What made you change to a 6SN7 preamp?

Great replies! Keep them coming. I've had great experiences with Brent Jessee, too. Props to him.

Thanks to everyone for posting. Just a couple of thoughts on what I've read so far.

First, clearly, people hear and can articulate a difference; I see patterns in the kinds of differences heard. This is helpful to me in anticipating *why* I might want to try a 6SN7 based preamp. 

Second, @decooney may throw some of the claims into some doubt with his statement:

another factor in responses so far may also relate to some people jumping up a level or two on design and improved parts quality with their next tube preamp purchase.

Strictly speaking, i.e bumping from something like a $1500 12Axx preamp up to a $3000+ 6SN7 based [a higher quality] tube preamp as a normal course of order.

Why? Because if some of you *simultaneously* purchased a better preamp AND a 6sN7 preamp, you could be mistakenly attributing the improvements in sound to the tube rather than the overall construction.

Thus, a question which controlled for this would ask whether your change in preamp was lateral in terms of construction quality and nevertheless there were improvements in sound which could safely be attributed to the tube?

I realize this is a very hard question to answer, for many reasons. But it is effectively the challenge implicit in decooney's observation.

I continue to learn a lot from this thread. Thank you all so much.

@big_greg There's a Herron preamp listed used that I have my eye on....someone stop me before I ruin a perfectly good marriage.

@lowrider57  Thank you for relaying the story about that upgrade. It bears on my question directly. Very helpful.

@moofoo  Your example, too, bears on the question. And as others have said, there's no substitute metric for actually hearing it. Expense, tube, design are all relevant to the question, though. 

@big_greg  Thanks for your comment about the Herron. I need to sell something before buying anything else, but I'll keep my eye on that Herron. My Quicksilver got upgraded with Mundorf and Vcap caps and sounds pretty good. A night and day difference would really be the reason to change.

@atmasphere 

when you dig into it you find out that the variables I mentioned above were uncontrolled in the comparison. 

Your understanding of these variables, and your cautious way of taking variables into account when you make comments, make you an invaluable voice in this forum. Thank you.

Lack of control over variables is what leads discussions into sometime wild and fun or confusing and conflictual directions. Of course, the room is almost never mentioned as a variable in almost any discussion, but that of course is a hard one!