Rmaurin,
>>Why did you install NOS tubes?
After owning the ARC SP-10 and LS5/PH2 for a combined 15 years, I was familiar with the sonic differences between some brands of 6DJ8/6922 tubes. The Amperex were much more to my liking over the stock russian based tubes in the ARC models. However, I had little experience with the premium tubes from Mullard and Telefunken from decades ago. When I decided to try the Io (the non-signature model), I had read a lot of information on A'gon about how some tube changes could transform the Aesthetix models. The stock Io sounded pretty darn good but I wanted to hear what all the hoopla was about so I bought a dozen or so Mullard, RCA, Siemens and Tele tubes and tried them in the Io. All that I had read was instantly confirmed: $500-600 as a starting point to change out some of the Sovtek tubes brought on a huge refinement - the sharp edge of the Sovteks was gone and a more lush presentation was there. Since that time, I have pretty much finalized a tube set to my liking for the 2-chassis Io at just a shade over $1000 that takes this unit far far beyond what I ever could have imagined possible. Once you hear this, there is no going back to the Sovteks. And when I did a similar change to a CAT Ultimate II earlier this year, only then was that unit even listenable; the Sovteks there makes this preamp way too fatiguing to my taste.
>>Why did have your Io modified?
If you realize that the Io and Callisto are designs that are now 10+ years old, just all the improvements in passive parts alone has to imply a major benefit to upgrading the internal components. I investigated what the component changes were between the standard and signature Io. Considering the cost would be $2500 to "upgrade" to the signature version, and all the hassle, cost and risk of shipping these to/from the Aesthetix factory, I contacted Steve Huntley at GNSC to see if he would be willing to pop off the tops here and give me some insights and estimates as to what could be done. And I had a good idea as to the premium parts used in the signature since I have a Callisto Signature.
I heard my unmodified Io in Steve's system and compared to his phono setup, the Io had greater bloom and midrange definition, but clearly lacked refinement at the frequency extremes and also had mediocre resolution. Based on what Steve could hear that day, he was confident that a dozen or so select component changes would be a good starting point to tackle some of these weaknesses. And a week or so later, all it took was a quick listen to realize Steve's efforts had paid off. I could have left it there for yet another level of updates but it sounded so mighty good that I needed to get it home to enjoy the improvements. And because Steve is also here in the twin cities metro area, I could meet with him personally, talk about the pros and cons of each update and the respective cost and do a little at a time as there is no shipping back and forth. I am very fortunate in this regard to have this service locally.
As time goes on, I am more and more a fan of modifications once I find a product that really captures the essence that I seek. The Aesthetix models do this and becuase they have so much room in their chassis to take on the premium parts that are now readily available, it makes a lot of sense to do so. And when going down this route, the improvements you gain are at a cost that is impossible to achieve through buying a new model or a factory upgrade. Michael Elliot, the chief engineer of Counterpoint and Aria components, explains it best
here.
For example, look at all the ARC line stages that have been their best model (LS5 I, II, Ref 1, Ref 2 I and II, and now Ref3) since the life of the Callisto. And imagine the cost it would have been to constantly upgrade from each to the next. The fact that the stock Callisto still competes after all this time indicates it was done right from the start. And if I can transform this design with $500-1000 in parts improvements to take it to the top of its class, then why would I want to "upgrade" to another model and take a multi-thousand $$ hit?
