Audio Research Ref 10 vs 40th Anniversary preamp


I was wondering what the difference in the sound between the Ref 10 and the 40th ? Not much wrote about that. I btw have the Ref 6 but never heard the 10 or the 40th. 
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minorl......... Ive had the 5se and now the 6.. On my system there was a " Oh My God " difference between the two. If it was not i would of never spent the extra money.To me it was money well spent to hear a Oh My God difference. I am very satisfied with the 6 .But was also very curious about how the 6 compared to the 40th, and the 40th to the 10. I guess folks will have different opinions on their own systems and ears.  
I had the good fortune (I guess) to have the REF 3, 5 at the same time to listen to.  No big difference for me to “justify” buying the 5. Especially with new tubes in the 3.  

So I waited.  I then bought a REF5SE because I heard it before and also compared it to the 3.  Big difference in the same system (mine).  Then a few weeks later I found out about the Auduo Research trade in-trade up program where the give you 75% of MSR for the trade in unit. Mathematically it was a no brainer.  I traded in the REF 5SE for more than I paid for it and also got a very good price for the 5 because it was a reviewer demo unit.  It had 24 hours on the unit.  In my system, a direct A/B comparison between the 5SE and the 6 was much like the difference between the 3 and the 5.  There was a slight difference but not jaw dropping.  

Same was was true for the 40 and the 10. Although to me more between the 40 and 10.  

A lot lot depends on two things to me.  If one can do a direct A/B comparison in the same system at the same time changing nothing but the unit, with the same music, matching levels first and the listening.  That is really the only real way to compare fairly. 

Any other way us dependent on memory and if one didn’t listen on the same system and (matching levels first) there would be too many variables. I play music on one unit first and establish a listening level.  Then I insert a white noise test disc and measure the respective level.  Then, I switch units and play the white noice source again and adjust the level until it matches the other level.  Then I play the music and listen.  I don’t change anything else, cables, source, equipment, etc. same room, etc.  
 
if the price was good, I’d take a 40 any day.  Same is true for a 10.  I heard a system in Santa Monica. With a 10 pre, 10 phono, 250SE amps, vandersteen 7 speakers . And stupidly expensive basis turntable, etc.  and in all my years in this, that was the first time that a system completely disappeared.  

Wow.  Optimal enchantment in Santa Monica .  

Oh yeah, I’d take a 10 any day. 

Enjoy
minorl,  please clarify.  Which unit did you trade in?  What unit did you buy?  I own a Ref 5SE and have been thinking about the Ref 6.  Just curious if ARC would do a trade up my Ref 5SE to the Ref 6 and how much they would charge.

Thanks

BIF