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Old 31st December 2008, 09:18 AM   #1
elac310 is offline elac310  France
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Default 220uF caps in MKT technology for PCB mounting

It would appear that small size 220uF caps are now available as non electrolytic types. I've just found this series made by Epcos:
http://www.epcos.com/inf/20/20/ds/MKT_B32520_29.pdf which uses metalised polyester as dielectric.

The 63VDC/40VAC version (the only voltage available for 220uF) would seem to be a good fit for many Aleph amps and it can be soldered on a PCB since lead spacing is only 37,5mm (1,5 inch).

Losses (tan delta) are - as expected - slightly better than say an electrolytic Panasonic audio cap. However, the high frequency stability is rather limited; page 35 of the datasheet suggests this type of cap can handle only less than one 1VDC above 1000Hz, which seems to exclude their use even in the feedback loop of the various Aleph designs which have a 220uF cap at this place.

Any opinions?
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Old 31st December 2008, 11:06 AM   #2
Magura is offline Magura  Denmark
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And where have you seen those for sale?



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Old 31st December 2008, 01:37 PM   #3
elac310 is offline elac310  France
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Good question...
I assume these products are fairly new and will be more easily available in due course. Smart cookies out there will probably manage to get a few as samples (??), if needed.
By the way, Wima's MKS4 series also include a 220uF MKT type rated 63VDC, which - it seems - exhibits slightly better characteristics at high(er) frequencies
http://www.wima.com/EN/mks4ue.htm
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Old 31st December 2008, 03:53 PM   #4
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Hi ,

Please do you know a shop, here in europe, where I can find those Wima series ?

thanks,
Paolo
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Old 11th January 2009, 12:19 AM   #5
elac310 is offline elac310  France
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Sorry. Still haven't found a dealer.

It turns out that Arcotronics have also two series that comprise the 220uF value : R60 and perhaps even better (due to good dv/dt) the JSP series which withstand 125C:
http://www.arcotronics.com/cms/index...d=41&Itemid=48
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Old 11th January 2009, 09:24 AM   #6
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Thanks,

Here are the wimas : www.conrad.de

Cheers,
Paolo
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Old 11th January 2009, 10:14 AM   #7
elac310 is offline elac310  France
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Yes, I know Conrad has Wima MKS4; but I checked again and the biggest they have on stock is 33F or so. Where did you see the 220F? (I went through the entire MKS4 range and also used the search function of their catalog)
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Old 11th January 2009, 10:40 AM   #8
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Exucuse me , you are right. Only 33mF.
I have paralleled some 22 big poly to make my cathode resistor bypass, those 33 are little thus acceptable imho.
Sure a single big one would be more easy...........

Cheers,
Paolo
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Old 11th January 2009, 12:18 PM   #9
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there are 68 uF wima MKT on ebay (maybe someone ask them to import those big boys?)
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Old 11th January 2009, 12:55 PM   #10
elac310 is offline elac310  France
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Many thanks to all for your input and kind readiness to help.
Values up to 100F (and above) are not too difficult to find in loudspeaker-crossover-type film capacitors; the challenge is to find a (film-type) alternative to 220F electrolytic caps (used in various Nelson Pass designs) that can be mounted fairly easily on a PCB (without the cap - or combination of caps being larger/heavier than the populated PCB...).
MKPs are better than MKT/MKSs (lower losses, better rise time etc.) but they are too large (see for instance http://www.mundorf.com/english%201.1/kondensatoren.htm and http://www.mundorf.com/english%201.1/kondensatoren.htm). In case of point to point wiring, this would not be so much of an issue, of course.
And often MKPs don't like high temperatures such as those present in ClassA (semiconductor) power amp enclosures.

Last point: it would appear that the radial 220F MKT/MKS type I've found so far in catalogues (but not in retail shops) seem to exhibit poor performance at high AC frequencies; could be an issue for the feedback cap in Aleph designs (or not ?? given that the signal present there is very small). Probably a small decoupling cap would do no harm... if, first, those dam' 220F MKT/MKS were available.

Chris.
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