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AR 3a Restoration


Shacky

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Finally starting digging into my recently acquired AR 3a. Serial numbers 53022 and 54211. Purchased from original owner in Rochester NY with guidance from Onplane (Jerry). Original owner said he purchased them while in the service in Hawaii in the '70's. They are in great shape. While I have them apart I'm going to go through them with new Caps, possibly new pots, re-foam woofers and general touch up.

First thing I notice is these are later serial numbers with earlier caps. I know to expect anything from AR. The tweeter cap on one is straight 6 uF and the other is a dual 6/2 :rolleyes: Must have been a special on the duals :P

Geez these woofers are built like a tank. I think you could set up an MRI with these magnets :)

I see the restoration guide recommends placing small resistors in series with newer caps to compensate for lower ESR than originals. Has anybody actually tried this? I'm using Dayton 100 + 50, 50, and Solen 5.9 (thinking of adding bypass cap - some russian military grade 0.047 I picked up and had great success with JBL L36 resto).

I have a set of new Ohmite pots I've been saving. But will check out the original pots first to see what shape they are in.

Want to wrap this up in next couple of days. Any advice or tips are welcomed.

Some pics of the speakers and crossovers:

IMGP3122.jpg

IMGP3178.jpg

IMGP3174.jpg

IMGP3176.jpg

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I see the restoration guide recommends placing small resistors in series with newer caps to compensate for lower ESR than originals. Has anybody actually tried this?

I did exactly that when restoring my 3As and my LSTs. Of course, I have no idea of the actual sound difference between doing this and not doing it (resistors) because I did not try them both ways. I based the decision on info provided by several people who are directly responsible for writing the restoration guide. They have a lot more knowledge than I do about the specifics and why it should be done. That being said, there is some controversy even among the experts as to whether it really matters or not.

I can say that the speakers, all with oem AR drivers, sound absolutely wonderful. Both sets will provide more treble response than I can deal with which makes me wonder about the claims that they are "laid back" speakers. They work perfectly with any sound source and any kind of musical material from solo violin to current pop/rock offerings. I think it would be difficult to match a properly restored AR3a with any currently available loudspeaker. I'm not sure you could match an LST at all - at least at any sane price.

I have a pair of Mageplanars and a Hsu Subwoofer in another room. I have always been impressed by their ability to develop a sound stage and their open/airy character. Of course the HSU will go WAAAAY down in the bass. The LSTs out perform this combination. True, they won't go as low but the sound is much better integrated and, on musical material, there is no apparent difference though I admit I don't listen to organ music which would show the HSU's ability to reproduce 20HZ.

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Hoping some of our experts can chime in. Does the variance in ESR have any effect on the crossover frequencies? And likewise does adding the resistor change the crossover frequency given the new caps have original uF rating?

If it's just a matter of toning down the tweeter and mid, can't I just do that with the pots? I plan to use new Mem Cor 15 OHM pots.

I was just playing around with the Mem Cors, originals, and some 8 Ohm L-Pads I had previously purchased for 2AX project but didn't like the sound. If I measure DMM across tabs 1 and 2, then B to 1 I get following:

Originals

1-2 constant 15.5 Ohm throughout renge

B-1 15.6 to 0.3

Mem Cors

1-2 constant 15.6 Ohm thoughout range

B-1 15.3 to 0.2

L-Pads

1-2 (infinity all the way) Just off full 40.7 to 8.4

B-1 (infinity all the way) just off full 40.2 to 0.2

Have no idea how to interpret but sure shows L-Pads ain't Pots :rolleyes:

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Hoping some of our experts can chime in. Does the variance in ESR have any effect on the crossover frequencies? And likewise does adding the resistor change the crossover frequency given the new caps have original uF rating?

If it's just a matter of toning down the tweeter and mid, can't I just do that with the pots? I plan to use new Mem Cor 15 OHM pots.

I was just playing around with the Mem Cors, originals, and some 8 Ohm L-Pads I had previously purchased for 2AX project but didn't like the sound. If I measure DMM across tabs 1 and 2, then B to 1 I get following:

Originals

1-2 constant 15.5 Ohm throughout renge

B-1 15.6 to 0.3

Mem Cors

1-2 constant 15.6 Ohm thoughout range

B-1 15.3 to 0.2

L-Pads

1-2 (infinity all the way) Just off full 40.7 to 8.4

B-1 (infinity all the way) just off full 40.2 to 0.2

Have no idea how to interpret but sure shows L-Pads ain't Pots :rolleyes:

Going from memory here, there is no shunt inductor on the 3a tweeter so there is

really no need to add the ESR resistor. You are correct in that turning down the

pot has the same effect.

The midrange does have a shunt inductor so you would want to add an ESR resistor

there as it primarily impacts the Q of that crossover section.

The woofer section, updated by AR usually included a computer grade

electrolytic which has very low ESR and therefore there is probably no reason to

include the ESR resistor there. I do seem to recall measuring some peaking in the

woofer XO lowpass and it could be toned down a bit by adding .33 to .5 ohms in

series with the woofer cap.

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Having done much experimentation, I am of the opinion that ESR compensation resistors are not necessary at all in the 3a. The old drivers, especially the tweeters, are variable in response these days, and ESR compensation is, at best, a shot in the dark in terms of expected outcome.

I lobbied for it not to be included in the 3a restoration document, as I didn't want folks to become concerned with such tiny details. In the end it was agreed to include it, if for no other reason than it is something that exists and can be experimented with. (Very slight sonic differences can sometimes be heard, but they are not necessarily better or worse in my 3a experience.) Further, capacitor testing conducted by John O. after the document was completed suggests that the ESR of the original electrolytic caps was likely lower (when new) than we previously anticipated.

The bottom line is that the issue is not worth losing sleep over, and they will never make or break a 3a restoration whether you add them or not.

Roy

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Agreed.

Although I was in favor of including the compensation resistors in the document, (primarily for pedagogic reasons), I concur completely with Roy's assessment below.

-k

Having done much experimentation, I am of the opinion that ESR compensation resistors are not necessary at all in the 3a. The old drivers, especially the tweeters, are variable in response these days, and ESR compensation is, at best, a shot in the dark in terms of expected outcome.

I lobbied for it not to be included in the 3a restoration document, as I didn't want folks to become concerned with such tiny details. In the end it was agreed to include it, if for no other reason than it is something that exists and can be experimented with. (Very slight sonic differences can sometimes be heard, but they are not necessarily better or worse in my 3a experience.) Further, capacitor testing conducted by John O. after the document was completed suggests that the ESR of the original electrolytic caps was likely lower (when new) than we previously anticipated.

The bottom line is that the issue is not worth losing sleep over, and they will never make or break a 3a restoration whether you add them or not.

Roy

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Having done much experimentation, I am of the opinion that ESR compensation resistors are not necessary at all in the 3a. The old drivers, especially the tweeters, are variable in response these days, and ESR compensation is, at best, a shot in the dark in terms of expected outcome.

I lobbied for it not to be included in the 3a restoration document, as I didn't want folks to become concerned with such tiny details. In the end it was agreed to include it, if for no other reason than it is something that exists and can be experimented with. (Very slight sonic differences can sometimes be heard, but they are not necessarily better or worse in my 3a experience.) Further, capacitor testing conducted by John O. after the document was completed suggests that the ESR of the original electrolytic caps was likely lower (when new) than we previously anticipated.

The bottom line is that the issue is not worth losing sleep over, and they will never make or break a 3a restoration whether you add them or not.

Roy

I second that motion :)

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Progress report:

Finally got wiring set up on one of the cabs. May not get A for neatness but midrange and tweeter check out OK. Used another AR screw to separate Woofer ground on back of speaker. Will put a loop from #1 to this woofer ground for regular use. Everything else is as original.

Trying to figure out how to cover the new pots so fiberglass doesn't get in. I was thinking of somehow tying a ziplock back around the two. I know Carl said he fabricates a wooden shell to fit over them with slots for wires. This may be toughest step for me.

IMGP3220.jpg

IMGP3218.jpg

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What are your thoughts on adding bypass caps?

Moi?

No way. Bypass caps are mostly useful for power supplies. They can be a good thing in a crossover if one is forced to run full-range audio through large electrolytics, like in a "passive subwoofer" application. In the case of the 3a, bypass caps won't do anything unless they are large enough to start upsetting the value of the existing cap, which seems self-defeating...

-k

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Progress report:

Finally got wiring set up on one of the cabs. May not get A for neatness but midrange and tweeter check out OK. Used another AR screw to separate Woofer ground on back of speaker. Will put a loop from #1 to this woofer ground for regular use. Everything else is as original.

Trying to figure out how to cover the new pots so fiberglass doesn't get in. I was thinking of somehow tying a ziplock back around the two. I know Carl said he fabricates a wooden shell to fit over them with slots for wires. This may be toughest step for me.

IMGP3220.jpg

IMGP3218.jpg

Jim, There is a fabric used as a "dust cloth" in furniture building. It is usually found attached underneath sofas and beds. You can usually find this at most fabric stores. It it is porous and will allow your pots to breathe and keep fiberglass dust out. I used this when I refurbed my AR2ax's to cover the woofer baskets. The original stuff AR used served a similar purpose (my guess) but I decided to replace it with new "socks" using the new material. Hope this helps.

Jess (pioneervato)

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I think what you are referring to is spunbond. It's very inexpensive and made of polypropylene most of the time.

Yes, adding that 4th terminal below the pots does present a problem with making a cover. On occasion I have also gone the cloth route. Stapling it around the pots as best I could.

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Having done much experimentation, I am of the opinion that ESR compensation resistors are not necessary at all in the 3a. The old drivers, especially the tweeters, are variable in response these days, and ESR compensation is, at best, a shot in the dark in terms of expected outcome.

I lobbied for it not to be included in the 3a restoration document, as I didn't want folks to become concerned with such tiny details. In the end it was agreed to include it, if for no other reason than it is something that exists and can be experimented with. (Very slight sonic differences can sometimes be heard, but they are not necessarily better or worse in my 3a experience.) Further, capacitor testing conducted by John O. after the document was completed suggests that the ESR of the original electrolytic caps was likely lower (when new) than we previously anticipated.

The bottom line is that the issue is not worth losing sleep over, and they will never make or break a 3a restoration whether you add them or not.

Roy

I have to disagree Roy, it is not a shot in the dark with the right measurement equipment and I do believe that it is important in designs such as the AR-11. I base this on actually measuring the crossover frequency response. It can also be important as I noted above in the AR-3a. I base this statement on simulations that I performed on a 3a model compared against published data from AR. I don't see any reason to make a blanket statement to either always use, or not use ESR resistors.

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[quote name='Pete B' date='Nov 20 2008, 08:27 PM' post='76436

I don't see any reason to make a blanket statement to either always use, or not use ESR resistors.

Hi Pete,

No blanket statements were intended, only an opinion based on my 3a experience in response to Shacky's request.

After many 3a restorations, I was simply trying to keep folks who typically don't have the "right" measurement equipment for ESR, or anything else, (which is probably 99.9 % of the visitors here) from worrying about something I personally have found to have a rather small subjective effect on that model.

Roy

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Ken,

Just checked the JBl bypass reference. Now I see they were bypassing mylar or electrolytic caps with poly as they were more like an ideal cap.

Why all the hub bub about the Theta bypass caps in speakers using current PP caps?

http://audioheritage.org/vbulletin/showthread.php?t=3555

Those JBL's were >designed< that way. Bypassing is a well-known technique. I've done it in several products. But >designing< a bypass cap into the circuit is different than >adding< a bypass cap to a circuit that is already properly designed.

If you want to start altering the response of your crossovers by adding or removing parts, and think you will get a sound you prefer, fine. But, you are gambling that you know something that the original designer didn't. (ie- AR spent all kinds of money trying to make the 3a work as ideally as possible. If the 3a's designers had wanted to use a few bypass caps, they would be in there, IMO&E.)

-k

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Finshed the mechanical resto today. Then the gods tempted my with a local CL listing for a 9090DB. Could not resist and appears at first glance the 3a's really like the added oomph of the 9090DB over my 890DB. But either combo is freakin' awesome!

Wow - now I know what you guys have been raving about. I kept the caps simple. Dayton 100+50 for woofer. Dayton 50 for mid. Solens 3 x 2 for tweeter. No bypass experiments here. I did pull out the woofer ground and added 4 screw on back to make these tuly bi-wire/ampable if I so desire. This was a testament to Jerry who is absolute generous gentleman for pointing me to these 3a's. Need to get the grills done and fix small corner chip that occurred while I was working them :P

Thanks for all the help and guidance! Here're a few more pics:

Woofer alone weighs 13 lbs

IMGP3240.jpg

IMGP3236.jpg

IMGP3252.jpg

And the new to me )tonight) Sui

IMGP3247.jpg

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As you can see I took the old surround and gasket down to bare metal. Does anyone still make the correct size cardboard gasket these days? I like the original look and may be interested in replicating down the road.

IMGP3209.jpg

Newer Pots I had purchased while Leed's had them. 6 Mom Cor's and 2 Ohmites. Would love to use these on a future AR 3 resto!

IMGP3211.jpg

IMGP3115.jpg

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In the picture of the woofer that's been refoamed you said you took the surrounds and gasket down to the bare metal. Does that mean you glued the surround to the metal frame without the shim? If so, that would put the VC down a bit lower in the air gap and could affect your overall performance. The shims for the surround and spider are there for a purpose to center the VC windings in the air gap.

I also wanted to comment about the picture of the front of your 3a without the grille in post #19. The badly finished baffle board in your picture is a prime example the point I was making to Mlluong in another thread here about the Asian 3a limited's great looking baffle boards.

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In the picture of the woofer that's been refoamed you said you took the surrounds and gasket down to the bare metal. Does that mean you glued the surround to the metal frame without the shim? If so, that would put the VC down a bit lower in the air gap and could affect your overall performance. The shims for the surround and spider are there for a purpose to center the VC windings in the air gap.

I also wanted to comment about the picture of the front of your 3a without the grille in post #19. The badly finished baffle board in your picture is a prime example the point I was making to Mlluong in another thread here about the Asian 3a limited's great looking baffle boards.

Carl,

Yes I did glue surround to bare metal. I went over to Newfoam brick and mortar here in Rochester to see if they had gasket - or as you call shim and they said no - and gasket is cosmetic only. I even pointed out it was below surround and I was concerned about cone hieght. But I had same thought as you and felt the slight additional hieght with the gasket under the surround could have impact. So two questions:

Do you feel glued to bare metal will make enough difference to cause any damage playing these?

Where can I get the proper piece?

Thanks,

Jim

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It all depends Jim on how hard you are going to push these. The gasket measures about 1/8 to 5/32's of an inch thick. Fortunately, you should still have the gasket under your spider which will help keep the VC in the proper position relative to the pole piece. However, if you have a soft, saggy spider then maybe not.

Check for spider sag.

As far as a new gasket/shim is concerned, consider fabricating one if you find you need one.

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  • 2 weeks later...

Trying out my Pioneer SX-950 on the 3a's. Very nice setup. The Sui manhandles the woofers. The Pioneer is little more gentle. Gobs of midrange and weeet top end. Man those dome midrange drivers are incredible. They bring out inner detail and clarity that is very special.

IMGP3365.jpg

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