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Old 4th November 2016, 01:03 PM   #1
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Default Tantalum caps DC block

i am interested in using tantalum caps for dc blocking on single ended output of audio signal for small headphone amlifier.if i want this device to work for as much years as possible(so no electrolytics to dry and no place for large film caps) ,is it ok for that purpose? it seems that it shouldnt be problem as they are all time polarised and only care should be that audio signal never reaches 0v or less,which wont happen because of se output of said device.

there is lot of bad things written on forums for tantalum caps but i think this could be one very nice use of them and cant find more info about this topic.
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Old 4th November 2016, 09:03 PM   #2
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Tantalum capacitors are very unreliable. They do wild things, like short or break. If your HP has any value for you, don't use tantalum. Make the enclosure a bit bigger and use metalized foil capacitors. Even common aluminium electrolytics are better than tantalums.
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Old 4th November 2016, 09:28 PM   #3
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Modern tantalium and niobium caps can perform fine. In the past (at least 15 years ago) they were as described but times have changed. Most of us have experienced the then unreliable drop type tantalium caps that shorted, exploded and when they worked they sounded terrible. Nowadays the industry uses them a lot. Every smart phone has them. AVX TPS series are very good for instance. The sources for coltan are dubious however as it is mainly found in african countries that have civil wars and the material was often traded for arms in the past. Some manufacturers swear they buy coltan from reputable sources....but we know the same stories of other resource materials. Some governments have no problem selling it and some countries have no problems obtaining it from flaky sources certainly when stuff is used in military devices. Just Google on how a large country got hold of titanium.

Not tantalium but also unusual in audio are the BC solid aluminium caps which are hard to find and meanwhile some series have been discontinued. Not cheap but these have some good audio properties like being able to be reverse polarized (coupling in DC circuits) and they are dry caps too.

Which values do you need and what sizes are they ?
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Old 4th November 2016, 09:31 PM   #4
rayma is offline rayma  United States
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Quote:
Originally Posted by tonitonitoni View Post
i am interested in using tantalum caps for dc blocking on single ended output of audio signal for small headphone amlifier.
Use a solid tantalum type of a voltage rating higher than the power supply voltage.
http://www.vishay.com/capacitors/tantalum/low-esr/
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Old 5th November 2016, 10:03 AM   #5
Elvee is offline Elvee  Belgium
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Polymer electrolyte caps are also a worthwhile option: they are dry, and exist for both aluminum and tantalum, and do not have the quirks of traditional tantalum.
Their performance is in general outstanding, except perhaps for a few minor characteristics, which are not relevant to this application
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Old 5th November 2016, 10:28 AM   #6
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Polymer caps are fine caps indeed. As I was reading last posts I just checked my "rare parts" stock. I do seem to have more solid aluminium SAL-RPM caps than I will ever need. I think I will put these in Swap Meet. Also still some Wima ultra rare 22 µF 16V 5 mm (!!!!) MKS2-XL film caps and a large quantity Black Gate caps of various series. Just bought a few 2SJ74 last week to discover today I have them in stock myself
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Last edited by jean-paul; 5th November 2016 at 10:34 AM.
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Old 5th November 2016, 10:47 AM   #7
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Tantalum Bead capacitors were notorious for going short circuit. The reason was designers using 12v capacitors on 5V supplies. They need the full voltage across them to keep going. Just like a NiCad battery.
They have excellent HF rejection when used as decoupling on HT rails.
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Old 5th November 2016, 10:49 AM   #8
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Mmm, advice on using tantalium caps in general is to use caps that are higher rated than the PSU voltage....
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Old 5th November 2016, 01:05 PM   #9
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interesting stuff, i am actualy already testing avx d case of kemet 100uf 6.3vhttp://capacitoredge.kemet.com/caped...T491D107K006AT. thing is that i first read about tantalum caps from manufacturer datasheets and hoped i figured it is good ,but later i found lot of bad things on forums,this is new batch of kemet branded caps that is supposedly reputable manufacturer.

i did tested this on my akgs but after reading i was afraid little so i must ask people who know better.

what can i do to test this caps for failure, to see if they fail short circuit or open?
how to simulate long term use?

i do have lot 10v 47uf film 1206 smd caps at hand but dont think could fit 2 on place of one avx-d on pcb ,and i prefer to use this pcbs i made already.
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Old 5th November 2016, 01:39 PM   #10
Mooly is offline Mooly  United Kingdom
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One of the failure mechanisms of older type tants was using them on a supply of already very low impedance (which is different to creating a supply of low impedance using tants). They could not absorb high dv/dt transients and this can lead to failure.

Just googling 'failure modes of tantalum capacitors' turns up a nice little pdf from Digikey:
http://www.digikey.co.uk/Web%20Expor...VX_failure.pdf
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