UID144368
威望79
金钱459780
交易诚信度7
主题124
帖子6362
注册时间2005-5-13
最后登录2025-5-3
超级会员
     
交易诚信度7
注册时间2005-5-13
|
John Curl (Parasound)
I published a paper in 1978 and Audio magazine article in 1979 that
showed this problem with ceramics, and we also found that Tantalum
capacitors did almost the same thing. With this particular test (with
normal test equipment) you could see the non - linearity of the Tantalum
capacitors as well as the ceramics. This still allowed us, in theory, to use
aluminum electrolytics -- we couldn’t find any real problem with them as
long as they were used properly -- or any kind of metal film capacitor.
A third type of distortion, which has been known for many years, but
had been forgotten about, is called dielectric absorption. This particular
problem used to be very important back in the 50s when people used to
solve many engineering problems with analog computers. These analog
computers would emulate mathematical equations with capacitors,
resistors, or amplifiers. Music will also evoke dielectric absorption. Music
tends to not be completely symmetrical at all times, and even though it
averages out in the long run it isn’t necessarily a test tone. If you put a
symmetrical test tone through a mylar capacitor for example you won’t
find any real problem. However if you use an asymmetrical signal you’ll
find that it does have dielectric absorption. This is where the dielectric
absorbs part of the signal and then spits it back later. Well this can’t be
good. Invariably you never get the musical peak, it cannot be completely
passed by the capacitor because the capacitor has to take some of the energy
from the musical peak. It stores it like a battery. Fortunately, this material
property isn’t shared by Polystyrene, Teflon, or Polypropylene, which is
why we tend to use these caps instead of mylar. Tantalum, aluminum,
and mylar are pretty bad in this area.
As a result of all this, we have to exclude many types of capacitors
because they all have some problems to a greater or lesser degree.
Ultimately we wind up with polystyrene, polypropylene, and Teflon. And
that’s why we tend to prefer these capacitors when we can. Except for the
use of aluminum electrolytic for power supplies , the more capacitors we
can eliminate the better it its. |
|