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Replace caps on AR 11s


Guest jsbegg

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Guest jsbegg

I have an original pair of AR 11s that are in very good condition. (new woffers installed about 4 years ago) With all the discussion I have read here today I have to ask, would there be any benefit for me to rebuilt the crossovers (caps) and where would I find information on how to do this?

Thanks

John

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Based upon my own experiences with my speakers and other speakers I've heard before and after new caps were installed, I would have to say absolutely yes. Do your homework finding the right values and get at the least Solen caps as they tend to be a good value for the dollar spent. If you don't properly form the caps before installing them into the crossover, be prepared for your speakers to sound harsh for a few hours until they settle down. And if you do form the caps, be very aware that Poly caps hold a charge for a very long time and need to be discharged properly to avoid being shocked.

As for the schematic, I believe one is available on the classic speaker pages under Acoustic Research.

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>>...would there be any benefit for me to rebuilt the crossovers (caps) and where would I find information on how to do this?<<

John,

Welcome to the AR forum.

You have come to the right place! Within this forum are threads that discuss replacing AR-11 electrolytic caps with modern polypropylene caps. I’ve just recently (within the past month) finished rebuilding my Dad’s AR-11 crossovers – my 5th and 6th AR-11 rebuilds. You can search the threads and if you have any questions ask away.

Rich

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>Is the AR-11 crossover schematic in the archives correct?<

If you are referring to the series wiring of the 50+72uF capacitors, no, it is not.

That's supposed to be a 120uF capacitor, not a 50 and a 72 in series.

Is there something else in question?

Bret

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Hi Bret,

I was wondering if the inductor values are correct as well. Is the woofer inductor 2.35mh and not the 2.85mh (#9) found in the AR-3a?

I'm thinking of putting one together to try with the reworked Tonegens.

Roy

PS Enjoyed your woofer posts and totally agree...the Woofer Overlord is smiling so far :-)

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Roy,

Re: the inductor. If you look at Rich's "subjective testing" thread, near the bottom, he's got PHOTOS!

It sure looks like a #9 to me.

Bret

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Roy,

The answer is yes, and no. In other words, it depends on when your AR-11s were built. You need to have the schematic in front of you as you read this post. (It took a couple hours to compose)

In another thread, I’ve posted pictures of two different AR-11 crossovers. One is very similar to the schematic in the archives. The “early” crossover was constructed on two boards. One small board mounted to the inside back and a large board mounted on the inside bottom of the cabinet.

The other is a “newer” crossover. If I could read the revisions (upper right corner) on the AR-11 system assembly blueprint I could tell you what date the crossover changed (revision “D”) , and when the fuse was deleted (revision “B”).

On the schematic:

If you have a very early AR-11 -- brass logos / binding posts and equalization switches are side by side – the schematic in the archives is “correct” with the following exceptions:

1) Can’t read the date, but very early on, possible pre-production, the fuse was eliminated.

2) The 72 MFD and 50MFD caps in the woofer circuit are actually paralleled, not in series.

To clarify some of the values:

1) Both equalization switches have a 3 Ohm and a 1.5 Ohm resistor.

2) The capacitor in the tweeter circuit is 10 MFD. (it looks like “101”)

3) The woofer inductor is 2.85 mH. (it looks like “2.35”) Another forum member and I resolved this a while back when he had to build AR-11 crossovers from scratch.

Note: The dot on the driver signifies the “marked” or “+” terminal of the speaker.

In addition to consolidating everything onto one board and getting rid of the terminal strip, the newer crossover has the following changes:

1) The midrange and tweeter caps were moved to the “+” side of the circuit -- connected to the red / “+” binding post. In the circuit, they come before the equalization switches.

2) A single 40 uF cap was used instead of paralleling two 20uF caps.

3) A single 120 uF cap was used instead of paralleling a 72uF and 50uF cap.

4) Different switches were used. Old- DPDT (on, on, on) New- SPDT (on, off, on)

5) The 3 Ohm tweeter equalization resistor was changed to 5 Ohm – 1.5 Ohm remained.

6) The 1.5 Ohm midrange equalization resistor was changed to 3 Ohm.

7) The 3 Ohm midrange equalization resistor was changed to 10 Ohm.

8) There is a significant difference in how resistors on the equalization switches are wired on the new crossover. The old crossover is as depicted on the schematic – in “series” on the positive side. On the new crossover The 5 Ohm tweeter resistor and the 10 Ohm midrange resistor is connected to the negative binding post.

Have I totally confused everyone yet? I had to draw wiring diagrams for both crossovers and compare / redraw the schematic for the newer crossover before I attempted rebuilding any crossovers.

When I rebuilt the older crossover, in addition to replacing the capacitors, I changed the switches and resistors. I rewired the circuit to the newer configuration. I had to use two board because the brace behind the woofer is lower on the back of the cabinet.

Rich

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Wow, thanks Rich....for both AR-11 threads! Its interesting to see the evolution of the AR-3a to the AR-11. It seems AR was struggling to replace those miserable pots with something more reliable in the AR-11. That and the new tweeter with its associated parallel inductor being the other notable difference.

Since this is the cap question thread...

At least in AR-3a's, my experience has been that replacing the 30 year old caps (that measure within spec) have a greater benefit to my peace of mind than to the sound.

Roy

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>What would be the best caps to buy regardless of price?<

John, sorry for the thread-drift.

If there is an answer to your question based on facts, I don't know it.

When you remove price as a consideration, then the audiophile community has a tendency to go a little nuts and get all alchemist on us.

If you haven't read the capacitor information available at

http://wwww.Northcreekmusic.com

I would encourage you to do so. Which capacitor is best is quite a can of worms up-to and including which capacitor is best for "this and that" tweeter, midrange, what-have-you. I am not suggesting that Northcreek's site contains the answer, but it does illustrate the problem with their being an answer.

As far as I know, nobody here has had the luxury of trying tens or hundreds of capacitor combinations to arrive at "best."

The absolute AR-conservators here have said, "don't fix them unless they are out of spec." I agree with them; I just suspect that they are all out-of one spec or another spec at their age.

I've tried two different cap brands with no clear indication that spending 10 times as much buys you 1.5 times the result, but I have a third, possibly foolish, trial-and-error experiment I'm going to try next (combining cheap and expensive caps in bundles).

Supposedly that yields a "best of each" result rather than a "worst of each" result, but I cannot confirm that. Shoot, I can't even confirm that the difference in cheap and expensive is audible and Rich has said that for him, comparing in-spec oldies to moderately expensive goodies, the difference isn't audible.

I know you wanted "the answer." I hope that I've at least given you enough information to know why that answer isn't available as verifiable fact.

If you rephrase the question to "what do you suggest?" Then I would suggest you do what I'm about to try (e.g. combining a 33uF 100v NP electrolytic with a 6.8uF 400v poly with a .22uF 600v film and foil to get 40uF total) That's slightly less expensive than buying a single high-quality 40uF capacitor and considering how little difference there seems to be between inexpensive and expensive caps, at least I believe the result will be acceptable if not mystical.

Bret

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John,

>>Thanks for all the information. What would be the best caps to buy regardless of price?<<

As Bret stated, you may have opened a “can of worms” by asking the “ money no object, best” question.

What Bret suggested is to experiment with bypassing. That’s an advanced solution that involves as much art as it does science. I’m not criticizing what Bret is going to do, I encourage him to experiment. I’m curious to read about what he finds out. I only point out that it is more involved than a one-for-one capacitor replacement.

If, by your question, you meant, “what do you suggest?” I can make some recommendations. You do not need to buy the most expensive boutique brand capacitors to get outstanding results.

In all my AR11 rebuilds I used North Creek Zen caps -- 100uF and 20uF paralleled for the woofer, 40uF for the midrange, and 10uF for the tweeter. When I bought these caps, they were on sale, (trying to reduce inventory prior to moving to a new, larger facility). They were a bargain and very price competitive with Solens. IMO the Zens are a wonderful cap and can only be improved upon by bypassing with Harmony or Crescendo caps, but this IS NOT necessary for the AR11. Because of their size you must rebuild the crossover on a separate board and move components around to get everything to fit. In the picture below, the woofer section is moved to the bottom, the midrange section to upper right, and the tweeter to the upper left.

http://www.classicspeakerpages.net/dc/user_files/337.jpg

If you don’t want to go that route, you MAY be able to fit Axon (a premium grade cap made by Solen) or Solen caps on the existing board. I was very pleased with the results of mixing Zens and Solens in a pair of AR90s after the Dayton’s didn’t work out.

Rich

post-100657-1111509086.jpg

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