Grail of ECC81/12AT7s! Not a cheap date at around $300-500 for a pair of NOS tubes (compare that though to $1200 each for ECC803S) but these glass bottles will last a long, long time and help realize the Doshi's full potential. The ECC801S, just like it's brother, the ECC803S, just sounds totally different from other tubes of its gender combining an effortless and uncolored quality, resolution of the smallest details, three-dimension solidity, incredibly low noise floor, low end dynamics and clarity that simply elude other tube manufacturers. Much of the Doshi review was carried out using either the Telefunken ECC801S or the Mullard 4024 tubes.
Staking a Claim
Is the Doshi the best phono stage on the market? If nothing else, the Doshi phono section certainly rates as the best "total" phono package. Yes, the Allnic H3000V demonstrates a little more instrumental palpability, the cj TEA1bc (with a high enough output MC cartridge) presents a little greater sense of the hall or the Avid Pulsare has a little more dynamic swing and impact in the bass but none of these phono sections come close to the Doshi's upper octave finesse, transparency, resolution, and soundstaging. All I know is that the Doshi has become my reference standard for phono stages and will be in the system for quite some time. Myles B. Astor
Doshi Audio Phono Stage