Aren't the spax7 specially made for lower noise than traditional 12ax7's? In other words, I don't mind other brands, particularly mullard, but the spax7 has a different design from what I understand to be extra low noise.
Hello Aramism,
and welcome,
that's the way I understood all the info on the spax7. I run them in my MP1, JMP1 and Voodu Valve. To me they sound great clean and driven hard.
They also come with a "sheath" covering them which is suppose to cut down on vibration and other microphonic noises. I did try the str-12ax7-a's but to my ears the spax7 had much more definition and clarity.
Mullard's also sound great in there, GT's not so much, kinda fizzy
I had a similar noise issue (not the siren part though) I ended up swapping the power transformer out of another MP1 I use for parts and it cleaned right up. Maybe someone else could chime in on that...MJMP, rnolan, mike b? Any of you have a power transformer issue before?