Adding optional capacitor 'box' to amplifier

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bobdebouwer

Member
Joined 2014
#1
Hi,

I recently bought mono power amps from a very small French brand 'Cairn', being the Cairn MEA 500. Very nicely built amplifier, sounds sweet and powerfull, and the case is absolutely beautifull. 130W 8Ohm, 250W 4 Ohm.

It has a 500 VA torrodial.

The Cairn MEA 500 has from the factory 37600 µF of filtering capacitors.

There is a factory extra option to use an external box 'full of capacitors' which they call the 'CAPA'. It contains 16 4700µF capacitors, increasing the capacity to 97000µF. This would allow for 40 A currents and improve the amplifier.

The external box however is extremely ugly. I wonder what it really adds to the amplifier? for esthetic reasons I would just remove those boxes, but if it really has an added value I would keep them and possibly make a nicer looking box for them, or try to put them somewhere where they are less visible.

thanks!
 
#2
It just keeps the supply rails up more than if it wasn't there, which means the supplies are less affected during bass notes when you're really pushing it.


It's the law of diminishing returns though, I think 37,600uF is plenty enough for any mortal.
 
#3
Thanks, it probably is, otherwise it wouldn't be an option, but I just wondered why first of all they bothered at all to make this option, and secondly why they just didn't put more capacitors in the amplifier instead of making it external.

I don't know honesty if 37600 µF is 'normal' or 'low' as I don't typically check this specification when I'm buying an amplifier.

It's used to drive my 2 front speakers, but below 80Hz there are 3 subwoofers taking over, so not sure if I need this. If it improves stability and the 'liftetime' of my power supply and transistors etc. I might consider using it.

But I'm not technical enough to understand the real impact.
 
#6
They might just be offering what they would have included for capacitance if money and space were no object. BUT they are both always a hindrance when you build a retail product and want to have some profit left over.
I’ve seen 150w amps with as little as 16,000uF all the way to 120,000uF.
I think what came stock is plenty, unless you consistently do intense audiophile critical listening or crank it up often.
 
#8
37,600 is more than enough.
Sounds more like rectifier killers.

Sounds like marketing

Difference heard will be = 0
Except of course amazing claims from people that already wasted
their money.
Which need to justify hearing nothing, but spending a lot.
 
#9
I own a PA amp 600 w/ch 4 ohms, 360 w/ch 8 ohms, at .15% hd. 650 w/ch & 400 w/ch if you clip it to 1% hd.
The E core transformer for both channels, 2 secondary windings, weighs about 25 lb.
It has 10000 uf + and - for each channel. The brand was known in the nineties for making the watt rating 24 hours 7 days a week, Peavey.
So I think your 37600 uf for 130 w/ch 8 ohm 250 w/ch 4 ohm entirely adequate.
Excess capacitance is useful for underrated transformers. @500 va, yours is twice the watt rating and should be adequate.
The real question for an old amp, is do the rail capacitors have the ESR to allow the watt rating to made today? You can check the watts with a scope or analog VOM (P=(V^2)/Z where Z is speaker or resistor impedance. Or you can disconnect and measure the capacitors with an ESR meter. I've found old capacitors go a little high on the capacitance, but double or triple the ESR of a fresh capacitor of same rating. I use 225 w 5 ohm logs from Dale to measure watts. I have 2 slider equipped 250 W 10 ohms ohmmite logs, to make 8 ohms, but those are not big enough for a 650 w/ch amp. Mount your resistors on metal stands to keep them from burning the floor, carpet, or work table. Don't touch the metal terminals of the speakers with both hands; these voltage levels are high enough to stop your heart if the current crosses it. No rings or jewelry on hands, wrists, or neck.
 
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#14
��I'm 50% French so I can say that, you don't want to hear what they say about us Belgians����

I'm going to open the amp today to check out of curiosity how much capitance is really in there. But reading all the comments here I won't use the capa box
 
#15
bobdebouwer said:
Out of curiosity I opened the 'black box'. Inside 18 capacitors of 2200 µF...Those lying French! Totally different from the fact sheet.
Click to expand...


It may have been re-capped with whatever diameter caps were available at the time (depending on how close they are to each other that is)
Sometimes it's hard to source the original uF value if they're stacked close to each other, uness you drop temp rating or actual value.
 
#17
I recall a meeting in the early 1990's with John Dunlavy and Graham Cohen, both venerable audio engineers, at the Duntech factory at Technology Park, Adelaide. Graham was there to demonstrate a new amplifier topology which so impressed John Dunlavy that he not only cancelled his own amplifier development program but offered Graham a position in the company on the spot. I had previously had discussions with both John and Graham about how big the capacitors need to be for a power amplifier from an electrical engineering / circuit simulation point of view. Graham's prototype had 2 x 40,000µF, but on this day Graham brought some of additional capacitors that could be plugged in to his prototype amplifier. With Duntech Sovereigns as the test loudspeaker we (John Danlavy, Graham Cohen and I) were all GOBSMACKED at the difference each doubling of capacitance made, right up until we ran out of capacitors at something like 320,000µF. We had all expected that 40,000µF was more than enough.
 
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