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Old 8th April 2013, 04:51 AM   #1
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Default Large value metalized polypropylene caps

Has anyone used the very large value MKP caps (>= 20 uF) that are usually in the "DC Link" category? Ideally would like to use them in a coupling application.

Just wondering if there is any measurable difference in distortion or linearity vs the <10 uF sized metalized polypropylene caps?
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Old 21st April 2013, 03:34 PM   #2
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Larger that 20uf at higher voltages are harder to find and get expensive for a quality types. Not sure about the voltage or your specific application. If you are looking for coupling applications in lower voltages and high value caps, you may consider using back to back quality electrolytics. Example, connect the neg posts of two 100uf silmic caps together, then use the two pos posts for the lead as if one cap. The net value is a 50uf cap that has some of the negative features of a single cap nullified. This technique is used by many manufactures including Denon and Marantz on some of the better equipment. You may also bypass this back to back set with a small film cap to improve/change the sound of the passed through signal. Good Modding!
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Old 21st April 2013, 04:03 PM   #3
jcx is offline jcx  United States
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"DC Link" capacitors are designed for use with permenant high Vdc across them, have low esl, esr for high current energy delivery in sw mode power supplies, self clearing electrode metallization

http://www.mouser.com/pdfDocs/WIMA_D...Capacitors.pdf

for small Vdc DC blocking, small audio signals the special features may not matter

for audio signal coupling, low V DC blocking, into hi Z circuitry just about any film cap will be fine - distortions of low order, very low level - never expected to be audible in Blind, controlled listening tests

all electros measure worse on audio distortion - but still at inaudible levels

non/bi-polar Al electors with full thickness oxide on both foils measures lower in distortion than the old "back-to-back" polar electro recommendation

Last edited by jcx; 21st April 2013 at 04:15 PM.
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Old 21st April 2013, 04:58 PM   #4
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Yes I agree with JCX. I assume that the reason for the need for a large value cap is that the load is not a high Z load. If this is not true then of course a MKP cap would be easily and better used.
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Old 21st April 2013, 05:55 PM   #5
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Thanks, I was just trying to see if the DC link caps had some undesirable properties related to it's high density for an MKP cap. Sounds like there is no problem, other than the cost.

The application is low/medium Z (10k) and low V DC bias.
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Old 21st April 2013, 06:12 PM   #6
jcx is offline jcx  United States
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large physical size itself can be a problem - makes for larger parasitic C to the world

and added distance between leads adds esl

ideally there will be one electrode "on the outside", marked lead - so you can connect the film cap with the orientation that gives the least operating problems with the outside electrode's parasitic C to the world


if you are only blocking single digit V then you can even get smt 10-20 uF mylar or acrylic parts for least physical size
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Old 21st April 2013, 06:31 PM   #7
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chris719,

DC Link caps are probably not the best choice for audio, they are intended for high power circuits and are designed to that end. They are extremely large and expensive, and will not perform any better than a good quality, standard polypropylene film cap, and in fact they may perform worse.
And I don't know your intended application here, but 20uF/10k gives a .8 Hz corner frequency, are you sure you need to go that low? 10 uF will give a 1.6 Hz corner at a significant saving in cost and physical space.

Mike
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Old 21st April 2013, 08:59 PM   #8
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10k is a rough guide, I haven't finished the design.

I have no desire to use them over standard value PP caps but if I needed a value of, say, 47 uF, that leaves me with a choice of several || normal MKP, large polyester, or NP electroytic, other than DC link MKP.

I'm aware there are no audible problems with a big NP electrolytic, but I like overkill.
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Old 21st April 2013, 09:07 PM   #9
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If you can deal with SMD, you might want to look at niobium electrolytics. Regards
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