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?
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?
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
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
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 125°C:
http://www.arcotronics.com/cms/index.php?option=content&task=view&id=41&Itemid=48
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 125°C:
http://www.arcotronics.com/cms/index.php?option=content&task=view&id=41&Itemid=48
Many thanks to all for your input and kind readiness to help.
Values up to 100µF (and above) are not too difficult to find in loudspeaker-crossover-type film capacitors; the challenge is to find a (film-type) alternative to 220µF 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 1.1/kondensatoren.htm and http://www.mundorf.com/english 1.1/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 220µF 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' 220µF MKT/MKS were available.
Chris.
Values up to 100µF (and above) are not too difficult to find in loudspeaker-crossover-type film capacitors; the challenge is to find a (film-type) alternative to 220µF 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 1.1/kondensatoren.htm and http://www.mundorf.com/english 1.1/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 220µF 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' 220µF MKT/MKS were available.
Chris.
Regarding cap size on the F4:
http://www.diyaudio.com/forums/showthread.php?postid=1187439#post1187439
http://www.diyaudio.com/forums/showthread.php?postid=1187439#post1187439
Dear all,
For what it's worth, there is a French distributor who has accepted to supply me with the Wima MKS. Wima has distributors in most countries, so you should get a cooperative one in your countries to.
Here, the Wima MKS4 220µF 10% 50VDC PCM 37.5mm are available at
Actipass Composants Electroniques
Parc Club Orsay Université
18/20 rue Jean Rostand
91400 ORSAY, FRANCE
Tel : 01 69 81 61 10
Fax : 01 60 12 20 16
Contact: Richard Briat
richard.briat[ATT]actipass.fr
For 6 pieces ordered, the retail price I got some months ago was 25.60 €/each cap; VAT needs to be added, as well as packing and postage (10€ for France); they asked 3-4 weeks delivery time since the caps are apparently made on demand and sent from the factory in Germany (Hurray, some more stuff which is not manufactured somewhere else...)
Cheers.
Chris.
For what it's worth, there is a French distributor who has accepted to supply me with the Wima MKS. Wima has distributors in most countries, so you should get a cooperative one in your countries to.
Here, the Wima MKS4 220µF 10% 50VDC PCM 37.5mm are available at
Actipass Composants Electroniques
Parc Club Orsay Université
18/20 rue Jean Rostand
91400 ORSAY, FRANCE
Tel : 01 69 81 61 10
Fax : 01 60 12 20 16
Contact: Richard Briat
richard.briat[ATT]actipass.fr
For 6 pieces ordered, the retail price I got some months ago was 25.60 €/each cap; VAT needs to be added, as well as packing and postage (10€ for France); they asked 3-4 weeks delivery time since the caps are apparently made on demand and sent from the factory in Germany (Hurray, some more stuff which is not manufactured somewhere else...)
Cheers.
Chris.
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