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Old 28th November 2006, 04:50 PM   #1
CarlosT is offline CarlosT  United States
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Default Capacitor Choices...What's Important?

I'm currently comparing various Panasonic caps for an IGC kit and wondered what are the more important specs. The kit calls for 1,000uf 63V caps and the kit comes with Panasonic NHGs. However, Panasonic makes other caps in that range that have higher endurance, higher ripple and lower impedance. What is important?

Panasonic NHG 1,000uf 63v

Cost $1.78

Size 16mm x 25mm

Ripple Current 930ma

Impedance .1

Endurance 2,000 hours


Panasonic FC 1,000uf 63v

Cost $3.33

Size 16mm x 35.5mm

Ripple Current 2,770

Impedance .036

Endurance 5,000 hours


Panasonic FM 1,000uf 50v (no 63v available)

Cost $1.30

Size 16mm x 25mm

Ripple Current 3,320ma

Impedance .016

Endurance 7,000 hours

Is it strange that the "better" spec'd FM caps are cheaper? Am I totally missing the picture here?
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Old 28th November 2006, 05:55 PM   #2
Nordic is offline Nordic  South Africa
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You did not quote ESR for any of those caps

The panasonics looks fine for a GC with 28V supply into 4 ohm.
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Old 28th November 2006, 06:22 PM   #3
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From what I hear, it is more the "sound" of the component itself than the specs that are important.

Many have said that the Panasonic FC is their cap of choice in GCs. The Rubicon ZL is also a good choice for inverted GCs (and the specs are excellent!)

Sometime ago, people were raving about the Black Gate caps. I don't know what their specs are, but I believe that they have a different sort of construction to the conventional electros. It seems as though BG caps have fallen from favour in the GC circles in the last couple of years...

As for specs, what we should probably look for are high ripple rate and low ESR. It makes for a longer life cap too, if I guess correctly.
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Old 28th November 2006, 06:55 PM   #4
CarlosT is offline CarlosT  United States
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I believe that the impedance rating is related to the oft-quoted ESR...lower is better? Anyway...I'm gonna give the FMs a try.
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Old 28th November 2006, 07:34 PM   #5
Nordic is offline Nordic  South Africa
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Yes lower is MUCH better, the lower, the faster the cap can "slew".

Forget about the capacitor as a capacitor for a second and only think of it being a resistor, now using ohm's law see how significant the impendance is on current delivery and ripple absorption.

I'm afraid what is good for a class A PSU is not good for a class AB, and probably vice versa.

I need to quote an article on solidstate PSUs from TNT audio

Quote:
You see, filter capacitors should be just that, FILTER capacitors, their energy storage function being of secondary importance. In many commercial units, these roles are present but reversed - larger value capacitors are used not only for filtering, which they cannot help but do, but also to act as energy reservoirs.
Of course, they always act that way, but the point is that they tend to be increased in capacity to cover for inadequate power transformer size and/or performance.
In such cases, you are not very likely to find high quality capacitors inside, but rather those of commercial quality. There are two basic reasons for this. The first is that they are cheap, and can be made to look good on ad photos and in ad sales blurb.
The second is that by connecting two capacitors in parallel, one not only doubles their energy reserves, but also cuts their output impedance in half. This is of course quite true, and in practice works every time without fail, but in essence is much less than we are led to believe.

So halved output impedance may still be above the values obtainable by using a single pair of high quality capacitors. Also, this view completely disregards capacitor charge and discharge speeds - good quality caps are expensive precisely because they are, among other things, very fast.
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.
One source of noise is a "power vacuum" where more power is required than can be instantly provided.
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Old 28th November 2006, 08:07 PM   #6
ash_dac is offline ash_dac  United Kingdom
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Hi,

1000uf !

Isn't that a bit low ?
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Old 28th November 2006, 08:16 PM   #7
CarlosT is offline CarlosT  United States
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That's what's showing in the Techdiy pages for that kit

http://tech-diy.com/lm3875kits.htm
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Old 28th November 2006, 08:19 PM   #8
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Quote:
Originally posted by ash_dac

1000uf !

Isn't that a bit low ?

Why?
Above about 1500uF at the chip of a GC with a normal unregulated or un-snubbered power supply is generally Not A Good Thing.
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Old 28th November 2006, 08:27 PM   #9
ash_dac is offline ash_dac  United Kingdom
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Quote:
Originally posted by falcott



Why?
Above about 1500uF at the chip of a GC with a normal unregulated or un-snubbered power supply is generally Not A Good Thing.

Ok so the main large caps are near the diode bridge ?
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Old 29th November 2006, 07:39 AM   #10
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Quote:
Originally posted by ash_dac

Ok so the main large caps are near the diode bridge ?

The GC doesn't like a lot of capacitance, so 1000uF - 1500uF close to the chips is about as much as you can give it. Some GCs don't even have any caps in the PSU...
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