Polyester Film Foil vs. Metalized Polyester Capacitors

[JRM]

Hi,

Metalized polyester film caps are much more readily available than film foil polyester caps (at least at my accessible suplliers) but they do have different construction types as can be checked at these links:
http://www.wima.com/EN/filmfoil.htm
http://www.wima.com/EN/metallized.htm

More than care about the technical advantages and disadvantages of each techonology, is there any influence in the tone between this two (as there is between film caps and electrolytics and ceramics)?
The question becomes relevant in trying to recreate (clone) some vintage effect pedals, like a 1973 Ram's Head BMP, that I believe uses the foil type ones (at least it's marked like that on the scheme).

Thanks,

João

[defaced]

I don't usually say this, but do a search.  This is easily one of the hottest topics in the audio world and has been hashed out many, many, many times.  I'll shorten it for you though: no one can agree so you'll have to do your own listening tests and judge for yourself. 

[JRM]

I did searched but haven't found nothing. I might have done something wrong, so I'll try again.

[Electron Tornado]

Capacitors are another source of myth in audio. I think most of what you'll find in audio circles will be anecdotal at best, and pure BS and hype at worst.

These may be the best questions to start with - why do manufacturers make capacitors out of different materials, or use different construction styles? What makes one 0.1uf, 250V capacitor different from another 0.1uf, 250V capacitor (micro Farads are micro Farads arent' they)?

If you find anything interesting on the subject, post a link.  


*** Actually, that site has some interesting info on caps. Click on the "Technical Info" button.

[R.G.]

These may be the best questions to start with - why do manufacturers make capacitors out of different materials, or use different construction styles? What makes one 0.1uf, 250V capacitor different from another 0.1uf, 250V capacitor (micro Farads are micro Farads arent' they)?

The difference between metallized and film-and-foil is pretty simple. The metal is much thicker on the film and foil, much thinner on the metallized.

This does the following:
- the metalized caps are smaller (thinner layers)
- the metalized caps are self healing - punch throughs burn off the metal at the hole and "cure" the short
- the foil caps have a much lower spreading resistance than metalized, which makes them better suited to high current and pulse applications.

I can concoct situations where you could hear a difference between the two (I think... you have to use high audio currents) but in low signal applications, I strongly doubt that even "golden ears" listeners could do better than random chance guessing between the two in a fair test.

[therecordingart]

I'm just rambling, but in my opinion if you pick two same value caps made of different materials that are both stable within the conditions they are being used....you probably won't hear a difference and if you do it is most likely expectation bias.

[Maudibe]

All caps being equal... erm

rise time, dissipation factor, voltage versus frequency... impedance versus frequency... tollerance, stability.... 

food for thought 

[JRM]

Thank you guys. From the additional search I did, I've found nothing more conclusive than:

"You can't tell the difference in low signal aplications"

And by the way, there's no "golden years" around here, just regular human tissue ones. And they work fine. I'll relax and enjoy the build first and the fuzz afterwards...

[Mark Hammer]

What I keep reminding people of is that any capacitor type will likely have some sort of property that makes it ideal for a certain context, but not necessarily "better" in any context.  the question to ask is whether film vs foil vs tantalum vs whatever makes a difference in our context (which is not the same as, say, studio quality music reproduction) and in the specific context one is interested in.

[chi_boy]

In my little world the biggest difference in those good quality caps, excluding ceramics for now, is avialability.  Panasonic and AVX were my goto brands. Now they are drying up. Wima is a little pricy and Epcos seems to be having production problems.  I built a project recently that looks like a Christmas tree with all the different colored box caps. 

[ddpawel]

Don't listen to guys saying "there is no difference".
Bulls*** and other s*its together.
There's a major differences in impedancy, capacitance is changing different with temperature and frequency, noise level & ...

Maybe this can help:

http://www.elportal.pl/pdf/k01/06_07.pdf

This pdf is in polish language, but you can read some properties from figures.

[Electron Tornado]

Don't listen to guys saying "there is no difference".
Bulls*** and other s*its together.
There's a major differences in impedancy, capacitance is changing different with temperature and frequency, noise level & ...

Maybe this can help:

http://www.elportal.pl/pdf/k01/06_07.pdf

This pdf is in polish language, but you can read some properties from figures.

Don't take this the wrong way, but unless someone is fluent enough in Polish, that article isn't useful. It's easy enough to see what they are saying, but it would be much better to be able to know what the author is saying.  I can see that some of the graphs cover the audio frequency range, or part of it, but there's still nothing to show whether that has any audible effect on how they will perform in a stompbox.

Can you translate the article?

[phector2004]

Knowing how the ear works, hearing is a very complex, dynamic system, but we're just not tuned to notice these kinds of differences.

I've swapped in half-cent cheapo ceramics for mylars for WIMAs and haven't noticed any change whatsoever. Mind you it wasn't a blind test, but if its obvious enough to NOTICE in the same circuit, it exists IMO. I've seen some sites with graphs and oscilloscope readings and other VISUAL representations, but the only variable that matters is how the ear picks it up.

The way I see it, you'll hear more "tone" blowing your nose than you would changing cap types

[Electron Tornado]

It's easy enough to see what they are saying, but it would be much better to be able to know what the author is saying. 

Sorry, that should read, "It's easy enough to see what some of the graphs are saying......"

[merlinb]

Self's new book has a wonderfully concise chapter on component distortion. See page 53 onwards for plastic caps:
http://books.google.co.uk/books?id=PvKPEFu2PVkC&lpg=PP1&dq=small%20signal%20audio&pg=PA53#v=onepage&q&f=false

In short, although they do produce measurable distortion, it is far too small to be audible even at 20Vrms signal levels. At the <3Vrms levels we use in pedals, it probably wouldn't even be measurable.
Compared with the distortion that your amp / other effects will inevitable add, plus unavoidable noise, it is a non issue. You won't hear the difference between plastic caps (unless it's because they have different capacitances!  )

[JRM]

When I've started this thread, I was more interested in understanding if and why there was any difference in tone between this two types of cap than which one is best. The question becomes relevant when one is trying to recreate (clone) some vintage effect pedals. All the guys that tried to answer that question pointed out that the differences are very, very small for the signal levels we usually have on guitar effects.

[ddpawel]

Metallized capacitors have a slightly better performance because the aluminum foil used has a lower resistance (lower dielectric loss) than thinner sputtered metallization on the dielectric. In addition, depending on the type and the metallization (or not) capacitors have a different capacity depending on the frequency, voltage, etc. Sometimes these differences are even a few percent!

So when you are at least several capacitors of the same type of difference will be slightly audible, but it will be. In some effects changes are even quite good hear.

[phector2004]

Don't forget to gold plate your circuit board, though... copper sucks tone like a dyson

[Electron Tornado]

Self's new book has a wonderfully concise chapter on component distortion. See page 53 onwards for plastic caps:
http://books.google.co.uk/books?id=PvKPEFu2PVkC&lpg=PP1&dq=small%20signal%20audio&pg=PA53#v=onepage&q&f=false

In short, although they do produce measurable distortion, it is far too small to be audible even at 20Vrms signal levels. At the <3Vrms levels we use in pedals, it probably wouldn't even be measurable.
Compared with the distortion that your amp / other effects will inevitable add, plus unavoidable noise, it is a non issue. You won't hear the difference between plastic caps (unless it's because they have different capacitances!  )

Thanks for the reference, merlinb. I found a copy of the book. Yeah, even any measureable difference is still too low to be a factor in pedals.  But just to be on the safe side I'm going to start using unobtainium.