My most disappointing purchase actually turned out ok in the end. As some of you may remember I bought a used Decware Zbox tube buffer a few months ago. When it arrived sans tube, I stuck in the only thing I had, which was a Sovtek 12AX7, which was listed as an option. Well it sounded awful. Just horrid distortion.
After I calmed down, I contacted Steve at Decware and he suggested a 12AU7. He said a high output DAC could overload a 12AX7. I should have gotten something cheap to try, but rolled the dice and bought a platinum grade Mullard.
Damn, now it sounded really good. It wasn't a magic fix that suddenly turned my somewhat mid-fi system into the something great, but it added a little midrange liquidity and opened up the soundstage a bit. Not bad for less than $300. I found myself enjoying the music more.
This experience is why I now have a tube pre coming my way. Hopefully the pre give me the same improvements but on a larger scale. I'll try the system with the buffer and pre together and the pre alone.
Just goes to show that initial opinions can be wrong, and maybe due to operator error.
Makes me leery of single post slamming or praising something. When something like the MAD pre I have ordered gain lots of favorable reviews, then I feel a bit more comfortable.