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Latest aquisition - AR91s


DavidR

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I'm always on the lookout for certain AR speakers for the right price. I like to tinker (yes, I'm a British car nut) and audio seems to be the newest flavor. I recently finished restoring a pair of TSW610s and my son chose them over the Polk RTA12C speakers I picked up for him a couple of years ago replacing his Klipsch Heresys.

The guy had these for sale at $100 and I asked what condition they were in. He got back to me a few days later and said the foam was shot and I could have them if I wanted them. I took the hour plus ride today. These were GRUNGY to say the least: Mold, Cobwebs, Spider webs and a yellow substance that looked like pollen. I should have taken pictures but I didn't want to bring them in the house with the mold. I did a clean up that took about an hour and this is what I got>>>

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I feel extremely lucky.

After cleaning them I hooked them up to my son's system and gently played them to see if all the drivers worked. All is good although the tweeters were very dim; but again they were very low volume. The guy had them in his cellar and hadn't used them in years.

I plan on replacing the caps in these and also replacing the binding posts with some nice 5-way posts. I would appreciate any advice on (1) removal techniques of the glue on the back side of the binding posts; (2) how to properly clean the switches. I plan on doing the work with the xover boards in place.

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"I feel extremely lucky."

Lucky indeed. Mildly sour grapes here, but good for you for snagging them. Yesterday morning I was offered the same deal, but then I never heard back from the guy. Those look like they should be fully restorable, and if you need a few new parts, even replacement tweeters, that should be no big deal. Take your time and clean out the cabinet interior well while you're there 'cuz hopefully you'll never have to go in again. Eager to see how they turn out.

As the saying goes, "You snooze, you lose."

Sigh........

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If they are the same speakers then sorry ra.ra

I've had a lot of bad luck with health issues lately.....I guess karma paid me a visit.

Looking for a crossover schematic. I couldn't find one (yet) in the Library.

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Nice catch - we had a pair of these in the mid-'80s, and they had a really well-balanced sound.

There's a chance (I'd put it at 50%) that there's walnut veneer under the brown paint on the speaker's face.

Feel like doing some experimental sanding? :)

Here's another crossover drawing.

post-100370-0-44961000-1402450826_thumb.

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Nice catch - we had a pair of these in the mid-'80s, and they had a really well-balanced sound.

There's a chance (I'd put it at 50%) that there's walnut veneer under the brown paint on the speaker's face.

Feel like doing some experimental sanding? :)

Here's another crossover drawing.

Happy to see you are hanging around.

Thanks for both schematics guys.

I was thinking it looked more like mahogany than walnut; but I'm not a wood expert.

The TSW610s I restored for my son are well balanced as well.

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DavidR,

Thought I could post the AR-91 dwg. documents for the AR-91, but I cannot find my files at the moment. Take a look in the library - - - Acoustic Research - - - Special Sections - - - AR drawings. You'll find lots of info about the AR-91.

"If they are the same speakers....."

does Rochester sound familiar? Bose 201's?

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Great find!

AR-Pro alerted me to a pair available near me for $75!! Here's the thread:

http://www.classicspeakerpages.net/IP.Board/index.php?showtopic=6565#entry94977

Post 7 shows before & after shots of the xo. I went a bit overboard. The can electrolytics may have been OK but if I were doing it today I'd use Masisound surplus caps to build up the 100 and the 24UF values.

My woofers had been refoamed but they looked awful so I sent them to Bill LeGall, who made them perfect.

WONDERFUL speakers. Sad thing is I don't have the right spot for them.

Anyway, Good luck with the restoration. Very well worthwhile. According to Steve F, "A properly-functioning set of 91's is clearly in the 'all-the-speaker-you'll-ever-need' category."

-Kent

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Thanks for the link Kent.

I probably won't get to these until the fall. Too many projects for the fair weather. Need to pull an engine/tranny from an MGB while I'm able and get it ready to sell.

I plan, at this point, to use Erse polyester caps on the 4, 8 and 24uF and their electrolytics on the 40 and 100uF caps.

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Attached are a couple of the AR-91 drawings I was trying to find for you yesterday. These, and several more, can be found in the Library. Not sure if they'll be any help to you, but sometimes I find them of great interest in understanding the original specs or construction of a certain speaker model. The first drawing is an assembly drawing, and I like these because they list all of the original parts, and this particular drawing has an excellent vertical cross section. The second drawing shows the layout and all parts of the crossover - - - not a simple one, with two switches, four coils, five capacitors and six resistors.

Apologies for low resolution quality of these images - - - when downloading from the Library, these tif files range from 2 to 4.5 MB, and I have shrunk the file sizes to near 100 MB jpg files for easy access. If you need more detail, access the Library or let me know if I can help.

Re: ar_pro's guess in post 6 about the (possible walnut) front baffle, one of the cabinet drawings has several notes on finish, and it is clear that both front and rear were intended to be painted.

Regarding x-o capacitors, those sound like really good choices: high performance, excellent value. When you get back to further posts, show us the MGB, too. Who doesn't like a classic British sports car?

post-112624-0-27673500-1402537186_thumb. post-112624-0-97258200-1402537197_thumb.

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Thanks the drawings ra.ra. Actually, I had found all the AR drawings yesterday and downloaded all of the AR91 and TSW610 xover drawings. I already had the AR90 drawings. We have a Samsung Smart TV that gets the internet so the drawings are huge on the screen. You could also use an HDMI cable from the computer to a TV HDMI input. Its great when you have poor vision like I do.

Roy C recommended the Erse polyester (mylar) caps to keep the sound closer to electrolytics vs polypropylene caps. I may go with a mylar 39 or 41uF (they don't make a 40) for the 40uF on the woofer but keep the 100uF an NPE. What do you think? good or bad idea?

I found out how to remove hot melt glue - isopropanol. Those old binding posts are the pits.

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Roy C recommended the Erse polyester (mylar) caps to keep the sound closer to electrolytics vs polypropylene caps. I may go with a mylar 39 or 41uF (they don't make a 40) for the 40uF on the woofer but keep the 100uF an NPE. What do you think? good or bad idea?

Roy also recommends Carli, sold by Madisound for the same reason. Carli caps are economical. And I already told you about the Madisound surplus caps. An NPE is fine for the 100uF. Just plan on replacing it in 30 years or so :D

-Kent

Looking at what's available, you need one each of the following per speaker: 4, 8, 24, 40, 100uF.

Here are some options:

Carli

3.9 ($1.35),

8 ($2.35),

20 ($5.95) . You'll have to make up the 24 with a 20+3.9, and the 40 as 2x20.

Bennic

NPE 100uF $2.95

Surplus Mylar

2.0uF $0.35 These have short leads but can be used for the 4uF and as part of the 24uF

Surplus Polypro

10uF $0.60 each. Can't beat these (and Roy uses them). Make your 20uF and 40uF values and save a bundle

Erse PEx

4.0 $1.23
8.0 $2.12
20.00 $4.14 (no 24 so parallel this and a 4.0uF)
39.00 $5.00 (no 40 but close enough)

Erse 6% NPE

100uF $1.31

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Thanks for all that info Kent. I hadn't noticed that the Erse 24uF polyester cap was min order of 500.

I'm very hesitant to use polypropylene caps because I've read many posts it will tilt the speaker's voice UP /brighter and I wouldn't like that.

What do I gain by using a polyester cap for the 40uF vs NPE for both the 40 and 100 caps on the woofer?

If I get 20 years from an NPE, I'm good. Might outlast me.

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This may be heresy--and I'll admit I use film whenever possible--but NPEs are perfectly fine for ALL the caps, but particularly the larger values.

Kent

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  • 2 weeks later...

I had some spare time the other day and decided to open up one of the speaker cabinets. Here's a couple of pictures of the xovers. I took the hot melt glue off the caps. There wasn't any glue on the binding posts - happy about that.

I've been reading stuff online about characteristics of different capacitor types. One article was down on mylar so I'm contemplating using Dayton polys for the 4, 8 and 24 and possibly Bennic NPE over the Erse for the 40 and 100uF. Does any one have an opinion on Bennic vs Erse NPE?

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I've been reading stuff online about characteristics of different capacitor types. One article was down on mylar so I'm contemplating using Dayton polys for the 4, 8 and 24 and possibly Bennic NPE over the Erse for the 40 and 100uF. Does any one have an opinion on Bennic vs Erse NPE?

  1. You will make yourself crazy "reading stuff online" about capacitors. Most is complete hooey.
  2. Mylar caps are a good choice. So are poly.
  3. Your 40 and 100uF caps are probably fine. You could buy a cheap LCR meter to check. About $15 on ebay.
  4. There is absolutely no difference whatsoever in quality/desirability or "sound" between Bennic & Erse NPEs.

-Kent

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You are absolutely correct with item #1.............and I am being driven crazy. Here's a link to the article that has made me consider poly caps : http://conradhoffman.com/cap_measurements_100606.html

I have an LCR meter from Parts Express but would probably want to replace them all while I'm in there even if they test OK.

Thanks for your input. This is my 1st attempt at xover rebuilding.

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DavidR,

Just curious.....did you remove the inner acoustic blankets that surround the tweeters and the mid-range speakers?

And confirming what ra.ra extracted from the drawings, the baffles and rear faces of my AR-91s are painted brown.

I replaced the foam surrounds several years ago. Otherwise, the speakers are original.

For a listening point-of-view, I believe that the AR-91s sound better than my AR-3s.

Steven

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@ Sadams: The foam around the tweeters and Mids had totally fallen apart and was all over the speakers.

I'm on the lookout for replacements.

There's only a few spots along the corner edges that need touch up with either the brown paint or stain.

Any recommendation on re-capping?

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  • 2 weeks later...

Here's a link to the article that has made me consider poly caps : http://conradhoffman.com/cap_measurements_100606.html

That site has other interesting articles, including a couple about upgrading Dynaco preamps. The author is a good guy and recommended some helpful edits for my KLH Model Eight restoration guide.

Having said that, I'll still use Mylar caps in speaker crossovers. And if the big metal "can" caps test OK (no more than 10% off) they may be better than new NPEs.

-Kent

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