Capacitors

[Guest SteveG]

This question is directed to Ken Kantor, but hopefully others will react.

Ken, As mentioned in the prior topic, I too have been confused by a lot of conflicting talk about capacitors. Many have suggested preemptive replavcement with newer polyprop. to replace electrolytic. Others have said don't bother or this will change the sound.

I have several pairs of AR speakers made in the 1970's and one pair from the 60's. I have noticed no detectable change in their sound and have never changed a cap (can't say the same for foam surrounds unfortunately). I have 4 questions on caps.

1) does changing these preemptively make any sense? I assume one would do this only if they become increasingly likely to cause a catastrophic failure with age that could damage drivers.

2) if preemptive replacement is not warranted, then what are the signs of cap. failure or deterioration? Is this subtle (creeps up on us so we don't necessarily notice it) or is deterioration more abrupt and unmistakable? What should we listen for?

3) if we do need to replace a cap, how easy is it to find the "right" one? Are they marked sufficiently well to assure we will be able get a replacement with identical specs, and are such identical-spec replacements even available? I am assuming that it would be audacious to think that we could improve on original design with different caps. unless newer designs are now available and have been evaluated by someone who really knopws ehat they are doing.

4) what is the working life of a cap? Might this be indefinite as long as they are not fried? Should we just ignore them and enjoy the music, until a problem becomes apparent?

Thank you in advance for taking the time to enlighten us. It would appear that your background gives you an unusual (unique?) ability to give us the perspective of the original design intentions for these speakers. I eagerly await your response.

Thanks Steve

[Guest]

I own quite a number of AR speakers, AR2ax, AR3, AR3a, AR7, AR17,

AR18, AR38s, AR12, AR25 and of course my latest addition AR9.

The only ones that I have replaced the caps on were the AR3a speakers and those I followed the suggestions contained in the Classic Speaker AR section. Specifically I replaced the tweeter caps with Mylar and the Mid and woofer with non-polarized electrolytic caps. The reason I used electrolytic is because the polypropylene and Mylar were very, very expensive. I could not discern any difference before and after the change. The AR3a had the big bricks acting as capacitors. The AR section has AR3a crossover specs and diagrams which are very useful. I used the exact cap values as diagramed. I have been building and repairing speakers for many years but do not claim

to be golden eared; It's a fun hobby for me and so far my wife and kids have not revolted.

[Guest SteveG]

Julian.

Can you share the reason you replaced the caps in the 3a's. I am a little confused as you said the sound was same before and after. Did you change them as "preventive maintanence"??

Thanks, Steve

[Guest]

I replaced the capacitors mostly on the recommendations of contributers to the AR site. Partly I just wanted to refurbish the total speaker and so while I had the woofer removed for the refoam work, I decided to poke around a bit. Of course the pots needed cleaning and one thing lead to another. I do not claim to hear any differance in the before and after sound. I guess it would have been Okay to keep the old crossover components. The new replacements did however have greater voltage values ( 250v versus 50v).

Maybe someone with technical expertise can answer whether electrolytic, Mylar or polypropylene can make a differance? By the way I used to subscribe to Speaker Builder magazine and have

built speakers and designed a variety of simple 2 way, 3 way, 1st order and 2nd order networks, as qaulity speakers back then were very expensive. Now I just buy old broken quality ( AR Advent, OHM Dynaco, JBL etc ) speakers, fix them and enjoy listening to all of them. I guess my hobby keeps me off the street corners. Julian

[Guest]

All I can say to Julian after reading his comments about capacitors is WOW. I envy the man who has the space for 10 sets of vintage (large) speakers! I own (3) sets and I'm borderline having to add an addition to my home. One can only dream....

[kkantor]

Boy, am I late... better change MY caps...

Think about caps just like you think about vacuum tubes. (If you think about vacuum tubes.) Sometimes they live effectively forever, they die at random, and the effects and rate of deterioration are largely determined by the circuit and conditions of use. Should you change most tubes preemtively? Won't help, can't hurt... unless the circuit is dependent on subtle values. Should you change very old or obviouly failing tubes? Yes, carefully, and not frivolously.

Cap technology really took off in the mid-70's. Before that time, electrolytic capacitors often deteriorated with age, with or without external clues. This problem was made worse by the fact that amplifiers were getting much more powerful, and speaker crossovers were exposed to voltages they were never designed for. A rash of cap failures was the result, and it is not uncommon for a 60's-era speaker to lose one even today. An experienced engineer can look at a cap and estimate its age, and statistical likelyhood of dying. It's hard to describe. Newer ones TEND to be aluminum tubes with a plastic coating, and some kind of perforation or hole to rupture and vent pressure if the cap fails. Older ones tend to be raw aluminum cylinders or some kind of hard or waxy material.

1- I don't think preemptive modifications make sense. It's mostly risk, and little reward. Skip it unless you are doing other work inside, see something that looks deteriorated, and want to spare yourself future effort. Or unless you find the activity fun, which it can be.

2- Most of the time, caps failures are pretty obvious. The tweeter goes away, or the woofer becomes very bright. If you don't notice a sonic change, I doubt you should worry.

3- No, caps are very rarely labelled for "series resistance," (an imprecise term). This property often has a noticable effect on sonics, and needs to be matched to the original by someone who understands it and can assess it. Sure, the effect is mild in the scheme of things, and the speaker will function reasonably with a generic replacement. But there will be some differences between cap types.

4- Life? As I mentioned above. Failures of 60's-era caps are pretty common. Failures of (quality) 80's and 90's caps are pretty rare, and are not expected to occur in the useful life of a speaker. No doubt there are crappy and over-stressed new caps, and caps from the 40's that will outlive civilization.

Hope this helps....

-ken

>This question is directed to Ken Kantor, but hopefully

>others will react.

>

>Ken, As mentioned in the prior topic, I too have been

>confused by a lot of conflicting talk about capacitors.

>Many have suggested preemptive replavcement with newer

>polyprop. to replace electrolytic. Others have said don't

>bother or this will change the sound.

>

>I have several pairs of AR speakers made in the 1970's and

>one pair from the 60's. I have noticed no detectable change

>in their sound and have never changed a cap (can't say the

>same for foam surrounds unfortunately). I have 4 questions

>on caps.

>1) does changing these preemptively make any sense? I assume

>one would do this only if they become increasingly likely to

>cause a catastrophic failure with age that could damage

>drivers.

>2) if preemptive replacement is not warranted, then what are

>the signs of cap. failure or deterioration? Is this subtle

>(creeps up on us so we don't necessarily notice it) or is

>deterioration more abrupt and unmistakable? What should we

>listen for?

>3) if we do need to replace a cap, how easy is it to find

>the "right" one? Are they marked sufficiently well to

>assure we will be able get a replacement with identical

>specs, and are such identical-spec replacements even

>available? I am assuming that it would be audacious to

>think that we could improve on original design with

>different caps. unless newer designs are now available and

>have been evaluated by someone who really knopws ehat they

>are doing.

>4) what is the working life of a cap? Might this be

>indefinite as long as they are not fried? Should we just

>ignore them and enjoy the music, until a problem becomes

>apparent?

>

>Thank you in advance for taking the time to enlighten us.

>It would appear that your background gives you an unusual

>(unique?) ability to give us the perspective of the original

>design intentions for these speakers. I eagerly await your

>response.

>

>Thanks Steve

[Guest SteveG]

Thanks to Ken and others for the advice. Looks like there is little risk in leaving well enough alone. Sounds good to me.

SteveG

[stan461]

Is there such a device as a capacitor tester?

[Guest dogmeninreno]

>Is there such a device as a capacitor tester?

Sure is. The problem I have found is that the testing device and the ear don't always agree with each other. The old AR caps usually were fine. They seemed to use a top of the line cap. Dale in Reno.....

[kkantor]

Almost all multimeters today include some kind of cap tester. But they are very primitive. Better testers, ones that can really test a cap under a variety of signal conditions cost upwards of $5K, and take a bit of knowledge to use. Even then, you have to take data at a number of points and analyze it.

Hey, those old drugstore "tube testers" sure sold a lot of tubes....

[Guest]

>Think about caps just like you think about vacuum tubes. (If you think about vacuum tubes.) <

Ken, or anyone who knows something, I've got this creepy problem with the tweeters in my AR 9s that I've discussed elsewhere.

My choices are: To try to find a real original AR9 tweeter said to be good, try to find a couple of matching replacement tweeters said to be good, or try changing tweeter caps and see if the two drivers I have are fine and it's the capacitors which are causing me to twist my head sideways like a dog being whistled to at close range.

I have inspected the crossovers for any sign of anything strange and can't find a thing that looks, feels, smells burned.

One of the electrolytics in the AR 9 crossover is a 6uF 50V. I can't find any. Not anywhere. Not in town, not on the internet.

Mylar or Poly I can find in that value.

Everything considered, I thought I might try capacitors without destroying the old ones. If the difference in sound between the two cabinets goes away I leave the new caps in. If the difference changes, but is still there, I reattach the old caps and cut the leads on the new ones. Back to square one: driver trouble.

So here's the question: If I get capacitors and find that they fix the difference in sound, what capacitors do I want to leave in there?

Mylar? I'm really not worried about the cost of four, even a terribly expensive four, capacitors. I am worried about goofing-up the original sound of the speaker. But I don't have the original sound now and I have to find the ugly pieces and cut them out.

Bret

[mrdb]

Capacitors do change characteristics and/or fail over time. Non-polar electrolytics have higher rates of failure than other dielectrics, such as polypropylene or polycarbonate. I don't know what type of capacitor is used in the AR. If you have access to a digital multimeter (especially one with a capacitance measurement function) you can check the capacitors. The typical failure modes will be a change in value, especially in the electrolytic types, leakage across the cap, and an increase in equivalent series resistance (ESR). You can measure leakage across the cap with an ohmmeter. ESR is more difficult to determine and requires more equipment and work. It sounds like you have access to the crossovers, so measure the caps (disconnected at one end) if you have a meter, or just replace them with an equivalent value polypropylene cap. I recently picked up a pair of KLH Five speakers with no tweeter output from either cabinet. The culprit turned out to be a dual-section non-polar electrolytic. The same cap was bad in each cabinet. I went ahead and replaced all of the caps in each crossover. I have more work to do (such as resealing the cloth surrounds), so I cannot comment on the ultimate sound quality quite yet. Walt Jung and Richard Marsh published an excellent article on capacitors and their sound relative to dielectric type, in Audio Magazine (February 1980 I believe). Here is a link. You might find it interesting. http://www.capacitors.com/pickcap/pickcap.htm

Bob

[Guest]

>You might find it interesting. <

I'm certainly going to give it the chance to be interesting. Thanks. Poly it is.

Bret

[Guest]

>Walt Jung and Richard Marsh published an excellent article on capacitors and their sound relative to dielectric type, in Audio Magazine (February 1980 I believe). Here is a link. You might find it interesting.<

I found it VERY interesting. . . to the point that I'm really interested in all the stuff in there I just don't understand.

But then, I've been reading white papers on speaker-wire and amplifier loads and all sorts of stuff.

I don't understand much of it, but it's interesting!

Wow.

Okay, if I understand what I read, any at all, there are characteristics of capacitors which aren't quoted. They require "study" to get a reasonable understanding of them. Empirical data sometimes contradicts a "listening test." Good grief.

Am I off into esoterica here and just need to worry about how many uF they've shoved in the can more than what they are made of? If not, how am I ever going to get an aluminum 6uF 50V cap since I can't find one, not one. Would that be any assurance that I didn't change the "voice" of my speakers? It looks to me like these guys are saying "no."

Bret

[Guest Jimmy764]

I own quite a number of AR speakers, AR2ax, AR3, AR3a, AR7, AR17,

AR18, AR38s, AR12, AR25 and of course my latest addition AR9.

The only ones that I have replaced the caps on were the AR3a speakers and those I followed the suggestions contained in the Classic Speaker AR section. Specifically I replaced the tweeter caps with Mylar and the Mid and woofer with non-polarized electrolytic caps. The reason I used electrolytic is because the polypropylene and Mylar were very, very expensive. I could not discern any difference before and after the change. The AR3a had the big bricks acting as capacitors. The AR section has AR3a crossover specs and diagrams which are very useful. I used the exact cap values as diagramed. I have been building and repairing speakers for many years but do not claim

to be golden eared; It's a fun hobby for me and so far my wife and kids have not revolted.

Can you tell me if you know where can I find tweeters for Acoustic research AR25???

I looked everywhere and I cant find anything, and if there is no way for finding them if you know any good replacement???

[redstone7]

Hello to all, I normally lurk in the shadows of those KLH folks but I have to weigh in here in a small way, I have spent some big money on fancy capacitors with varied results, of the two pairs of AR3a's I have here the older series pair sound plain and bass-less now and the newer series 3a's have wonderfull bass and low midrange but the high-mids and treble are weak............I went through Madisound who seems to have the best selection and I bought ClarityCaps using the PX range for the bass and midrange and the SA range for the tweeters!!? I thought it would be a great thing like it was with my KLH Model 5's but it wasn't, those KLH's just sing with the ClarityCaps, the same thing happened with a pair of Altec Model 9's...............I should have just left the caps and the woofer surrounds alone. BUT I'M ONE OF THOSE THAT WANTS LONG TERM RELIABILITY, anyway that's my two cents worth, Rob

[RoyC]

Hello to all, I normally lurk in the shadows of those KLH folks but I have to weigh in here in a small way, I have spent some big money on fancy capacitors with varied results, of the two pairs of AR3a's I have here the older series pair sound plain and bass-less now and the newer series 3a's have wonderfull bass and low midrange but the high-mids and treble are weak............I went through Madisound who seems to have the best selection and I bought ClarityCaps using the PX range for the bass and midrange and the SA range for the tweeters!!? I thought it would be a great thing like it was with my KLH Model 5's but it wasn't, those KLH's just sing with the ClarityCaps, the same thing happened with a pair of Altec Model 9's...............I should have just left the caps and the woofer surrounds alone. BUT I'M ONE OF THOSE THAT WANTS LONG TERM RELIABILITY, anyway that's my two cents worth, Rob

Rob,

I'm guessing that the KLH's really needed the caps, as the KLH originals were notorious for failing. Original AR-3a caps, on the other hand, were of higher quality and have a better track record. The type of caps used in the AR-3a have virtually no bearing on overall bass response or tweeter output, so if you used the original values, the new caps are not the cause of your problems. You used very high quality film caps, so you have ensured long term reliability. Now you can concentrate on your 3a issues.

AR-3a bass response issues are often associated with improper wiring (ie. out of phase) or improper stuffing amounts, assuming the woofers are all original and functioning properly. Hmmm...what did you do to the surrounds?

Many 3a tweeters are showing signs of deterioration, resulting in reduced output.

I would look into these possibilities before second guessing your cap replacements.

Roy

[zaqueing]

Link to the 1980 Audio Magazine is no longer good. Here's a current one.

PICKING CAPACITORS

Walter G. Jung and Richard Marsh

Reprinted from Audio Magazine, February and March, 1980

http://www.reliablecapacitors.com/pickcap.htm

[Carlspeak]

This whole thread feeds perfectly right into my "Good, Bad and Ugly Cap" thread here:

http://www.classicspeakerpages.net/IP.Board/index.php?showtopic=6354&pid=90898&st=0entry90898