In 9McBb.1407$8y1.13274@attbi_s52, "MasterCBer" wrote:

Well lets see here DOC and Frank
Have you tried a Large farad cap on your amp?

I use caps on just about everything mobile. They work great to get the low-end
from an audio amp. No, I don't run an RF amp, base or mobile. Yes, I have
intalled a few; and yes, they do run better with a big cap on the power leads.
By 'better' I mean that the audio is cleaner and IMD is reduced.

I thought not.

No you didn't.

So unless you have then don't cut it.

Frank you need to learn what ESR is you ****en dum ass.
These cap have a very LOW ESR as I said in my first post I or do you not
read very well.

From Cornell Dubilier:

381LX473M016A452
47000 uFd @ 16 VDC
0.017 ohms @ 120 Hz
0.013 ohms @ 20 kHz

Now you can probably find farad-sized electrolytics -advertised- for lower ESR,
but they don't tell you the frequency or conditions under which that ESR was
measured. There are engineering standards for measuring such things as ESR.
Industry has to deal with these standards all the time. But as long as these
caps are not marketed for industrial use the manufacturers can declare an ESR
that is measured in any way they want, even by measuring the cap in a series
resonant circuit with a high impedance source. IOW, it's a lot of hype, just
like the ridiculous gain figures that are advertised for some CB antennas. About
the lowest -real- ESR you will find among those ultra-high-density caps is about
0.2 ohms, and it will cost you most of a paycheck (two or three paychecks if you
have a McJob).

The problem here is one that has existed since the first capacitor was invented:
There is a tradeoff between charge density (uF per cubic inch) and ESR. Whenever
the physical size of a capacitor gets too large, it usually dictates a different
type of capacitor. A 1 farad air capacitor would have an extremely low ESR, but
it would probably be as big as an aircraft carrier (which would introduce other
problems, but those are ignored for the sake of this example). If it was an
oil/paper capacitor it might be as big as a house. Even an aluminum electrolytic
of 1 farad would still be quite large for a mobile application. So these monster
caps are built with a different type of electrolytic process, one that packs
more farads into a smaller space, but at the expense of increased dielectric
absorption/hysteresis, i.e, a higher ESR.

Put more simply, if these big caps were as good as the advertisers claim them to
be, they would have replaced aluminum electrolytics a long, long time ago. They
haven't. Put even more simply, if it looks too good to be true, it probably is.
If you don't believe me, buy one and measure it yourself. You will need a very
low impedance source and load, then measure the difference in ripple voltage on
a scope. Post the results.

And just to make my point about smaller caps in parallel being better than one
big cap:

381LX472M016H012
4700 uFd @ 16 VDC
0.113 ohms @ 120 Hz
0.085 ohms @ 20 kHz

Put ten of the 4700 uFd caps in parallel and you have 47000 uFd, but with an ESR
of 0.0113 ohms @ 120 Hz and 0.0085 @ 20 kHz, which is better than the 47000 uFd
capacitor. This value would drop the source impedance (in my example from the
previous post) from 0.0163 ohms to 0.0067 ohms, meaning the voltage will only
drop 0.53 volts on a peak. So in this example, the caps give back three-quarters
of the power that is missing from the peaks when run without the caps. Compare
that to any size cap with an ESR of 0.2 ohms.






=============

"...but I admitted I was wrong, Like a man! Something you and QRM
have a problem with. You guys are wrong and you both know it and
are both too small to admit it."
---- Twistedhed ----

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