Restoring a set of AR LST

[roundhome]

Those crossovers are not from the factory. Not a chance. Here's my read:

Over the years, several LST owners have contacted me about the possibility of removing the autotransformer and replacing it with a garden variety crossover and a level switch. For whatever reason, they became convinced that the transformer was a problem. What you have is the result of one of these modification attempts.

-k

Ok I have 10 LST's front and back wired one pair original the other 8 salvaged from being striped out

These ones have AR two board type crossover but look like AR11main board crossovers in them. all but one tweeter are AR 11 or 10Pi The holes filled in on the back match the mounting holes for the late LST back wired ones .

The AR crossover is the early 2 board 100 uf or 120 uf cap I have three types of AR 11 crossovers out right now this don't look like any of them the small board is the same as my early ones. If I had to take a shot at it I would say its a AR11 crossover

My 8 have AR 11 mids and tweeters and will have AR11 crossovers to hard to find LST crossovers.

If it were me replace the one tweeter and recap the crossover and enjoy. the 4 i have done sound great

and I'm one that bugged Ken about doing this it also matches Roys paper on taking out the xformer and switch's

Jim

[Cube4Square]

I went back to the last owner and asked him when he bought these speakers, he said it was '78/'79 timeframe, so this crossover was designed/installed at that time or earlier. I doubt someone would have gone to that trouble, then immediately sold them, so probably safe to say '77 or earlier, but either way, 30+ years ago this design was apparently created and implemented in this and probably other LST's. Was this due to better parts available, improved audio, failure of the original components or perhaps all of these?

Secondly, I'm afraid I need some help understanding which is the oddball tweeter as they all look similar to me. As well, what are AR11 tweeters? Were they used in certain AR models only? Below are the pics again to help ID the offender.

Thanks so much for all the feedback, thus far. At least I know the current design should render good sound (assuming I don't make things worse, of course) with minimal restore effort. When I get ready to start working on them, I'm quite sure I will be very annoying with the most basic of questions.

[soundminded]

So what do you think the OP's best option is? Try to rebuild the original crossovers from schematic, or live with these the way they are? Was the autotransformer that appears to be missing from this pair an off-the-shelf part, or custom-built for AR?

This looks like an excellent candidate for triamplification with an active crossover. This would overcome all of the problems of the crossover network, level controls, etc. LST was developed before inexpensive equalizers, active crossovers, and amplifiers were available. The rotary level switch and autotransformer were intened to facillitate adjustment of the voicing. This can be accomplished with addition of an equalizer for even greater flexibility. Given the difficulty of reverse engineering the crossover network to accomodate what looks like an AR3a woofer and midrange drivers and AR 11 tweeters, this would IMO be the easist and surest solution to the problem. The next best solution would be to use the AR3a crossover design except for the tweeters which might benefit from usng the AR 11 design if it is different.

[KlausDK]

Secondly, I'm afraid I need some help understanding which is the oddball tweeter as they all look similar to me. As well, what are AR11 tweeters? Were they used in certain AR models only? Below are the pics again to help ID the offender.

The most right side tweeter on the most right side picture is an AR-3a/LST generation tweeter (with the three small orange dots around the tweeter dome). The AR-11 tweeters (200011-1) were used in the AR-11 and AR-10Pi model speakers, for more information on the drivers used for these models, you could also take a look at the "Restoring the AR-3a" document found here:

http://www.classicspeakerpages.net/library...ring_the_ar-3a/

It looks like the right side woofer (the one with the bigger dust-cap) is missing the masonite ring between the foam surround and the metal chassis, for reference look at left side woofer, it was probaly lost in a refoam job.

BRgds Klaus

[Carlspeak]

..........It looks like the right side woofer (the one with the bigger dust-cap) is missing the masonite ring between the foam surround and the metal chassis, for reference look at left side woofer, it was probaly lost in a refoam job.

BRgds Klaus

Certainly not out of the realm of possibility. I once had to fabricate a set of 3a woofer masonite surround shims for a customer to unknowingly removed them during an ill fated self-attempt at refoaming.

[genek]

I went back to the last owner and asked him when he bought these speakers, he said it was '78/'79 timeframe, so this crossover was designed/installed at that time or earlier. I doubt someone would have gone to that trouble, then immediately sold them, so probably safe to say '77 or earlier, but either way, 30+ years ago this design was apparently created and implemented in this and probably other LST's. Was this due to better parts available, improved audio, failure of the original components or perhaps all of these?

This makes for quite a mystery, because in 1977 every LST ever sold would have been practically brand-new and still under its original five year AR warranty. All those non-original tweeters make me wonder if the then-owner blew all the originals out and blamed it on the crossovers.

[Mexicomike]

This makes for quite a mystery, because in 1977 every LST ever sold would have been practically brand-new and still under its original five year AR warranty. All those non-original tweeters make me wonder if the then-owner blew all the originals out and blamed it on the crossovers.

Agree with that - I had an AR3a that was repaired under the warranty during that time frame so it makes no sense that those drivers are there from that period when AR would have replaced them for free (including boxes and shipping). It's also difficult to believe that someone in that timeframe would have arbitrarily decided to "improve" the speakers since they were considered one of the best speakers available. At first glance it seems to me that they were "bodgered" at some point much later in their history but since the information you have indicates that is not the case, I can't come up with any explanation at all UNLESS the information you are receiving from the previous owner is in error...

[mluong303]

Can you take high resolution pictures of the entire back of both speakers. There are so few screw holes being drilled on the back to attached the original AR-LST Xover. That was why I suspect these were prototype with the newer crossover boards when I first see your posted pictures. Do the 2 center grill panels have small hole punched through which indicate the used of the original 6 position switch? Post pictures of the 2 center grill panels as well if you could.

Minh Luong

[KlausDK]

Woofer masonite ring is replaceable as Carl mentions.

Found this picture of a Cross over from an AR-11 in another post on CSP, doesn't it look a lot like the ones in your LST's?

BRgds Klaus

[Cube4Square]

This makes for quite a mystery, because in 1977 every LST ever sold would have been practically brand-new and still under its original five year AR warranty. All those non-original tweeters make me wonder if the then-owner blew all the originals out and blamed it on the crossovers.

I think this may be close to the actual scenario. I have a receipt from the original owner of his amp/preamp purchase and it includes the address. He lived on the University of Georgia campus at the time! So, apparently some college kid with probably a lot of disposable income got them, blew them, then wanted to get them "amped up" and had the funds to do so?? This is about the best scenario I think we will be able to draft.

The 2nd owner confirmed the only modifications he has ever done were to refoam/recone the woofers, nothing to the crossovers or other drivers. He also reconfirmed the timeframe, so I feel pretty confident we could assume '78 at the latest these mods were done. Unless, of course, there is away for me to determine the manufacture date on the drivers??

[genek]

I think this may be close to the actual scenario. I have a receipt from the original owner of his amp/preamp purchase and it includes the address. He lived on the University of Georgia campus at the time! So, apparently some college kid with probably a lot of disposable income got them, blew them, then wanted to get them "amped up" and had the funds to do so?? This is about the best scenario I think we will be able to draft.

The 2nd owner confirmed the only modifications he has ever done were to refoam/recone the woofers, nothing to the crossovers or other drivers. He also reconfirmed the timeframe, so I feel pretty confident we could assume '78 at the latest these mods were done. Unless, of course, there is away for me to determine the manufacture date on the drivers??

AR was very generous in its warranty service during the Villchur/Allison years, but I wonder if perhaps Teledyne became a bit less so after Allison's departure. Perhaps the original owner blew all the tweeters, the dealer/factory rep denied warranty service because they judged that the speakers had been abused and the owner did this instead.

I suppose the best way to proceed from here is to refoam the woofers and see how they sound. Unfortunately, you can no longer say that you have "an original set."

[Cube4Square]

Woofer masonite ring is replaceable as Carl mentions.

Found this picture of a Cross over from an AR-11 in another post on CSP, doesn't it look a lot like the ones in your LST's?

BRgds Klaus

Well, to me, that looks pretty darn close to being exact! So this was an AR crossover afterall, not a custom built crossover.

I'll take some better overall pics to show the backs of the speakers.

[genek]

Well, to me, that looks pretty darn close to being exact! So this was an AR crossover afterall, not a custom built crossover.

I'll take some better overall pics to show the backs of the speakers.

The silkscreening of the terminal IDs on the back are an indication that it is a real AR crossover; it's just not the right AR crossover.

[RoyC]

Well, to me, that looks pretty darn close to being exact! So this was an AR crossover afterall, not a custom built crossover.

I'll take some better overall pics to show the backs of the speakers.

After seeing your photos, there is no doubt that the crossovers in your LSTs are AR...but for which AR model?

The stickers with the numbers "4" and "9" on the large coils suggest an AR-11 or AR-3a crossover. The AR-11 crossover had one more small inductor than your photo shows, so you may have an AR-3a crossover with an AR-11 or AR-3a Improved switch arrangement (instead of the 3a's potentiometer/level controls). The missing AR-11 inductor was required for the later AR-11 tweeter found as replacements in your cabinets.

The values printed on your capacitors should tell you which crossover you have. Find the numbers followed by "uf". If you see "6uf" for the small, blue cap, "50uf" for the silver cap, and "150uf" for the largest, brown cap, you essentially have AR-3a crossovers...not AR-11.

The codes on the Sprague caps in your photos indicate a production date for them of 1976, so the original manufacture date could very well be 1977+/-, as you have been told.

You may have LST cabinets/mids/woofers, with (mostly) AR-11 tweeters, AR-3a crossovers...and AR-11 switch/terminal boards!

With the exception of the autotransformer arrangement, the LST crossover was very much like the 3a. In fact, now I am wondering if you simply have an original LST crossover modified with switches in lieu of the autotransformer/level control (and associated components). That would explain the transplanted terminal board (AR-11?) and switch arrangement. Even if this is the case, unfortunately, your AR-11 type replacement tweeters were not used with this crossover.

Roy

[roundhome]

After seeing your photos, there is no doubt that the crossovers in your LSTs are AR...but for which AR model?

The stickers with the numbers "4" and "9" on the large coils suggest an AR-11 or AR-3a crossover. The AR-11 crossover had one more small inductor than your photo shows, so you may have an AR-3a crossover with an AR-11 or AR-3a Improved switch arrangement (instead of the 3a's potentiometer/level controls). The missing AR-11 inductor was required for the later AR-11 tweeter found as replacements in your cabinets.

The values printed on your capacitors should tell you which crossover you have. Find the numbers followed by "uf". If you see "6uf" for the small, blue cap, "50uf" for the silver cap, and "150uf" for the largest, brown cap, you essentially have AR-3a crossovers...not AR-11.

The codes on the Sprague caps in your photos indicate a production date for them of 1976, so the original manufacture date could very well be 1977+/-, as you have been told.

You may have LST cabinets/mids/woofers, with (mostly) AR-11 tweeters, AR-3a crossovers...and AR-11 switch/terminal boards!

With the exception of the autotransformer arrangement, the LST crossover was very much like the 3a. In fact, now I am wondering if you simply have an original LST crossover modified with switches in lieu of the autotransformer/level control (and associated components). That would explain the transplanted terminal board (AR-11?) and switch arrangement. Even if this is the case, unfortunately, your AR-11 type replacement tweeters were not used with this crossover.

Roy

This is the same the other inductor is under the fiberglass this is a AR11 crossover

how about another idea left over cabinets found at factory and some one there made these

[genek]

This is the same the other inductor is under the fiberglass this is a AR11 crossover

how about another idea left over cabinets found at factory and some one there made these

I raised that possibility earlier, but I think the mismatched tweeter set that includes an original 3a/LST driver argues against that. If this had been done at the factory during the ADD years or later, one tweeter that old would not have been used. My vote for the most likely scenario is someone with an original 3a-based unit repeatedly blowing out tweeters, replacing them over a period of time with later drivers as the originals became unavailable and eventually replacing the crossovers.

[Mexicomike]

One thing I don't understand, regardless of what actually happened - why would someone choose the 10pi tweeters over the 3a tweeters? Didn't the 3a tweeter have better dispersion? I recall that the 10pi could handle more power but in a system like the LST, with 4 tweeters, was that an issue? Running a Phase Linear 400 I blew a tweeter on my 3As twice back then (replaced both times at no charge by AR) but the LST was a whole different deal, power-handling wise. Did people actually blow out LST tweeters due to excessive power?

[genek]

One thing I don't understand, regardless of what actually happened - why would someone choose the 10pi tweeters over the 3a tweeters? Didn't the 3a tweeter have better dispersion? I recall that the 10pi could handle more power but in a system like the LST, with 4 tweeters, was that an issue? Running a Phase Linear 400 I blew a tweeter on my 3As twice back then (replaced both times at no charge by AR) but the LST was a whole different deal, power-handling wise. Did people actually blow out LST tweeters due to excessive power?

http://www.classicspeakerpages.net/IP.Boar...ost&p=61616

It's easy to blow the tweeters of even the most robust classic era AR. Just aim it out your window, feed it continuously loud rock music and pump out 120 dB SPL using a 30 WPC amplifier cranked all the way up to maximum on the volume control for the length of a four-hour outdoor kegger.

If as the OP has determined from the seller this mod was made in '77 or later, that's well after the last classic era 3a/LST rolled out the door at AR. Maybe the original tweeters had already transmuted to unobtanium. And we have no idea how many replacement 3a/LST tweeters this pair may have gone on to consume even after the mod before their owner realized that the original crossover was not the cause of the burnouts and switched to ones with higher power handling so he could continue to misuse his speakers.

[Mexicomike]

"It's easy to blow the tweeters of even the most robust classic era AR. Just aim it out your window, feed it continuously loud rock music and pump out 120 dB SPL using a 30 WPC amplifier cranked all the way up to maximum on the volume control for the length of a four-hour outdoor kegger. "

I understand the blowing of tweeters with underpowered amps but it's a bit difficult for me to imagine that someone would pay the money that LSTs cost back then and then drive them with a low powered amp but I guess anything's possible. And, yes , they were not designed to play at 120db levels (even if they could actually get there) so even with sufficient power to drive them without amp distortion, they wouldn't live long at those levels. It would take a lot of power though...My LSTs on demanding music will get to around 105 db at 6 feet from the speaker before my 270WPC McIntosh amp activates it's powerguard circuit. So adding another 15db would take another 1350WPC...

[genek]

I understand the blowing of tweeters with underpowered amps but it's a bit difficult for me to imagine that someone would pay the money that LSTs cost back then and then drive them with a low powered amp but I guess anything's possible.

Especially in the OP's idea of the owner being a college kid with lots of disposable income (probably access to Mom and Dad's).

[Cube4Square]

Hard to say for sure the exact scenario, but I imagine the original owner may have had a lesser quality amp during his college days perhaps. He literally lived in a house that bordered the University, so I can only imagine there were some "rockin" days. In April of '78, he bought the Phase Linear Amp/Preamp in Athens, GA, then apparently graduated/moved to Richmond, VA which is where the 2nd owner bought them, so also odd to me that the original owner sold his fairly new system after a year or less (person I bought them from recalls getting them in '78/'79 timeframe), so he either had a lot of disposable income or life after college was more difficult than anticipated. ;-)

[rl1856]

Hard to say for sure the exact scenario, but I imagine the original owner may have had a lesser quality amp during his college days perhaps. He literally lived in a house that bordered the University, so I can only imagine there were some "rockin" days. In April of '78, he bought the Phase Linear Amp/Preamp in Athens, GA, then apparently graduated/moved to Richmond, VA which is where the 2nd owner bought them, so also odd to me that the original owner sold his fairly new system after a year or less (person I bought them from recalls getting them in '78/'79 timeframe), so he either had a lot of disposable income or life after college was more difficult than anticipated. ;-)

Or got tired of replacing blown tweeters.

[kkantor]

One thing I don't understand, regardless of what actually happened - why would someone choose the 10pi tweeters over the 3a tweeters? Didn't the 3a tweeter have better dispersion? I recall that the 10pi could handle more power but in a system like the LST, with 4 tweeters, was that an issue? Running a Phase Linear 400 I blew a tweeter on my 3As twice back then (replaced both times at no charge by AR) but the LST was a whole different deal, power-handling wise. Did people actually blow out LST tweeters due to excessive power?

Sure. Driving out to Norwood to get replacement tweeters for my LST's every few months was the way I first "met" AR. I'm pretty sure that it always happened when the speakers were pointed out the window into the courtyard of the dorm. Because the LST tried valiently to radiate the same spectrum into the entire front hemisphere, it ate a lot of power without getting very loud. (By contrast, my friend and floor-mate built rather huge JBL Olympus's, and we were constantly comparing and tweaking. They didn't fit very well into the window, and got pretty beamy. But, they had no problem with outdoor party levels.)

My Dynaco 410 would also make an unbelievably rude noise when over-driven just so with the LST's.

-k

[kkantor]

BTW- AR started giving me newer generation tweeters as replacements at some point, simply because the older ones were not in production. What there was available certainly wasn't going to be given to someone who was a frequent visitor to the will-call desk.

- k

[kkantor]

Especially in the OP's idea of the owner being a college kid with lots of disposable income (probably access to Mom and Dad's).

Not me... like many audiophiles, I lusted and saved for speakers. Fixed and traded to get my LST's, which were being sold by a dealer for $600/pr.

-k