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guidance in restoring AR-1's


shadetreehifi

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Perhaps some of the other members will be able to answer our mutually inquisitive ponderings, but it sounds to me that you're starting on this journey with far more than "zero" knowledge. Hey..... you're re-building old 12" woofers!

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I've refoamed one pair of woofers (on a thrift-store pair of Cerwin Vega AT-15's, for outdoor parties and such, when spl is the overriding consideration) and I've rebuilt the crossovers on some Realistic Mach Ones, some AR4x's, and a pair of Original Large Advents. My fine motor skills are adequate, but it's the knowledge base surrounding these speakers twice my age where I'm starting from zero. Thanks for the vote of confidence!

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Yikes!!! ..... my age sort of parallels the age of the early AR's, so I'd have to say that you're in rather good shape - - - your knowledge definitely exceeds your years. Still, I do advise that you proceed slowly, and in order to get the best result for your project, you should listen to, and learn from the experienced people in this forum who are willing to share their knowledge and experiences.

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My sentiments exactly. That's the reason I gave the Altec drivers to Bob. He's been building speakers longer than I've been listening to music. He showed me the cone and voice coil for the Altecs, and they were light enough you could forget they were sitting in your hand. I figure I can handle the heavier woofers, but the Altecs are not the kind of driver I want to have turn into a "learning experience."

I've been going back and forth on whether to replace the voice coil on the one woofer. The coil has been buffeted on the bottom, but Bob showed me a low-tech solution that involved running the barrel of a ball-point pen around the inner diameter of the bobbin to smooth it out, after which it doesn't protest to fitting around the pole-piece, though it's not as smooth initially as the unblemished coil of the other woofer. Once it's seated, I can't detect any rubbing...but if this was my car, and we were talking about a possible burnt valve, I would replace it. On the other hand, there is experienced advice coming from this forum to save the original spider, which, although a tad less firm than the other, still seems serviceable.

So having never replaced a voice coil before, it seems to me that the leads coming off of the coil have a tight tolerance, if you're not going to disturb the spider glue, since they pass beneath it on their way out of the cone. What are my options here? Can I use a solvent to unglue the spider in such a way as can be reused? Or should I try to join the new coil leads to the old close to the coil? Or should I leave the old? I've attached an image of the "improved" voice coil for reference.

I'm all for economy, but not the false kind. At the same time, in my experience working on cars, the old adage "if it ain't broke, don't fix it," when talking about a component like a voice coil or a head gasket, has merit. One doesn't preemptively replace a head gasket, simply because there are so many tolerances which must be disturbed to get to it. What do you think?

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Well, the frankenwoofers are back in business. I ended up staying with the original voice coil after smoothing the frayed edges of the bobbin, and after seeing the dramatic difference replacing the sagging spider made, I decided to go ahead and replace both spiders. I had to modify the spiders to be able to glue them on the same place on the cone rather than to the voice coil, but everything lines up and there is no rubbing that I can either feel or hear. I made new shims for the spiders and surrounds out of "hardboard" from the home depot, which seems to me to be very close to the masonite material originally used.

Bob at the speaker shop hasn't gotten around to the Altec drivers yet (I knew it would be awhile when I engaged his services; he is thorough but not speedy), so I followed the directions on the back of the cabinets and jumpered the terminals to defeat the mids/tweeters and use only the woofers. It's a bit bizarre to listen only to the woofer frequencies by themselves, but when paired up with my original large advents, they sound great.

So far, only a handful of hours (break-in time for spiders?) of play, but my initial impressions are that the frankenwoofers have more low-end, producing sympathetic vibrations from appliances and such around the room where the Advents do not. The Advents, though, seem to have a more forward responsiveness in the bass range, reproducing kick drums and things like that with more punch. Perhaps this is a product of introducing a bit of stiffness into the spiders, and will ameliorate over time? Or perhaps this is a characteristic of the AR3 woofer sound?

I'm chomping at the bit to get the Altec drivers in there and see how they sound. My go-to reference piece for clarity and dynamic range is Beethoven's emperor concerto with the London symphony orchestra. With the Advents and the AR-1's together, I'm looking forward to a treat.

A while back I acquired a second set of Advents and rebuilt the crossovers for a birthday gift for my dad. There for a while there were two sets of Advents in the living room, and they sounded sweet. I'm hoping for a similar phenomenon.

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Still no Altecs to drop in, but I am pleased to report that the AR frankenwoofers have "opened up" once they were given some exercise. They now sound more powerful throughout their range than the Advent woofers. Of course, this is completely subjective, as I have no test equipment of any kind other than my own ears.

Also, a question about cones: one of the AR woofer cones was out of round, so that on one axis the cone edge was low and on a perpendicular axis the edges were high. This made it tricky to refoam, as I had to babysit the foam as the glue set. For those of you experienced in repair, what if any changes does this make in sound? I don't believe I can detect any difference in the sound of the two woofers.

Another difference between the two repaired woofers is that for one, I used a wider shim to which to attach the foam. For the first one, I used the original shim (I found it in a box of miscellaneous odds and ends that came with the speakers. it was the only one), It was about 1/4 inch wide, which gave the foam a very slender ledge to hold on to. I made the other shim about 3/8 to 1/2 inch wide, which made the refoaming much easier. The shim does not protrude into the rolled area of the foam. Again, my ears can't detect a difference, but I am curious if in theory there could be differences in speaker dynamics because of decreased resonance or the like?

Truly frankenwoofers.

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Good news from the speaker doctor today: he is able to source a pair of original Altec cones for the 755a's. Also, the original gaskets were able to be salvaged, so once he is finished the drivers should be in "original" condition.

Looks like my original low-cost restoration is out the window at this point, but given the historical and collector's value of these drivers, as well as the significance of the donor's relationship to me, I feel that it's worth it.

Probably it will be another couple of weeks before the AR-1's are back together and playing music. Anticipation...

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Ok. I'm asking for opinions. Not necessarily (but not excluding) judgments based upon quantitative data. Listening impressions. I know the subject of the relative value of the 755a has come up on this and other forums before. I've read the posts. I'm probably going to be into these drivers for 3 or 4 hundred by the time all is said and done (which for me, humanities graduate student that I am, is 1/3 my monthly income). This is not because I would like to sell them. I'm not a good salesperson, whatever it is I am. I don't have the fire in the belly for salesmanship.

I am doing this restoration for the sake of the person who gave these speakers to me, for whom these speakers, given to him when he was just starting out (in the 70's), were his first "real" speakers. Also, I think they ought to sound pretty danged good, no matter whether they are the "last word" or no. What I am looking for is to cut through the mystique of the market. I am well aware that market value is a fickle, and to a certain way of thinking, worthless indicator of, well, worth. I drive an 80's model Porsche which I've fixed up myself, and if I were worried solely about what I could sell it for, I would never have undertaken the first turn of the wrench.

So for those of you who have heard the 755 in any of its iterations, whether in Altecs or AR's, what are your listening impressions? What is it good for? From what I've read, it is a faithful reproducer of the human voice and of certain instrumental frequencies. So it was designed as a PA driver...innovation thrives upon accident. Splenda (or so I've read) was discovered while trying to design an insecticide (source: New Yorker magazine).

Ok, enough exposition. Any firsthand impressions of this driver? Granted, I've not listened to it myself yet, but then, I feel that's the best scenario, so that I can test my ears (the control) against the variables of other listeners' opinions (ok, so that's backwards in terms of scientific method, but that's the way I make decisions).

Thanks in advance for any input. The more viewpoints the better. In the end, of course, these two things on the sides of my head will be my guide. But I'd like to have as much input as possible.

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I first heard an AR-1 in 1977, and its mid & upper range presentation made it markedly inferior to the AR-3a's that I owned at the time.

It's been written that the Altec driver was an expedient choice for AR, and the company didn't waste any time in replacing it with the domed mid & tweeter used in the AR-3.

There is a tremendous mystique surrounding that Altec driver, and I would not expect rational people to be able to penetrate it.

In other words, unless one intended to construct whatever box/baffle/horn is currently in favor, and drive the thing with half-watt SET amplification, it's doubtful that the "magic" of the 755A would ever manifest.

The AR-1 is a historic speaker, and it's great to be able to keep a vintage system intact; but by itself, the AR-1 will need HF augmentation to be considered full-range.

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The AR-1 is a historic speaker, and it's great to be able to keep a vintage system intact; but by itself, the AR-1 will need HF augmentation to be considered full-range.

So some time down the road you may want to augment the high end with a pair of MicroStatic tweeter arrays. That's what they were designed for. Sometimes can be had for $100/pr or maybe less. Here's a thread. There are others http://www.classicspeakerpages.net/IP.Board/index.php?showtopic=3251&hl=microstatic#entry68788

I've used them with KLH Twelves and AR-3a's but they are kind of superfluous with those speakers (at my age anyway). But they would be a good addition to the AR-1. Despite their name, the MicroStatics were conventional cone speakers.

Another popular tweeter for the AR-1 was the JansZen 130 electrostatics. They were true electrostatics and if you find a working pair they'll be rather expensive.

Good luck with those pieces of history!

Kent

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Ok. I'm asking for opinions. Not necessarily (but not excluding) judgments based upon quantitative data. Listening impressions. I know the subject of the relative value of the 755a has come up on this and other forums before. I've read the posts. I'm probably going to be into these drivers for 3 or 4 hundred by the time all is said and done (which for me, humanities graduate student that I am, is 1/3 my monthly income). This is not because I would like to sell them. I'm not a good salesperson, whatever it is I am. I don't have the fire in the belly for salesmanship.

I am doing this restoration for the sake of the person who gave these speakers to me, for whom these speakers, given to him when he was just starting out (in the 70's), were his first "real" speakers. Also, I think they ought to sound pretty danged good, no matter whether they are the "last word" or no. What I am looking for is to cut through the mystique of the market. I am well aware that market value is a fickle, and to a certain way of thinking, worthless indicator of, well, worth. I drive an 80's model Porsche which I've fixed up myself, and if I were worried solely about what I could sell it for, I would never have undertaken the first turn of the wrench.

So for those of you who have heard the 755 in any of its iterations, whether in Altecs or AR's, what are your listening impressions? What is it good for? From what I've read, it is a faithful reproducer of the human voice and of certain instrumental frequencies. So it was designed as a PA driver...innovation thrives upon accident. Splenda (or so I've read) was discovered while trying to design an insecticide (source: New Yorker magazine).

Ok, enough exposition. Any firsthand impressions of this driver? Granted, I've not listened to it myself yet, but then, I feel that's the best scenario, so that I can test my ears (the control) against the variables of other listeners' opinions (ok, so that's backwards in terms of scientific method, but that's the way I make decisions).

Thanks in advance for any input. The more viewpoints the better. In the end, of course, these two things on the sides of my head will be my guide. But I'd like to have as much input as possible.

the below thread addresses some of the questions but in my opinion, live with them for a while and A/B them with whatever you can find, one thing is for certain, @ $400 invested you will always get more out of them monetarily than you have put in should you desire a change......as to the belief that they are only good for a certain type of music, I disagree - I just played through a 180 gram remastered Catch a Fire, mono vinyl Beggars Banquet, vinyl Sonny Rollins, and remastered Back in Black cd and they tore through them all.....ears and listening are subjective experiences - go with what sounds good to you.....if you can find some janszens it becomes an even richer experience...

http://www.classicspeakerpages.net/IP.Board/index.php?s=d74883436a907efb5302036ffcdb7a01&showtopic=7986

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  • 3 weeks later...

I picked up the Altecs from the shop today. They look great. Upon installing them, though, there is only faint and sporadic sound. I know it's not the drivers, since I heard them tested at the shop, so it must be the pots. I disassembled the pots and cleaned them as best I could with emery paper and deoxit, but still no luck. Written on the pot is 25ohm 1.00 amp. I've looked around, but have had trouble finding pots with resistance that low. What sources would you all recommend?

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More frankenspeaker goodness. I was not able, after much cleaning of pots, to get sound from the Altecs. So I replaced the pots with some cheap ones from Radio Shack. Still no sound from either one.

I noticed that one pot is rated 25 ohm, and the other is rated 8 ohm. The schematic I pulled up here (http://www.classicspeakerpages.net/IP.Board/uploads/post-3-1160628556.jpg) shows 15 ohm. ???

In any event, I am now looking at other components of the crossover network that could be at fault. I don't have an LCR meter, so I am probably looking at taking the cabinets to the speaker shop again for diagnostics.

Has anyone here had experience with either inductors or capacitors going bad? What is the failure mode? My oil-filled capacitors show no signs of leakage, and the jumpers between them look good...

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Update: I decided to go back around and clean all the post connections inside the cabinets, and lo and behold, the "A" post was loose in both cabinets. I now hear good signal coming through the Altecs. So that is great news.

Now my question is: what is the proper resistance for the pots? I took out an 8 and a 25 ohm, and put 25's in both. The schematic I found on this forum has a 15 ohm pot. Suggestions? What effect would varying the resistance of the pot have on frequency response?

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Actually it does affect frequency response. More resistance in the circuit will lower the crossover point. It is the reason attentuation circuits are typically comprised of both series and parallel resistance. The amount of change depends on the type of control and the resisitor values used.

Roy

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Actually it does affect frequency response. More resistance in the circuit will lower the crossover point. It is the reason attentuation circuits are typically comprised of both series and parallel resistance. The amount of change depends on the type of control and the resisitor values used.

Roy

This why I should leave these type of answers to the pros!

Sorry if I mislead anyone..... :wacko:

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At long last, I'm listening to these speakers! I've tried some James Taylor, Emmylou Harris, K.D. Lang, and Bonnie Raitt to get a sense of the vocal reproduction. They sound very natural, if a bit dark. In comparison to the AR1's, my Advents and AR4x's sound like they are adding a generous sprinkling of high frequency. It sounds to me like the AR1 is heavy in the upper range of the woofer (not unpleasantly) but lacking in the upper frequencies. The Advents and AR4x in comparison sound generous in the high frequencies but recessed in the mid bass.

One question I have is this: if I were to lower the resistance of the pots in the AR1's, could I up the relative volume on the Altecs? That would be nice, I think. But since I'm ignorant of circuit dynamics, I would like to know what effect raising or lowering the resistance of the pot will have on the tweeter response.

From Roy's response, I would guess that setting the 25 ohm pot for maximum tweeter response would be the minimum resistance rating of the pot. But I can't quite get my head around the ratio of series to parallel resistance in relation to frequency response.

I suppose my next move is to try a 15 ohm pot, as per the schematic, and see how that sounds.

Thanks for the info. It feels good to be learning new things.

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Your Advent & AR-4 speakers have actual tweeters to handle the HF, which certainly makes a difference in tonal balance.

As has been mentioned, many original AR-1 owners sought out the Janszen electrostatic tweeter to enhance HF output; and AR wasted little time in replacing the Altec driver with the domes used in the AR-3 - it's pretty certain that they knew the AR-1 had a compromised high frequency output.

Rather than modifying the original crossover, how about investigating an add-on tweeter, like a vintage Microstatic or perhaps a current-production model?

Parts Express has some very interesting HF drivers available.

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That's interesting. If I were to go the microstatic route, or something similar, how would I hook it up with the AR's?

Edit: I think I may have answered my own question. Looking at some of the parts-express offerings, I'm seeing piezo tweeter arrays which contain built-in crossovers, so that they may be wired in parallel with existing speakers. Interesting.

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