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Metallized caps where space is tight?

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Posted on March 24, 2017 at 22:08:31
Thermionic27609
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I've read these forums enough to be familiar with the usual recommendations for interstage coupling caps, but sometimes, there simply isn't space for large film/foil or PIO capacitors, especially on a PCB. I've seen the messes people have made trying to shoehorn huge capacitors into tiny spaces.

In cases where you have limited space and a radial, metallized polypropylene capacitor is pretty much all that will fit, what are the best options in capacitors that are readily available?

I know that Wima has a good reputation in the MKP4 and MKP10, and some seem to like or prefer the Vishay Roederstein types like the MKP1840. I also noticed a KP1836 on Mouser that's a stacked polypropylene film/foil with a metallized polyester "carrier film." No idea if that would be good or bad. I've read completely contradictory opinions on the Panasonic ECW series although I know some people whose opinions I respect who like them.

In this case, I need capacitors rated at least 600V.

 

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RE: Metallized caps where space is tight?, posted on March 25, 2017 at 00:44:03
Cleantimestream
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ERO MKC {no longer made} sound better than most other MKP {smoother highs, same detail} ... about 20 dollars for 8 of them (.33 uF/400 V}. They are quite small.
The Mind has No Firewall~ U.S. Army War College.

 

RE: Metallized caps where space is tight?, posted on March 25, 2017 at 00:45:58
Michael Samra
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There are actually quite a few options out there. First,can I ask you what kinds of amp and the value of cap that you need? The reason I ask is this. The Golden SE-40 is a circuit board amp that used .22uf Wima caps. I replaced them with .1uf 400v K40Y-9 caps and I lost no bass whatsoever that you could hear.That is because the corner freq was 8hz vs 6hz which had no effect that you would feel or hear.This is also the value that Sonic Craft used in their upgrade kits..

Speaking of which,the SonicCap Gen 2 are a metallized poly that are very good as well and they fit in several places.The Solen Film and Tin foil are a wonderful cap that is made with a smaller profile,but it is much heavier due to winding techniques.
"For every complex problem there is an answer that is clear, simple, and wrong" H. L. Mencken

 

RE: Metallized caps where space is tight?, posted on March 25, 2017 at 08:27:36
Thermionic27609
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I need a 0.1uF 600V capacitor, and the PCB holes are 20mm apart. It's between the input gain stage and the LTP PI/driver of a Dyna MkIII-based amp. The PCB is crowded, so there's not much room to work.

 

Sprague 716P, posted on March 25, 2017 at 08:58:33
Chip647
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They are awesome.

Polypropylene Film & Foil Capacitor, Copper Leads, 31.8mmL x 13.7mmT x 23.6mmH

you will have to bend the leads to fit 20 mm spacing, but if you have 6mm on each end space, these are definitely a good way to go.

 

RE: Sprague 716P, posted on March 25, 2017 at 09:39:05
Thermionic27609
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"Polypropylene Film & Foil Capacitor, Copper Leads, 31.8mmL x 13.7mmT x 23.6mmH"

I'm not sure which capacitors you mean.

Oh, must be 716P. I have a drawer full of those. The overall dimensions still make it pretty cramped and put it on top of other hot parts.

 

RE: Metallized caps where space is tight?, posted on March 25, 2017 at 11:47:07
Thermionic27609
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Also, I do like the Solen SM film and tin foil, and I've sometimes wondered why these seem less popular, especially for the price. I can only assume that it's some kind of marketing/brand perception issue. In other words, they're tied to the perception of Solens as metallized film capacitors that are good, but not the best.

I am highly aware of the significance of marketing and brand perception in audiophile circles.

 

RE: Metallized caps where space is tight?, posted on March 25, 2017 at 15:05:24
Cleantimestream
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You made mention size was paramount, any true foil will walk all over most metallized caps. These are an example of size
The Mind has No Firewall~ U.S. Army War College.

 

RE: Metallized caps where space is tight?, posted on March 25, 2017 at 15:25:01
Tre'
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Are the ERO 1864 MKCs foil?


Tre'
Have Fun and Enjoy the Music
"Still Working the Problem"

 

RE: Metallized caps where space is tight?, posted on March 25, 2017 at 16:37:23
Eli Duttman
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Can you gain room by mounting the part on the "abnormal" side of the PCB?

I'm among the very last people to suggest ceramic dielectric in a coupling cap. position, but your mechanical constraints ARE a problem. Unlike most ceramic caps., NP0/C0G dielectric is tolerable as a coupler. A link to an AVX brand part is provided below. Not surprisingly, the part is big, but lead forming could make it a "winner". Also, some ambient heat is OK.


Eli D.

 

RE: Metallized caps where space is tight?, posted on March 25, 2017 at 18:22:09
Cleantimestream
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No. Tre', foil code would be FKC or just kc or kp for polypropylene with some manufacturers. I have some Wima FKC .03 @ 400 V but they are quite rare... I have never seen NOS values any higher although I know they were made. Polycarbonate caps were quite expensive to make and can withstand higher heat than any other cap and still keep their characteristics.
The Mind has No Firewall~ U.S. Army War College.

 

Is there room in the vertical direction,.., posted on March 26, 2017 at 08:29:22
Lew
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perpendicular to the plane of the PCB? If so, you could mount a variety of film and foil caps in that orientation (i.e. vertically with the "bottom" lead buried into the PCB). The distal lead then just bends around 180 degrees to enter the PCB 20mm downstream. I've done this many times to circumvent space problems.

 

RE: Is there room in the vertical direction,.., posted on March 26, 2017 at 08:50:02
Thermionic27609
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I could mount axial caps vertically. I work on Farfisa Combo Organs, and they did that all the time. Of course, the fact that Farfisa did it doesn't exactly inspire me to adopt the practice. It does cause the end caps of some brands of capacitor to pop loose over time.

In the end, I think I've figured out a way to mount a film & foil capacitor on the underside of the PCB that won't cause any problems.

I guess my takeaway from this thread is that no commercial metallized film capacitors are acceptable. But then, how is it that capacitors like Auricaps and SonicCaps are OK? Winding capacitors is not something you can do in your garage. It has to be done by a capacitor manufacturer that's contracted to make them. Do they use a thicker metallization layer?

 

RE: Is there room in the vertical direction,.., posted on March 26, 2017 at 14:19:23
Lew
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When circumstances dictate, I have used Auricap XO and Dynamicaps, which are both metallized polypropylene film capacitors, and both types have been acceptable to me for sonics. I'd use them in a heart beat, ahead of using an electrolytic, for example. Some like them better than some film and foil types. This is all a matter of opinion in the end. I have no experience with Sonicaps, but Mike Samra has more experience with a wider variety of capacitors than anyone I know.

I don't know what a "Farfisa Combo Organ" is, but I have had zero issues mounting film and foil capacitors in the vertical orientation on a horizontal PCB, when space is at a premium. I've done this extensively during the restoration and tweaking of a pair of Beveridge direct-drive amplifiers that develop mega-high voltages in the output stage. Any capacitor that is so cheaply constructed as to have the end cap "pop loose" must be regarded as a POS to begin with. Perhaps an organ is subject to severe vibration so as to stress the leads; this is pure conjecture on my part. Even then,...

 

RE: Is there room in the vertical direction,.., posted on March 26, 2017 at 15:04:17
Eli Duttman
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How much of Auricap, Sonicap ... is "boutique" panache? Metalized polypropylene is not terrible, but it is not as good as film and foil. It definitely is more volumetrically efficient and that is what the OP needs.

A link to a mechanically suitable part (20 mM. lead spacing) follows below. The data sheet suggests (happy surprise) copper leads.


Eli D.

 

We don't disagree..., posted on March 26, 2017 at 17:33:08
Lew
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My post was in response to the OP who wrote at the end of his previous post, "I guess my takeaway from this thread is that no commercial metallized film capacitors are acceptable."

I was offering up two brands of metallized polypropylene that I have found to be "acceptable" when using film and foil types was not an option. Of course, "acceptable" is in the ear of the listener. I can only name two brands, because I found those two to be superior to a few others, which I did not name. (For sure, I've tried Solens, REL, and Sprague brands.) But I certainly have not tried every single other option, and I certainly would not say that Auricaps or Dynamicaps are superior to even film and foil types, always my first option.

In answer to your question, I have no idea how much of Auricap's or Sonicap's reputation is BS. I just listen for myself. I wouldn't recommend Sonicap, because I have never experimented with that brand. For that matter, Dynamicaps are in some cases as physically large as a good F&F, so not much of a help in tight spaces.

 

Metallized caps require significant break-in time..., posted on March 26, 2017 at 19:51:04
Interstage Tranny
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Just like Teflon and Polystyrene, as well as using High Voltage rated caps in Low Voltage applications, break-in time can require dozens or many dozens of hours playing real music, before sounding "relaxed."

Even the smallest, thinnest metallized propylenes can sound "usable" after they settle in.

 

Sprague 715P and 716P are Epoxy Coated, Heat Resistant..., posted on March 26, 2017 at 19:52:43
Interstage Tranny
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These caps are very tolerant of heat...

 

Metallized caps where space is tight..., posted on March 26, 2017 at 19:54:22
Interstage Tranny
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Polycarbonate caps are very underrated...which can also keep their costs down...

 

RE: Metallized caps require significant break-in time..., posted on March 27, 2017 at 02:23:30
amnesiac
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i like the blue phillips pp for cheap compact cap. good enough for nagra tubes. I haven't used them since the ky,s came but they are nice for power supply. I thought about trying them again recently for signal they are nice soft blurry mid and real clean sweet treble. much better then the awful wima red. I know this is bad but years ago I used to put one across a electro for ps bi pas in preamps and they used to sound really good.

 

RE: Metallized caps require significant break-in time..., posted on March 27, 2017 at 11:59:12
Eli Duttman
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I/T do you have any experience with exposing MKP caps. to AC, as a run in method?

I call for MKP bypassed by film and foil, when large valued O/P couplers are needed.


Eli D.

 

RE: Metallized caps require significant break-in time..., posted on March 27, 2017 at 13:52:38
Thermionic27609
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I do believe in film capacitor break-in, and for more critical applications, I will put them across the AC mains for a couple of days.

A materials engineer working with polypropylene told me that he found it plausible that changes would occur at the boundary between foil and dielectric, especially with applied AC voltages.

 

RE: Metallized caps require significant break-in time..., posted on March 27, 2017 at 14:27:21
Eli Duttman
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Do you use anything to limit current, when running caps. in?

Another factor that may be relevant is dielectric absorbtion.


Eli D.

 

RE: Metallized caps require significant break-in time..., posted on March 27, 2017 at 15:51:32
Thermionic27609
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No, I don't limit current. I thought that was the point of breaking a capacitor in via this method. The rapid cycles heat the capacitor slightly. Why should being placed across 120V AC mains be harmful to a 600V capacitor -- unless it's very large?

Leslie amps use 0.1uF 600V capacitors for arc suppression in the 120VAC motor switching, and orange drops last for decades in that application.

 

RE: Metallized caps require significant break-in time..., posted on March 27, 2017 at 17:26:26
Steve O
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I believe one has to approach cap ratings with caution when the cap is going across the AC line. Depending on mfgr, a cap rated for 600/630VDC may have a very much lower AC line rating. If the cap is designed for across the line use it will almost always carry a specific AC rating and an "X" designation. As I understand it, the problem with AC line ratings is that while the nominal voltage may be 120VAC, there can be multi-KV spikes due to switching of inductive loads and other events. X/Y caps are designed to deal with these events and also have a defined (safe) failure mode.

I'm not aware of any audio grade cap carrying an X or Y rating and so would be inclined to use some form of current limiting during an across-the-line break-in process such as a properly rated fuse or even an incandescent bulb matching line voltage.

 

RE: Metallized caps require significant break-in time..., posted on March 27, 2017 at 17:49:25
Michael Samra
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I believe one has to approach cap ratings with caution when the cap is going across the AC line. Depending on mfgr, a cap rated for 600/630VDC may have a very much lower AC line rating.

I have actually seen those caps with a 1.2kv rating,mainly because of AC spikes.
"For every complex problem there is an answer that is clear, simple, and wrong" H. L. Mencken

 

RE: Metallized caps require significant break-in time..., posted on March 27, 2017 at 18:30:43
Thermionic27609
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One does have to approach capacitor ratings with caution, but I am a professional amp tech with years of experience at this. Yes, capacitors do have different DC and AC voltage ratings, ratings that are usually noted on the datasheet. For example, most 1600 to 2000V DC rated capacitors are only rated 500 to 700VAC, but it's not a linear relationship. As the DC voltage ratings go up, the AC ratings plateau.

You frequently find 600V polyester film capacitors installed in guitar amps as "death caps." They could easily end up across the AC line, depending on how the ground switch was set or how the amp was plugged in. And some amps have capacitors across the output tubes plates in parallel with the output transformer. Those can see very high AC voltage swings.

For reference, both the 400VDC and 600VDC 716P types have a 200V RMS frequency-dependent AC rating. The rating starts to decrease around 12kHz, but at lower frequencies like 60Hz, the full rating applies.

 

OK..., posted on March 27, 2017 at 18:45:49
Steve O
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...as a pro, you already know of cap rating idiosyncrasies and what might happen if not heeded. And that if used, a "death cap" should carry a type "Y" rating.

 

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