Where to buy AR-9 Surround parts?

[Pete B]

Your welcome David,

Feel free to email or post more questions.

I don't want to over worry here many would probably just refoam and go with it but I'd at least change the tweeter and mid series caps, a total of 3 per system.

Pete B.

[dynaco_dan]

>Your welcome David,

>

>Feel free to email or post more questions.

>I don't want to over worry here many would probably just

>refoam and go with it but I'd at least change the tweeter and

>mid series caps, a total of 3 per system.

>

>Pete B.

Hi David;

I'm always a little behind, but now I will add my 2 1/2 cents worth.

You started off with the same problems most all of us have, at least those that own speakers with foam surrounds.

My suggestion would be to do what costs you the least stress and money first.

I believe that you should re-foam the necessary drivers only now.

Printout all of the members comments that have been directed to your original write-up.

Live with the knowledge of what changes you can do in the future as budget allows.

Re-foaming can't be put off, caps can.

You have more knowledge at no cost now, you can also, in the mean time, explore this wonderful site for past topics pertaining to similar issues.

Good luck with your choices and please keep us up to date with your progress or questions.

Hifi is a very relaxing hobby.

[Guest Bret]

>I'm sort of confused in this part. Should I go with high end caps or just some caps of proper capacitance from radio shock? Does it make any difference?<

You're confused!? At least you keep good company.

It makes a difference, and my experience is that the difference is *not* highly questionable. But be careful around here when discussing capacitors.

Remember first lines of the Desiderata,

"Go placidly amid the noise and haste,

and remember what peace there may be in silence.

As far as possible without surrender

be on good terms with all persons.

Speak your truth quietly and clearly;

and listen to others,

even the dull and the ignorant;

they too have their story."

I really don't even want to "go there" about caps. It's been the subject of an amazing amount of debate and frankly, I don't have the gear to test-for "correctness" in the end-result. (an anechoic chamber for starts) So your guess is as good as mine as to what might be the most "correct."

Maybe this'll help you decide what to do, though:

An 80uF non-polar (sometimes called bipolar) electrolytic capacitor costs $1.80.

An 80uF "Solen" metallized poly cap is $19.75 in the 400V version.

A Jantzen 80uF poly cap is $23.21.

A "Dayton" 80uF poly cap would also have to be "built" of smaller values and would be in the neighborhood of $18.00.

A North Creek 80uF cap would have to be two caps, also, and would cost about $56. Starts getting expensive. . .

An 80uF "Kimber Cap" would have to be "built-up" from smaller values and would cost well over $100.

And we could go up and up from there.

And then there are all the other possibilities.

"Other possibilities?" you ask?

Yeah like, well, let's say you mixed and matched capacitor types to build-up specific values hoping to avoid the worst performance, but not being too obsessed about the best. You might put a 68uF electrolytic with a 10uF poly with a 2uF film and foil, save money over buying an esoteric 80uF poly and. . . who knows? Maybe you would have the very best possible solution!

In the library is the story of someone restoring an AR-94. They were very thorough in building-up replacement capacitors and used "square waves" and an oscilloscope to determine which combinations of which capacitors at what specific stepped-values passed the square waves most cleanly. . .and then went with that combination. I don't have the wherewithall or parts-bins available for that and I'm not convinced the test is valid, but it "sounds good," doesn't it? You could sell that idea day-in and day-out whether it has any merit or not.

_________________________________________________________________

I know this is getting long, but just keep going a little while longer.

_________________________________________________________________

One thing several of us have found is that the higher-quality capacitors make more difference in the smaller values. That is, you might could do a 70uF non-polar electrolytic and a 10uF poly to "form" an 80uF cap and not be able to tell much difference between it and paying more for a single poly cap.

I doubt seriously that you'd gain much by spending $100+ on "audiophile" caps over a $20 Solen for an 80uF.

BUT. . . once you get down to the 20s, 10s, 8s, 6s, 4s. . . somewhere in there it gets more critical at the same time that it gets less costly. I cannot tell you exactly where the change occurs; I don't know, and it may be a continuum. So depending on your budget you may decide to buy really excellent 4, 6, and 8uf caps; then get not-quite so expensive 10-40uF caps, then get modest 80-470uF caps, then go el-cheapo if you replace the 2500uF cap. I would always by-pass (that is, parallel a small poly cap along with) any eletrolytics I used.

A 4uF electrolytic is $0.40, a North Creek poly is $4.55. The Solen is $2.50, the Dayton is $1.85. You need two 4uF caps if I remember correctly so you can spend from $0.80 to $9.00, but even if you wasted the $8.20 (and you don't), in the overall scheme of things you haven't wasted much. If you get Solens at $5.00, by not going with the "audiophile" North Creek caps you save a whopping $4.00 per pair!

Shunning the light for $4.00 is a decision only you can make.

Now, having told you all the possibilities I'll tell you that I won't use anything but poly caps again and I'll "by-pass" the small values with a fractional "film and foil" type cap. Why? Because that has yielded a really nice result in one of my "experiments."

My Radio Snack doesn't keep enough capacitor inventory to be of any help with this. If you use an eletrolytic capacitor you have to use a "non-polar" type. The easiest thing to do is to order online from Parts Express, Madisound, Mouser, Digikey or someone else of your choice.

Again, I leave you with excellent news:

No matter which type of capacitor you decide to use, any of the new capacitors will sound better than the old out-of-spec caps and will protect your drivers. Since you have not had extended listening experience with the 9s, nor will you have an A/B possibility, no matter what you choose to do you will be thrilled with the result.

The info you want is here:

http://www.classicspeakerpages.net/dc/dcbo...mesg_id=5&page=

Check-out the jpg in the second message. I only corrected it. We share someone else's excellent effort.

A little more Desiderata seems prudent at this point:

"Avoid loud and aggressive persons,

they are vexations to the spirit.

If you compare yourself with others,

you may become vain and bitter;

for always there will be greater and lesser persons than yourself.

Enjoy your achievements as well as your plans."

I've been as much help as I can be at this point.

Bret

[dynaco_dan]

>>I'm sort of confused in this part. Should I go with high end

>caps or just some caps of proper capacitance from radio shock?

>Does it make any difference?<

>

>You're confused!? At least you keep good company.

>

>It makes a difference, and my experience is that the

>difference is *not* highly questionable. But be careful

>around here when discussing capacitors.

>

>Remember first lines of the Desiderata,

>

>"Go placidly amid the noise and haste,

>and remember what peace there may be in silence.

>As far as possible without surrender

>be on good terms with all persons.

>Speak your truth quietly and clearly;

>and listen to others,

>even the dull and the ignorant;

>they too have their story."

>

>I really don't even want to "go there" about caps. It's been

>the subject of an amazing amount of debate and frankly, I

>don't have the gear to test-for "correctness" in the

>end-result. (an anechoic chamber for starts) So your guess is

>as good as mine as to what might be the most "correct."

>

>Maybe this'll help you decide what to do, though:

>

>An 80uF non-polar (sometimes called bipolar) electrolytic

>capacitor costs $1.80.

>

>An 80uF "Solen" metallized poly cap is $19.75 in the 400V

>version.

>

>A Jantzen 80uF poly cap is $23.21.

>

>A "Dayton" 80uF poly cap would also have to be "built" of

>smaller values and would be in the neighborhood of $18.00.

>

>A North Creek 80uF cap would have to be two caps, also, and

>would cost about $56. Starts getting expensive. . .

>

>An 80uF "Kimber Cap" would have to be "built-up" from smaller

>values and would cost well over $100.

>

>And we could go up and up from there.

>

>And then there are all the other possibilities.

>

>"Other possibilities?" you ask?

>

>Yeah like, well, let's say you mixed and matched capacitor

>types to build-up specific values hoping to avoid the worst

>performance, but not being too obsessed about the best. You

>might put a 68uF electrolytic with a 10uF poly with a 2uF film

>and foil, save money over buying an esoteric 80uF poly and. .

>. who knows? Maybe you would have the very best possible

>solution!

>

>In the library is the story of someone restoring an AR-94.

>They were very thorough in building-up replacement capacitors

>and used "square waves" and an oscilloscope to determine which

>combinations of which capacitors at what specific

>stepped-values passed the square waves most cleanly. . .and

>then went with that combination. I don't have the

>wherewithall or parts-bins available for that and I'm not

>convinced the test is valid, but it "sounds good," doesn't it?

> You could sell that idea day-in and day-out whether it has

>any merit or not.

>

>_________________________________________________________________

>

>I know this is getting long, but just keep going a little

>while longer.

>

>_________________________________________________________________

>

>One thing several of us have found is that the higher-quality

>capacitors make more difference in the smaller values. That

>is, you might could do a 70uF non-polar electrolytic and a

>10uF poly to "form" an 80uF cap and not be able to tell much

>difference between it and paying more for a single poly cap.

>

>I doubt seriously that you'd gain much by spending $100+ on

>"audiophile" caps over a $20 Solen for an 80uF.

>

>BUT. . . once you get down to the 20s, 10s, 8s, 6s, 4s. . .

>somewhere in there it gets more critical at the same time that

>it gets less costly. I cannot tell you exactly where the

>change occurs; I don't know, and it may be a continuum. So

>depending on your budget you may decide to buy really

>excellent 4, 6, and 8uf caps; then get not-quite so expensive

>10-40uF caps, then get modest 80-470uF caps, then go el-cheapo

>if you replace the 2500uF cap. I would always by-pass (that

>is, parallel a small poly cap along with) any eletrolytics I

>used.

>

>A 4uF electrolytic is $0.40, a North Creek poly is $4.55. The

>Solen is $2.50, the Dayton is $1.85. You need two 4uF caps if

>I remember correctly so you can spend from $0.80 to $9.00, but

>even if you wasted the $8.20 (and you don't), in the overall

>scheme of things you haven't wasted much. If you get Solens

>at $5.00, by not going with the "audiophile" North Creek caps

>you save a whopping $4.00 per pair!

>

>Shunning the light for $4.00 is a decision only you can make.

>

>

>Now, having told you all the possibilities I'll tell you that

>I won't use anything but poly caps again and I'll "by-pass"

>the small values with a fractional "film and foil" type cap.

>Why? Because that has yielded a really nice result in one of

>my "experiments."

>

>My Radio Snack doesn't keep enough capacitor inventory to be

>of any help with this. If you use an eletrolytic capacitor

>you have to use a "non-polar" type. The easiest thing to do

>is to order online from Parts Express, Madisound, Mouser,

>Digikey or someone else of your choice.

>

>Again, I leave you with excellent news:

>

>No matter which type of capacitor you decide to use, any of

>the new capacitors will sound better than the old out-of-spec

>caps and will protect your drivers. Since you have not had

>extended listening experience with the 9s, nor will you have

>an A/B possibility, no matter what you choose to do you will

>be thrilled with the result.

>

>The info you want is here:

>

>http://www.classicspeakerpages.net/dc/dcbo...mesg_id=5&page=

>

>

>Check-out the jpg in the second message. I only corrected it.

> We share someone else's excellent effort.

>

>A little more Desiderata seems prudent at this point:

>

>"Avoid loud and aggressive persons,

>they are vexations to the spirit.

>If you compare yourself with others,

>you may become vain and bitter;

>for always there will be greater and lesser persons than

>yourself.

>Enjoy your achievements as well as your plans."

>

>I've been as much help as I can be at this point.

>

>Bret

Great write-up as usual, Bret;

Even with most technical discussions being way above me, I still enjoy reading them.

I have another 2 1/2 cents worth to add here.

I did read somewhere recently, a person said that even with Solen capacitors of the same values, there was a difference in sound, with the different voltage ratings, I'm guessing now, of 200 volts and 600 volts rating.

There seems to be a universal comment I read of the change in sound as well, for better or worse, in the breaking in period over 40 - 100 hours or so.

I do believe the commenter suggested they improved with usuage.

Long gone are the simplistic .5% Harmonic or Intermodulation amplifier distortion days.

Even seeing waterfall plots in Sterophile Magazine are a different approach compared to early Stereo Review speaker tests.

I see a few strong wills on this web site, very smart people with far more knowledge and experiences than I.

I always look forward to different views and opinions.

Please accept that there will always be differences and even the small steps you suggested above, are a welcome and interesting option for myself to consider as well.

Thank you again for sharing all of your continuing wealth of knowledge.

[Pete B]

I noticed that you asked some other questions in this thread. There are two main concerns when the caps need to be reformed, one is that the capacitance goes up, second the breakdown voltage goes down.

The capacitance increase will move the crossover point down and stress the mid and tweeter far beyond their capabilities. This effect is level independent but the chance for damage is greater as you turn it up. The voltage breakdown means that the cap acts more as a resistor than a cap when the voltage increases beyond the breakdown point and this would be level dependent. The 50V rating on the caps was marginal to start with.

It was stated in this thread that the 2500 uF is not critical, why would AR use an expensive computer grade cap if it was not critical? The fact is that a lot of current flows through this cap and it will age much faster due to heating if a lower grade (higher ESR) cap is used.

Pete B.

[Guest Bret]

You have NO idea how very happy I am that you brought this up. This has been bugging me for years. I hope that being an engineer-type you can turn the only information I have about this into English and make it make sense. I think most of this discussion took place before you came aboard, or at least before you started posting regularly.

In the Library is an article about the AR-9 by Tim Holtz. It says,

“In the AR-9 the method chosen was to control the “Q” electrically as follows:

1. If a resistor is placed in series with the woofer, the “Q” is raised, while the acoustic output is reduced.

2. A woofer has its highest impedance at the system resonance frequency. Two woofers in parallel could safely be used in the frequency range near resonance, but not at other frequencies.

3. If a way can be found to put a resistor in series above and below the resonance frequency, but out of the circuit at and near resonance, the impedance, “Q” and output level might be adjusted to give the ideal system combination.

This is exactly what has been done in the AR-9. At the resonance frequency, the two woofers are in parallel, doubling sound pressure level in that region.”

And later:

“At and near the system resonance frequency, the choke and capacitor are essentially a short-circuit; the presence of the resistor is irrelevant. As the signal frequency increases, the impedance of the resonant circuit also goes up - - and the speaker system output goes down! By selecting precise values for the components, and using a choke coil with low internal resistance, “Q” and impedance are smoothly controlled to yield extended bass response with full amplifier protection.”

Then the LST manual says this:

“A large capacitor in series with the autotransformer prevents excessive amplifier loading at subaudible frequencies where the transformer’s inductive reactance decreases.”

Pete, as far as I’ve found, even doing a long search through the discussions, this is about as much authoritative information as we have as to the function of these large capacitors.

“Amplifier protection” against ultra-low impedance loads, seems to be the function of these caps in the LST and 10pi and they seem to have a different implementation but essentially the same function in a 9.

The shame of it is that as much as I’d like to do a little “experimenting” I feel like the “curve” of the 2500uF cap’s going resistive would be particularly critical and changing that to a more linear poly would be a mistake.

I also think (if you can call this thinking) I see that the “crossover point” of this capacitor is somewhere in the 19Hz range, meaning that it “becomes” essentially a wire somewhere in the really low frequencies. If the cap is increasing with age (and oddly, these seem to remain almost right on “spec” uF-wise, while even the huge can 470uF seems to drift) the point at which the cap “becomes” a wire is actually getting further and further from audibility. Whatever a terrible aged capacitor DA and DF measure is doing, it’s doing most of the damage where sound is felt more than heard, so while a test instrument might pick this up rather easily, my ears really don’t know what a 28Hz pedal tone sounds like anyway (and my room may not even allow me to hear it). My guess (listening to recapped speakers without this monster cap in them) is that whatever effect this cap is having, it’s having almost no effect by the time the frequencies reach the point where ears can identify a sound.

But I admit that I could be SO far off-base with all of this that I’m embarrassed to even tell you how I was thinking about it. But. . . well, I’m not afraid to look stupid if it causes someone to correct me and we all learn something. I couldn’t figure-out how to “model” it with the software that I had (my Thinkpad died and I lost it all).

So, again, I’m REALLY glad that you brought this up and hope you can tell me whether I have anything right or everything wrong. I’m going to venture-into my 10pi’s again soon and it would be no problem to replace one 2500uF cap with 2500uF of cheap poly caps or electrolytics and see if it makes a difference. Would you think this is a worthwhile “experiment?” Since it is non-destructive, I don’t mind doing it.

Oh, one more data-point for you. When AR was using Sprague Compulytics the 2500uF in the 10pi was a Compulytic. In the AR-9 this became a “Callins” and I’m not sure if it’s considered “computer grade” or not. Obviously the original, original LST cap wasn't "computer grade."

I still wish we could get data-sheets for the original caps in these speakers so it would be possible for the hobbyist to closely match all the parameters.

message # 4178 from Rich has as much good information and advice as I've found.

Bret

[soundminded]

I would not experiment with the 2500 mf cap in the woofer circuit of the AR9. This is a component of a critically tuned resonant circuit whose magnitude and center frequency of Q are precisely adjusted to compliment the inverse impedence characteristics of the two AR 12" woofers in parallel in their enclosure. Any change (including an air leak in the enclosure) will alter the performance of the circuit. Even a small change can make a radical difference especially if Q is high. Changing either the magnitude or center frequency by selecting a capacitor with a higher or lower ESR or a different value C risks detuning it and a very low impedence of two ohms or less across the amplifier at some frequencies. It would also alter the bass response negatively by placing the electromechanical speaker resonance and the electrical filter resonance out of sync. This is equivalent to changing the LC filters in the IF stage of a tuner throwing it out of alignment. I waited to respond until I had time to download the circuit again to be sure.

[Guest Bret]

>This is a component of a critically tuned resonant circuit whose magnitude and center frequency of Q are precisely adjusted to compliment the inverse impedence characteristics of the two AR 12" woofers in parallel in their enclosure. Any change (including an air leak in the enclosure) will alter the performance of the circuit.<

Right you are. That was what prevented me from "messing" with it. (that and not being able to hear anything "missing" or "messed-up" compared to other speakers which don't need this big-ol' cap).

But you open a can of worms. I think it has been pretty-well established as fact that these particular old caps are. . .well, old. It is unrealistic to think that they are performing so close to original spec as to make less difference in "Q" than a minor air leak.

So while we are all very happy to have read how to prevent air leaks and we'll all be very careful that our cabinets are sealed and we'll all go to the trouble and expense of trying to get "original" drivers and not alter the wadding. . . without being able to solve this problem we run the potential risk of ignorantly straining at gnats while casually swallowing elephants.

Nobody seems to have the answer, and without an answer our AR-9s die, hence my willingness to "try something / anything," once, anyway.

Or can you reassure me that IF the old caps are garbaging-up the signal that it is mostly happening at subsonic frequencies?

Bret

[soundminded]

Like all things there are the tools of the trade and the skill to use them. There are some here who are perfectly at home with it and able to perform these tasks with great precision having understood both the theory and how to impliment it. And then there are those who could only tinker haphazardly accomplishing little or nothing of value and jeopardizing what they already have. For those, the best advice I think is to at most, replace the capacitor in kind with as close a replacement as they can find and trust to the skill of the original designers keeping the system physically maintained as best they can. If it is clear that there is a problem with this tuned circuit which cannot be resolved satisfactorily this way, then they should get the assistance of someone with the required skill and not experiment with this critical circuit on their own.

[Guest nathanso]

Does this also apply to the 350uF caps in the AR90? I'm looking at recapping and re-edging a set of newly acquired AR90s.

[r_laski]

>>Does this also apply to the 350uF caps in the AR90? I'm looking at recapping and re-edging a set of newly acquired AR90s.<<

Nathanso,

Some of us sucessfully rebuilt AR-90s crossovers with new caps including the 350uF cap. I used a combination of 200uF, 100uF, and 50uF North Creek Zen caps paralleled together. These were extremely discounted at the time, so they were cost effective / comparable to Solens. Solens would be a good choice (IMO). I used a combination of Solens and North Creek Zens in the crossover and was very pleased with the results.

Search this forum for AR-90 threads. Some of us posted details of our projects and our results. I even reported how the AR-90 DID NOT improve when I tried to cut cost by using Dayton caps from Parts Express.

Please start a thread to chronicle your AR-90 project and to request any more assistance. And, please post your results.

Rich

[Guest baumgrenze]

David,

I read through this thread and I think some responders might have read the word "reforming" and not seen that possibly you meant "refoaming." You did mention the word "tear." ar_pro did respond by suggesting Bill Miller, who comes highly recommended here. I just sent him the woofers from a pair of AR-2AX's I bought in 1967. One of the spiders came loose; I blame it on allowing my son to persuade me to watch the film, XMen.

I would direct your attention to a message I stumbled on yesterday when I was digging through the AR Forum.

Take a look at #8033, "RE: Sealing drivers in older AR cabinets" by tysontom. It got my attention.

If the foam surround on your woofers looks torn, I wouldn't pass anything like a strong bass signal through the speakers. Read tysontom's last sentence. "On the other hand, air leaks -- if bad enough -- could cause unrestrained woofer motion at sub-sonic frequencies with the resultant eventual damage that you have described." Then look at the photo of the voice coil below.

Earlier today I asked if "all foam surrounds are equal." I expected the same kind of brisk discussion you got about capacitors. I've garnered no responses.

I'm pleased with the performance of a set of surrounds I installed on a pair of AR-18's (bookshelf speakers with 8" woofers) which were included in the $50 price I paid for a pair of AR-5's at an estate sale. I now want to refoam these and I want to be as well informed as I can be.

[Guest David in MA]

>David,

>

>I read through this thread and I think some responders might

>have read the word "reforming" and not seen that possibly you

>meant "refoaming."

That's what I meant...sorry about that.

>If the foam surround on your woofers looks torn, I wouldn't

>pass anything like a strong bass signal through the speakers.

>Read tysontom's last sentence. "On the other hand, air leaks

>-- if bad enough -- could cause unrestrained woofer motion at

>sub-sonic frequencies with the resultant eventual damage that

>you have described." Then look at the photo of the voice coil

>below.

I used gasket tape from partsexpress to seal in...it seems to work well...so far, anyways...

>

>Earlier today I asked if "all foam surrounds are equal." I

>expected the same kind of brisk discussion you got about

>capacitors. I've garnered no responses.

That I don't know either. You'd think that having different material for the surround will make some difference. As to how much in sound, I can't say...

>I'm pleased with the performance of a set of surrounds I

>installed on a pair of AR-18's (bookshelf speakers with 8"

>woofers) which were included in the $50 price I paid for a

>pair of AR-5's at an estate sale. I now want to refoam these

>and I want to be as well informed as I can be.

I used partsexpress on this site's recommendation. I thought about having it done but the shipping cost was too much for my AR9 woofers...it came out nice and I'm in heaven...