CAT Preamps vs Amps

Bart,

>> but I'll bet you that the Amperex 12AX7 D getter long
>> plate (circa 1950's at 200 to 300 a pair)will
>> significantly outperform the EI 12ax7.
maybe so. The $ amount is a bit too extravagant for me - I cannot convince myself to spend this much on NOS tubes!
I also tried the Telefunken 12AX7. I think that I had a smooth plate pair (if memory serves me correctly). Like Rayhall wrote, I found the Tele 6922/Tele 12AX7 combination the best. The Amperex 7308 USN-CEP/Ei12AX7 combination the 2nd best.

>> John is also correct about Ken Stevens adamantly
>> rejecting swapping the stock tubes in the CAT U2,
Having spoken to Ken Stevens several times at length, he informs me that he has "optimized" the CAT preamp design for the Sovtek 6922. That's why he's so insistent on retaining those tubes. I didn't ask him specifically what he meant by "optimized" but I surmise that he means creating the bias specifically for that tube to run it in its most linear region + the power supply filtering for its heater supply.

>> so why are you referring to his rejection of the
>> Mullard as a suitable replacement for the stock
>> tubes
Again, speaking at length w/ Ken Stevens informed that the Mullard tube was ill-suited to the design on the CAT. As you know, certain tube types work well with certain tube preamps i.e. if a certain preamp uses a 12AX7 then not all brands of 12AX7 will suit this preamp. The CAT is no different - the Mullard tubes make the CAT perform at its lowest. I found the same when I tried a Mullard pair generously lent to me by Jafox.
However, I did write the following in my original post:-
"Of course, one is allowed to tube roll any & every tube that one has on hand - nobody is there to stop the user from doing this. However, I've found it worthwhile to solicit an opinion from the designer/manuf before doing so. If nothing, I take his words under advisement."

I'll have to listen to an Aesthetix Callisto & determine for myself how its sound compares & contrasts to the CAT preamp. I'm not convinced that the CAT can be faulted for the lack of portraying space, decays & harmonic textures.

Bombay, if you followed Ken Stevens advice you would still be using the stock tubes. Have you considered the cost differential between the stock tubes and Teles or Amperex may be the deciding factor in Ken Stevens tube selection?
The 6922's or 12ax7's have certain output parameters that are the same regardless of the tube manufacturer. That is why they are measured by classification (6922, 12ax7, 12at7, etc.) not by manufacturer. So for you to say that Ken's design was optimized for the Sovtek is absurd. Does it sound optimized to your ears or any other ears on this post with the Sovteks? Bart

Bart,

>> So for you to say that Ken's design was optimized for
>> the Sovtek is absurd.
I'm merely conveying to you what he told me. For a clarification you should call Ken & ask him yourself what he exactly means.

Bombaywalla - The reason my response came off as defensive was because I made an effort here to convey my observations; these descibed the strengths and weaknesses of the two preamps under test. Never did I refer to either as terrible. That (dis)hono[u]rable title belongs to a few other preamps that I have auditioned over the years and noted here on A'gon.

I do indeed take a manufacturer's or an audiophile's suggestion for a starting point to use a specific cable, tube, matching component, etc. But the road to refinement on a per-system basis is only possible if we experiment with other options, and some of these will likely be contrary to the initial suggestion/advice we got. The Mullard tube is a classic example here. It did not work for you - but it worked for me ... if nothing else, as a significant improvement over the stock tube used to "voice" the product.

Another factor is that my tests were with the UII and yours with a Mk III. Besides our very different systems, could the difference in the CAT preamp models be a factor for our opposing conclusions with the Mullard 6922? .... very possible. And the same for the Tele 12ax7? .... again, very possible. Can you imagine that one brand of 12ax7 might lock in for the CAT line stage and another lock in for the CAT phono stage? ... And swapping these two could be a worse result that what we had with the stock tubes? This is exactly the case between the Io and Callisto for both the 6922 and 12ax7. Afterall, they were designed by the same engineer and also voiced with Sovtek tubes. And yet when other tubes are tried, the two components react very differently to the same 12ax7 or same 6922. Even Mr. Spock would be perplexed by such a outcome.

I think that if we evaluate a tube's performance, or anything else such as a cable, with a specific product, all of our conclusions about that specific tube or cable are relative to the one product under test....and in the context of that system. We can not judge the performance of that tube or cable onto another product until we repeat the test process for the product.

What I was trying to do with the resources available to me, was to max out the CAT UII and max out the Io/Callisto and in the final analysis, the results for each was very impressive. But through so many changes to each, tubes and cabling, a "house" sound for each became very evident...and the design engineers' priority in a resultant sound for each became evident. We can tweak and refine a product to get it to be a little more to our liking, but if we still find something lacking, we must continue our quest to find a more suitable product; expecting a $1200 pair of golden tubes to save the day is not realistic.

Btw, I did a lot of playing of 6922/12ax7/12au7 with the JL-3s. With Mullards and Teles here, the JL-3's performance took quite a step forward - hardly a surprise. And this was long before I ever had the UII here. I have paid a lot more money for a component change and gotten less improvement than I have with some of these $200-300 tube "upgrades".

I don't mean to get so philosophical here, but so many people here, as shown by the multitude of "best of" threads on A'gon, are obsessed with what is best.....and there is no such thing.

Bart - I get the DAC and Io back from GNSC tomorrow. Once I burn these in for a couple weeks, then try out a matched octet of Brimar 12ax7's for the Io's first stage, the pair in the Callisto and pair in the DAC, I will be ready to borrow some Stealth cables. Hopefully the JL-3s will return very soon too. I am very excited to try the Steath products. I will keep you posted on this.

John

I have been following this thread since its start along with two others: Cat Ultimate/Tube Rolling and Cat vs. Aesthetix vs. Supratek. My experience compared to others is limited to a novice level and recently in the past 4 years resumed my interest again after 12 years of absence from the hobby. During this time I have upgraded my system which is currently B&W Nautilus 801's, Bryston 7BSST Monoblocks and the Cat Ultimate MKII pre line stage only. My digital source is extremely old and is the weakest link being a Nakamichi OMS7aII CD player (at some point this will be my next upgrade). Speaker cables are AQ Volcano biwired and AQ King Cobra Interconnects.

I would like to first say that I fully appreciate all of your passion that you have imparted. I previously have owned a modded Counterpoint SA-3 pre, Audio Research LS25 MKII and now the Cat Ultimate MKII. This has the stock tubes, which are the Sovtek 6922 in the V6, V7 and V10 position and 12AX7Ei in the V8 and V9 position. The A.R. LS25 MKII without a doubt (for me at least) was more detailed and refined. I have not heard the Aesthetix, but can only imagine the detail that Jafox is talking about. With the A.R. there was more sense of a separation in soundstage. Background vocals were very distinguishable almost to the point of "seeing where they stood." Even with this musical detail that the A.R. gave, it lacked body & soul, as if a veil were over the music, sterile-like. Don't know how else to describe it. Maybe due to the Sovtek tubes. My desire was to combine the Counterpoint and AR into one unit which I believe to some degree the Cat has achieved. The opportunity came to purchase the Cat and upon direct A/B comparison in my system I was sold on the Cat. I will fully admit that some of the detail has not been duplicated to the same degree which the A.R. gave, but ever so minutely. The Cat over all gave body and soul back to the music. Hopefully soon I will be looking into tube rolling the Cat (but for now my hectic schedule doesn't permit it). There is an ever so slight slant towards the top end of being overbearing or grainy, maybe again this is due to the Sovteks, or possibly the B&W 801's, don't know until I try different tubes (any precautions with changing tubes in the Ultimate MKII?)

The ultimate in music reproduction (no pun intended) will always be continullay strived for and I don't believe ever fully achieved, but the input of other Audiogon members such as Rayhall, Bombaywalla and Jafox is extremely valuable and appreciated. Especially to those as myself who do not have the resources at hand to compare, nor the bigger obstacle of a budget. I know that we can get passionate about our gear and its performance because I do! Throw into the mix the tonal differences of each ones ear and most important of all our own preference which is unique to each one of us, that's what makes us individuals.

Thanks for the great effort which will cut out alot of trial and error and for the most part narrow things down for us. Hats off to you all!