johnheath

Film capacitors
« on: June 23, 2020, 07:01:18 AM »
Hi all...

I am sitting and looking for film capacitors at mouser. I am specifically looking for coupling capacitors and these seems to be "pushed" by mouser. I have seen these at a Swedish site as well and since I have not tried them before I wonder if you people with your vast experience can say anything about them... useful, good, bad or other perhaps?

They are quite cheap that is all I know so far :)

Best regards

// John
Nothing is impossible - It just takes some more time


Re: Film capacitors
« Reply #1 on: June 23, 2020, 07:11:38 AM »
They are ok, for lower THD get metalized polypropylene, they are a bit more expensive thou.

johnheath

Re: Film capacitors
« Reply #2 on: June 23, 2020, 07:30:59 AM »
Thank you Sir

Yes that is what I normally use... Now I see that these are metallized polyester.

What would the difference be? You mentioned "worse" THD. Would that be a noticeable difference?

Best regards

/ John
Nothing is impossible - It just takes some more time

Re: Film capacitors
« Reply #3 on: June 23, 2020, 07:37:18 AM »
Thank you Sir

Yes that is what I normally use... Now I see that these are metallized polyester.

What would the difference be? You mentioned "worse" THD. Would that be a noticeable difference?

Best regards

/ John

Not as bad as a nasty ceramic or tantalum cap, but worse than polypropylene, it also depends on what its being used for and the voltage across it. As for THD, it has higher THD than polyprops, whether you can hear it or not its up for debate...

johnheath

Re: Film capacitors
« Reply #4 on: June 23, 2020, 07:39:46 AM »
Not as bad as a nasty ceramic or tantalum cap, but worse than polypropylene, it also depends on what its being used for. As for THD, it has higher THD than polyprops, whether you can hear it or not its up for debate...

Thank you

Ok, maybe get a handfull and try them out could be an idea.

Thanks again

// John
Nothing is impossible - It just takes some more time

johnheath

Re: Film capacitors
« Reply #5 on: June 23, 2020, 07:55:28 AM »
Btw... how would they do in a passive EQ? I just found out that they some more obscure values at hand and their size is comfortable small compared to many other film caps.

Best regards

// John
Nothing is impossible - It just takes some more time

squarewave

Re: Film capacitors
« Reply #6 on: June 23, 2020, 09:29:10 AM »
I always test builds extensively for distortion and noise using FFT software and I have never personally observed a film capacitor that exhibited any significant distortion at all so generally I assume that a modern film capacitor in a small signal audio circuit is going to perform with near perfection regardless of the cost. Maybe tube circuits are different. I don't do tubes. Is it possible that some specific cap under some confluence of circumstances could generate higher than normal distortion. Sure. But so far I haven't run into an issue with bad film caps. If you're doing mass production maybe test large batches from different suppliers for distortion, DC issues, temp stress or whatever before signing off on that particularly cheap part. But if you're doing one-off builds or small batches, just test the finished product. If the THD of the device is acceptable, move on.

BluegrassDan

Re: Film capacitors
« Reply #7 on: June 23, 2020, 09:32:15 AM »
Go for polypropylene, even if just for peace of mind. Better quality than polyester for coupling.

johnheath

Re: Film capacitors
« Reply #8 on: June 23, 2020, 09:57:51 AM »
I always test builds extensively for distortion and noise using FFT software and I have never personally observed a film capacitor that exhibited any significant distortion at all so generally I assume that a modern film capacitor in a small signal audio circuit is going to perform with near perfection regardless of the cost. Maybe tube circuits are different. I don't do tubes. Is it possible that some specific cap under some confluence of circumstances could generate higher than normal distortion. Sure. But so far I haven't run into an issue with bad film caps. If you're doing mass production maybe test large batches from different suppliers for distortion, DC issues, temp stress or whatever before signing off on that particularly cheap part. But if you're doing one-off builds or small batches, just test the finished product. If the THD of the device is acceptable, move on.

Thank you Sir

The EQ in mind is a REDD EQ 100Hz and 10kHz cut and boost... I'll try these caps and see how they behave. I am implementing this EQ in a 8-tracker mixer build

Best regards

// John
Nothing is impossible - It just takes some more time

johnheath

Re: Film capacitors
« Reply #9 on: June 23, 2020, 10:00:10 AM »
Go for polypropylene, even if just for peace of mind. Better quality than polyester for coupling.

Thank you Sir

Peace of mind yes... finding the right values with polypropylenes is difficult though. I can of course add caps in series or parallel to get the right value but that is equally annoying I suppose

Best regards

// John

Best regards
Nothing is impossible - It just takes some more time


Re: Film capacitors
« Reply #10 on: June 23, 2020, 10:00:19 AM »
Btw... how would they do in a passive EQ? I just found out that they some more obscure values at hand and their size is comfortable small compared to many other film caps.

Best regards

// John

Douglas Self made several tests with polyprop and polyethylene caps on Sallen Key filters, distortion depends on the position of the cap in the circuit, in some places you can use polyethylene without a considerable increase in distortion, whilst in others you need polyprop. If you want to live a happy life just use polypropylene and forget about it. EQ's should also use high grade caps, you can use polypropylene or ceramic C0G/NP0 depending on the size of the cap.

squarewave

Re: Film capacitors
« Reply #11 on: June 23, 2020, 10:29:33 AM »
Douglas Self made several tests with polyprop and polyethylene caps on Sallen Key filters, distortion depends on the position of the cap in the circuit, in some places you can use polyethylene without a considerable increase in distortion, whilst in others you need polyprop.
Just curious but do you have a reference for this. I just find it difficult to believe that there is any scenario where it would make any real difference. Do you have a link or a post that describes the details?

Re: Film capacitors
« Reply #12 on: June 23, 2020, 10:34:24 AM »
Just curious but do you have a reference for this. I just find it difficult to believe that there is any scenario where it would make any real difference. Do you have a link or a post that describes the details?

It is described in his active crossover book, page 310 of the 2nd edition. Even him doesn't know why this happens, he just found experimentally that you can replace some but not all capacitors with polyester, and achieve the same distortion as if a polyprop were used.

squarewave

Re: Film capacitors
« Reply #13 on: June 23, 2020, 10:50:59 AM »
That page is not in the preview on Amazon but page 307 is (I won't reproduce here because it's copyrighted) and it looks like the difference between polypropylene and polyester is 0.0025% at 10Vrms. If that is what it takes for you to have a "happy life", you need to get out more.

Re: Film capacitors
« Reply #14 on: June 23, 2020, 11:02:17 AM »
That page is not in the preview on Amazon but page 307 is (I won't reproduce here because it's copyrighted) and it looks like the difference between polypropylene and polyester is 0.0025% at 10Vrms. If that is what it takes for you to have a "happy life", you need to get out more.

 ;D ;D ;D ;D

Distortion with polyester is 0.0025% whilst polyprop is 0.00025%, no small difference, can you hear it? I don't know but one is always in pursuit of perfection.

JohnRoberts

Re: Film capacitors
« Reply #15 on: June 23, 2020, 12:03:34 PM »
Douglas Self made several tests with polyprop and polyethylene caps on Sallen Key filters, distortion depends on the position of the cap in the circuit, in some places you can use polyethylene without a considerable increase in distortion, whilst in others you need polyprop. If you want to live a happy life just use polypropylene and forget about it. EQ's should also use high grade caps, you can use polypropylene or ceramic C0G/NP0 depending on the size of the cap.
yup... I recall back when I was working at Peavey engineers in the digital group were apparently even cheaper than me... ::) they would populate active filters with the cheapest capacitors in our system and measure the distortion. If the (cheaper) capacitor caused measurable distortion, they used a better (still inexpensive) film cap one at a time until the more expensive caps stopped making an improvement.. In active filters depending on the topology, different nodes will experience more or less voltage swing (a likely driver for nonlinearity caused by voltage coefficient).   I generally just started with the better while still inexpensive film caps. 8)

I am not an advocate of using unblind listening test for design decisions, but typically to check my work for a final blessing. That said, you can do null testing to compare component differences with much higher resolution. Build up two otherwise identical circuits and subtract one from the other. The residual left after that subtraction reveals the difference (it doesn't tell you which one is different, only that they are different). Of course you need to match circuit voltage levels and component values closely to realize a deep null. The beauty of null testing is you can also get a sense for the nature of the difference... nasty or mild.

JR 
Don't only half-ass tune your drums. Visit https://circularscience.com to hear what properly "cleared" drums sound like.

BluegrassDan

Re: Film capacitors
« Reply #16 on: June 23, 2020, 12:34:13 PM »
The WIMA FKP3 and MKP4 series are well regarded in EQ circuits.

Whoops

Re: Film capacitors
« Reply #17 on: June 26, 2020, 09:48:43 PM »
;D ;D ;D ;D

Distortion with polyester is 0.0025% whilst polyprop is 0.00025%, no small difference, can you hear it? I don't know but one is always in pursuit of perfection.

I'm always in the pursuit of more distortion and character....

Re: Film capacitors
« Reply #18 on: June 26, 2020, 09:55:39 PM »
I'm always in the pursuit of more distortion and character....

Yes, in audio there are no rules, one person's trash is another person's treasure, like squarewave mentioned, perhaps I need to get out more  ;D

Whoops

Re: Film capacitors
« Reply #19 on: June 26, 2020, 10:28:14 PM »
True.

Having the Panasonic brand on a Film cap is enough for me to use it


 

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