film caps

[saxtim]

Hi,

I used the search function but couldn't really find an answer to this question - I assume it probably has been covered before, but still I'll ask again.

Can anyone explain the difference in types of Film capacitors?

The store I order from (www.vorlac.com.au) has several different types, and I'm not sure what the difference is:

Metallized Polyester Box type (MKT)
Polyester (not metallized?) Vorlac says these are 'Greencaps'
Polystyrene Film/Foil (more expensive and appear to be in smaller values than the polyester)

Then at another local store Jaycar, you can get:

Metallized Polypropelene

On top of all of this there is:
Mylar (which i think is the same as M. Polypropelene?)
Orange Drops (I think is a brand name for a specific company's Polyester cap)

So can anyone explain the difference between M. Polyester, Polyester, Polstyrene, M. Polypropelene, Mylar and Orange drops??  

Is there a reason to choose one over the other (despite say polystyrene being useful for smaller values).


Thanks

tim

[Peter Snowberg]

Welcome Tim,

My feeling is that all film caps are good, but some a better than others depending on the application. In pedals you can use anything you want. I use the green Xicon Mylar caps and like them just fine. For tiny values I prefer silver-mica, but in some cases better technology and performance is not the same as better sound. In some cases you might want to use a good quality ceramic for what it does to the signal.

There are two basic film construction types, metalized film, and film & foil. The film and foil caps I think produce the best tone, but if they short in a tube circuit, they can end up blowing themslves apart. The metalized parts have the advantage of "self healing" if the film fails, and they're ususally cheaper, but to my damaged ears they don't sound as good. That's all in tube amps, in a stompbox the difference is much less thanks to the low voltage.

The film can be made of a number of different materials....

Polyester (Mylar) and polypropylene are great materials for use everywhere.
 
Polystyrene is better still, but the values you can get are more limited and they don't hold up to the heat in a tube amp. They also tend to have delicate leads but they sound awesome.

There are also polycarbonate (Lexan) caps that are amazing, but they're pricey comparred to mylar.

The ultimate dielectric plastic is probably PTFE (Teflon), but you don't see these in any pedals I know of.

Orange Drops were made by Sprague, which is now called SBE. There are several types that all get lumped together... some great, some not as great. I think they're all polyester or polystyrene. I really like the SBE 418 series, and the 715 series is OK, but the difference is pretty small even in most tube amps. I think the 715 series uses steel leads... they're not copper; I can tell you that.

Keep in mind the tonal quality stuff is totally subjective and your mileage (kilometerage :?) may vary.

Take care,
-Peter