JohnSwenson;618558 Wrote: > I've actually looked into this quite a bit. Originally I was very > skeptical of burn in, but after having experienced it I set about > trying find out whats going on. > > What I found was that there are two classes of componants that can > exhibit significant burn in effects, capacitors and magnetic components > (chokes, transformers). > > ALL magnetic devices in the audio path that have magnetic "cores" > exhibit burn in, its a property of the magnetic materials. These work > by collections of atoms called magnetic domains chainging orientations > due to applied magnetic fields. For a freshly manufactured piece of the > metal the properties of this "orientation flipping" change as they are > flipped. As they flip back and forth the amount of energy required to > make the flip and various other properties change slightly. After a > while things stabilize and it stops changing. Some of these materials > will tend to gradually revert to their original state if you don't use > them for a long time, so you have to burn them in again after a long > period of unuse. > > Capacitors are more interesting. A capacitor consists of two metal > "plates" separated by an insullator (the dialectric). When a voltage is > developed between the plates it creates an electric field between them > which produces a force between when. When that force is varying (say > from a music signal) that force also varies. This creates vibrations > between the plates, causing the distance between the plates to vary, > changing the capacitance along with the signal. This gives rise to > distortion of the signal. Its not very much but it IS there and is > measurable. > > To make this worse almost all capacitor construction techniques produce > mechanical resonances in the audio band. These resonances particularly > affect transients, again its not a large affect, but it is measurable. > > > Thus changes to the mechanical resonances of a capacitor can affect > what it does to a signal. > > Take for example a film and foil polypropelene cap, as its used the > "micro vibrations" can slightly change the relationships between the > film and the foil, changing the resonant properties. Sort of like "the > contents of this box may have settled due to handling". > > There is a type of capacitor that exhibits this effect to a very large > degree: the paper in oil capacitor. The dialectric is a sheet of paper > soaked in oil. As the cap is used the vibrations cause the oil to > further penetrate the paper matrix, significantly changing its resonant > properties. After about 50 hours this process reaches a stable point. In > this condition the capacitor is very well damped and has very low > resonance effects, which makes it one of the best sounding capacitors. > BUT during the "burn in" period those resonances vary significantly, > causing the cap to sound horrible for part of that time. > > Its really startling how bad these caps sound during the burn in, its > like everything is getting sent through a guitar fuzz box! The first > time I built something with these caps I was very perplexed by this, it > sounded very good at first, but after about 5 hours it sounded terrible, > I thought something had burned up, come un soldered etc. But everything > seemed fine, all the voltages were right where they were supposed to > be. I let it play for another day, and it started sounding much better, > after two days it sounded way better than it had originally. > > I have tried several different brands of paper in oil caps and they ALL > do this, but the time frame can vary from one to another. > > One primary feature of paper in oil caps is a high voltage rating so > they tend to only get used in tube circuits. They work VERY well in SS > circuits as well, but are rarely used commercially because they are > fairly expensive and are large. > > Because metalic cored magnetic components and paper in oil caps are > almost exclusively used in tube circuits, people with SS gear may > notice very little burn in. (anything with caps in the signal path will > have SOME burn in, but its probably pretty small) > > There is a lot more to say on the subject, but thats all the time I > have right now. > > John S.
I'm familiar with the PIO cap problem - but they are exotic components - likewise chokes. I don't accept that there is an as yet undocumented law of the universe that states that certain things (but not other things!) ALWAYS get to sound better after a period of burn-in... in fact it would be contrary to the second law of thermodynamics... Why does nothing get worse? - what about entropy? -- Phil Leigh You want to see the signal path BEFORE it gets onto a CD/vinyl...it ain't what you'd call minimal... Touch(wired/XP) - Audiolense 3.3/2.0+INGUZ DRC - MF M1 DAC - Linn 5103 - full Aktiv 5.1 system (6x LK140's, ESPEK/TRIKAN/KATAN/SEIZMIK 10.5), Pekin Tuner, Townsend Supertweeters, Blue Jeans Belden Digital,Kimber 8TC Speaker & Chord Signature Plus Interconnect cables Stax4070+SRM7/II phones Kitchen Boom, Outdoors: SB Radio, Harmony One remote for everything. ------------------------------------------------------------------------ Phil Leigh's Profile: http://forums.slimdevices.com/member.php?userid=85 View this thread: http://forums.slimdevices.com/showthread.php?t=86359 _______________________________________________ audiophiles mailing list [email protected] http://lists.slimdevices.com/mailman/listinfo/audiophiles
