Originally Posted by vvs_75
Any good news on testing? I really can't wait to get this kit!
Like a lot of us from time-to-time, other things get in the way. I don't think Dsavitsk has had much time to check out the noise issue, unfortunately. The noise is a highly-variable phenomenon. It's completely inaudible with some headphones and some tubes, but will manifest itself with others. Either way, it's never anything that you hear with the music. I still listen to mine (the older proto) as my primary amp. I've never been one for soundstage comments, but this amp has it in spades. IOW, even if I know there's a slight noise issue, I prefer the musicality and imaging of the Torpedo, anyway. This is just my opinion, of course, but there's stuff there that you will never hear with a solid-state or hybrid amp.
KSC-75's with 6J6 tubes seem the worst for the noise. 5964 tubes seem the least noisy, whereas with some headphones such as Sennheiser HD25-II's - even with the 6J6 tubes - the noise is completely inaudible. That's very odd, because one would think that with completely closed in phones like the HD25's, you'd be able to hear every flaw. With the lid off, Dsavitsk reports that he can't hear any noise. With the lid on, he can, which is another really odd thing, because the case is completely aluminum and shouldn't have any effect unless it's RF noise. So,the problem is definitely that the tubes are picking up the noise through the air. In my testing, the addition of the choke helped and we will recommend that now instead of the resistor - but it may have had more to do with providing more shielding to the tubes than anything in the circuit. It's all in the tubes. I guess you get what you pay for when using $2 tubes. I think the 5964's are $4 ea, so they're a bit better, IMHO.
Some of you who have built a Starving Student and remember the structure of the 19J6 tubes may be able to remember that the grid in this tube family is somewhat exposed outside of the plates. The grid is actually stretched between copper posts that are on the outside of the plates, so the grid wiring connecting to those posts is exposed. There have been issues, too, of the Starving Student picking up noise through the tubes, whether cell phone, computer, etc. The 5964 tubes seem a bit more conventional in construction and have plates that completely enclose the grid structure. This may explain what's going on.
In any event, we may decide to go ahead with the kits anyway - with full disclosure of the noise issue. As I said, it's my preferred amp regardless - and I'm using 6J6W tubes right now and the resistor instead of the choke. Hopefully, Dsavitsk will have something to add soon.
Edited by tomb - 10/29/11 at 11:07am