Avid Pulsus Phono Stage
n olden days, BCD (before compact disc), there was no such thing as a separate phono stage. Every preamp provided three things: source switching, volume control and gain and EQ for phono playback. But with the advent of CD and its rapid domination of the market, the phono stage soon moved out of the preamp and into a separate box (or boxes), rendered redundant for the majority of listeners, an optional extra for the few.
For those who had a record collection and still listened to it, this may have been seen as a backwards step. Upgrading your preamp now involved buying a separate, often costly device with which to play your records. But every cloud has a silver lining and the introduction of dedicated phono stages also signaled the arrival of dedicated power supplies, isolated circuitry and a more committed audience willing to reward a designers drive for better performance. The result was a whole range of improved phono stages with enough gain for moving-coil cartridges, the versatility to load them properly and dedicated power supplies that reduced external interference.
My audio interest goes back decades before CD, and I have a fair-sized record collection to prove it, many of my favorite LPs not duplicated in my CD collection. Until I began using the George Mark line-level preamp, with its internal DAC, about five years ago, I always had preamps with their own internal phono stages. But now I was left with a large LP collection and a good turntable, tonearm and cartridge but no way to connect the 'table and play the records. I did have a nice CD collection with more than enough new discs to make ignoring my LP collection easier than it might have been, especially given the ease of use CDs offered, but after three or four years, all of that idle music, many of the discs among my favorites, ate at me and I had to do something about it. I had to find a phono stage, one I could afford and that would satisfy me in sonic terms.
So I got out my store of audio mags and hit the Internet. I found a few units that that interested me and didnt break my bank. But none of them said "order me." Then I ran across the Avid Pulsus. In everything I had read about Avid products, all of the company's phono stages and turntables, dynamics were prominent in the discussion. For me, dynamic linearity -- linear changes in level at both macro and micro levels -- is numero uno in audio reproduction. Without it I find that every system, no matter how well it does anything else, sounds like a wide-bandwidth radio, not like live music at all. So the constant reference to the dynamic performance of the Pulsus struck an important nerve with me.
Soon enough, an Avid Pulsus was resting on my doorstep, sent to me for review. It retails for $2195, and so you dont have to skip to the last paragraph Ill tell you now that I am the owner of that review unit.
he Pulsus is an unobtrusive two-box solid-state unit consisting of the audio electronics in one chassis and a DC power supply in the other in order to ensure minimum interference. Both enclosures are essentially identical little black boxes, roughly 5" by 8" and a little under 3" high. Being small and solidly made, the enclosures help to control resonance, a factor I find more and more important in a high-definition system. (Ive heard cases where cleaning up mechanical interference has eliminated bass overhang to the point where youd think the woofer had been completely redesigned.) RIAA equalization is done passively, the necessary components located between two separate gain stages. This seems to be the popular way of handling it these days, in contrast to olden days, when it was done actively within a negative-feedback loop. The current fashion for reducing or eliminating feedback makes this type of equalization an increasingly rare option, while the excellent performance of todays phono stages suggests thats no bad thing.
The Pulsus lets you alter both gain and loading over a useful range. Gain can be set at 48, 60 or 70dB, covering moving-magnet as well as medium-and low-output moving-coil pickups. You can vary load resistance among 100, 300, 500, 1000, 5000, 10,000 and 47,000 ohms and capacitance among 100, 200 and 500pf settings, which should allow you to load just about any cartridge properly. Settings are selected using banks of small DIP switches on the bottom of the phono-stage chassis. I didnt have any problems changing them, but if you do, a small screwdriver will do the trick. It would be nice if these controls were larger and on the front panel, but this would make the Pulsus a lot more expensive and for most of us theyre a one-time setting.
The power supply is substantial, heavily regulated and using a 35-watt transformer thats a lot bigger than it has to be. Avid is obviously a fan of oversized power supplies; their much more costly Pulsar has a power supply thats almost ten times larger than that of the Pulsus. Im a big fan of large power supplies too. They ensure that a device maintains performance and specs even when under extreme stress. Its not hard to achieve good specs under low stress, but there are cases where a musical peak can be a very short burst of 30, 40 or even 50dB above the average listening level. A unit needs to be able to meet those demands -- and recover afterwards, even from a very short overload. This is where a good power supply proves its worth.
I connected my VPI HW-19 turntable, still carrying the Shure V15 V MR cartridge (not the later XMR) with Jico stylus, to the Pulsus. I always use the Shure with the damper brush down because I like the effect of damping on signal decay. Its also essential to use the damper with my Fidelity Research FR64fx tonearm, which has higher effective mass than is ideal for the Shure, and the damping mitigates the associated problems. I checked the overhang and set the tonearm level with the platter as a starting point for VTA, but 'arm height needed to be set precisely and you dont often get that lucky. Initial listening was very nice, but not something for which I would trade my CD player.
Setting VTA on a tonearm that has just a sliding pillar, as mine does (and most 'arms without a micro-adjustment facility), can be a pain. I improved the performance on my first try, but I knew it could be better. I could kick myself for being cheap when I purchased the FR64fx. I should have bought the stabilizer base with the fine VTA adjustment. Hindsight is always perfect. But then I recalled a trick taught to me about 30 years ago by George Bischoff (of Melos, Pipedreams, Scaena and GeorgeMark Audio). I dont know where George learned it, but since I had never come across it before, I call it the Bischoff Method.
First, set the tracking force of your pickup in the middle of the recommended range. Then roughly set the VTA as well as possible, varying the pillar height to give as focused a sound as you can in a few minutes of quick adjustments. Alternatively set your 'arm parallel to the platter. Tighten the 'arm height screw. Then take advantage of the vertical tracking force (VTF) adjustment on the 'arm. This can normally be precisely adjusted without too much trouble (although some unipivots that combine VTF and azimuth on an uncalibrated counterweight are not so simple). Dynamically balanced 'arms like the Fidelity Research (as well as the SME 5 and Linn Ittok and Ekos) make it especially simple. Make very small changes back and forth, beginning with just a couple of hundredths of a gram. Increasing the VTF lowers the angle the cantilever makes with the record surface and vice versa. If your initial VTA setting was close, then the sound should lock into precise focus, indicating youve hit the correct VTA, while even a tenth of a gram change in VTF should have no effect on tracking performance if you started from the middle of the recommended VTF range. This method is not perfect, but given that its a one-time setting on an 'arm like this, it delivers way better performance much more easily than trying to adjust the 'arm height in ever-smaller steps.
While most of my listening was with the Shure V15 V MR, I also used two other pickups in order to ensure that results were consistent with other cartridges. One was a Technics EPC-205C Mk 2, also with a Jico stylus, another excellent moving-magnet cartridge. I also used a Goldbug Clement II, a lower-output moving-coil cartridge, to check the performance of the Avid Pulsus on its higher gain settings. In both cases, the results were essentially similar to those with the Shure, save for the expected differences in the three cartridges. The alternative pickups were slightly softer and airier in the upper octaves. The Shure was crisper and less subtle there, but more assertive in the lower octaves. The higher gain options resulted in no discernable alteration in musical, dynamic or tonal performance when compared to the moving-magnet setting.
ecause dynamics are of primary importance to me, the first recording I put on to get a sense of a systems -- or rather a components -- dynamic capabilities is usually the Evgeny Kissin CD of Pictures at an Exhibition [RCA 63884-2]. A concert piano is just about the hardest single instrument to reproduce, because it is capable of monster dynamic swings, sometimes lasting for just split seconds and then dying quickly away. Its a mighty test of both the ability to handle the rapid rise in signal level and also its proper decay. Overshoot or softening on the leading edge are obvious as stridency or a loss of percussive impact, while if the decay lasts too long, it muddles the notes that follow.
I dont have the Kissin version of Pictures on LP, but one of the joys of searching through old software is discovering forgotten treasures, in this case a recording of the Beethoven Piano Sonata No.23, "Appasionata," by a Japanese performer, Ikuyo Kamiya playing a real battleship, a Bosendorfer Imperial [RCA RDC4]. A direct-to-disc, 45rpm recording, it was exactly what I needed for testing dynamics. Serious low-frequency energy is often compressed on a record because the grooves needed to maintain that kind of musical power are too wide to track properly -- and they take up too much space. Commercially, thats a loser, and commercial considerations trump fidelity. But this was obviously not a normal commercial recording, and it didnt disappoint. Energy seemed to just fly off the keys, and lower registers were powerful enough to sound nearly live in level. If youve been close to a concert piano you know what Im talking about. Heres one place where a CD can ultimately beat an LP. As long as you dont exceed the mathematics of dynamic range, the CD can be totally accurate. I dont believe an LP can match the digital disc, at least if its recorded at a decent level. But shorn of such practical considerations, the reproduction here was totally rocking, filled with drama, energy and excitement. The Pulsus really felt like it got every last bit of dynamic energy off of the LP, an LP at the limit.
I next put on that audiophile war-horse The Sheffield Track Record [Sheffield Lab 20]. I had forgotten over the years just how dynamic and powerful this LP really is. I cranked it to the sort of levels you shouldnt maintain for very long, just to see if it would put the Pulsus in any peril. There were no problems. Once again, dynamics soared effortlessly and decay was rapid and clean with no apparent overhang. In addition, this time I got to hear some awesome dynamic interchange between multiple instruments, without any bad interactions or confusion -- another good omen.
I love British folk music, my favorite group being the original Pentangle of the late '60s and early '70s, an all-acoustic ensemble of two guitars, drums, upright bass and a pure-voiced female lead singer. Usually called folk rock, in this one case where folk jazz might be even more accurate (lead singer Jacquie McShee was originally a jazz vocalist). One of the first CDs I always play is The Pentangle [Castle 06076 81120-2]. Unfortunately most of my Pentangle LPs are on the Warner Bros. label. The Pentangle was the first non-classical recording reviewed in Stereophile, and it got a very positive review for both music and recording quality, but J. Gordon Holt received a ton of letters asking what he was listening to -- that the recording was barely okay. It turned out that Gordon had a Transatlantic pressing and most readers had the remastered Warner Bros. LPs, which were two-dimensional, less well defined and less focused than the British pressing.
But once again, luck played a part, and amongst my LPs I uncovered a Linn pressing of the Pentangle album, Basket of Light [Demon Records Trandem 7]. Hopefully this will keep happening, this rediscovering of old gems. It feels like getting great software for free. I still have plenty of my collection to search through.
This recording didnt disappoint. The transients of the two guitars were clean and fast with no sense of overhang, similar to the sound of the Pentangle CDs I have. Jacquie McShees voice had that subtle throatiness I expect from good reproduction. Imaging was very good -- this was the first time I took real note of the systems imaging with the Pulsus in use. Imaging is important to me but a secondary factor. If its there, I love it; if its not, I usually dont miss it. Thinking back to other recordings, I recalled that imaging had varied from okay to very good. Thats a good sign. It means that the imaging was a function of the software, as it should be, being reproduced accurately by the Pulsus rather than added by the replay chain. But when it was good, it was very, very good, with a real sense of space, volume and especially height, creating a three-dimensional view of the music of Basket of Light.
I noted how well the drums were reproduced. The Pulsus allowed me to sense that moment just before the drumhead was hit as well as the decay after the strike, the sign of a very good component. Ive often heard systems, with software I know, where the drum was very clean, but all I could hear was the drum beat itself. You dont get the echo-like effect of the decay after the strike. Thats not bad, but its not an A+ either, as it was with the Pulsus.
Im a big fan of Charles Ives' work. On the B side of one of my Ives albums [Deutsche Grammophon 2530 048] I found Carl Ruggles' Suntreader, a very Ivesian piece but with its own personality. The recording by Michael Tilson Thomas and the Boston Symphony again confirmed the dynamic capabilities of the Pulsus. Drums were good enough to make me imagine the real thing and imaging was beautiful, a continuous swathe of sound from right to left, with a sense of space further to the sides and of height above the orchestra. There was also a slight brightness to the strings, not the first time I heard this.
Of all the albums I played, it was these last two that summed up the personality of the Pulsus. All phono stages have a personality. Getting the RIAA curve exactly right demands extreme precision, and Ive never heard a totally flat response with any LP Ive listened to. Some very fine sounding phono stages are often quite a bit off, with a hill-and-dale measured response of a dB or so in spots. With the Pulsus, I consistently sensed a tad of brightness -- not much, just the tiniest amount, so one would define it as heightened or illuminated rather than absolutely neutral. Its just that littlest bit, and it will be important to you if you are very sensitive to it. Im not referring to the highest octaves here, but to the upper midrange, about where a midrange driver crosses over to a tweeter or slightly above. But then, isnt that where most brightness usually is? Its rarely a top-octave problem.
Another characteristic I noted was a sense of weight and palpability in the bass and midbass. This was particularly apparent when playing Suntreader, but it was present with everything I played that ventured that low. Its not a frequency-response thing. Ive seen response curves for the Pulsus, and even with the difficulty of getting a flat response with RIAA equalization, its dead nuts flat there. It sounds like a little bump, although I dont believe it is. More than likely it is a result of the dynamic response of the unit. More importantly, the bass was tight and very well damped. If it werent, it would be one of those characteristics from my list of factors Id jump on, one that would disqualify the Pulsus for my own use. I like the effect; it added a sense of liveness and substance to the reproduction.
It was this barely noticeable brightness and innate feeling of power and mass that defined the personality of the Pulsus. It was possibly why Ive also seen the Avid described as more for pop than classical music. I guess if you think of pop as loud and classical as properly behaved, that makes some kind of sense. But pop music is usually loud though not dynamic. In that sense, its often less exciting than classical, where dynamics range all over the scale. I recall many discussions with Gordon Holt in which he deplored audio gear that smoothed out classical sound. He wanted the trumpets to blare and the dynamics to jump. The Avid Pulsus does just that.
That solid bass also meant that you had better make sure that there are no bass problems or low-frequency feedback issues with your system. The Pulsuss bass response was not rolled off at all. It continued all the way down, well into single digits, so youll either need a rumble filter somewhere in the system, or better still some good acoustic isolation for your turntable. Be sure your 'arm/cartridge combination doesnt resonate too low in frequency or too vigorously. Tonearm damping (or cartridge damping, like the brush on the Shure V15 V MR) can be your pal. Some suspended 'tables handle this on their own. Otherwise a good isolation device below your 'table can help. I have my speakers about 20 feet away from my turntable and in another room, while the turntable is still mounted on a modified Lead Balloon stand with lots of added mass as well as racquet balls for decoupling.
Finally, before getting ready to pen this review, I put on Bonnie Koloc's Close Up [Epic 34184]. Koloc is a fabulous female vocalist, easily in my top five, who made some wonderful recordings in the '70s and '80s, none of which has ever made it to CD. So a phono stage was a true gift, allowing me to listen to all of her albums that I have. On Close Up, the imaging changed again to match the recording. It was almost holographic. There was a super cleanliness to individual instruments and to Kolocs voice. I heard her vocal soar effortlessly, almost Ella-like in its lack of constraint. On "Clocks and Spoons," theres a recording of tap dancing, and the crispness and cleanliness of the individual taps really allowed me to hear just how much information the Pulsus let through -- and just how clearly it defined and arranged that information.
iven everything I've said about the Avid Pulsus, is it too good to be true? That depends on whether its character and capabilities match your demands as precisely as they match my own. In my system, the Pulsus was a perfect fit, and Ill repeat what I wrote earlier in this review: I bought it, and with each passing day and each record played I enjoy it more and more. I rediscovered old favorites and uncovered hidden gems, a mother lode of musical pleasure from past decades of record collecting. Ask yourself what sort of listener you are, and if you are anything like me, youll love what the Avid Pulsus does for your LPs.
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