I have only a couple comments to add to Jafox’s post. First it should be pointed out once again how pleased I was with the Calypso. (And still am.) But in order to fully appreciate what a great pre-amp the Calypso is you must read my review, and understand I have tried a number of ~$5000 pre-amps during the years. The Aesthetix is in its own category when competing with its rivals.
Secondly it’s very important to point out that Jafox and I are night and day in our system directions, yet we both without ever meeting, created extremely similar tonal qualities in our systems. For the two of us to be this pleased with a piece of gear (Callisto) says volumes about how special it truly is. When Jafox comments about the BAT pre-amp I cringe. When he discusses the other great (complex at times) pre-amps I roll my eyes. I have not found the magic of the Aesthetix designs in other products within the context of my system. The Callisto is truly a great product and if you are considering a line stage in this price range than you must already have a great amount invested in your system. To not audition this product would be cheating yourself from knowing its’ potential.
I can only imagine the improvements we will hear with N.O.S. tubes. As I discussed in my review of the Calypso, tubes made a very significant difference in the quality of sound. Albert Porter has posted a couple times over the years the tube combination that best enhances the Callisto’s sonic qualities. Below is a reprint of that (Without A. Porter’s consent no less) I will ask Audiogon if they can amend my original review as I should have included this.
TUBES FOR AESTHEITX
Regarding the comments by Bud and Rayhall, the 6922 Sovtek would be my first change. For additional midrange and air, try the Siemens 6922 CCa or the Amperex US Military 7308 CEP. If either of these produce too much midrange presence, try the Mullard 6922 (gold pin). Realize, that when you upgrade to one of these higher resolution NOS 6922's you are listening with more intensity to the weaknesses of the remaining (original) tubes. You are judging the replacement, plus all that it exposes downstream. If after changing to the CCa or CEP, you find that there is too much "grit" in the sound, try swapping the 6SN-7 as described in my long post. After that, if you are feeling adventuresome, trade out the first stage 12AX7 tubes (Io only). Note, these 12AX7's are the ones I warned about, get TESTED, ultra noise tubes for this position. My first choice and the most beautiful sound is the Telefunken 12AX7. Other options are the RCA 5751, a US Military version of the 12AX7. The 5751 will alter the tonal balance somewhat, as it is not an exact replacement. There will be a slight loss in gain, with improved signal to noise and lower distortion. Overall, the sound will be a bit more on the dry side. One final suggestion would be the 12AX7 French Mazda. A good sample of this will produce significant improvements in high frequency transparency, especially compared to the Sovtek. However, the Mazda has not been without problems in my experience. The samples I received are not equally reliable or equally low noise. Some will play perfectly for many months while retaining their original "voice" while other samples will develop horrible micro-phonics and tube noise in as little as a week. This is a situation that could lead to disappointment with the Io, when in fact, the tubes are the culprit. Unfortunately, there must be some risk and experimentation within your own system to determine what is best.
Secondly it’s very important to point out that Jafox and I are night and day in our system directions, yet we both without ever meeting, created extremely similar tonal qualities in our systems. For the two of us to be this pleased with a piece of gear (Callisto) says volumes about how special it truly is. When Jafox comments about the BAT pre-amp I cringe. When he discusses the other great (complex at times) pre-amps I roll my eyes. I have not found the magic of the Aesthetix designs in other products within the context of my system. The Callisto is truly a great product and if you are considering a line stage in this price range than you must already have a great amount invested in your system. To not audition this product would be cheating yourself from knowing its’ potential.
I can only imagine the improvements we will hear with N.O.S. tubes. As I discussed in my review of the Calypso, tubes made a very significant difference in the quality of sound. Albert Porter has posted a couple times over the years the tube combination that best enhances the Callisto’s sonic qualities. Below is a reprint of that (Without A. Porter’s consent no less) I will ask Audiogon if they can amend my original review as I should have included this.
TUBES FOR AESTHEITX
Regarding the comments by Bud and Rayhall, the 6922 Sovtek would be my first change. For additional midrange and air, try the Siemens 6922 CCa or the Amperex US Military 7308 CEP. If either of these produce too much midrange presence, try the Mullard 6922 (gold pin). Realize, that when you upgrade to one of these higher resolution NOS 6922's you are listening with more intensity to the weaknesses of the remaining (original) tubes. You are judging the replacement, plus all that it exposes downstream. If after changing to the CCa or CEP, you find that there is too much "grit" in the sound, try swapping the 6SN-7 as described in my long post. After that, if you are feeling adventuresome, trade out the first stage 12AX7 tubes (Io only). Note, these 12AX7's are the ones I warned about, get TESTED, ultra noise tubes for this position. My first choice and the most beautiful sound is the Telefunken 12AX7. Other options are the RCA 5751, a US Military version of the 12AX7. The 5751 will alter the tonal balance somewhat, as it is not an exact replacement. There will be a slight loss in gain, with improved signal to noise and lower distortion. Overall, the sound will be a bit more on the dry side. One final suggestion would be the 12AX7 French Mazda. A good sample of this will produce significant improvements in high frequency transparency, especially compared to the Sovtek. However, the Mazda has not been without problems in my experience. The samples I received are not equally reliable or equally low noise. Some will play perfectly for many months while retaining their original "voice" while other samples will develop horrible micro-phonics and tube noise in as little as a week. This is a situation that could lead to disappointment with the Io, when in fact, the tubes are the culprit. Unfortunately, there must be some risk and experimentation within your own system to determine what is best.