AR2a pair from the wayback pile ...

[tgmartin]

Maybe not breaking news but I thought a quick AR2a refurb story wouldn't hurt.

Victims are a pair of AR2a in utility cabinet pine ply that are stained a walnut hue. These are the type with 1 3/8" hard phenolic dome tweets like the AR3 and the 2 x 5" fiberglass stuffed cone mids in the plastic hog trough. I vaguely remember plugging them in at the time they were acquired long ago, finding there was NO top end and sticking them in the pile of "retirement projects" without really doing any research.

I didn't remember that they were "a" models so, thinking they were just AR2 without a real tweeter, I kept a look out for some high frequency help like the Microstatic tweeter array, MS-1. As luck would have it I just recently pulled the trigger on a set right before I dug these old dogs out from WAY back in the pile. SURPRISE! Being "a" models, they should already have all the help they need up there. Problem was still no sound from mids nor tweet. I guess they hadn't healed up, even with the 25 year rest!

These speakers were actually in very good shape compared to many I've seen pics of. They never had the grilles removed and it looks like nobody ever tried. After removing all the staples (except one!) I used the paint can opener approach and popped the first one open to inspect:



I followed some recommendations on AK and elsewhere about pulling the woof. Scraped out and saved the caulking squeeze out from around the aluminum frame then used an oversized machine screw and wedged it in one of the mounting holes. This provides a point where one can get some leverage with a small Wonder Bar (or claw hammer I suppose) and lift the frame out without boogering up the cabinet or driver.



Made a quick drawing of the crossover stuff and disconnected enough wires to measure caps, drivers and inductor.

4uF = 5.2uF (replaced with 4.1uF)
6uF = 7.9uF (replaced with 6.4uF)
L1 = 1.25mH
Pots = 16ohm wire wound
Woofer = 6ohms DCR
Mids = 1.7ohms DCR (both drivers in parallel)
Tweet = 2.1ohms DCR

The caps hadn't drifted as badly as I would have thought but they were far out enough that I replaced them with the old standby Dayton 5% Poly Film units cause I had 'em.

Pulled the wire wound pots and found the typical condition where the wiper wasn't making contact due to corrosion. THIS be why no tweety sounds was happenin'! The nice thing is that these old pots were MADE to be maintained with a convenient wire bail to hold the body together. What America Used To Was. Go Figure. A Dremel wire brush combined with some crocus cloth and a DeOxit bath followed by some dielectric grease as a SWAG to delay future corrosion and it's back among the living. Like many others, I think it would probably be a good idea to find a preferred setting for the pots and simply make a fixed resistor network to replace each of them, but not right now ...



Buttoned stuff back up and DANG! Everything works! On this one at least. The woof surround even seems to hold air. This speaker sure sounds nice. Nothing earth shattering but I imagine at the time they were made (old wax block cap had date of 1964, 62 years!) they were probably right up there in terms of "HiFi". Not too shabby nowadays either ...

Tomorrow, AR2a #2!

 

[tgmartin]

Alright, Round Two Action!


Same story as yesterday. It all worked out just like the other one except this time I GOT ALL THE STAPLES! Something BAD must be waiting for me up ahead ...

Here's a pic of the oversize machine screw mentioned in the post above for pulling the woofer:



And a pic of sunlight through the cloth woofer surround. Not too bad ...



While I had this second one apart I also took readings:

4uF = 5.5uF (replaced with 4.1uF)
6uF = 8.2uF (replaced with 6.5uF)
L1 = 1.24mH
Pots = 16ohm wire wound
Woofer = 6ohms DCR
Mids = 1ohm DCR (both drivers in parallel)
Tweet = 2ohms DCR

These things sound pretty good so far but I haven't really had a chance to get them situated where I could make any critical listens ... Here's part of the reason that I don't have a couch in my "Living Room":

 

[tgmartin]

I have a question:

After attempting to put these AR2a speakers through their paces I found that the Mid drivers don't seem to be working properly. They do make sound and the MID control seems to affect them in the way it should, from what I've read. The problem is that they are not NEARLY as loud as I think they should be. With the woofer and dome tweeter active it's difficult to hear them even with my head right on them. I doubt this is the way they're supposed to be.

I've read that there is a common condition where the fiberglass "damping" that's inserted between the cone and frame eventually pushes the voice coil out of the magnetic gap causing them to quiet down. The surrounds on these do seem to be pushed out a ways, not level with the flange on the frame, but not so the surrounds are tearing away from it. See the pics above.

I really wanted to get these things functioning with the 5" cones just to see what they may have sounded like when new. I have a set of the "x" mid/tweets coming and can make new replacement panels for them but I wanted to determine whether there may be a remedy for the current drivers. They are somewhat warped and rippled like the majority of them that I've seen in pictures but don't appear to be as pushed out as some. Of course I don't know if the units in pictures functioned properly either.

What's the concensus on these poor things? Just toss the 5" cone mids and make 2ax out of them? Or, can I dump time and sweat equity in them and possibly expect a reasonable outcome?

 

[RxDx]

I'd upgrade. You're probably already getting the max out of the originals.

 

[tgmartin]

Thanks for the input, RxDx!

I was able to locate a pair of loose 5" Carbonneau drivers that I have here. I pulled the fiberglass damping out of one and found that the spider was indeed distended from its natural position and stuck that way.



It still made audio without any noticeable rubbing or obvious distortion. I was able to temporarily pop the cone and spider back to a more normal position and the speaker didn't seem to really change output level at 400 and 1kHz (my little Fostex tone generator has a limited selection of frequencies).



Admittedly, this is pretty subjective but it doesn't seem that the voice coil's position in the gap on this unit has a great deal of impact on output level. It might be a leap but it leads me to think that the units in my refurbed speakers may actually be operating close to how they were intended to.

In more reading, Tom Tyson had typed:

"The crossover network was designed to compensate for the specific characteristics of the speaker, and the end result was output that was slightly depressed, but actually quite smooth for its time. The lack of output was somewhat intentional, but the "dullness" when compared with other midranges of the time was actually a smoothness."

I think I WILL try to do the conversion to 2ax when I receive the CTS/AR drivers as I think these speakers would be more to my liking with a bit stronger midrange presence.

 

[RxDx]

I think I WILL try to do the conversion to 2ax when I receive the CTS/AR drivers as I think these speakers would be more to my liking with a bit stronger midrange presence.

I did this to a pair of AR-2s, and it totally transformed the sound in
a very positive way.

 

[tgmartin]

Now THAT'S more like it! A world of more better. Although these treated CTS mids are a bit "beamy", I can HEAR them. The 5" crossed pairs were either always too quiet or they got that way over the years. These speakers were in storage for probably 20 years before I dragged them out last month, recapped and got the pots cleaned up. I knew they HAD to sound better than they did.

YAY RETIREMENT!

Pointed question regarding this 2a to 2ax conversion:

As I was in the middle of performing the conversion and confronting the detail of the added 6 ohm resistor paralleled with the CTS mid/tweet I found it odd that I NEVER see this paralleled 6 Ohm resistor in ANY of the 2ax schematics found online. I understand that this might be to simply lower the impedance of this "new" mid/tweet assembly to make it closer to the "old" dual 5" combined impedance. It seems that those 5" in parallel might have been pretty low impedance as they read approx 1 ohm DCR. But, why no schematic showing this added resistor in the mid circuit?

It seems that finding a factual AR-2ax schematic is as rare as HEARING an actual fact these days.

I see that a change may have been made in the wiring of the mid pot in FACTORY 2ax crossovers. The 2a mid pot has only 2 connections, one side of the resistance and the wiper. The other end of the resistance is not connected to anything. It appears that FACTORY AR-2ax crossovers may have this "floating" terminal attached to the YELLOW wire. Does this make up for the 6 ohm resistor somehow or are ALL the schematics I've found incorrect?

Anybody want to point me to the REAL schemos?