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AR-4x Surgery photos--not pretty (and long)

Brian4561

Brian4561

Active Member
Last night, I decided to finally start recapping one of my sets of AR-4s. After having rebuilt the crossovers in a pair of AR-2s I figured I could handle it.

So after opening one up, I gloved up and got to work. Once getting through the regulation AR black speaker gunk and brown paper towel I found this:

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Is this the dreaded AR rockwool? Having never seen rockwool before, I don't know. To me it kinda looks like the yellow fiberglass, but I'm no expert, so I'd love a second opinion.

Once the fuzzy innards were dissected to visualize the problem areas, the recap procedure went smoothly. A Dayton 20 uf metal-poly cap replaced the original wax paper monstrosity. The next step was to clean up the pot. This is where the complications come in.

The pot was VERY BADLY corroded. In fact, at first, I thought that I might not be able to save it. I first tried my usual method of Scotch Brite and alcohol. No luck. Then I stepped up to a Dremel tool with a nylon brush. That still was not enough. Finally, I was able to make some headway against the corrosion with the dremel wire brush. AFTER cleaning, here is what the pot looked like:

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As you can see, the pot suffers from the afteraffects of serious corrosion. The center pad has sections that have corroded away entirely. What is left is very badly pitted. One of the pads on the wiper has also almost corroded away. With some Deoxit and Deoxit Shield, I was able to get it to where it tested as mostly working, with a few areas where it was open. It will have to do until I can find a suitable transplant.

Having done all I could, I closed it up with the standard Moretite rope caulking. She is now resting comfortably and should pull through. She still needs that transplant, though, so she's not out of the woods just yet.

:D
 
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Very nice pics and thread.

I can tell you that stuff is indeed 'acidic' rockwool, and it without a doubt it exacerbates/accelerates the pot corrosion process. You should absolutely replace it with modern-day stuffing - not turkey stuffing :smoke:

Cheers & enjoy the restoration!
 
Cool, I'll be rebuilding my AR4X's soon so this is good timing. Maybe we could do it here but I was going to start a thread with all the items needed and where to get them to rebuild these speakers. Like the caulking, stuffing, caulk, sealant for the surrounds, bypass for the switch, caps, which filler to use on the veneer, which stain if any, tung oil, fabric for the grill covers. Did I miss anything? All of these items are posted here on AK but I've never seen it all in one thread.
 
Well, I guess this old newbie will pull out my own and will be watching this thread with interest. Brian, those close ups are among the finest I've seen, WOW!! Practicing soldering this week hoping I don't produce the "coldies". Duff, a one thread re furbish theme on these popular speaks would be great. Sure wish I had more to contribute.
 
Excellent thread. Member Birddog and I both have some AR4xs to restore. This will hepl greatly. Thanky!
 
brian, that's certainly rockwool. i recapped my 4x's last month and had the clearly yellow fiberglass inside. my pots were pristine, compared to yours (sorry :sigh: ), but i bypassed them anyway. i have yet to do other than clean the cabinets, and still have to replace the grill cloth and polish the badges.

here's what i used (for each speaker), maybe by the end we can come up with a complete list:
*one solen 20uf/400v polypropylene capacitor (parts express)
*one package of grey rope caulk (ace hardware brand), used most of it
*rubber cement, for the cloth surrounds
*60/40 rosin core solder for resoldering; i resoldered all the connections except for the connections to the pots.
*rtv silicone sealer (high heat), a bead of which holds each solen cap to the board
*electrical tape, to wrap the wirenut where i bypassed the pot, and to hold the cap until the rtv dried
*sticky-backed velcro to attach the grills (i cleaned off the old hotglue with a razorblade)
*mineral spirits and 0000 steel wool to clean the walnut

i still have to take some oxalic acid to the top of one to remove the dark circles, then will have to reoil it to make the color match. i haven't looked yet for the grill cloth, but have a couple of good stores locally for the 25 thread count linen.

i think that's it. they sound great, and when my back is healed will go up in our bedroom as computer/music speakers, connected to a pioneer sa-7100 amp.

if this was helpful i can do the same with what i got for my 2ax's, too.
 
Duffinator said:
Cool, I'll be rebuilding my AR4X's soon so this is good timing. Maybe we could do it here but I was going to start a thread with all the items needed and where to get them to rebuild these speakers. Like the caulking, stuffing, caulk, sealant for the surrounds, bypass for the switch, caps, which filler to use on the veneer, which stain if any, tung oil, fabric for the grill covers. Did I miss anything? All of these items are posted here on AK but I've never seen it all in one thread.
Click to expand...

Good idea Duff. I have a pair I need to work on and I would love to have a "how to" thread to follow with good pics. It will be my first speaker rebuild.

Terry
 
I've got a pair of 4x tore down and waiting on a cabinet refinish and recap. I'll certainly post my progress here.

Hey, there's almost as many people here rehabbing 4x around here as there are people modding Insignias. I wonder who's getting the better bang for the buck.



...NOT!!!!
 
IF you don't want to shell out for replacement pots (currently $24 each or so, if you can find them), the 8 ohm PE L-pad will replicate the resistance of the pot "wide open" at a 1/4 turn. Attach the tweeter and use your ohm meter to find the sweet spot. You're looking for 15.7 ohms across terminals 1 and 3. Mark it, and you'll be fine.

There is a good AR-4x restoration thread by Andyman (with pics) somewhere around here, do a search you guys! :music:

Thread is HERE, just to be helpful. :stupid:
 
Brian4561 said:
As you can see, the pot suffers from the after affects of serious corrosion. The center pad has sections that have corroded away entirely. What is left is very badly pitted. One of the pads on the wiper has also almost corroded away.
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Brian, ozmoid is on target. You are going to want to run that pot wide open. Here is the chart for the 4ax which has the 1.5 inch high quality tweeter that was first introduce in the AR-6.

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Your 4x has the older 2.5 inch tweeter which will start "rolling off" both sooner and faster.

You might even consider a complete by-pass of the pot as shown below.

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I can pretty much guarantee, that by-passing will in no way, shape or form prevent the "roll off". At best, you might be able to delay the start.

Anyhow, it's the type of mod you can try on one speaker and see how it sounds compared to a speaker with the pot wide open.

As always, we at AK love to read about the results of "experiments", so please, Brian, share what you hear.

Regards,
Jerry

PS: There is also a very simple mod to by-pass just the pot wiper and this will nail the tweeter to the pots' "wide open" position that ozmoid recommends.
 

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Bypassing the wiper as Jerry details above will give you maximum output on the tweeter without shifting the crossover point, and is a good fix for the burnt wiper contact. The Ar-4x is pretty amazing for it's size in the bass department, you might find that solution gives you good balance with the woofer. If they seem too "bass light", you won't have a choice except repair or replace the pots.

The AR-4x is an AWESOME speaker for it's size, I've never heard anything that can compare in it's class.
 
ozmoid said:
The AR-4x is an AWESOME speaker for it's size, I've never heard anything that can compare in it's class.
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We'll see. I want to compare mine to my ADS L420's. The ADS have a 7" woofer and 15% smaller cabinet. They sound pretty good for a small bookshelf speaker. I'm placing no bets either way but if I did it would be for the AR4x's.
 
Ok, here's some information on AR speakers that I clipped from classicspeakerpages.com and thought I'd share:

RE: stuffing density

Stuffing *density* is not the appropriate parameter by which early AR speakers should be compared. A major issue for the designer was setting the cabinet Q correctly. If too little stuffing, the cabinet would be underdamped, if too much it would be overdamped. AR's designers determined the appropriate stuffing weight to meet each speaker's design parameters; the final weight in a given speaker did not yield a common density. Examples:

Early AR-4x: AR-#4 woofer coil-- 18 oz. (511 gr.) fiberglass or 1.7 lb./cu-ft.

Later AR-4x: AR-#5 woofer coil-- 12 oz. (340 gr.) fiberglass or 1.15 lb./cu-ft

Early AR-3a (sn < ~38,500): AR #7 woofer coil, Alnico magnet woofer-- 28 oz. (795 gr.) fiberglass or 1.18 lb./cu-ft.

Late AR-3a (sn > ~39,500): AR #9 woofer coil, ceramic magnet woofer-- 20 oz. (567 gr.) fiberglass or 0.844 lb./cu-ft.

All AR-4x and AR-3a cabinets have interior volumes of, respectively, 0.65 and 1.48 cu-ft. The stuffing weights many of us have measured were within ~10% of the design value.

These numbers are only for fiberglass. When using an alternate fiber, a different quantity will be required to obtain the correct damping; but other parameters will not be the same.

John O'Hanlon
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Speaker Stuffing Study

So anyway, its clear that I need to get that uber-nasty rock wool out of my cabinets and replace it with something else. Does anyone know where one might find suitable fiberglass in quantities less than 'insulating the attic' or 'building a boat' bulk? I mean, I only need about 48 ounces of the stuff and there's really nowhere in my apartment to store multiple cubic feet of that itchy garbage.
 
Brian4561 said:
So anyway, its clear that I need to get that uber-nasty rock wool out of my cabinets and replace it with something else.
Click to expand...

Brian, I don't understand. Why are you putting yourself through all of this?

That "sound absorbing" fiber in your 4x's does the correct job. The problem with rock wool is the high sulfur content accelerates corrosion in the pots.

Simply by-pass the pot or the pot wiper and you are back in business. If you think that you can get away from "itchy" material by going to fiberglass?? Guess again!

It's miserable stuff to mess with.

Regards,
Jerry
 
john o'hanlon recommended to me i could purchase small bags of fiberglass insulation at home despot. from john's email:

6. Replace the stuffing.
================
If you have yellow fiberglass, return it to the box -- use exactly the same amount. If you have rock wool, you may do the same, but it is recommended that you replace it with 12 oz. of fiberglass. Home Depot sells little "handy bags" of fiberglass insulation, or you or your neighbor may have some left from a job. Remove its paper/aluminum backing, and cut it into 3-4 inch squares, then uniformly stuff throughout the cabinet. Weigh it carefully! Please do this in garage or outside to keep tiny glass particles out of your nose or off your skin. When done, remove gloves, and wash hands in cold water, as it shrinks pores of skin and prevents retention of errant glass fibers.

so pass by any home construction site/remodel, and ask for a couple of square feet of insulation...should be enough to do the job. or, head to the despot and see what they have.

good luck!
 
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