AR-6's with zobel

[steelglam]

Hello,

First post here. Glad to join the forum.

I recently picked up my first set of AR speakers, a pair of AR-6's. I pulled the woofers to do a refoam and was surprised to see a zobel (capacitor-resistor) wired to the woofer's terminals. My question is: did AR-6's come stock with a zobel wired to the woofer, or was this a modification that a previous owner made to the particular speakers that I have? An internet search confirms that the woofers in my speakers are definitely those used by AR...they look the same and have the flat dust cap.

It seems that there are several different versions of the AR-6, so for clarity sake mine have the three-position rear toggle switch (increase, decrease, normal), two rear terminals, front-wired tweeters, and a large blue Sprague capacitor in the crossover. The date on the paper on the rear of the speakers says 6/74, and the serial numbers are 40071 and 40253.

Thanks for any insight!

[kcbluesman]

Attached is a PDF with schematics for two versions of the AR-6, including one with the zobel circuit. It was originally provided by member Rlowe.

You may also want to search in CSP for a thread regarding "AR-6 crossover".

I just opened up a pair of AR-6's with the crossover shown in the second schematic to replace the surrounds and modify the crossover. I believe that several of the experts on this forum have suggested that eliminating all components except a 6uf cap (instead of the existing 10uf) will yield a much better sounding speaker.

If you pursue this modification, it would appear that you could choose to leave the three-way switch in place to fine tune the response of the tweeter. I don't know what the opinion of the experts would be as regards leaving the switch in the circuit.

SF

[kcbluesman]

This time with PDF attached, I hope!

AR6 Schematic.pdf

[kcbluesman]

By the way, do your woofers have a gasket glued to the frame? And if so, is the edge of the surround glued on TOP of the gasket? From what I can tell, this is how mine were done, but I'm not sure. On other speakers with gaskets that I've worked on, the surround is glued to the basket, and the gasket goes OVER the edge of the surround.

The surrounds had already been removed when I got these AR-6's, but as I said, it appears that the edge of the surround was glued on top of the gaskets...I can see just a few small bits of the original surround on the tops of the gaskets, and some roughness where the top layer of the gasket was slightly damaged...ostensibly from removal of the surrounds.

Sure would appreciate any help you can provide.

[ra.ra]

steelglam:

Welcome to CSP. If possible, we all love to see pics describing your conundrum - - - you are usually able to get more useful feedback when you describe with visuals. I have never seen the woofer situation you describe, but a recent similar discussion can be found here.

http://www.audiokarm...ad.php?t=432835

[kcbluesman]

• The "AR-6 Crossover" thread (March 30, 2006, started by Roy C) has pics of the woofer with the zobel circuit.
  

[kcbluesman]

Based on other information that I have found, along with the aforementioned thread, plus the fact that I own four AR-6 speakers (all purchased by the original owner in the early 70's while in the Far East) with the three-position switch and the zobel circuit glued to the woofer with no signs of modification, I would suggest that the individual in the AK thead claiming that the zobel circuit is NOT original is incorrect.

[ra.ra]

I've read that "AR-6 crossover" thread before and had a little difficulty following the chronology of the dialog - - - based on the posting times, the thread seems to have been initiated by guest rvinisi in post #10 on 28 march, but the 30 march date of Roy's post shows up in the #1 spot.

http://www.classicsp...topic=1687&st=0

The claim in the AK thread must've been directed only towards the US version of the AR-6 (which is shown in Roy's photos of march 30), but it sounds as if OP steelglam and kcbluesman (and Rlowe, from Australia) are discussing the early Euro version with the single coil and the tweeter switch, which seems to be the only version of AR-6 with this 'zobel' circuit.

I was confused about your reference to the single 6mf cap until I found the statement by KlausDK - - - "The adjustment of the X-over frequency, that happened to the AR-6, could have been made to adjust to the natural roll-off frequency of the AR-6 woofer, thus the only component needed was the 6 myF capacitor for the tweeter (instead of the 10 myF used earlier)." Even then, I found it difficult to determine if he was referring to the early Euro AR-6 (single coil, three-position switch) or the later Euro AR-6 (no coil, two position switch). If Klaus was stating that the later (and simpler, no coil) AR-6 crossover used only a single 6mf capacitor, it seems that would make its x-o identical to the crossover in the AR-7 (see attached).

[kcbluesman]

I believer that your comment about the commonality between the crossovers of the "later Euro" AR-6 and the AR-7 is correct. RoyC pointed this out to me in a conversation i had with him some months ago.

[steelglam]

Thanks so much for the all of the help and information.

A few follow-up points/responses and questions.

First, I will have to look at the crossover again but from what I recall, my speakers seem to be the second ones listed in the schematic provided by kcbluesman. I recall only a single coil in the crossover, as well as the big blue Sprague cap (couldn't see the value when I originally viewed it) and resistors for the tweeter switch. And yes, the switch on mine has three positions and of course, the zobel is there.

Second, I will re-check the woofers and see where the gaskets are and get back to you kcbluesman. I didn't notice where they were when I pulled them originally.

Third, I will try to post some pics of the zobel and crossover soon.

Fourth, thanks for the info. about the possible mod, replacing the 10uf cap with a 6uf one. Perhaps I will try that. kcbluesman, you said that the mod involves removing all components but the cap. It's clear that the coil is to be removed as part of this mod, but to keep the tweeter switch functioning as you say, wouldn't you have to keep the 3 ohm resistors in place for the tweeter switch to work properly?

Finally, as a general point, do you think that zobels serve their purpose well, or on the contrary do you think they are detrimental to the sound/performance of the speaker? It seems that the mod to which kcbluesman is referring would involve removing the zobel, so I'm guessing it's generally recommended to get rid of the zobel (even if you don't do the mod)?

Thanks again, folks!

[kcbluesman]

I'm not advocating the modification...just reporting that some of the more knowledgeable folks seem to feel that it is an improvement. This is based, from what I can tell, on the fact that a later European version of the AR-6 used this crossover (a 6uf cap for the tweeter and a resistor for that model's two way switch).

However, it is not clear that this version of the AR-6 uses the same drivers as the ones you (and I) have.

As for the existing crossover (same as yours)...I just finished replacing the caps in one of mine (and replacing the woofer surround), with no changes to the crossover design. Upon first listening, I like it quite well....although I will know more after I get the second one done and do some extended listening. Unfortunately, I'm hearing just a bit of sibilance from the tweeter...I hope that it is not damaged!

My plan is to try the 6uf, simplified versionn with my other pair and compare them to the "stock" version...assuming that I can first verify that my drivers are the same as those used in the above-mentioned "later" Euro version (or in the AR-7, which also uses the simple 6uf crossover).

As regards making this mod but leaving the 3-way switch intact...yes, you would need to leave the switch and the two resistors connected to it in place if you want to control the output of the tweeter. I can see no reason why this would be a problem, but would certainly welcome other opinions.

Finally, as regards attachment of the surrounds on these woofers; I've concluded that they indeed did mount on top of the gasket on the rim of the basket. My woofers have a masonite ring under the spider, and I would need to depress the cone to mount the surrounds to the frame without the gasket. With this in mind, and seeing what appears to be residue from the old surrounds on the gasket, I pulled the trigger and glued the new surrounds on top of the gasket. I hope my impatience didn't lead to a mistake!

The serial numbers on my AR-6's are all between 37070 and 37078, and the sticker on the rear of them shows AR's address in Norwood, MA. This would suggest that they were made in the USA, not in Europe. What about yours?

[ra.ra]

It will be interesting to learn of the results from kcbluesman regarding his experiment with the different crossovers in his two pairs of AR-6's - - - I think with s/n's so close, it's pretty much a guarantee that the drivers should be the same in all four speakers. Still, I am not able to fully follow the discussion on the gasket and the masonite and the surrounds, so again, a couple pics would be beneficial to describe the situation.

Gotta say I'm still a bit perplexed by the entire production timeline of the AR-6 - - - various drivers and crossovers; various Massachusetts factories and foreign countries. And, it was less than fully descriptive for me to simply refer to the single coil, three-position switch version as "Euro", since clearly it, too, was manufactured in U.S. in later years. For perspective, my AR-6's, with Cambridge labels, have serial numbers which represent the earlier production (31xxx), and they have two coils, rheostat pot, three speaker wire terminals, and a single 10 mf cap. Unfortch, when these came to me they never had all the original drivers and now, a la Humpty-Dumpty, I've been trying to piece them back together again.

Thanks for confirming that the AR-7 and "later Euro" AR-6 crossovers are identical, but it is unclear if this simpler 6mf, no-coil crossover was ever installed in U.S. mf'd AR-6's. Also, I don't know if the move from Cambridge to Norwood coincided with any specific changes to product manufacturing - - say, for example, with the AR-6's? I suspect that the history is not that simple, direct or straightforward. With the AR-7 (and AR-8 and LST-II) representing the tail end of products considered among the "classics" (walnut, linen, etc.) and being in production less than 2 years each (1973-74 or 75), it actually surprised me a bit to notice that my AR-7's have labels with Cambridge address. Most likely, the two facilities operated concurrently for some period during the transition.

In any case, send updates on your projects when you are able.

[kcbluesman]

To clarify...I'm quite sure that the drivers in all four of my AR-6's are the same, and all are original.

However, before I try the simple 6uf crossover in one pair, so that I can compare it to the other pair with the stock crossover, I want to be sure that my drivers are the same as those used in production versions of either a) the AR-6 with the simple 6uf crossover, or the AR-7, which used the same simple 6uf crossover. In other words, I only want to try the 6uf crossover with the same drivers that provided such (reportedly) good results.

I agree about the confusing history of the AR-6, and its mix of crossover designs and woofers. From what I have gleaned so far, the tweeters never changed....but I could certainly be wrong on this point!!

I'll post some pics of my woofers when I get a chance.

[steelglam]

Finally, as regards attachment of the surrounds on these woofers; I've concluded that they indeed did mount on top of the gasket on the rim of the basket. My woofers have a masonite ring under the spider, and I would need to depress the cone to mount the surrounds to the frame without the gasket. With this in mind, and seeing what appears to be residue from the old surrounds on the gasket, I pulled the trigger and glued the new surrounds on top of the gasket. I hope my impatience didn't lead to a mistake!

The serial numbers on my AR-6's are all between 37070 and 37078, and the sticker on the rear of them shows AR's address in Norwood, MA. This would suggest that they were made in the USA, not in Europe. What about yours?

The serial numbers on mine are 40071 and 40253. And the labels show the Norwood address, as yours do.

Also, I checked the woofers again tonight, and the gasket is underneath, not on top. Perhaps someone refoamed yours at some point and decided to add a gasket to the top?

[Rlowe]

I've read that "AR-6 crossover" thread before and had a little difficulty following the chronology of the dialog - - - based on the posting times, the thread seems to have been initiated by guest rvinisi in post #10 on 28 march, but the 30 march date of Roy's post shows up in the #1 spot.

http://www.classicsp...topic=1687&st=0

The claim in the AK thread must've been directed only towards the US version of the AR-6 (which is shown in Roy's photos of march 30), but it sounds as if OP steelglam and kcbluesman (and Rlowe, from Australia) are discussing the early Euro version with the single coil and the tweeter switch, which seems to be the only version of AR-6 with this 'zobel' circuit.

I was confused about your reference to the single 6mf cap until I found the statement by KlausDK - - - "The adjustment of the X-over frequency, that happened to the AR-6, could have been made to adjust to the natural roll-off frequency of the AR-6 woofer, thus the only component needed was the 6 myF capacitor for the tweeter (instead of the 10 myF used earlier)." Even then, I found it difficult to determine if he was referring to the early Euro AR-6 (single coil, three-position switch) or the later Euro AR-6 (no coil, two position switch). If Klaus was stating that the later (and simpler, no coil) AR-6 crossover used only a single 6mf capacitor, it seems that would make its x-o identical to the crossover in the AR-7 (see attached).

There is an earlier discsussion on the AR-6 in Mar 2007.

The link has the last comments at the top of the page.

http://www.classicsp...tur,#entry62161

[kcbluesman]

The serial numbers on mine are 40071 and 40253. And the labels show the Norwood address, as yours do.

Also, I checked the woofers again tonight, and the gasket is underneath, not on top. Perhaps someone refoamed yours at some point and decided to add a gasket to the top?

So, the edge of the surrounds is glued to the gasket, correct? Versus the more typical arrangement, in which the surround is glued to the basket itself and a gasket is placed over it.

I assume your woofers have the masonite "plate" under the spider as well?

I am listening to my first pair right now...restored to stock. They are quite nice, with a good, tight low-end....especially for their size. They sounded ok with a Pioneer SX-950 that I restored, but much better with another of my workshop amps - a British Fidelity A-100. They are not "blow you away" good, but very enjoyable.

[steelglam]

So, the edge of the surrounds is glued to the gasket, correct? Versus the more typical arrangement, in which the surround is glued to the basket itself and a gasket is placed over it.

I assume your woofers have the masonite "plate" under the spider as well?

I am listening to my first pair right now...restored to stock. They are quite nice, with a good, tight low-end....especially for their size. They sounded ok with a Pioneer SX-950 that I restored, but much better with another of my workshop amps - a British Fidelity A-100. They are not "blow you away" good, but very enjoyable.

Sorry, I wasn't clear. What I meant was that there is a gasket glued to the underside of the basket, not on top of the basket. You cannot see the gasket unless you remove the woofer from the cabinet and turn it over. Which is what I've tyically seen with Advent's, AR's, EPI's, etc. The surround--well, what is left of it at this point (I have to refoam them)--is glued to the basket, as you typically find. There is no gasket that is placed on top of the surround, or to which the surround is glued.

I'll check for the masonite plate under the spider and get back to you. I didn't look for it.

[kcbluesman]

Sorry, I wasn't clear. What I meant was that there is a gasket glued to the underside of the basket, not on top of the basket. You cannot see the gasket unless you remove the woofer from the cabinet and turn it over. Which is what I've tyically seen with Advent's, AR's, EPI's, etc. The surround--well, what is left of it at this point (I have to refoam them)--is glued to the basket, as you typically find. There is no gasket that is placed on top of the surround, or to which the surround is glued.

I'll check for the masonite plate under the spider and get back to you. I didn't look for it.

You are referring to the thin foam gasket that serves as an air-seal between the cabinet and the woofer. I was referring to a much thicker and more rigid gasket which fits into the outer rim of the woofer basket. Generally, these are glued OVER the edge of the surrounds and used for cosmetic purposes, to provide a more finished look. In the case of my woofers, they are used to raise the glueing surface for the outer edge of the surrounds...which appears to be necessitated by the masonite ring under the spider. What I don't understand is why that ring was used in the first place. I've seen other references to AR woofers with this ring, but no explanation of its purpose.

If your woofers don't have it, this would seem to indicate that the AR-6 had at least two different woofer versions.

[kcbluesman]

If your woofers don't have it, this would seem to indicate that the AR-6 had at least two different woofer versions.

Correction: "at least two different versions of the ceramic magnet woofer". As per the other threads discussing the AR-6, we already knew that there was an Alnico magnet version which preceded the ceramic magnet version.

[steelglam]

You are referring to the thin foam gasket that serves as an air-seal between the cabinet and the woofer. I was referring to a much thicker and more rigid gasket which fits into the outer rim of the woofer basket. Generally, these are glued OVER the edge of the surrounds and used for cosmetic purposes, to provide a more finished look. In the case of my woofers, they are used to raise the glueing surface for the outer edge of the surrounds...which appears to be necessitated by the masonite ring under the spider. What I don't understand is why that ring was used in the first place. I've seen other references to AR woofers with this ring, but no explanation of its purpose.

If your woofers don't have it, this would seem to indicate that the AR-6 had at least two different woofer versions.

Yes, I was referring to the thin foam gasket that goes between the woofer and cabinet. Mine do not have a gasket on the top of the outer rim of the basket.

[KlausDK]

If Klaus was stating that the later (and simpler, no coil) AR-6 crossover used only a single 6mf capacitor, it seems that would make its x-o identical to the crossover in the AR-7 (see attached).

That is what I was referring to, latest European version of AR-6. Enclosed schematic also thanks to RLowe.

BRgds Klaus

VISIO-KlausM-AR6.pdf

[kcbluesman]

That is what I was referring to, latest European version of AR-6. Enclosed schematic also thanks to RLowe.

BRgds Klaus

Klaus -

I am planning to modify the crossovers in one pair of my AR-6's (the ones with the zobel glued to the woofers) to duplicate the crossovers in the "latest European version" that you referenced in your posting.

However, before doing so I would like to know if you believe the drivers in my version to be the same (or very close the same) as those used in that European version. I'm not sure that I want to move forward if they are significantly different.

On a related note...my web searching seems to indicate that my AR-6's are also referred to as a European version. Do you know if this is correct? The labels on the back of each ot them show AR's USA address.

And one final question to further take advantage of your expertise....as I noted earlier in this thead, my woofers have a masonite ring under the spider, and the outer edges of the surrounds are glued on TOP of paper gaskets in the outer rim of the basket. Any ideas as to the purpose of the masonite ring?

Thanks very much for any help or insight you can provide.

[ra.ra]

Thanks to Klaus and RLowe for the fine little schematic.

My earlier inference that switched AR-6's were all Euro products was misleading. From what I can glean, AR-6's produced in the U.S. started as 1-pot/2-coil/3-terminal (v.1) and later evolved into a 3-pos. switch/1-coil/2-terminal product (v.2). These two versions are represented in kcbluesman's attachment in post #3. Both of these employed the 10 mf cap.

In Europe though, I think, the product began with the crossover of version 2 (v.2), and later was simplified to become almost identical to the AR-7 (v.3) with the 2-pos. switch, 6mf cap and no coil. However, I do notice in Klaus' AR-6 schematic that this speaker has three terminals and not two like the AR-7 that I am familar with.

I would think that for anyone to be able to confidently confirm any similarity of drivers, it would be most helpful to provide part numbers or photos, and preferrably both. I know that I'm still curious about the masonite and the surround attachment, but I still don't understand what it looks like.

[kcbluesman]

The woofers in my version of the AR-6 (the ones with the glued-on zobel) have a tag on the bottom of the magnet with the following information:

AR-6

Made in USA

10708

Additionally, the magnets are stamped with the number 561 7401.

As for the masonite ring, I'm going to guess that it's purpose is to allow for more travel of the former and cone (to avoid bottoming out). This in turn raised the cone. This meant they had to find a way to raise the outer edge of the basket...which was accomplished by a paper gasket the same thickness as the masonite. Otherwise, the surround would extended outward when at rest (if it had been glued to the basket directly), restricting its inward movement.

Perhaps this was how the woofer was originally designed, but I would suspect that it was more likely an interim step in which they were moving towards standardization of this driver but were in the interim mixing remaining and new parts in one unit. I'm sure someone knows, but in the meanwhile I'll just pretend that I'm right.

And on that note, I'm moving forward with the crossover modification. If it's inappropriate for my drivers, I'm sure my ears will tell me (or perhaps my nose, if I burn up the tweeters).

[kcbluesman]

As for the masonite ring, I'm going to guess that it's purpose is to allow for more travel of the former and cone (to avoid bottoming out).

Duh. Coil, not former.