Non-Polar Electrolytic vs. Polypropylene Film Capacitors

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gtforme00

gtforme00

Member
Joined 2004
When you give a value of <0.1ohm for instance, what do you mean? Is 0.1ohm the limit of measurement for that test condition?
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Yes, measurements with a < sign are below the reliable limits of measurement for the test setup. I could probably improve the the quality of those measurements to get down past that resolution with a proper test fixture and more time to tweak the settings on the impedance analyzer.

This project started as a "lunch break" project. This is my daily time where I can borrow the lab tools for a few minutes to perform some personal tests. Given the time rush, it is difficult to optimize the settings properly, and I had to settle with "good enough for my purposes". Now that more interest has been expressed, I might revisit these tests with more capacitors and a proper test jig.


The esr of capacitors isn't so critical because their reactance is so high at low frequency. For instance 3.3uF at 100Hz has a reactance of 482 ohms so an ohm of ESR doesn't really make much difference. Even at 10KHz, the reactance is 4.8ohms. Not to say it's not important, it needs to be taken in context and of course, it's the opposite for inductors, ESR is the essence of inductance.
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This is a good point, and one to which I will have to give some thought. The whole motive behind these tests was to find out whether it would be preferable to replace some rather large 92.5uf value electrolytics with film capacitors in the NHT M3.3. These capacitors are in series with the mid-bass drivers, so it seemed intuitive to use the lowest ESR available. What I did not consider, as you have pointed out, is that the ESR is a fraction of the reactance at the frequencies of interest (100-300 Hz).

Impedance = Resistance + Reactance

Reactance of Capacitor = 1/(2*pi*frequency*capacitance)

Measured Impedance of 96.9uF Capacitor at 100Hz = 16.96 Ohms

Calculated Reactance of 96.9uF Capacitor at 100Hz = 16.42 Ohms

Equivalent Series Resistance = Impedance - Reactance

Equivalent Series Resistance of 96.6uF Capacitor at 100Hz = 0.54 Ohms

Impedance difference due to Equivalent Series Resistance = 100*(1-(16.42/16.96)) = 3.18%

Not as small of a difference as I had originally suspected, but still gives validity to your point.

I would like to simulate this non linear resistance in a crossover schematic, to see how much error the ESR of a capacitor could introduce in the frequency response of the filter.

Good day all,
David
 
A

automaticmojo

Member
Joined 2010
Capacitor SnakeOil and Misinformation

Old post I know- but it makes a great point that well designed crossover takes in to account the type and characterstics of capacitors-such as these 'lowly" bipolar electrolytics.
Zobel networks are a classic case-I would leave stock as stock.
Amazes me- people laud about the sound-then when replacing them comment on how much better -for example poly's are.
Old electrolytic caps drift, and are a maintenance item- but I too am in the school of sticking with the stock types in a well designed speaker.
A lot of the so called superior sound in caps is hog wash IMHO-and more of a justification of spending $40 on a cap- when the stock $1.25 would have worked fine, and actually worked better with the stock crossover, because it was taken into account when the speaker and crossover were designed.
Of course if you rengineer the crossover to poly/film types-then your fine.

gtforme00 said:
Would a moderator please make the above correction?

An update to my inquiry on capacitor ESR and crossover design.

First, I was a bit redundant in specifying both ESR and DF, as they are inextricably linked for a given frequency. DF = 2*PI*F*ESR*C*(100 for percent). However, it is nice to see the ESR to get a grasp of the resistance each capacitor represents.

Second, in private conversations with a loudspeaker engineer (The above mentioned Jack Hidley from NHT) he confirmed that an experienced designer will take into account the ESR of both capacitors and inductors. Furthermore he stated that the ESR was taken into account in the design I am cloning (NHT M3.3) and that I should try to match the Dissipation Factors given in the specifications. This was good for me to discover, as I had purchased at least one film capacitor to replace an electrolytic, a substitution which I will no longer be using.

Now, it is very common to hear discussion of Inductor ESR, but this is the first confirmation I have seen that capacitor ESR should be considered when designing loudspeakers. This does NOT automatically invalidate all designs which have not taken this into account. The differences among the ESRs of various types of film capacitors are fairly small, however there is a significant difference between the ESR of film type capacitors and that of electrolytics. The practice of swapping electrolytics for film capacitors to "improve" a design is immediately called into question.

There is no paradigm breaking news here, and to some this may even be old news. This is just one more small block of knowledge to add to the vast amount of information available on this forum.

So what practical lessons should we take away from this experiment? If one is designing a crossover with electrolytics, one should be aware that the ESR of the capacitor will have a small effect on the drivers actual response, and that some software is not capable of modeling this (in my experience Speaker Workshop). Similarly, if an existing design has an electrolytic, be aware that there will be a deviation from the design if a film type capacitor is substituted. Whether this deviation will be perceived subjectively as an improvement is outside the scope of this discussion.

I hope that this discussion has been as informative for the readers as it has been for the author.

Regards,
David

P.S. Next up, can I measure "voltage coefficient of capacitance", and how do different types of capacitors compare?
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B

Boogieman

Member
Joined 2004
Thanks for that post (helps me on my JBL Ti6K x-over rebuild)

gtforme00 said:
Would a moderator please make the above correction?

An update to my inquiry on capacitor ESR and crossover design.

First, I was a bit redundant in specifying both ESR and DF, as they are inextricably linked for a given frequency. DF = 2*PI*F*ESR*C*(100 for percent). However, it is nice to see the ESR to get a grasp of the resistance each capacitor represents.

Second, in private conversations with a loudspeaker engineer (The above mentioned Jack Hidley from NHT) he confirmed that an experienced designer will take into account the ESR of both capacitors and inductors. Furthermore he stated that the ESR was taken into account in the design I am cloning (NHT M3.3) and that I should try to match the Dissipation Factors given in the specifications. This was good for me to discover, as I had purchased at least one film capacitor to replace an electrolytic, a substitution which I will no longer be using.

Now, it is very common to hear discussion of Inductor ESR, but this is the first confirmation I have seen that capacitor ESR should be considered when designing loudspeakers. This does NOT automatically invalidate all designs which have not taken this into account. The differences among the ESRs of various types of film capacitors are fairly small, however there is a significant difference between the ESR of film type capacitors and that of electrolytics. The practice of swapping electrolytics for film capacitors to "improve" a design is immediately called into question.

There is no paradigm breaking news here, and to some this may even be old news. This is just one more small block of knowledge to add to the vast amount of information available on this forum.

So what practical lessons should we take away from this experiment? If one is designing a crossover with electrolytics, one should be aware that the ESR of the capacitor will have a small effect on the drivers actual response, and that some software is not capable of modeling this (in my experience Speaker Workshop). Similarly, if an existing design has an electrolytic, be aware that there will be a deviation from the design if a film type capacitor is substituted. Whether this deviation will be perceived subjectively as an improvement is outside the scope of this discussion.

I hope that this discussion has been as informative for the readers as it has been for the author.

Regards,
David

P.S. Next up, can I measure "voltage coefficient of capacitance", and how do different types of capacitors compare?
Click to expand...

FINALLY :D
I have been googling and reading about capacitors, coils and resistors in PASSIVE cross overs the last three days.

My idea was to replace a broken resistor since it showed infinite resistance to begin with. Being on it i chose Mundorf MOX resistors due to their non inductive characteristic and good accruacy (+/-2% vs orignal +/-5%)

While I had the x-over out (which was quite messy) i thought I might as well check all components and maybe upgrade the inline caps for the tweeter since it sounds quite sharp on s words (where words end with s and especially when females sing). So the seatch began and I enden up on 2 x Mundorf supremes.
Then I read about how crappy electrolytics were so I thought that I might as well exchange them too, ending up on a HUGE Mundorf MCAP (50x75mm) I would have needed to place it on the back of the PCB to fit it.
Then I heard abour ?radiophonics? and started to think if such a huge roll of metal foil might pick up more vibrations than a tiny roll of electolytic soiled foil.
And then came ESR into the game (my god is it ever gonna end?) so started looking for how to replace a lytic with a film and after a day of oogeling I found Your reply above.

Based on what You are saying it is definitely NOT RECOMENDED to change an electrolytic for a film cap unless i meassure it and adapt with a resistor for ESR but still resistors are not changing with frequence so not the same thing anyway.
The question is if JBL did think of this when making the Ti6K speakers (their flagship 2002) or if they just thought that a film cap was way to expensive even for those 7000 dollar speakers? Hmmm...I could try if it wasnt due to the mess to desolder it all (capacitors, wires, coils being directly connected to binding posts - they ALL have to be desoldered to access xover and to be able to do that I have to desolder the speaker elements due to short leads)

I have attached an image of the x-over and scematics and which components I will change (green) and was thinking to change (Red) but will probably not any more

[OFFTOPIC] History around the broken resistor
The resistor break was cuased by a broken tweeter which was caused by a high amplitued pulse from the amp which was caused by a poor connection of RCA cable shield on my Emotiva AMP which was caused by the new Emotiva RCA cables (recomendation, do not buy/use them).
The cables easily slid on to my Emotiva AMP....TOO easy obviously because as amp started up i heard an extremely high electronic noise and imediatelly turned it off.. After fixing all cables (clamping harder) i restarted and everuyhing played as it should BUT the tweeter voice coil had been totally burnt so I wanted to check the x-over before starting it up and one resistor said infinite resistance so totally burnt as well.
 
M Gregg

M Gregg

Disabled Account
Joined 2010
bmxmen said:
I have heard that all film capacitors will be beter from electrolitycs. Im thing to change my capacitor in kathode. I need 100uf,black gate N or something from film capacitors, what will be beter?
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In my experience different capacitors sound different in the cathodes of power tubes. YMMV.

I use silmic 2. I have tried the Cerafine and find them a bit harsh.

The problem with film caps is again they can sound different, so you pick your poison some film caps can sound bright.
Some can seem to wipe the HF..So it depends what floats your boat.:D

I am looking at Kaisei as a possible cathode bypass cap. (I haven't tried them yet!)

If you can find a film cap that you like then obviously it will stand the test of time..ie they don't dry out but physical size is an issue.
I don't believe that just finding a film cap that is the right size and capacitance is the issue if it sounds awful.

This isn't about dropping names of expensive caps if you can find an electrolytic that sounds good go for it!

The thing to remember is reliability if your cathode cap goes short circuit in the cathode of a power tube it can cause major damage..so protect what you can where you can by whatever means you can!

Regards
M. Gregg
 
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B

bmxmen

Member
Joined 2012
I have SE amplifier with E86C-6N30P-QB2/250 tubes. And i have bypased 6N30P cathode. Allready i have puted plate choke to anode for E86C, and grid choke for Qb2/250, power tube is on fixed bias. So i have lots of gain, i have full amplifier power when i putt volume on 12Hour. So it is pasible to throw away this capacitor. Like we all know, best cacacitor is no capacitor:)
 
D

DF96

R.I.P.
Joined 2007
myweb.tiscali.co.uk/g8hqp/
bmxmen said:
Like we all know, best cacacitor is no capacitor
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Do we all know this? Some capacitors are essential. Then the best capacitor is the most appropriate one: right value, right dielectric, competent manufacture etc.

Omitting the cathode bypass capacitor will raise output impedance and so may lead to boomy bass and a generally more uneven frequency response. Some people may prefer this, but it is not hi-fi.
 
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