True Film capacitor?

[JamieMcC]

Has anyone here used a true film-foil (ie NOT metallised film) polypropylene capacitor before, I was wondering how it might work for a bypass?   

[Grainger49]

I have used a lot of PP caps for bypass.  But I just assumed that the higher priced ones are foil not metalized. 

I have used Obbligato Film/Oil (black) for bypass in both power supplies and audio path applications.  I have used the KK Teflon caps in both positions. 

[Paul Birkeland]

We provide film and foil capacitors in the Reduction, and the feedback has been positive, though they are coupling and EQ caps, not bypass caps. 

[galyons]

That was pretty standard in the 90's. MultiCap Film & Foil Polypropylene & Tin foil, (PPFX), was ubiquitous.  They might sound a bit dated today, as caps have gotten much better. (IMO, the exception to "better" is true paper in oil, metalized polyprop in oil is not the same!)

Bypass caps on inter-stage and output is a matter of taste and debate.  In some cases I found benefit, others not so much.  My first try is usually a small value Teflon or silver mica. There are also some nice film and foil caps available.  Easy to try.  Just clip in and listen. Fun, actually!

Cheers,
Geary

[Doc B.]

I think it was the "multi" that was the dominant influence on the sound in those caps. They were in effect bypassing themselves. My experience generally has not been positive with paralleled caps. For an example of a single (not parallel afaik) polypropylene and tin foil cap the Axons that were made that way in the 90s were quite good sounding. I suspect the current production tin foil and film caps are very similar and also quite to my liking.

[JamieMcC]

Interesting info thanks I decided to pick some up and give them a try at worst I can add them to my slowly growing spare parts box.

Also picked up from the same seller some F&T capacitors four, 50uf film capacitors for £12.50 going to roll them in the Crack see how they sound (F&T are rumoured to be a OEM supplier for Mundorf).

True film capacitor

(https://forum.bottlehead.com/proxy.php?request=http%3A%2F%2Fi.ebayimg.com%2Ft%2F10pcs-Unusual-True-Film-Foil-NOS-Capacitors-0-22uF-220nF-250Vdc-%2F00%2Fs%2FMTYwMFgxMjAw%2Fz%2FaUQAAOxyf1dTHyuW%2F%24_12.JPG&hash=60b9b8ab41f32a5b2d0c52d6a997e2885d1aa321)

F&T 50uf films

(https://forum.bottlehead.com/proxy.php?request=http%3A%2F%2Fi.ebayimg.com%2Ft%2F4pcs-F-T-Polypropylene-Film-Capacitors-50uF-10-250Vdc-%2F00%2Fs%2FMTYwMFgxMjAw%2Fz%2FAvgAAMXQEgpTGGRW%2F%24_12.JPG&hash=0a36487d505ea5adcee3343e1751aade354d8698)

 

[Grainger49]

Ok, I have TWR, Solen, Clarity, Mundorf, V-Cap, Wonder Cap, Aerovox, Aerocube, GE, WMF, CDE, MPK, Obblagato and Wima PP true film caps. 

I have used a number of those bypassing power supply caps.  I have used the KK Teflons bypassing audio path caps in two instances, my Ack! dAck! and my Paramour Parafeed cap (10uF Obbligato black Film/Oil).

In both of the above cases of bypassing the signal caps they have stayed for many years.

[corndog71]

I believe it was Paul Joppa who told us that you measure the capacitance between the outside of the cap and each lead, the lowest capacitance is the outside wrap.  I measured a Mundorf and it was 59pF and 49pF.  The 59pF is the outer wrap lead.

I think someone needs more coffee. 

[mcandmar]

My dyslexic mind didn't catch that one either, i was too busy trying to work out how you measure the capacitance from a non conductive outer covering?

[Paul Joppa]

Well, I don't recall it and it's not that easy. Sorry I don't have time right now to devise a good method and test it, but I think you have to use all three terminals - two cap leads plus the probe or foil wrapped around the outside.

[mcandmar]

I think i know where you are going with that.  The other method i have seen (think i posted a link to it) was to connect a probe and its ground lead across the cap then hold it in proximity to a mains cable or transformer and measure the ripple, then switch the probes around and repeat.  Whichever orientation gives the lower ripple is the inner foil end.  I tried it with a handful of caps and it seemed to have consistent results for each brand of caps.

[Grainger49]

Paul,

Am I thinking of your method of dotting a choke?

[Paul Joppa]

Paul,

Am I thinking of your method of dotting a choke?

Ah!  Yes, I'll bet that's it!

[Grainger49]

I believe shortly after you posted the method I dotted the choke I'm still waiting to put in my Eros.   Hard to pull it from the system to mod it.

[JamieMcC]

I did try the method of using a LED I had read about to find the inner-outer foil orientation, due to my daughters persevering curiosity I had to abandon my experiment prematurely.

The theory was that with a small led and battery the led will only light up when the current is passed through the capacitor in the direction of the least resistance. Now this did happen, however my experiment was rather a cobbled together amateurish affair and did not last more than a few minutes before I had to pack it in so was unable to see if this was able to work with any consistently or not.

I used a spare HMLP-6000  a 1.5v battery and a 50uf 250v capacitor.

I really don't know if it would work or not but thought it easy enough to try.