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Aesthetix Io Signature Phono Preamplifier Review

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Aesthetix Io Signature Phono PreamplifierDescription

The original Aesthetix Io phono stage was first introduced in 1995 and has earned quite the reputation as one of the world’s finest phono preamps. The designer is Jim White, formerly of Theta Digital fame.

The Aesthetix Io Signature Phono Stage with the volume control can be used as your only pre-amplifier in a system with vinyl and one other source. It can also be purchased without the volume control and used separately as an add-on phono stage with a very good line preamp. The power supply will probably be mistaken for a power amp by visitors to your listening room. You can add an additional power supply for totally dual mono configuration if you want to go really crazy. The power supplies are divided into two main sections. First, there is the heater power supply and then the primary supplies.

It only takes one glance to see that the Io Signature is a very serious phono stage. The Io Sig I had in for review was the version with one power supply and dual mono volume controls. I used it single-ended, although it can be used as a fully balanced preamp as well. Ever since I went to two systems, one all vinyl, and another on the main level of the house that is all digital, I have been on a search for a phono stage with a built-in volume control that was as good or better than my Shindo Masseto preamp. The Io Sig seemed like a likely candidate, so I asked Garth at Musical Surroundings if I could take a listen and he was gracious enough to say yes.

The unit I had in for review had Aesthetix’s High Resolution Volume Control which is a 46-position, true balanced constant input impedance stepped attenuator. It was custom manufactured to Aesthetix’s specifications. They use dual mono circuit boards, one volume control per channel, truly balancing both legs of the signal.

The Aesthetix has a high gain/low noise, all-tube circuit. It is capable of amplifying low output moving coil cartridges. It has very flexible gain and loading adjustments that make the Io Sig work well with a large range of cartridges. The phono stage contains three main amplification sections with an output buffer stage. The first section is a high gain, low noise, zero feedback single-ended amplifier consisted of two specially selected low-noise 12AX7 vacuum tubes per channel. They feed a high-gain, low-noise differential amplifier which uses two more 12AX7 tubes per channel. The signal is then applied to the third amplification section, nearly identical to the second which also uses two 12AX7 tubes per channel. The RIAA filter is next in the signal path, a purely passive design that uses very high grade capacitors and non-inductive resistors throughout. The back panels reflect true dual mono circuit boards and balanced circuit topology.

The Power Supply Chassis of the Io has a high voltage insulated transformer and both transformers utilize special damping material for lower mechanical noise. It uses custom Wima bypass capacitors to replace the standard film caps.

The Signature versions use custom-made inter-stage Teflon coupling capacitors, replacing the polypropylene units, which cost over 15 times more per capacitor. There are some specialized applications where very small-value Teflon capacitors are used in the Io Signature. All of the input and output wiring is Cardas Teflon coated signal wire.


The Aesthetix Io Sig is sensitive to placement, even that of power cord. You need to be sure not to place the main unit on top of the power supply. You need to also be sure the AC cords are plugged in with correct polarity. If you have noise problems then try moving things around, because with a little care with positioning the Io Sig is really, very quiet. It also needs plenty of warm up. I found it sounded much better after it had been on for an hour or more.

This is a phono preamp that is a joy to listen to. It provides a signal that your system can turn into beautiful music, so let talk about how it sounds.

The Top End

The Io Sig MkII has a beautiful sounding top-end. In my system it sounded as extended, and airy as any I have heard. It has definition that is both detailed and musical. The Io Sig has quicker transients than I have heard from any other tube phono stage. Simply put, the top-end has the beauty of the very, very best tube phono stages combined with the speed and power of the best sand phono stages.

The Midrange

The midrange is always where audio products make it or don’t for me, and I think for most music lovers, too. The Io Sig excels at that very layered and textured midrange that you only get from the best of the best tube preamps and phono stages. It never sounded overly warm, but it had a wonderful big sound that was well fleshed out, but never over blown. Just listen as the bow plays strings; they sound accurate, smooth, musically sweet, but with plenty of attack and decay. Brass instruments have just the right amount of bite combined, with a very nice ambience. The brass literally exploded into the room, but at other times it sounded ever so smooth and airy. These are exactly the two extremes I often hear from live music.

Voices sound very alive, beautiful, and very natural. Some of you might like a touch more warmth, and you can get this with a little tube rolling, but for me I like it just the way it is. Part of what allows the voices to seem so alive is how quiet the background was and how it never emphasized surface noise.

The Bass

I have to admit I was shocked that the Io could better the bass of my Masseto. The bass was simply state-of-the-art. It’s fast, tight, very deep, has plenty of slam, and is just plain powerful. At the same time it beautifully reveals the textures of music in a very natural and controlled manner. Like the Wavac and Shindo tube gear I use for reference, the Io Sig is not the phono preamp for you if you’re looking for a warm, romantic bass. I really enjoyed how it sounded on tympani drums, acoustic bass, and organ music. The bass is truly musical. It reproduces drums, acoustical and electric basses with incredible impact. It has a fundamental rightness that sets the listener at ease.

These incredible characteristic of the bass is carried all the way up into the mid-bass. It gives you quick fast attacks followed by beautiful full decay that lets you hear different layers of the timber of the instruments. I want to state again that this preamp has bass that has great impact and speed, but with the bloom, and air you expect from a truly exceptional tube preamp.

Imaging and Soundstaging

Most of you know this isn’t the most important thing to me, but I do expect any good system to let the speakers disappear, and most importantly, for the soundstage to never distract from the enjoyment of the music. You know I had rather talk about scale, depth, and space than pinpoint imaging or how exciting it is to hear a voice or an instrument coming from a foot or two outside the speakers. The reason for this is that when I go to hear live music, which I do often, I seldom hear a soundstage or pinpoint imaging.

Still, the soundstage and imaging of the Aesthetix was everything I have come to expect from truly musical tube preamplifiers. It was holistic, had great scale, and a solid presentation. It did all this without any of that unnatural floating instruments and voices in space like some abstract work of art. Not that I don’t like abstract art, I even own a couple, but I find that kind of imaging kind of distracting when listening to music. Overall, the soundstaging was superb, with great depth, width, and even a nice vertical presentation. Likewise, the imaging was superb in my book; it had a nice cushion of air around the instruments, but still the imaging was very solid without ever having that phasey sound.

Dynamics, Micro-dynamics, and Flow

The Io Sig MkII has superb dynamics, as well as great micro-dynamics. Both of these are qualities that greatly allow you to be emotionally involved with the music. Another important part of emotionally involving music is the flow factor. Along with dynamics and micro-dynamics you need to have rhythmic bass that is well controlled to have great musical flow. The Io Sig Mk II was very good in this area, but this is one area that it was just a hair behind the Shindo preamps.

Specific Examples

I love bass, cello, and violin music. I listened to three Gary Karr albums and in every case, the Io plays cello with warmth and life without a hint of bass hangover or even the slightest amount of boomy-ness. Violins were sweet and extended easily into the upper registries without ever seeming bright or strident. It did seem very intense and sometimes even aggressive, as it should on this piece. In fact the pace and timing was just uncanny.

The emotions you experience as the bow is slowly pulled across the strings are so moving I had to write this after it was over. You can hear layers and textures of the tones of the strings as you hear the differences they each make as the bow passes over them.

Ella and Louis is one of my favorite albums. On cut 2, ‘Isn’t This a Lovely Day,’ the Io lets us hear the beauty and lushness of Ella and the gravely power of Satchmo. The voices are very prominent, and the horn seems a little too polite, but the overall experience is to just want to listen. I don’t want to overstate the case, but I sat down to listen to two cuts and ended up listening to the whole album. Then I got up and put on Billie Holiday, not for reviewing, but just because I wanted to hear her on this set up.

Elvis is Back has Elvis’ version of ‘Fever’ on it. This cut will tell you if a system is all about slam and tightness or if it’s about emotion, music, and feeling what the musicians and singer are trying to convey. It can be about both. I discovered with the Io in my system it came closest to having both I have achieved so far in my room. It also still lets you hear the decay, the reverb, and how close Elvis is to the mic.

Listening with NOS Tubes

As good as this phono preamp is, and it is one of the very best, I still couldn’t resist Garth’s offer to hear it with NOS tubes. He called one day near the end of the review and said he had purchased a complete set, and if I would I like to have them shipped directly to me. Like I said, I couldn’t resist. Man what a set of NOS tubes they were. There were three different matched quads of 12AX7s. The first was a quad of Telefunken small shield, round rib 12AX7s, the second quad was Philips Miniwatt 12AX7s, and the last quad was round getter, rib plate Mullard 12AX7s . The 6922s were Philip Gold Pins, and the 6sN7 GTBs were Raytheon Short Bottle tubes. Like I said, a very nice group of NOS Tubes.

So what do the NOS tubes do for the sound? Well that depends on how you use them, but my favorite was with the Telefukens in the first stage, and the Mullards in the second stage, and then the Miniwatts in the last stage. This produced the most transparent sound and a top-end with nice detail and air, but no tendency toward edginess.

Overall the preamp had a more beautiful top-end, a more transparent and more organic sounding midrange, and more tuneful bass with the NOS tubes, but I would not want anyone to think they have to spend the kind of money these tubes cost to enjoy this wonderful preamp. These tubes could come later or not at all and you will still have one of the very best phono preamps available at any price.

A Few Words of Caution

None of these have to do with the sound, but I do have a few words of caution to anyone thinking about purchasing this state-of-the-art phono stage. First, like a great sports car the Io Sig MkII is not for the casual user. This is an all out attempt at making the very best, and sound was never compromised for convenience. There is the assumption that the buyer of a phono stage at this price point is capable of reading and following instructions. Second, it’s big, very heavy, and takes up a lot of room. Not only does it take up a lot of room, it also can’t just be placed anywhere you happen to plop it down. I got hum when I set it too close to its own power supply or my power amp. Third, even though I didn’t have any problems, everyone I talked to about the Io Sig MkII warned me to be careful that it was fully powered down before changing anything, and it takes nearly twenty minutes to power down. I heeded these warnings and had no problems at all. Lastly, it uses lots of tubes and if you want to put the kind of NOS tubes in it that were supplied to me, it will cost a small fortune. Still, as I have already said this is not necessary for the Io to sound incredible.

Now having given those few warnings, let me say for those of you who value the very best of tubes combined with the very best of solid-state, it will surely be worth the effort. For you will be rewarded with a truly realistic and musical experience.


The Io Sig MkII is a very special product. It has as much and as natural-sounding air than I have ever heard. The same is true of its bloom and harmonic correctness. When it comes to dynamics, it’s the best I’ve ever heard. The Io Sig MkII does all this while adding very little of its own sound to the music. I have my doubt that there is anything out there that could really better this, but I’m always game to try to find it and tell you about it.

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