First, my wife is a very impartial and impatient person who I inflict my audio changes to. I did the same A/B test that an Optometrist does to a patient. No hinting as to which I preferred. She indicated she clearly preferred one direction over another and it was just as obvious to me. Same in both audio rooms systems.
Second, after 33 hours burn-in time, the fuses sounded mostly as good as they initially did. I listened every 10 hours until 70 hours when the sound was quite exhilarating. Record noise diminished 75% (alot) and the pleasure of hearing records with less than good vinyl or condition was tremendously improved. It’s more effective than adding the SimplyVinyl SugarCube pop and click remover but better since it removes even more vinyl noise. I intend to add that device next year to my tape loop for 78s and LPs with lots of pops and clicks (we are talking 1000s of records).
Third, CDs improved in similar ways but I have an idiosyncratic sounding EAR Acute player because I use the earliest stock Amperex 6922s which have huge tonality, dynamics, mids and bass with a rolled off high end (slightly covered sound with less ambience) when I listen at the increased global feedback setting on my amps (I have this feature in 2 db steps from 2 db to 8 db range). When I use the minimum feedback, I have a leaner, less tonally rich sound from CDs (perfect for my LPs & 78s) but great ambience and openess as well as slightly tighter bass. I think it’s time to change the fuse in the CD player (which is plugged into the Teslaplex SE not the black duplex). That may alter the sound beneficially. I’ve tried about a dozen other NOS 6922 brand tubes and they just don’t sound as compelling (i.e. gold pin Amperex have fantastic mids and highs but no bass, Siemens were dry and lifeless, etc with the stock JJs okay comparatively speaking).
As I’ve stated before and as several other contributors have said, they’ve tried many tweaks over the decades. Some work, some don’t. The degree that they affect the sound also varies. Almost all of our audio systems are different. One naysayer should get off this site as he does not contribute anything positive, only cynical negativism to our enjoyment of our avocation..
As to why such great recordings were made in the 50’s and 60’s, first they used simpler but effective power supply and design technology (and cleaner A/C lines back then-no digital hash). Second, they used state of the art tubes with metallurgy unavailable today with proprietary construction. Third, simpler miking, done correctly to capture the sound and not so much the ambience aka wrongly miked recordings by Yarlung today as an example. There are probably more reasons which I can’t think of currently.
I’m so excited about my "new" audio system, I’m going back to listen for another few hours.
