James L. Darby
Think quick - what company makes mostly preamps, preamps and nothing but preamps (except for one 300b monoblock they recently added)? I only know of one: Purity Audio Design. No music servers, no speakers, they don't even make cables, though I was just told they plan on expanding their line to include other unique products. That tells me that if preamps are your main bread-and-butter, they better be pretty outstanding. For starters, each unit is hand-built in the state of New York, here in the good old USA. All of their preamps are tube basedf, no solid-state for them. In fact, there is not a transistor to be found anywhere in the circuitry.
Just looking at the Purity Reference gives you a clue that it is something special, starting with its unique trapezoidal case which helps reduce airborne resonance. The case is not made of aluminum or any kind of metal at all; it's acrylic, known for its anti-resonant properties.
Why is resonance a problem, especially with preamps? Preamps are tasked with taking the tiniest electronic signals generated by source components and amplifying them to levels that amplifiers can turn into watts. When you're working with such ultra low level signals, any vibration can have a much more substantial negative effect than that of any other component, with a turntable perhaps being the exception. What that means is, you can have great cables, amplifiers and speakers, but if your preamp is substandard, then everything else is compromised.
The casing is just the beginning of the long line of high-end features built into the Purity Reference. For instance, there are three sets of fully balanced inputs, three sets of unbalanced inputs and two sets each balanced and unbalanced outputs. That's 6 total inputs. When an unbalanced input is selected, the signal still passes through the input transformer maintaining a low output impedance as well as the resolution and transparency transformer coupling is known for.
All of that balanced circuitry significantly adds to the cost of the unit, perhaps doubling the price. I actually asked Bill Baker who is co-president and designer at Purity Audio along with Joe Jurzec if they had considered making a model without all the balanced circuitry to lower the price for those who don't have other balanced components. We at Stereomojo are always looking for ways to save our readers some bucks. He replied, "Throughout the design process, several configurations were tested both with and without the balanced option as well as with and without transformer coupling. In the end, it was the transformer coupling that provided us with the best sound which is always our primary focus. In our designs, this also allows the sonic benefits of transformer coupling with even the single ended connections at both the inputs and outputs. If having this feature degraded sonic performance, it would not be found on our products".
One indicator of the quality of a product is how many rooms you see it playing in at audio shows, borrowed by amp, speaker or other companies that don't make preamps but want the best available to showcase the sound of their product. Purity preamps are frequently seen as we go from room to room. I understand that Purity gets more requests for such shows than they can fulfill.
Inside the reference
After working with so many components over the years, an indicator of quality can often be found in how the switches and knobs feel. It's like the difference between the controls in a 1960 Jeep versus a new Mercedes S class. The Purity Reference is definitely in the S class of preamps, especially the volume control. It's just so silky and substantial feeling. You know that there's some serious quality there just by operating it. It turns out that the volume control was one of the most tested and engineered features of the preamp. There are many ways to implement a volume control, but according to Bill the best sounding volume control next to autoformers is one that has the least resistance in the path and can maintain consistency throughout all frequencies and it's for that reason they chose to use relays. In this case, not one, but two; one for each channel so you do have control over the balance between channels but without the sonic interference of a balance control. The source selector is also relay driven with the relays placed close to the jacks for the same reason; it adds to the purity. Shortest signal paths were used throughout. Again, costs more but sounds better.
Other key features include Teflon tube sockets, no common ground between any inputs, 100% point to point wiring with no PCB, ROHS silver solder used, not the cheap stuff.
The Purity Reference uses two 12AU7 tubes for line amplification with tube life said to be greater than 10,000 hours. My unit came with vintage circa 1960 NOS 12AU7's. No cheap off-the-shelf tubes, either.
The remote control deserves special mention, it's simply superb. Made of heavy aluminum, it has more functions than any stereo preamp we've seen. You can change inputs with touch of a button, change the balance between the two channels with one large digital readout which can easily be read across a big room for each channel indicating level, mute and another unique feature, phase inversion. It's amazing what a difference that can make in some recordings. A little blue light indicates when it's on. Other little blue lights indicate the source selected.
Speaking of blue light, whether it's intended or not I do not know, but beneath the unit and visible when listening in the dark, is a very subtle pool of cool blue light, just enough to give a cool floating effect, yet not at all intrusive. The large digital volume readouts ARE intrusive when listening in the dark, but thankfully, the remote let you extinguish them from your chair. If you do make volume changes, the lights come on for about 10 seconds and you watch the numbers go up or down, at least letting you know that the unit is receiving the signal and responding and how much the volume is adjusted.
A special note also has to highlighted for the remote volume control. It's designed to move in 1 db increments, so a quick touch and you see the numbers go up by 1. I use the volume control a lot finding just the right level for each track so it sounds just right - realistic. The remote of the Purity Reference is so precise and so easy to adjust that it just makes that process almost automatic, it requires no thought. One of the best ever.
I said the blue lights come on for about 10 seconds, even in "dark" mode each time you adjust the level. For me, that's about 7 seconds too long and I'm always impatiently waiting for them to turn off. I wish that was user adjustable.
While we're in the wish category, every time you turn the unit on via the front facia "on" button (not hidden on the rear like so many), it resets the volume to a safe low level (good), but it also does not remember the last input used. While It's not a big issue, I wish it did since I use one source much more than others.
There's not much that can be said about the "sound" of the Purity Reference because it doesn't add much "sound" of its own, it simply gets out of the way and lets the "purity" of the original recording come through in all its glory. It sounds more like a good passive preamp without the flaws a passive can introduce - more on that in a minute.
The ease in which it allows the listener to hear the finest details and nuances of any performance is simply amazing. each interment or voice is defined in its own space with lots of space around it, some call it "air", that lets the realism shine without ever sounding etched, like there are tiny scratches outlining them or distortion of any kind. Things that are made of wood sound woody, things that are metallic sound just so. Solo vocals especially sound almost eerily separated from the background with a sense of real flesh and blood voices with no electronic haze. They also sound rounded with a more noticeable 3D effect rather than just a flat face singing. It's like you could almost tell if Linda Ronstadt was wearing eyeliner or not when she recorded "Shattered". Ok, that was pure hyperbole, but you get the picture which is what the Purity Reference does so well - present a realistic picture, a visible almost "reach out and touch" quality that is uncanny.
Symphonies and large orchestras are a delight as they are laid out before you with tangible layers between the front sections, usually the strings, and the woodwinds in their space, back and a little higher with the brass further back and higher still with percussion usually in another layer and higher still - on well recorded performances of course. It's really quite an impressive panorama that gives you the belief that a full 100+ piece ouches CAN perform in your room!
Another sonic feature is the frequency bandwidth you hear. There is never the sense that anything is rolled off on either end of the extremes. It defies what many find objectionable about tube sound in general.
Bass especially was outstanding in its fullness and weight and definition even at the extreme bottoms of things like pipe organs and roaring double basses. Again, texture is something that is often missing in lesser components at the bottom end. The sound of a tympani head or even the mallets used or the all important in pop, rock and jazz recordings, the essence of the kick drum. Great engineers spend hours, sometimes days, trying to get the sound of a single kick drum to sound just right and fit in the mix so that it drives the rhythm. Here you can hear the fruits of their efforts.
I should note that due to several uncontrollable issues, this review of the Purity Reference has been terribly delayed, but it has been in my system as my reference for more than a year. I know it well. I have no desire to change it.
PASSIVE vs ACTIVE
We often get questions about passive preamp vs. active. Simple logic would dictate that a passive preamp, or no preamp at all and dimly patching direct to a power amp, would be purer and therefore better. I've tried two rather pricey passives in my reference system and just didn't like the sound. I really didn't know why what was casing the problems I heard, but they just didn't sound right. I've also tried the direct route. Again, against all my most stanch male logic and search for a less expensive way to get great sound, it just never worked for me sonically. The sound was about as "pure" as Miley Cyrus.....
So, I asked Purity guru Bill Baker about this and here's what he said: "I have never found a system to be to my liking without a quality active preamp in the mix. I have heard systems that did sound better when going directly to an amplifier with either a built in attenuator (in the source) or sometimes a passive preamp. The reason for this was due to the fact that the preamp and amp combination were not a good match so taking the preamp out of the picture produced better results.
There are a lot of people out there that will only use passive preamplifiers as they feel passive provides the purest signal transfer when a high end design active unit will often surpass any passive. Unfortunately, ultra high quality active preamps rarely come cheaply. The other downfall of a passive is the impedance issues with amplifiers. For this reason, passive preamp designs are usually only suited for tube amplifiers with high input impedances and low input sensitivity. i.e. easy to drive.
This is not to say that a system cannot sound very good with a passive design but in my opinion, a good active unit will likely outshine a passive. Often times it is a case of a good passive will sound better than an inferior active unit.
Another area that I find passive a cannot commit compete in is dynamics. Unless the system as a whole is built around a passive unit (this includes source components, amplifier, speakers and yes, cables), a passive cannot produce the output required for proper dynamic control.
While it is true that many active preamps, especially tube units, can add some coloration to the sound, there are other aspects of preamp design that designate any sonic signature being introduced. Some add/attenuate a signature of there own which may or may not be to consumers' liking. The goal with Purity was just that..."purity"... without adding or subtracting too much from the original signal."
I know that won't end the debate on active vs passive, but it's nice to know that at least one guy who knows music and the things that reproduce it in our homes, agrees with my findings. In addition, do you recall what I said about seeing Purity preamps in several rooms at audio shows? By the same token, I don't ever recall a passive preamp that had been "borrowed" or a source run direct into an amp without a preamp at a show. Again, if you've worked on an amp or speaker for years and want it sounds its best at a show? That doesn't mean it's never happened, just that I can't recall noticing. What does that tell you?
We are partial to tube preamps, especially in conjunction with solid state power amps. That could change someday as solid state is improving quickly, but even so in many sales brochures and conversations with transistor component makers, it's notable how often they say how "tubelike" their amp sounds without having tubes. The Purity Audio Design Reference linestage (or preamp) is mostly designed for those want close to the best sound available (Purity does make more expensive or perhaps "better" models" for those more economically enhanced), but your other components should have fully balanced inputs/outputs to justify the extra cost this circuitry demands. If so, it is difficult to think of preamp, tube or solid state, that represents a better performance, not only from a sonic standpoint, but that of features like the remote control that does everything but turn it off/on.
We enthusiastically bestow our rare MAXIMUM MOJO AWARD on the outstanding Purity Audio Designs Reference Linestage.
Congratulations to Bill Baker and Joe Jurzec!
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