My wife is a front-line professional violinist who works with the San Francisco Ballet Orchestra. I mostly listen to jazz and cabaret music, which she likes. But when I put on something classical she hated it. She said that strings sounded harsh and screachy. Uh-oh... I had dropped $1500 on a piece of gear unheard and here she was giving me grief. Mind you, we spent $12,000 on her violin bow a few years ago, so I had some slack here. You don't want to know what players at her level pay for a violin...
I tried swapping out the provide RCA clear tops with Brimer Mazda 6CG7 tubes, which seemed to help. I also put in plenty of burn-in hours, which also helped a bit, but still it wasn't right. Discussion with Troy suggested there might be an impedance issue with the load the SP13 was facing.
My loudspeaker is the Linkwitz Orion system, which is tri-amplified and comes with an active crossover, which is what the SP13 feeds into. An e-mail to Siegfried Linkwitz revealed that the input impedance of the Orion crossover was 10 kohms, which is much lower than the SP13 was intended to work with. Once we realized this, Troy sent out some 1.5 uf metalized poly caps which I installed.
Wow... What a difference! It sounded good before, but now it's frightening. I was listening to Taj Mahal last night and it sounded like we were sitting in the studio. The acapella tracks were amazing. And my wife approves the sound of strings now Thank Goodness.
The point behind this tale is to be aware of potential impedance issues if your tube preamp if feeding into something solid state. If it's some Mystery Gizmo, make a point of finding out what its input impedance is. This took my preamp from something wonderful to something startlingly amazing.
Thanks for the help Troy!