Post by garym on May 15, 2016 19:39:19 GMT -5
I bought this pair of AR3a's in '72, while a college student. They performed admirably for 20 years, until the foam surrounds on the woofers began to deteriorate in the early '90s. Pulled the woofers, packed them up for shipment to an outfit in Massachusetts for re-foaming, but before sending them wife and I decided to buy new speakers (a pair of JBL L100T's). So the AR3a's and their packed woofers have been sitting in my storeroom for the last 20 years.
During that time I built several DIY speakers, and two weeks ago decided I could re-foam those woofers myself. Visited the Classic Speakers Pages and DL'd their comprehensive booklet "Restoring the AR3a".
www.classicspeakerpages.net/
Restoring these speakers has become a kind of cottage industry. One guy in NY state maintains an eBay store, Vintage-AR, and offers all kinds of parts and accessories for AR speakers. Restored pairs of AR3a's typically sell on eBay from between $1200 and $1800, depending on condition.
(For you audiophiles under 50, the AR3 and AR3a from Acoustic Research were, from the introduction of the 3 in 1958 through the 3a in '67 until the early '80s, widely acknowledged to be the most accurate loudspeakers available. They were the "standard of the industry". AR invented the acoustic suspension woofer, the first woofer design which could produce a 30Hz tone with less than 5% distortion. The AR3 also introduced the dome tweeter and midrange --- a design now ubiquitous for tweeters. A pair of AR3's is on permanent display in the Smithsonian).
The woofers in these speakers used a very soft, thin foam surround. Nearly all of them will deteriorate over time.
Deteriorated AR3a surround NOTE: I grabbed this photo from the 'net. Had refoamed my own before deciding I should take photos. My woofers looked the same. All the rest of the photos are mine.
As it turned out, one of my woofers also had either a broken spider or former. After the old surround was removed the cone listed strongly to one side. So I found and bought a used woofer identical to mine on eBay, already re-foamed.
All the AR3/3a experts recommend replacing the crossover capacitors and either cleaning or replacing the level pots. The original caps were 10% electrolytics, which drift from their nominal values over time. I replaced them with 5% metalized poly caps. Replaced the original pots with new L-pads.
Original crossover
New caps and pots
Cabinets re-stuffed, woofer leads extended, baffle boards re-painted, ready to re-install drivers.
Re-installing one of the tweeters presented a challenge. To remove the first one I simply clipped its leads at the terminal strip on the baffle board. But when re-installing it those leads would barely reach. There is no slack. So I decided to try de-soldering the second, in order to preserve another quarter-inch of lead. The tweeter voice coil tails emerge from under the dome, extend about 1-1/2 inch, and are soldered to a braided copper lead. Alas, while de-soldering the lead from the terminal I also heated it enough to de-solder the joint between one of the the voice coil tails and the braided copper lead.
This voice coil wire is literally hair thin and extremely fragile. Now I had to solder a new lead to this delicate wire. Stripped a length of 22 ga braided copper wire, coiled it tightly around a straightened paper clip to form a small wire tunnel. Slipped the voice coil lead into the tunnel, crimped it with a pair of needle-nose pliers. Tested the splice with a multimeter. Open circuit!
But I quickly realized the problem --- that hair-thin wire is coil wire, which means it is coated with an insulating varnish. I had not removed the varnish from the section inserted into the tunnel.
Normally, with ordinary coils, I just scrape the varnish away from the ends to be soldered with my pocket knife, until I have shiny copper showing. Obviously can't do that with this tiny voice coil wire --- the slightest slip would cut it. But I had some brush cleaning solvent, which will dissolve almost all paints and varnishes. So I dipped a soft cloth in brush cleaner and began gently stroking what remained of the voice coil tail --- now only about 3/4 inch long. You guessed it --- the stroking broke the wire again!
I now had about 1/8 inch of voice coil tail left. But maybe the solvent had removed the varnish. So I made another, shorter wire tunnel, managed to get the stub into it, crimped it. Tested again . . . 3.2 ohms. Yay! Heated the crimp splice and applied a drop of solder, tested again --- still had a good circuit.
Now I know what an eye surgeon's life is like.
Top photo is of tweeter with new leads.
Also replaced the grill cloths and polished the brass badges:
Was surprised the cabinets were in such good shape after 40 years of neglect. They cleaned up well --- they look out-of-the-box new.
Grill cloths in place for listening tests. They sound every bit as sweet as I remembered. They will be replacing those Klipsch RF7-II's (seen in the background) in my living room system.
During that time I built several DIY speakers, and two weeks ago decided I could re-foam those woofers myself. Visited the Classic Speakers Pages and DL'd their comprehensive booklet "Restoring the AR3a".
www.classicspeakerpages.net/
Restoring these speakers has become a kind of cottage industry. One guy in NY state maintains an eBay store, Vintage-AR, and offers all kinds of parts and accessories for AR speakers. Restored pairs of AR3a's typically sell on eBay from between $1200 and $1800, depending on condition.
(For you audiophiles under 50, the AR3 and AR3a from Acoustic Research were, from the introduction of the 3 in 1958 through the 3a in '67 until the early '80s, widely acknowledged to be the most accurate loudspeakers available. They were the "standard of the industry". AR invented the acoustic suspension woofer, the first woofer design which could produce a 30Hz tone with less than 5% distortion. The AR3 also introduced the dome tweeter and midrange --- a design now ubiquitous for tweeters. A pair of AR3's is on permanent display in the Smithsonian).
The woofers in these speakers used a very soft, thin foam surround. Nearly all of them will deteriorate over time.
Deteriorated AR3a surround NOTE: I grabbed this photo from the 'net. Had refoamed my own before deciding I should take photos. My woofers looked the same. All the rest of the photos are mine.
As it turned out, one of my woofers also had either a broken spider or former. After the old surround was removed the cone listed strongly to one side. So I found and bought a used woofer identical to mine on eBay, already re-foamed.
All the AR3/3a experts recommend replacing the crossover capacitors and either cleaning or replacing the level pots. The original caps were 10% electrolytics, which drift from their nominal values over time. I replaced them with 5% metalized poly caps. Replaced the original pots with new L-pads.
Original crossover
New caps and pots
Cabinets re-stuffed, woofer leads extended, baffle boards re-painted, ready to re-install drivers.
Re-installing one of the tweeters presented a challenge. To remove the first one I simply clipped its leads at the terminal strip on the baffle board. But when re-installing it those leads would barely reach. There is no slack. So I decided to try de-soldering the second, in order to preserve another quarter-inch of lead. The tweeter voice coil tails emerge from under the dome, extend about 1-1/2 inch, and are soldered to a braided copper lead. Alas, while de-soldering the lead from the terminal I also heated it enough to de-solder the joint between one of the the voice coil tails and the braided copper lead.
This voice coil wire is literally hair thin and extremely fragile. Now I had to solder a new lead to this delicate wire. Stripped a length of 22 ga braided copper wire, coiled it tightly around a straightened paper clip to form a small wire tunnel. Slipped the voice coil lead into the tunnel, crimped it with a pair of needle-nose pliers. Tested the splice with a multimeter. Open circuit!
But I quickly realized the problem --- that hair-thin wire is coil wire, which means it is coated with an insulating varnish. I had not removed the varnish from the section inserted into the tunnel.
Normally, with ordinary coils, I just scrape the varnish away from the ends to be soldered with my pocket knife, until I have shiny copper showing. Obviously can't do that with this tiny voice coil wire --- the slightest slip would cut it. But I had some brush cleaning solvent, which will dissolve almost all paints and varnishes. So I dipped a soft cloth in brush cleaner and began gently stroking what remained of the voice coil tail --- now only about 3/4 inch long. You guessed it --- the stroking broke the wire again!
I now had about 1/8 inch of voice coil tail left. But maybe the solvent had removed the varnish. So I made another, shorter wire tunnel, managed to get the stub into it, crimped it. Tested again . . . 3.2 ohms. Yay! Heated the crimp splice and applied a drop of solder, tested again --- still had a good circuit.
Now I know what an eye surgeon's life is like.
Top photo is of tweeter with new leads.
Also replaced the grill cloths and polished the brass badges:
Was surprised the cabinets were in such good shape after 40 years of neglect. They cleaned up well --- they look out-of-the-box new.
Grill cloths in place for listening tests. They sound every bit as sweet as I remembered. They will be replacing those Klipsch RF7-II's (seen in the background) in my living room system.
