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Old 10th August 2008, 11:39 PM   #21
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What differences should I expect between say Panasonic (good bang per buck) vs Epcos/Siemens Sikorel capacitors (ie 10,000uF)?

These power supplies (one per channel) are for a Class A amplifier.

Do the capacitors only make a big difference if the transformer is under rated (by the way I am using two 300VA transformers - one per channel)?

What is the most important specification for a power supply capacitor (High Ripple Current, Low ESR, etc)?
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Old 11th August 2008, 08:41 AM   #22
AndrewT is offline AndrewT  Scotland
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Quote:
Originally posted by thanh1973
These power supplies (one per channel) are for a Class A amplifier.
.....................................if the transformer is under rated (by the way I am using two 300VA transformers - one per channel)?
Hi,
if the transformer of a ClassA amplifier is under-rated it will run hot.
A 300VA transformer should be down rated to ~70% when feeding a capacitor input filter. leaving ~200VA as the maximum output from the filter.

If the continuous demand from the ClassA amplifier exceeds 100watts then your 300VA is too small.
Don't ask your transformer to run a continuous load of >50% of capability.
BTW,
25W of ClassA output power will usually require at least 100W of dissipation.
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Old 11th August 2008, 08:59 AM   #23
Nordic is offline Nordic  South Africa
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Quote:
Originally posted by thanh1973
What differences should I expect between say Panasonic (good bang per buck) vs Epcos/Siemens Sikorel capacitors (ie 10,000uF)?
I would expect, longer life, higher ripple, lower ESR/ESL, and most importantly according to the PSU article over at TNT, faster chargeing...
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Old 11th August 2008, 01:07 PM   #24
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How should this affect the sound?
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Old 11th August 2008, 01:11 PM   #25
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Quote:
BTW, 25W of ClassA output power will usually require at least 100W of dissipation.
Is that 100W per channel?
Or 100W total (ie 50W per channel)?
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Old 11th August 2008, 01:37 PM   #26
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Per Channel
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Old 11th August 2008, 03:14 PM   #27
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Quote:
Originally posted by Predator864
Per Channel

Why is it so satisfying knowing your "puny" 15W/ch amp pumps out 200W of heat ?

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Old 11th August 2008, 03:19 PM   #28
Nordic is offline Nordic  South Africa
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Quote:
Originally posted by thanh1973
How should this affect the sound?

I quote from the page....

"By way of example, a typical commercial value capacitor, rated at 10,000uF/63V and costing some Euro 8-9, will have a speed of 30-40V/uS at best. An equivalent Elna for Audio series black, costing some Euro 15-25, will have a speed in the range of 80-90V/uS, i.e. at the very worst, double the speed of the best case in commercial cap land. A Siemens Sikorel cap, costing some Euro 20-30, will slew at over 100V/uS - but at a price.

And this is hard to ignore if you want good quality sound. What's the use of ultra fast electronics, capable of tremendous speeds, if they will be bogged down by slow capacitors, which will appear as speed limiters? I can't help being sarcastic here - this is why in so many cases the advertised amp speed is never achieved in real life.
Many manufacturers measure the speed of the input stage only, and far too few of the overall amplifier - the second group will always show much less impressive results. So beware of wild figures, they are most probably not truly representative of the amp as a whole, on an input-to-output basis.
"
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Old 12th August 2008, 11:46 AM   #29
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Hi Nordic,

How does the speed of the cap affect the amplifier?

My uneducated guess is it only changes the time it takes to charge the cap. Does this mean a shorter charging spike with a higher current value? Some people actually put a resistor between the diode and cap to reduce the charging rate.

Can you point me to any threads about this as I can't recall seeing any?

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Old 12th August 2008, 12:11 PM   #30
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On second thought, wouldn't the cap only need to be fast enough to keep up with charging positive sine wave 50Hz or 60Hz (times 2).
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