Some tube preamps will suffer noise if the cover is off. I changed out a tube , was listening to it and was wondering where the noise came from. Another tube, still noise. I pulled out my tester to make sure it wasn't a bad tube. Found out accidentally it was from the cover being off. Probably explains why the cover is so thick and heavy.
The Accidental Tweak
Recently I turned my system on as usual and started listening to an album I know pretty much by heart. Halfway into it, a small voice in the back of my head started saying the system sounds really good today.
And it did sound fine. Maybe even... better than usual? No way I thought, I haven’t done anything to it. I must just be in a good mood.
It was not a life-changing improvement; just a bit more airiness, a tad more definition.
My Krell preamplifier made a world of difference when I introduced it to my system. I bought it in a still-working but near-death condition, and I started a regimen of fixing problems, listening for a couple of weeks, taking measurements, troubleshooting, fixing more stuff, all the while keeping tabs on bias and temps and DC offset.
The inside of this pre is gorgeous - all discrete, top-shelf components, not an IC in sight, the PCB laid out as if by a choreographer; it harks back to Krell’s long-gone heyday.
The cover was off during that process, ostensibly so I could check on stuff, but honestly I didn’t mind admiring the beautiful audio craftsmanship inside. Eventually its maladies were cured and I screwed the cover back on, I figured better before I spill a cup of coffee over the PCB.
Then it hit me: something did change, the cover went back on. Presumably that’s what I was hearing: it must have completed a Faraday cage around the pre’s sensitive single-ended circuitry, restoring shielding it probably needed because it sits inches from a pair of large, EMI-spewing monoblocks. The cover blocked the EMI / noise and that’s what I was hearing - or rather, not hearing.
But the true beauty in this is that I made this tweak completely unbeknownst of myself. In my mind I was putting a lid back on, not completing a Faraday cage, thus my brains never had a chance to develop the smallest expectation. To the opposite, I was trying to convince myself that I could not possibly be hearing anything (even though I was hearing something), because I had done nothing to my system.
So I know for sure that the sound improvement I heard, albeit subtle, was real, and that I believe is a rather unusual treat in this hobby.
Would love to hear similarly unintended improvements that happened to you guys.