Review: Aesthetix Callisto Signature and the KT-66 Tube preamp

Yes your correct Cmo that the KT66's can be expensive and could not be done for production units but what surprised me is that Jim White never experimented with his own unit to see how these tubes would sound with his own system even after some people including Mr. Albert porter reported back with very positive results from changing the tubes. If I was a designer I would like to satisfy my own curiosity and know for my self how these tubes improved the sound of my preamp. Other improvements like upgrading the female rca’s jacks to pure copper Vampire’s (the stock cardas sound very poor in comparison) and changing the male IEC in the power supply to the much better sounding Furutech are not that expensive and made a very nice improvement on my Jadis JPS 2 preamp.

Johnny

Cmo,
The Mullard (dimple plate) gold pin is what I run in my Aesthetix Callisto. In the Aesthetix Io, the 6922 of choice is the old diamond bottom Telefunken 6DJ8.

Oddly enough, the Telefunken does not sound as good in the Callisto nor does the Mullard sound as good in the Io. Although the same 6922 tube is supplied from Aesthetix, they perform different jobs in the two units. In the Callisto the 6922 is paired with either 5692's or 12AX7's depending on input or output side.

In the Io it's in the output and not directly paired with another tube (as near as I can tell from the circuit). So as usual, the answer is not always tube "X" is best, depends on where it goes.

I don't know if the link I provided in my earlier post opens where you can read all the comments. I had problems clicking on other posts from within my link and got a server error. If that did not make it, I can copy and post it here. I discussed at length the differences between Siemens, Amperex, Mullard and others.

ALbert,

AS always thanks for your input on all things audio. I was unable to open many of the comments in the link you provided either. If you have time I am intersted in your findings on the various tube swaps you mention in your earlier post.

Chris

Finally I found a little loose change so I could not resist trying the KT66 tubes after Chris’s high praise. I got a used pair of Genalex and an unused pair of Marconi KT66. Currently I run with only one P.S. for the Callisto as well as one for the Io. Four large chassis here are tough enough to find available space….I have no idea where I could store two more of these beasts. And so I have held out for Michael Elliot’s preamp to determine if I go that way or an all-out 6-chassis Aesthetix setup.

After trying out several EL34 tubes last year in the Callisto and Io, two clear winners stood out. My favorite was the UK Mullard. As I reported on another thread, this made a huge improvement which set the stage to replace all the 12ax7 and 6922/6DJ8 tubes in the audio chassis. The fatigue and edge of the stock Sovtek EL34 was gone. The other tube, which is much less expensive and readily available is the JJ Tesla EL34. I was reluctant to try the JJ Tesla as I had major reliability problems with JJ Tesla KT88 tubes a few years ago with an ARC VT130 amp. But the JJ Tesla EL34 is really mighty fine in terms of keeping up with the UK Mullard’s tonality and dimensionality strengths. When I did this KT66 comparison test last night, I had forgotten how mighty good the Tesla EL34 can be.

The new reissue Mullard EL34’s have a wonderful coherent tonality. But they are absolutely flat in dimensionality. Gone is the incredible harmonic richness, ambience and front-to-back placement as portrayed so well with the UK Mullard and Tesla. I also tried the Svetlana and Electro-Harmonix EL34 but these too were rather lifeless much like the reissue Mullard. In a budget pinch, the JJ Tesla EL34 would be the clear choice but that last wee bit of portrayal of space and openness with the UK Mullard brings on more of the goose bumps factor.

And now the KT66 experience. I started with a pair of UK Mullard in the Callisto and the Tesla EL34 in the Io. First off was to focus on the Callisto. Two LPs were used – Alan Parsons Gaucho with singer Lenny Zakatek and a Carly Simon compilation LP. Both of these singers have a wonderful range with great body to the tone of their voice. After a few listens to Gaucho, I switched to the Genalex KT66 in the Callisto. The difference was immediate. Whereas the UK Mullard portrayed the music as “right there”, the Genalex portrayed the musicians far far distant. It was like I had to really listen hard to bring them into the room and enjoy the music. Tonality was fine but that immediacy was simply gone. I did not hear any detail or extension at the frequency extremes with the Genalex over the UK Mullard. About ½ hour later, I returned to the UK Mullard EL34 and the magic was back. My thought was that perhaps the Genalex or even the KT66 tube was not a good match here. I then dropped in the Marconi KT66. Wow, this too was a huge change. And it was quite the opposite to the Genalex. The Marconi was quite vivid with a huge projection into the room. A few tracks later and it had relaxed a bit more to my liking. And there was indeed more low frequency presence with the Marconi but to me it was more like one-note thumping rather than a bass range that integrated well with the rest of the range. A return to the UK Mullard brought a return to tonal coherency…..and a more natural top end. And with the latter came more spatial cues and ambience. In the final analysis with the Callisto, the Genalex was way too distant and the Marconi which initially was vivid and rich became too fatiguing and lacked the refinements of the UK Mullard. And the Marconi was quite a ways behind the Tesla EL34 as well.

I left a pair of Tesla EL34 in the Callisto and started with UK Mullard in the Io. The focus now was to change tubes in the Io. To make a long story short, the Genalex and Marconi exhibited exactly the same sonic signatures with the Io PS as they had with the Callisto PS. The same tubes can be polar opposites between the Callisto and Io audio chassis but here in their power supply chassis, the result was identical. The Genelax was way too mellow and distant and the Marconi was again too forward on top which got in the way of the music’s dimensionality …. and the bass with the Marconi was also boomy and just not natural. A return to either the UK Mullard or Tesla EL34 in either or both power supply chassis brought on a degree of musicality that the KT66 tubes simply did not deliver for me. Oh well…..I was so excited going into this trial but in the end, the lowly EL34 tubes survived being shelved.

On the comment by Albert on the small signal tubes, wow, my observations match so well. For the Io, I just love the Tele 12ax7 throughout. But I also find the Ei 12ax7 tubes work well on the first input stage as they are super quiet. But with the Callisto, the Tele 12ax7 is so boring and dull. I need Mullard 12ax7’s here to bring on the dynamics and life on the top. And then the issue of 6922/6DJ8. I have been running with gold pin Mullard 6922 on the Callisto and Io but just last week I finally got a chance to try the Tele 6DJ8. A quad of these in the Callisto was too much of a good thing but I really liked a pair of these and a pair of the Mullards for a balance between dynamics and tonal coherency to the trebles with a nice bloom in the mids. But the huge surprise was the pair of Tele 6DJ8 in the Io. WOW! This was as dramatic over the Mullard 6922 here as the Mullard 12ax7 was over the Tele 12ax7 in the Callisto. It is amazing how a few select pairs of tubes out of 80+ in the system can make such a huge difference vs. the others. You really need to try out as many as you can and all over to make these little discoveries.

John

Wow John, sure sorry to have steered you wrong on this one........ I wonder what the deal is? The sound you are describing is certainly not what I am hearing in my system. The Kt-66 does give a "slightly" more laid back presentation, but I would just describe it as a deeper soundstage. Are the Genelex' you are using grey glass? ..... Anyway, if you ever want to sell those babies I might be interested.

Maybe Albert will chime in on this one again to shed some light.

Chris