Quote:
Originally Posted by
blaser 
Thylantyr,
Can you pls post your thoughts for everybody to see? PMs will deprive many from learning.
You can probably write a big story just on one issue. You can probably
write a book if you include more issues. This thread would go way
off topic.
Here's one simple issue.
The conventional power supply design uses a simple transformer for 50/60hz operation to mate with your house voltage.
Not these kind;
http://www.transformersmovie.com/
But these kind.
http://en.wikipedia.org/wiki/Transformer
The output connects to diode(s) to make a rectifier, usually full wave, but full wave
bridge rectifiers are more common. It converts the AC to DC but it's not
a clean DC, it has ripple.
Green = ripple
http://en.wikipedia.org/wiki/Rectifier
The output of the rectifier connects to the power supply capacitors to smooth
out the ripple.
http://en.wikipedia.org/wiki/Capacitor
Pic #2 shows the capacitor installed and ripple reduced.
http://hyperphysics.phy-astr.gsu.edu...ic/rectbr.html
You can see when the capacitor discharges and recharges again on the
next cycle. So, capacitor refresh is determined by that transformer frequency.
If the frequency is low and you want less ripple, then you need to install
more capacitance in the power supply design. High end esoteric home
amps may have 100,000uF of capacitance per voltage rail, maybe higher,
but it's a big chassis to hold all those caps. A cheap home amp may have
5,000uF give or take. There is nothing written in stone on how much you
should use, usually the physical design of the amp will limit your choice,
so even if you wanted to make an uber amp with 100 volt rail voltage and
10 farads of capacitance, it would be a huge.
***
Another type of power supply is a high frequency switching power supply,
SMPS is a common name {switch mode power supply}. A common design may
use AC to DC conversion {minus big transformer} and the raw DC connects to a
few caps for smoothing, then that high voltage DC connects to a smaller dinky
transformer but it switches at a much higher frequency, for audio purposes, SMPS
are in the 50,000 - 200,000 hz range. This is huge compared to 60hz
transformers. To switch the transformer on/off at 50khz - 200khz you need
semiconductors {transistor, etc}.
Imagine the ripple you get, it's uber high in frequency so... you don't need
very high capacitance because the refresh rate is so high that you can accomplish
the same task with just a few thousand microfarads of capacitance.
To answer the question. You can have a big 60hz based power supply inside
a gigantic power amplifier with 200,000uF of capacitance, but on the same
token you can have a clever, more modern power supply design with 2000uF
{100x less} and accomplish the same task because it's a SMPS design.
EP1500 - 60hz power supply design {big transformer}
http://home.pacbell.net/lordpk/proam...r_EP2500-1.jpg
PLX3402 - SMPS {dinky transformer}
http://home.pacbell.net/lordpk/proam..._PLX3402-1.jpg
[yellow square on the right]
The PLX is rated for about 1000w more watts.
If you were to judge the amps just on rail capacitance without knowing
the power supply design, it would be hard to form a conclusion. Also,
adding more capacitance to a SMPS design may not bring that much to
the party - from an audible point of view - , but you can measure the
voltage stabilizations it offers. I've done these experiments with my PLX.
I beefed up the primary caps {big blue ones} and the SMPS caps {small banks},
with some huge caps. I can measure things but it's too hard to distinguish
the improvement if you were to do a listening test.
