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There were many posts in the past about these caps. The general consensus was that they are good in power supply. Some even reported that there may be other uses for them in audio.
I previously tried a variety of these caps in speaker crossovers. The results were uniformly negative.
Doing research on the subject, I have gone through spec sheets from different manufactures (a link to Kemet is provided; other manufacturers have similar specs). These caps are rated for 50-60 Hz, and manufacturers caution against using them wherever high levels of harmonics are present. A striking thing is their poor high frequency performance. They have pretty good loss factor (tgδ) of 0.0002 at 10 Hz, but at 120 Hz tgδ is 0.0005, or 2.5 times higher, and at 1,000 Hz it is 0.005, or 25 times higher! No wonder they sound bad.
Bypassing these caps with better quality lower value ones does not make much sense. Due to their non-inductive construction, they present low impedance path to high frequencies.
Taking this info into account, I wouldn't use these capacitors anywhere except the input position of a power supply.
Follow Ups:
I have a question.
How does a bad "loss factor" at high frequencies cause "poor high frequency performance"?
I just tested a GE Dielektrol 25uf 660AC motor run cap with a audio generator and a scope.
The cap is in series with the signal that is driving a 100k resistor.
The FR is ruler flat to the limit of the generator (225kHz) and a 10kHz square wave looks perfect.
What am I missing?
Tre'
Have Fun and Enjoy the Music
"Still Working the Problem"
It is similar to transistor distortion. A typical Best Buy transistor amplifier has distortion of less than 0.1%, compared to 5% of a 2A3 amplifier. But which one sounds better?
For motor run capacitors, tgδ of 0.005 at 1,000 Hz means that signal losses at this frequency are 0.5%. This is so little that it can be ignored for practical purposes, as long as insertion loss of a capacitor is concerned. But insertion loss figure tells nothing about distortion.
Looking closer at the phenomenon of dielectric absorption (aka dielectric memory), which is largely responsible for capacitor losses, one could see that influence on the signal may be not so benign. To demonstrate dielectric absorption, a capacitor is charged to, say 100 V, then shorted for 10 sec. 10 sec after the short is removed, residual voltage on the capacitor is measured. In most organic dielectric capacitors, this residual voltage is 2-5% of initial value, and in electrolytes it could be as high as 15%. Not small.
At the molecular level, polar dielectrics (e.g. vegetable oil in motor run capacitors) consist of molecules with positive charge on one end and negative on the other, or dipoles. When voltage is applied to capacitor, dipoles orient themselves in electric field. When voltage polarity changes, dipoles re-orient. Re-orientation takes time, causing dielectric hysteresis (similar to magnetic hysteresis). Effects of hysteresis increase with frequency. How much distortion is caused by dielectric hysteresis, I don't know, but one sure thing is that this type of distortion increases with frequency.
Examples of polar dielectrics: paper, mylar, PCBs, mica, some ceramics, vegetable oil.
Non-polar dielectrics: polypropylene, polystyrene, teflon, mineral oil.
The difference between polar and non-polar dielectrics is quantitative rather than qualitative. All substances have positive and negative parts in their structure. Only vacuum is true non-polar dielectric.
...You mention DA as a possible source of "capacitor distortion". I've wondered about this because the theoretical model of DA is relatively simple and should be very easy to simulate in spice or maybe even wire up and measure...at least at a high level. And yet, at this point I've never seen this done WRT audio apps. DA is a known issue with certain analog circuits like S&H and integrators but I'm not sure what's known transfers well to audio.
FWIW, the non-electrolytic caps that exhibit the greatest DA using my somewhat crude technique are the Russian K40s, esp after exposure to temperatures of say 150F. For this reason I've been reluctant to use them.
I think the simple part is dielectric constant ε, which is somewhat related to dielectric absorption. ε is a coefficient indicating how many times capacitance is increased by a given material compared to vacuum. Materials with high dielectric absorption usually have high ε.
Dielectric absorption and permitivity may not be easily susceptible to modeling. In the idealized situation, the relaxation time parameter is used, which is time needed for elemental dipoles of dielectric to re-orient upon instantaneous change of electric field. The assumptions are linear, homogeneous, isotropic materials with uniform response to changes in electric field. Real situation is far from these assumptions. Dielectric memory, as capacitor shorting experiment shows, persists for a very long time (seconds), indicating that relaxation times in real materials may have wide spread. Plastic films are highly anisotropic. How linear and uniform dipole response to applied electric field is, only God knows. Modeling has been successfully used to predict such gross phenomena as losses or capacitance changes with frequency (BTW, another source of capacitor non-linearity), but I doubt its usefulness in calculating distortion.
...I guess that's my point; lots of doubt and speculation regarding DA effects in audio but no actual testing or even modeling. The fact that high DA electrolytics have been (relatively) successfully employed in audio causes one to doubt its importance but doubt there is.
The high level model of DA I've seen is a network of series RC networks paralleled across the ideal C. The time constants of the networks are a range of many seconds to many tens of seconds. Even if not an entirely accurate model, it ought to useful in determining whether or not DA is indeed something of audible concern. If nothing else, it should be easy to model and examine for gross high level effects.
Perhaps the difference in capacitors is in fact measurable, but not represented as frequency response, THD or RMS intermodulation. Transient distortion in amplifiers is a neglected subject, and I am highly suspicious that it accounts for much of what we hear that is otherwise impossible to explain.
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Buy Chinese. Bury freedom.
Alexander Pushkin, "Mozart and Salieri". One of my favorite audiophile citations.
Dielectric absorption is only one source of capacitor distortion. There are several others. One is capacitance change with frequency, and one more is capacitance change with voltage. Distortion due to capacitance change may be quite serious - any change in capacitance causes changes of voltage across the capacitor. Yet one more is capacitors acting as mechanotransducers, which I posted on a while ago. This was about capacitors acting as low quality electrostatic speakers and low quality condenser microphones at the same time.
Maybe capacitor distortion has been studied, and we just don't know? However, it seems more like there is no interest to this subject in the field of electronic engineering. We'll have to do it ourselves if we want to know. But even if we find that capacitor distortion is low, who is going to be convinced? I know from experience that some capacitors sound better than other, and avoiding capacitors in the signal path is a good practice. People whose judgment I trust preferred the sound of transformer- or direct-coupled amplifiers to that of capacitor-coupled amplifiers.
"it seems more like there is no interest to this subject in the field of electronic engineering."
I posted here on this exact subject earlier this year. We (at my day job) had just discovered that the capacitance of modern multi-layer capacitors changes markedly with voltage. So much so that the capacitors - for bypassing purposes - virtually disappear. Only a few manufacturers of these components are publishing the relevant data.
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Buy Chinese. Bury freedom.
.
Have Fun and Enjoy the Music
"Still Working the Problem"
Where we were using the motorun caps were in the power supplies of tube amps.There,they happened to work well for filtering 120hz.They are metallized poly film caps with an oil additive for additional cooling.I think the Klipsch Belle crossover used a small motorrun for bass but can't be sure.
I don't use motorruns in crossovers but use them in Cary Amp power supplies to replace the series connected 1200uf caps with a parallel connected 70uf motoruns.That yields a big improvement.
Now that Panasonic,CDE,Wima,and others are making reasonably priced large value film caps,motoruns have fallen by the wayside,much due to their physical size.
"For every complex problem there is an answer that is clear, simple, and wrong" H. L. Mencken
My even bother with motor run caps?
Many of the ones I've seen are a large as Hand Grenades?
So many other good choices out there, at half the size.
Steve
Yeah, but a lot of the motor runs are much less expensive than the those high end caps.
Who needs expensive high end capacitors in a power supply?
Even inexpensive Solen caps are better than almost all Electrolytic caps.
Steve
Have you priced solens lately? compare a 47uf/600v solen to what a similar motor run would cost and you will see what I mean.
Obbligato Paper oil will way outperform motor run caps in crossovers.
They are not cheap either. I do like them though, and used them in my last amp build. Still, if you are trying to do things on a budget, motor runs can have their place.
Parts Express has the caps cheap. Like $6.75 for 4.7uF as used on a tweeter. Likely cheaper than a motor run. Expensive ?????????????
I said 47 uf. You are looking at the wrong cap.
$29.50 for 47uF. That is not expensive for 47uf in a quality cap. If great audio is not important to you, then use a $10 motor run capacitor.
They are not mutually exclusive.
I have cde in my10yse ht running 18 hours a day for 8 years.Great voice.I just picked some dc link caps 900 volt 50uf for less the 20$ I think these could be the future. I am hoping there will be more of these showing up for sale. These are isckra brand and are very compact and test about .23 esr. I got some 750 75uf's also. .23 too.
Something weird some of my favorite oils tested much higher. Could this account for the tone? Could a higher esr help with stability in signal path?
I tested k72p Russian Teflon. the metal ones (not alloy). no measurable esr!? just no value where it should be. I bought more to try more in my stuff.
elna silmic tested lower then many oils!
Finally A pair of hovland foil caps I bought many years ago for the first tube preamp I ever built. Never payed so much $ since 400 volts 2uf. I tried them in lots of things. Liked them best on focal tweeters tested .3! higher then I expectedRussian red tin can cap tested low same as the dc link if my memory serves me right.
Edits: 05/17/17
The idea of small capacitors in a power supply is just not appealing to me. There are good things about motor runs - few other types compare to them in low ESR and high current capability. Many have ratings in thousands of volt-amperes. Take in your hand and feel the thing, as Ukrainian proverb says.
I don't disagree with you.I love film caps in the power supply but sometimes room constraints only permit use of lytics.The new poly film caps of high of capacitance are very good.They have made them smaller but still much larger than a lytic in capacitance comparison. Take a look at the caps I put here for comparison.Here is a 51uf Solen at 630vdc and a 370vac MR good to 700vdc and the 50uf@500v Panasonic. Notice the difference in physical size but you can get CDE film caps and Wimas that are 600vdc to 900vdc that are smaller as well.
100uf MR cap,100uf at 630vdc Solen film cap and 100@500v Pannasonic film cap.While the voltage rating of the MR is 370vac,it is good to 700vdc at least because of the oil.
"For every complex problem there is an answer that is clear, simple, and wrong" H. L. Mencken
Edits: 05/05/17
In most cases, you cannot fit these big cans into an existing design, where DC Links and other compact caps may be quite handy. DC links don't have the current capability of motor runs, but they have pretty good loss factor at 10 kHz and thus not restricted to 50-60 Hz operation.
so dc link not suitable for powersupply?
or should using for first cap be avoided?
Exactly
So many people look at 50-60 Hz operation labeling on the cap and think that is what the cap is limited to and it's just not true.They put this rating on to designate it for non rectified appliance applications as that's what they are mostly used for. They often call big 12v batteries automotive batteries but that doesn't mean they can only be used in automotive applications but that is what their intended use is.
"For every complex problem there is an answer that is clear, simple, and wrong" H. L. Mencken
.
I used ASC BlueLines in my last build - I quite like the sound of tht amp, but I have not compared the BlueLines to other capacitors. i've chosen to go with ClarityCap TC in my current build. I'm not convinced the TCs will do it for me, so may try "better" metallised dry poly or go back to the BlueLines.
Or try to minimise the effect of the last PS cap by using a quality film and foil as partial ultrapath. Decisions, decisions... best get the amp built first!
Cheers,
91
"Confusion of goals and perfection of means seems to characterise our age." Albert Einstein
But when I look at their specs, I see no difference from other motor run caps. Same construction, same materials, 50-60 Hz rating.
I have a batch of 120 uF ASC motor runs that I bought at bargain price. Time permitting, I will test how they sound in series with a high resolution tweeter.
I use the ASC in tube power supplies. Have you tried this type compared to other types of power supply caps like, electrolytic, Solen, DC link, etc...
8 uF 600 VAC Ronken (US-made) motor runs in a 1934 PPP 2A3 amp in place of the original PIO capacitor block. It was OK, but the original was better. Ronkens weren't broken in though, and that could explain the difference
I found that the 100uf x 370vac asc 386s caps took at least 50 hours before they really started to sound good and still improving.
and that antique oil cap block was sure broken-in.
But even if motor runs are capable of good sound, I would still prefer capacitors designed for high frequencies.
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