AR2ax (Early) Tweeter Dome Suspension

[Aadams]

Did you skip the step where you compare the 2nd, untouched, tweeter to the restored tweeter?  I can't find your analysis of that comparison. 

Apparently pots had enough unit to unit variation in performance that they had to be measured and preset before being installed in a specific position to make it simple for the user to set up a stereo pair. Most of us found out about the notches after the fact.  If you are going to keep appearance and parts as original, installing the pots as original is very simple compared to your tweeter work, which practically none of us can do.

I still think original is always preferred but in the case of pots, unless they were spotless, would replace the original pots with LPads and resistors or modern pots.  The pot tab notches become superflous.  If you keep the speakers you will revisit those pots.

The AR2ax incorporates the super tweeter in a way that makes the unmeasured performance of your repair easier to accommodate if it is extending too far into the midrange.  The tweeter was originally designed for the AR3 which had very specific performance requirements to blend with the dome mid at 7500hz.  If its natural rollof is not correct it would be noticeable in an AR3 application.

All that matters is your tweeters sound like a matched pair.

All Classic ARs sound very similar,  If you want your speakers to sound like an AR, this is the target for an AR2ax  EDIT  with the controls set to full increase.  They will sound unbearable in a normal room to most listeners.  I think you are within range.

 

 

 

 

[ReliaBill Engineer]

Another thing on this second speaker. Some pretty shoddy factory assembly!

Where was the QC????

Of the 6 mounting screws in the woofer, only 4 were holding it in! 2 screws were covered in putty, complete with fingerprints. Left side, below. (Top positions of the woofer if set in vertical position.)

Below, close up of the putty-covered screws. The top screw in this pic is “stripped.” It’s there, but just turns in place. The bottom screw is missing. No screw!! Never added!
 

What happened? The “T-nuts” were only inserted half way. They were dangling in the holes and not fully clamped into the drilled holes in the baffle. So the top screw could not self tap. I guess the factory worker ran out of time to do it right. Must’ve been late on a Friday….

 

 

 

Below, you can see the nuts mounted only halfway into the baffle surface. The other 4 are firmly mounted into the plywood. Guess the assembly person was in a big hurry…

 

 

 

Below, original configuration of wiring, pots, coil, capacitor:

[RoyC]

6 hours ago, Aadams said:

Did you skip the step where you compare the 2nd, untouched, tweeter to the restored tweeter?  I can't find your analysis of that comparison. 

Apparently pots had enough unit to unit variation in performance that they had to be measured and preset before being installed in a specific position to make it simple for the user to set up a stereo pair.

It wasn't the variation in the pots. The notches were model specific and were there to place the arrow of the pot shaft in a specific position relative to the white dot. It was meant to position the pot so it would provide the appropriate amount of attenuation from full increase to the dot in accordance with that model's specifications. I only mentioned them to illustrate the fact that AR never intended, nor implied, that the dot was the halfway mark of the pot's rotation.

The comparison is always the interesting part when refurbishing these tweeters. Due to the nature of the construction of the old beasts, achieving consistent results is a challenge...regardless of the material used to suspend the dome.

[Aadams]

1 hour ago, RoyC said:

The notches were model specific and were there to place the arrow of the pot shaft in a specific position relative to the white dot.

So the board ,3a 2ax etc, received specific notches for the pots somewhere after it was cut and printed  but before it was populated and wired.  Is that correct?

[ReliaBill Engineer]

7 hours ago, Aadams said:

 

Did you skip the step where you compare the 2nd, untouched, tweeter to the restored tweeter?  I can't find your analysis of that comparison. 

 

I “analyzed”, or recorded a comparison. Same track, same cartridge, same preamp/amp. But the 2nd speaker has the original capacitors in it. I haven’t yet replaced the caps. Pots are clean and good; no dropouts or scratchiness, both drivers respond smoothly to pots being turned (ear at driver).
 

Untouched. Pots set to 100%:

The first one:

 

Tweeter untouched:

 

Below, right side:

 

Below, left side:

 

[ReliaBill Engineer]

As for replacing the pots, all 4 are perfect. Like they came out of the factory yesterday. They were never stored in a garage, barn, ministorage unit or attic. 
 

I was very specific in how I clamped the domes, how I mixed the red elastomer and clear, and how I applied it. I’m not anticipating troubles duplicating it for the second dome. But I will test play the 2nd speaker after replacing the caps, prior to any work on the dome.

[RoyC]

5 hours ago, Aadams said:

So the board ,3a 2ax etc, received specific notches for the pots somewhere after it was cut and printed  but before it was populated and wired.  Is that correct?

Yes...even though the pots themselves could vary between 15 and 16 ohms. This variance is not very significant, however, when the parallel resistance of the pot is taken into account. The white dot was considered a starting point, but did have a specified resistance value for each model.

[ReliaBill Engineer]

12 hours ago, Aadams said:

Did you skip the step where you compare the 2nd, untouched, tweeter to the restored tweeter?  I can't find your analysis of that comparison. 

 

Here is a direct comparison of the 2nd speaker with caps replaced. Original caps measured 5.8 uF and 8.7 uF. In both, pots are at 100% increase position:
 

Untouched:

 

Caps replaced. Pots wire brushed and reassembled; pots were clean and shiny. Original tweeter, untouched:

 

So I’m going to rebuild this tweeter also. Probably sounds like it did from the factory. I prefer the sound below. 
 

 

[RoyC]

13 hours ago, ReliaBill Engineer said:

Another thing on this second speaker. Some pretty shoddy factory assembly!

Where was the QC????

Of the 6 mounting screws in the woofer, only 4 were holding it in! 2 screws were covered in putty, complete with fingerprints. Left side, below. (Top positions of the woofer if set in vertical position.)

What happened? The “T-nuts” were only inserted half way. They were dangling in the holes and not fully clamped into the drilled holes in the baffle. So the top screw could not self tap. I guess the factory worker ran out of time to do it right. Must’ve been late on a Friday….

Below, you can see the nuts mounted only halfway into the baffle surface. The other 4 are firmly mounted into the plywood. Guess the assembly person was in a big hurry…

It is actually not all that unusual to find this.

The drivers were nearly glued in with putty in those days, so performance was not likely to have been affected, and the grille frames were hot glued in place, so nobody would likely see it. Pulling the woofer with all that gooey putty under it probably wasn't going to happen if the cabinet was sealed properly. The only other eyes on them would have been in a service center, given AR's very generous warranty. I'm sure AR never expected it to be a topic of conversation a half century later through something called the "internet." 

When reinstalling the T-nut dab some epoxy around the outside of it, tap it in, and tighten a screw through it while it dries. The T-nut hole itself is sometimes stripped, so the glue can be very helpful. When reinstalling the woofers don't use too much downward pressure when starting the screws, as it can dislodge the T-nuts. It is likely how it occurred most often in the factory. It sucks when it happens after most of the screws are already installed.

I've been servicing AR, as well as many other speaker brands, for over 40 years, and have found some very interesting things along the way. Many years ago I spoke to a former AR factory tech (amplifier section) who recounted the story of a speaker returned due to an unpleasant odor, especially when it was driven at higher volumes. When it was opened to investigate, they found the remnants of a sandwich in it!

Btw, KLH woofer screws are much worse. The cabinets don't have T-nuts, just lots of stripped screw holes in flaky particle board cabinets.

 

 

 

 

[ReliaBill Engineer]

I know you’re right, Roy. It made no difference in performance of the woofer. Just surprised to see it! All I did was use a pair of channel-lock pliers to press the T-nuts in, and the screws tightened up perfectly. I had to dig around to find a pan head screw that fit for the missing screw.

I decided not to “adjust” the pot positions. All I did was remove the retaining springs and open up and separate the pots. Then clean, lube the shafts with a smear of silicone dielectric grease, reassemble and replace the clips. 

[Giorgio AR]

13 hours ago, RoyC said:

It is likely how it occurred most often in the factory

Your intervention is a small masterpiece of real life ... a pair of AR LSTs of mine has the rear connectors reversed (red / black) in a speaker, perhaps a tired worker made the wrong assembly.
Following the color, the woofers are out of phase.

I found the photo of the rear speaker with the positive and negative reversed, this is my "wrong" speaker

That's correct!

[ReliaBill Engineer]

On 4/11/2023 at 5:38 PM, RoyC said:

It wasn't the variation in the pots. The notches were model specific and were there to place the arrow of the pot shaft in a specific position relative to the white dot. It was meant to position the pot so it would provide the appropriate amount of attenuation from full increase to the dot in accordance with that model's specifications. I only mentioned them to illustrate the fact that AR never intended, nor implied, that the dot was the halfway mark of the pot's rotation.

The comparison is always the interesting part when refurbishing these tweeters. Due to the nature of the construction of the old beasts, achieving consistent results is a challenge...regardless of the material used to suspend the dome.

I’m curious…..

Have you had occasion to measure crossover responses of the mids and tweeters (AR-3 series and AR-2 series) using the 15/16 ohm pots used as voltage dividers? Doing simple math, the impedance load on the capacitors changes with pot slider position.

[scottie munoz]

On 4/12/2023 at 1:04 AM, RoyC said:

It is actually not all that unusual to find this.

The drivers were nearly glued in with putty in those days, so performance was not likely to have been affected, and the grille frames were hot glued in place, so nobody would likely see it. Pulling the woofer with all that gooey putty under it probably wasn't going to happen if the cabinet was sealed properly. The only other eyes on them would have been in a service center, given AR's very generous warranty. I'm sure AR never expected it to be a topic of conversation a half century later through something called the "internet." 

When reinstalling the T-nut dab some epoxy around the outside of it, tap it in, and tighten a screw through it while it dries. The T-nut hole itself is sometimes stripped, so the glue can be very helpful. When reinstalling the woofers don't use too much downward pressure when starting the screws, as it can dislodge the T-nuts. It is likely how it occurred most often in the factory. It sucks when it happens after most of the screws are already installed.

I've been servicing AR, as well as many other speaker brands, for over 40 years, and have found some very interesting things along the way. Many years ago I spoke to a former AR factory tech (amplifier section) who recounted the story of a speaker returned due to an unpleasant odor, especially when it was driven at higher volumes. When it was opened to investigate, they found the remnants of a sandwich in it!

Btw, KLH woofer screws are much worse. The cabinets don't have T-nuts, just lots of stripped screw holes in flaky particle board cabinets.

 

 

 

 

I second that, I have more issues with trying to get klh woofers, especially the sets of sixes and fours I've found that first got the screwed in woofers!  Pita! 
 

Roy's epoxy suggestion should became a law for all!

-scottie

[ReliaBill Engineer]

In my case, the 2 T-nuts were never driven into the plywood. There were no marks from where the barbs had ever touched the plywood. They had been only partially (half way) pushed in. Once I clamped the nuts into the plywood, the screws worked perfectly. The screws didn’t push the T-nuts out when I drove them in with a screw driver. 

[RoyC]

13 hours ago, ReliaBill Engineer said:

I’m curious…..

Have you had occasion to measure crossover responses of the mids and tweeters (AR-3 series and AR-2 series) using the 15/16 ohm pots used as voltage dividers?

I have not, Bill.

[ReliaBill Engineer]

Just thought I’d ask, Roy. Maybe I can model the response. I don’t have any sophisticated test equipment for measuring actual output/response.

 

I’ve started on the 2nd tweeter rebuild:

Im going to try something different this time. I’m going to mask off around that strip of electrical tape under the lead wires. Then remove the electrical tape stuck to the faceplate and plywood. Then I’ll use black acid-free silicone sealant in place of the tape. Let the base silicone cure. Then after the dome is reset in the gap, I’ll more neatly cover the leads in the black silicone sealant. I don’t care for the tape.

 

Below, dome carefully removed. Picking out the remaining yellow foam from the gap and notches:

 

[ReliaBill Engineer]

Finished the 2nd tweeter rebuild last night. Sounds great! It sounds just like the first tweeter I rebuilt. Later today I’ll do another recording of this speaker, to compare the before and after. 
 

 

[ReliaBill Engineer]

Here is the second tweeter, rebuilt:

 

Sounds just like the first one. I’m listening to them as a stereo pair, for the first time since both tweeter rebuilds. Wow!! Very gratifying.

 

Before tweeter rebuild:

 

[ReliaBill Engineer]

Just an FYI….
 

I bought these new for $12 each. I wasn’t sure what condition I’d find my pots in on this pair of early 2-ax. Turned out they were in like-new condition.

I tried one of these out. It fits nicely. But 20 ohm. Sounded fine! It bleeds off less current from the tweeter or midrange, since these are used as voltage dividers, and sounds fine. But I’d have to make a cover for them to keep the fiberglass out of the wiper mechanism, but that’s easily done. Temporarily I used plastic from a 2-liter bottle to make a “hood” while I tested for sound/function. It displaces no volume, open on the ends. 
 

 

 

 

 

 

[ReliaBill Engineer]

Sound check. Stereo playback. Much less than ideal placement. Listening for buzzes, rattles, any distortion. Playing a track from a 1964 Billy Vaughn record using the Shure V15V-MR cartridge. Tweeter pot at 85%, Midrange at 75% settings on both speakers. Pretty much recommended factory settings.
 

 

[ReliaBill Engineer]

Just found the left woofer has partially delaminated under the surround, where the surround is glued to the outer rim of the basket. Heard a buzzing noise. Not a big deal, but has to be repaired before I do anything else.

[ReliaBill Engineer]

So, I fixed the woofer, checked the other one, it’s surround is secure. 
 

I’ve been listening to these a lot over the last several days. I’m not wanting for treble at all. These don’t need an “augmenting” super tweeter. I’ve read that many times from owners of both the 3/3a and 2ax.  Long discussions about which tweeter and which crossover point to use. It isn’t needed on these. These have ample treble output that is clear as a bell.

 

The tweeter surrounds are thoroughly “seated”, and stable. I’ve played them very loud, and thoroughly exercised them. They’ll sound good for the next 50 years.

 

Below, 1963 recording of the Dave Brubeck Quartet, “Take 5.” Cymbals are clear, proper volume. Balanced with the sax, piano. Drums are fast, tight and low. 

This is from the 1963 compilation album commemorating Rexall Drug’s 60th Anniversary, 1903-1963. Using a Shure V15 Type IV cartridge with original stylus:

 

[Aadams]

39 minutes ago, ReliaBill Engineer said:

’ve been listening to these a lot over the last several days. I’m not wanting for treble at all. These don’t need an “augmenting” super tweeter. I’ve read that many times from owners of both the 3/3a and 2ax owners. Long discussions about which tweeter and which crossover point to use. It isn’t needed on these. These have ample treble output that is clear as a bell.

Good job getting them to match. 

[ReliaBill Engineer]

1 hour ago, Aadams said:

Good job getting them to match. 

I added some content above.

[Aadams]

53 minutes ago, ReliaBill Engineer said:

added some content above.

I meant, you did a good job, getting them to match.  Paul Desmond sounds good.