“ AR-LST, after Forty Six Years of Use”

[frankmarsi]

Some further reading  I need to do:

 

 

 

More: https://www.google.com/search?ei=eRjlWtekApKQ_Qb8sobIDw&q=ar-lst+cross+over+values&oq=ar-lst+cross+over+values&gs_l=psy-ab.3...8076.11934.0.12417.11.11.0.0.0.0.67.579.11.11.0....0...1..64.psy-ab..0.0.0....0.xbL90jGIYAg

[ra.ra]

4 hours ago, Stimpy said:

But, I knew they were old capacitors, and I didn't want to leave them as is.

I've certainly been guilty of this approach as well, and while I've probably re-capped speakers that may not have required it, the work expenditure is always very satisfying and gives me a sense of accomplishment and security towards the future, as you already know. But also, with these old AR's, I have come to view original electrolytic caps differently - - - the small black/red Callins or Temple caps give me nowhere near the level of confidence that the blue-orange-purple Sprague Compulytics do. Each situation is unique, however, and requires its own solution, but I choose to place my faith in what I've learned from the many more knowledgable voices in this forum who have measured, tested, and performed surgery on dozens and dozens of these old relics. From my limited experience, I think those Unicon caps are probably pretty reliable - - miles ahead of the Callins but perhaps not as steadfast as the larger Sprague cans.

4 hours ago, Stimpy said:

You have the AR9 tweeters, try them.  If the impedance matches the original LST tweeters, it shouldn't hurt anything.  At worse, they'll be too bright.  But, they may surprise you, and sound much better.  Where's the harm?

Nominal impedance rating of these drivers should be no problem. Experimentation is half of the fun with this hobby - - I fully agree - - but with the LST already on the endangered species list (and having substantial market valuation), there needs to be a process of baby steps before reaching for the drill or Dremel to make the stubborn cabinets cooperate with this modern tweeter "upgrade". Harm?....what harm? Unnecessary cabinet butchery is normally irreversible, so my advice would be to proceed with caution before damaging these rare collectibles. Stimpy, we know you have several of these large AR classics, so how would you propose addressing the crossover issues? 

8 hours ago, frankmarsi said:

I haven’t given what you speak of a thought but, now I’m curious that you may be absolutely correct.

Frank, I remain very impressed with your enthusiasm and ability to amass such a military-grade wartime armory of vintage AR drivers, but I would hate to see you inflict undue pain or torment or damage to your beloved speakers. Sometimes people need to be protected from themselves, and I'm fully in your court here, trying to help out, just waiting for a more experienced gearhead to explain why my slow-down advice is foolhardy. I really enjoy successful hybrid projects, but I'm feeling a bit like Debbie Downer here. While others are all green-light pedal-to-the-metal, I suggest slowing down and heeding the yellow caution traffic light. While assembling a collection of (20) AR-9 tweeters, did you ever ask, study, or confirm if this was a suitable replacement driver for your LST's? Fretting about bits of sawdust makes me think maybe you've never performed a re-cap before - - in which case, you do need step-by-step directives. We are nearly 30 posts into this thread, yet no one has collaborated with or confirmed the success and/or effectiveness of this proposed tweeter transplant. This is my primary concern here, and until this proposed substitution becomes substantiated with validated testimonials, I'll try to be the voice of the angel on your shoulder.

With a pair of AR-9's and three pairs of LST's, if you are worried about being "without any music" for any time, I'd suggest you consider hiring a new chief-of-staff for audio scheduling assistance.           

[ar_pro]

I've never had my paws inside of an LST, but I have compared the sound of an AR-3a against a stock AR-91, and my little AR-91/AR-3a project from a couple of years ago, and I can say that I can definitely hear differences between these three systems. 

I've always loved the sound of the 3a, and by extension the rare LST, but I have a preference for the characteristics of the AR-9 series systems, which generally seem less reticent, to coin a descriptor.

And I think ra.ra's caution to go slowly is advisable, and Frank should consider if he'd be happy with LSTs that have AR-9 DNA in their high end, as well as consider the cautions regarding the AR-9 tweeter's ability to properly cross over to the LST's mids with a newly-capped, but still stock network.

In a nutshell, I think that with this change, there'd be a good chance that they would not sound exactly like brand-new LST's, nor even what Frank has grown accustomed to over the years.

Also, does an "intermittent thump" sound like a speaker problem? If it's shared by all of the LSTs, I'd think that it was a source issue.

[frankmarsi]

ra.ra,  your kindness and consideration are very much appreciated. 

I will hold-off on any installation of those tweeters for the moment.

Although I was under the impression that if I install the front two as a sort of test, it sounds like a good idea to start with.

I must admit a while ago "RoyC." suggested to me to do the two front ones first and he didn't indicate any unforeseen problems though, since I told him that I prefer older AR speakers with a little more high-frequencies in the mix, he felt I'd be satisfied. Earlier, I didn't want to bring him into this situation as I see some folks casually suggest others contact him.

He must be overwhelmed and or bothered by now. He's not on salary of course and responds out of the goodness of his heart so, I refrained from contacting him though, he would be the one who has more info for me regarding the tweeters. My problem which hasn't been addressed so far is the source of the noise I'm getting out of one speaker out of four. Could it be a speaker 'cap' or?

Although I'm feeling that I would like to install all 16 of the AR-9 tweeters, I still have my fears of burning them out. When listening to properly set-up AR speakers, if one doesn't get carried away like I do, it's amazing how little the original tweeters are called upon to operate. In fact the 'Micro-Static' tweeters do such a good job and handle so much power, (they're rated at 16 ohms).it's amazing how the carry on. As an owner of AR speakers since 1972, my first question to myself was why are they tweeters so low in their output. But, back then being 22 yrs.old and they were such a big expenditure for me, and after reading countless test reports during that era, I felt this was the way it was meant to be. After numerous burnt tweeters and the use of micro-statics, I felt I needed more high-frequencies to be satisfied and that the AR concept and portrayal of the highs was just not for me. I didn't want JBL or other maker's highs, but I would happy somewhere in between.

Again,  my post was primarily about the thumping noise I'm getting, and I do think it's a X-over 'cap', (though, I'm not absolutely certain it's the cause), I thought it was high time I install new 'caps' and the tweeters that I've been holding on to for so long.

Thank you for your input.

FM

P.S.    It's  good to have an angel on my shoulder. So few have LST's and even though, they're so similar to other AR speakers, they do have their differences.

[frankmarsi]

@ ar_pro, if a capacitor is going, I believe it may sound that way I can imagine but, I'm not a technician so I really don't know, which is why I brought to these pages. 

Of course, I could be very wrong and it may actually be one channel of one amplifier. Each of these two items are machines so, almost anything is possible after so much time in use and time passing.

Either way, I have a problem and I need to correct it ASAP.  I'm not happy about this problem of course and it's gnawing at me.

FM

[DavidR]

FWIW, Ken Kantor (perhaps the last engineer at AR) recommends using NPE (non polar electrolytic) capacitors when restoring old AR speakers. The use of film will alter the voicing as they behave differently in a circuit than NPE caps. Film caps aren't affected, to any great degree, by frequency as are npe caps.

I'm using NPE caps in my AR10Pi and AR9. My 90's will be a mix as I already had film caps. However, I am happy with the 2nd recap on my 91's using film. The 1st go at it left something to desire.

[frankmarsi]

@ DavidR, an unknown to me but, a very good point nonetheless.

Your experience is what is of value here, and is obviously needed.

Now, as ra.ra has suggested,  I'll slow down a bit in hopes of even more wisdom being put forth.

FM

[Stimpy]

1 hour ago, ra.ra said:

I've certainly been guilty of this approach as well, and while I've probably re-capped speakers that may not have required it, the work expenditure is always very satisfying and gives me a sense of accomplishment and security towards the future, as you already know. But also, with these old AR's, I have come to view original electrolytic caps differently - - - the small black/red Callins or Temple caps give me nowhere near the level of confidence that the blue-orange-purple Sprague Compulytics do. Each situation is unique, however, and requires its own solution, but I choose to place my faith in what I've learned from the many more knowledgable voices in this forum who have measured, tested, and performed surgery on dozens and dozens of these old relics. From my limited experience, I think those Unicon caps are probably pretty reliable - - miles ahead of the Callins but perhaps not as steadfast as the larger Sprague cans.

Nominal impedance rating of these drivers should be no problem. Experimentation is half of the fun with this hobby - - I fully agree - - but with the LST already on the endangered species list (and having substantial market valuation), there needs to be a process of baby steps before reaching for the drill or Dremel to make the stubborn cabinets cooperate with this modern tweeter "upgrade". Harm?....what harm? Unnecessary cabinet butchery is normally irreversible, so my advice would be to proceed with caution before damaging these rare collectibles. Stimpy, we know you have several of these large AR classics, so how would you propose addressing the crossover issues? 

Frank, I remain very impressed with your enthusiasm and ability to amass such a military-grade wartime armory of vintage AR drivers, but I would hate to see you inflict undue pain or torment or damage to your beloved speakers. Sometimes people need to be protected from themselves, and I'm fully in your court here, trying to help out, just waiting for a more experienced gearhead to explain why my slow-down advice is foolhardy. I really enjoy successful hybrid projects, but I'm feeling a bit like Debbie Downer here. While others are all green-light pedal-to-the-metal, I suggest slowing down and heeding the yellow caution traffic light. While assembling a collection of (20) AR-9 tweeters, did you ever ask, study, or confirm if this was a suitable replacement driver for your LST's? Fretting about bits of sawdust makes me think maybe you've never performed a re-cap before - - in which case, you do need step-by-step directives. We are nearly 30 posts into this thread, yet no one has collaborated with or confirmed the success and/or effectiveness of this proposed tweeter transplant. This is my primary concern here, and until this proposed substitution becomes substantiated with validated testimonials, I'll try to be the voice of the angel on your shoulder.

With a pair of AR-9's and three pairs of LST's, if you are worried about being "without any music" for any time, I'd suggest you consider hiring a new chief-of-staff for audio scheduling assistance.           

Now, first and foremost, I wouldn't normally advocate anyone altering a classic speaker cabinet, in order to implement a modification.  Unless, a mod was the only way to keep a prized speaker in a playable state.  Then, there's not much choice, especially with vintage speakers.  So, if I were Frank, I'd only try the AR9/LST tweeter swap, if the AR9 tweeters were a physical drop-in replacement.

As to crossover mods, I was again thinking about my AR-1MS speakers.  They use a 0.75" dome tweeter, similar in appearance to the AR9 tweeter.  The face plate is different, but the domes look alike.  In looking at the 1MS crossover, it uses a 2nd order crossover, with a 5.0uF tweeter cap.  By playing with crossover calculators, I found the 1MS woofer and tweeter crossed over at around 2950KHz.

Next, the LST uses a 1st order crossover, with a 6.0uF cap on the tweeters.  Again, by playing with a crossover calculator, the 6.0uF cap would high-pass at approximately 3300KHz.  Now, a single 6.0uF capacitor, is a 1st order 6dB crossover, and doesn't offer as much protection as a 3rd order AR9 crossover.  But, the LST splits the high signal among 4 tweeters instead of one.  The AR9 tweeters wouldn't be working too hard, unless driven to extremely loud levels.  Though, we know Frank wouldn't do that!  So, maybe this could work?*

 

*All speculation on my part.  Especially so, considering how 'iffy' some crossover calculators can be!  As such, my crossover frequency 'guesses' may not be 100% accurate. 

[ra.ra]

Frank, if this AR-9 tweeter ends up being a suitable replacement with safe and desirable results, then by all means, full steam ahead with your intended project. I am simply questioning the apparent 5K to 7KHz frequency gap that the manufacturer's specs suggest with this proposed array of drivers - - your high-end cartridges would feel insulted by this 2 KHz omission in the speaker sound path, and this issue is the primary aim of my attempted helpfulness. Like you've already implied, I, too, often prefer the more modern mid and tweet drivers for their extended HF range, but they still need to be able to sync up and play well with the larger drivers behind the tenor and bass sections of the orchestra. And again like yourself, I pay close attention to any and all of Roy's advice, so the forum would benefit greatly from his (or any other experienced members') experience or wisdom on the suitability of this proposed tweeter transplant concept.  

I'm not really thinking about the 'thump' issue, but ar_pro's suggestion might be pertinent regarding a possible glitch in the source rather than the speaker.

1 hour ago, ar_pro said:

...my little AR-91/AR-3a project from a couple of years ago...

Yes, this is one of the 'hybrid' projects that I really loved. Great work!  

21 minutes ago, Stimpy said:

Unless, a mod was the only way to keep a prized speaker in a playable state.

But we now know that the early 3/4" dome tweeters are restorable by Chris in NJ, and I think this option would classify as a true restoration without all the concern about driver compatibility.

24 minutes ago, Stimpy said:

...if the AR9 tweeters were a physical drop-in replacement.

I believe the face plates and screw alignments would fully comply, but the wiring requires either drilling the tweeter plate or the baffle board to accommodate the rear-wired tweeter. Is that still a drop-in?

57 minutes ago, DavidR said:

FWIW, Ken Kantor ... recommends using NPE ... capacitors when restoring old AR speakers.

Or, in the case of the robust Sprague Compulytics, maybe leaving the originals in place for additional years or decades, like I have done on several pairs of AR-6's and AR-7's since they measured well and sounded terrific. I know many people have advocated wholeheartedly for film caps everywhere (longevity!... grandchildren!), but I sort of like this idea of using simple, inexpensive electrolytics for vintage speaker re-cap projects, even if I don't fully understand the argument for maintaining original ESR values.

DavidR, you have plenty of AR's big-boy models - - - what are your thoughts about the suitability of the AR-9 tweeter for Frank's project(s)?  

[Stimpy]

Did any versions of the Cello Amati speakers use the AR9 era drivers?  Or did any Cello speakers use the AR9 drivers?  If so, why can't Frank? 

 

[DavidR]

10 hours ago, ra.ra said:

DavidR, you have plenty of AR's big-boy models - - - what are your thoughts about the suitability of the AR-9 tweeter for Frank's project(s)?  

If the tweeter can handle the lower frequencies then all is good PROVIDED he doesn't have to alter the cabinet to install them.

If they don't work out he will make $$$ reselling them on eBay.

[DavidR]

10 hours ago, Stimpy said:

Did any versions of the Cello Amati speakers use the AR9 era drivers?  Or did any Cello speakers use the AR9 drivers?  If so, why can't Frank? 

Mark Levison may have created a different xover.

https://www.audiogon.com/listings/monitors-cello-amati-ar-lst-type-model-updated-in-2013-2013-10-04-speakers-00914

[ra.ra]

Just a little more food for thought here. This first attachment has been shown in other discussions on this forum but may be of some interest here - - it is a page from the Tim Holl paper on the AR-9 series and describes some of the thought behind the design of the tweeter and mid units. 

The second image shows a side-by-side comparison of response curves of the AR-92 (with same mid/tweet as 9, 90 and 91) and the LST. Clearly, the p/n 029 tweeter does have output below the x-o point of 7000Hz, but it appears to be diminishing. Likewise, the LST midrange appears to fall off quickly above 5000Hz.

Frank, if you do end up doing some testing on this tweeter substitute, I'd suggest to do it with the new tweeter outside of the cabinet, thereby avoiding any unnecessary or premature drilling of the faceplate or the cabinet front panel. However, it is still likely that some type of crossover adjustment would probably be required.  

[RoyC]

On 4/28/2018 at 10:48 PM, frankmarsi said:

ra.ra,  your kindness and consideration are very much appreciated. 

I will hold-off on any installation of those tweeters for the moment.

Although I was under the impression that if I install the front two as a sort of test, it sounds like a good idea to start with.

I must admit a while ago "RoyC." suggested to me to do the two front ones first and he didn't indicate any unforeseen problems though, since I told him that I prefer older AR speakers with a little more high-frequencies in the mix, he felt I'd be satisfied. Earlier, I didn't want to bring him into this situation as I see some folks casually suggest others contact him.

He must be overwhelmed and or bothered by now. He's not on salary of course and responds out of the goodness of his heart so, I refrained from contacting him though, he would be the one who has more info for me regarding the tweeters. My problem which hasn't been addressed so far is the source of the noise I'm getting out of one speaker out of four. Could it be a speaker 'cap' or?

FM

Hey Frank,

I'm good...I too appreciate and enjoy ra.ra's eloquent and insightful posts. Between those and other thoughts, you have received some sage advice, so I'll just make some comments based on reading through this thread.

-I agree with AR_Pro regarding the "thump". I've never heard something like this caused by a crossover cap. Have you switched over the amp leads to see if the sound follows the leads or stays with the same speaker? I'm inclined to believe it is in the electronics chain somewhere. If not, it is probably a woofer issue.

-The AR-9 tweeter is virtually identical to the AR-11 tweeter except it has a recessed dome. Both tweeters have more output, greater response into lower frequencies, and greater power handling than the original 3a/LST style tweeter. These tweeters have parallel coils serving them in the AR-9 and AR-11 crossovers because they have greater output into the midrange frequencies. The coils serve to attenuate the tweeter's influence on the upper mid response and increase power handling. (This is why a parallel coil is used when replacing an original 3a style tweeter with the HiVi tweeter replacement.) The AR-11 tweeter was used in the AR-3a Limited with a 4uf cap and .16mh parallel coil, (and 8 ohm L-pad). In the AR-11 it was used with a 10uf cap and .1mh coil. Unlike the later tweeters, the original 3a/LST tweeter only requires a single 6uf cap. No coil is needed to electrically roll off its response at lower frequencies to achieve the desired crossover point with the midrange.

-The challenge when implementing any non-original tweeter is coming up with a way to integrate it in a satisfactory way. Electrical crossover charts are useless for this purpose. Physical and mechanical characteristics are as important as electrical parameters when determining the proper crossover modifications. Dome mass/material, suspension compliance, magnet strength, dome damping material (if any) are among the more obvious considerations. With that said, the unique 3a/LST tweeter's DCR is around 2.5 ohms and the AR-9/11 style tweeters are near 4 ohms.

-Given your satisfaction with outboard tweeters, the original LST high frequency response may not be your goal...which is why I suggested simply replacing the front tweeters with your later specimens to test the waters. Since you would not be tempering the AR-9 tweeters with parallel coils, they will provide greater output than the original tweeters. I would be more concerned with too much rather than too little output from the later tweeters.

-With apologies to Stimpy, other variables are in play when someone seems to hear significant differences between film caps of the same value...whether it be Clarity Caps, Solen, Dayton, etc, or for that matter, mylar/polyester caps. With that said, many LST's are equipped with Sprague caps, which are usually just fine as is.

If I were restoring a pair of LST's for personal use today I would simply send the tweeters to Chris to rebuild. There is no better way to get the old beasts to sound as "original" as possible with minimal effort. The downside for you, Frank, is that the simple cap-only crossover makes the more fragile original tweeter prone to damage at high volume levels...On quiet nights I believe I've faintly heard your NJ music on the wind here in upstate NY.

Roy

 

 

[DavidR]

26 minutes ago, RoyC said:

On quiet nights I believe I've faintly heard your NJ music on the wind here in upstate NY.

and I laughed and laughed and laughed upon reading this

[ra.ra]

Agree with DavidR - - that last line brought me a hearty chuckle, too - - but that was simply a great post from Roy, particularly the comments about the variables in driver construction and the function of the tweeter circuit coils. I had completely forgotten that Frank is using the external tweeter arrays, so Roy's comments about the precise project objectives are worth re-examination. 

I should have clarified that posting the response charts was not intended to serve as any sort of prescriptive design tool - - rather, I just wanted to show how the two drivers under discussion (LST mid and AR-9 tweeter) performed in their intended environments. These technical graphs are often difficult to comprehend for many of us (like me!), but I do enjoy seeing in a visual presentation how the various drivers perform and literally "cross over" each other, and also to better understand a range of frequencies that two adjacent drivers share. Nonetheless, the key to driver substitution (and the part requiring true expertise), as Roy has already noted, is creating the satisfactory integration of the non-original component - - in this case, the AR-9 tweeters.    

[frankmarsi]

4-30-18 6P.M.

Gentlemen, good to see that RoyC. showed up.  I was getting kind of worried and felt maybe he wouldn't.

He wasn’t kidding about hearing my system as far as up north where he lives. He's an honest person.

After not much thinking, planning or anything one is supposed to do, I decided to try the two tweeter at a time approach. This is something Roy had suggested to me a long while ago. Though I have that freaking lawn tractor situation, it may have to take priority as the grass is going to be much greener. 

I haven't determined if it's one channel in one amp or what yet, either way it will be solved though, I'll have to pack it up and send it out which is a chore in of itself at approx. 50+ lbs.  Of course it'll mean listening to only one set of LST's until the amp returns. 

FM

This or,

 

Or this?

 

 

[DavidR]

Can you pop a wheelie on that mower? If not then go with option 1.

BTW, have you had any work done on that Carver amp? I had a modded M-1.0t that had several added transistors. I'd get a loud 'sound' when driving my 90's hard. The 90's were new to me so I thought it might be them BUT it ended up being a counterfeit Sanken transistor. I found out when it let go on my 901s. Thank GOD it was the Bose as the voice coils are tough and it took the 70VDC.

[Stimpy]

Hey Frank,

With your stacked LST's, do you stack with both pairs tweeters up, or do you invert the top speaker, so the speakers will be tweeter to tweeter?  Just curious, if you've tried both configurations or not?  If so, which was better?

Thanks.

 

[DavidR]

Is this you Frank?

[ar_pro]

One of those stacks is listing to starboard....

[Chris1this1]

Hi Frank, 

Here's a thought, 

clean the contacts on your spectral balance switches. As a fello LST owner,  I know there is a thump while turning the knobs due to capacitor charge dumps and inductor ringings (like a switching power supply) so possibly you could have an intermittent contact. 

Now for the tweeter experiment, keep in mind the LST has the tweeters in series/parallel arrangement, so all four need to be working if you want to really make judgement on how the AR9 tweeters will perform. 

[djcheung]

Hi all,

Just purchased a reasonably priced pair of LST. They look okay with everything 'original'. I haven't connected up yet and want to get the woofers refoamed first. The fuse holder on one of the speakers is broken. Any idea where I can get a replacement. I can get the fuse here in the UK.

This is going to be a long project.

Didn't release how big and heavy they are until I tried to lift them !!!

Best regards,

David.

[RoyC]

18 hours ago, Chris1this1 said:

Now for the tweeter experiment, keep in mind the LST has the tweeters in series/parallel arrangement, so all four need to be working if you want to really make judgement on how the AR9 tweeters will perform. 

That's a really good point, Chris. Dead tweeters in the cabinet would be a problem.

Roy

[Aadams]

3 hours ago, RoyC said:

That's a really good point, Chris. Dead tweeters in the cabinet would be a problem.

Which raises the question.  Mr. Marsi are you sure ALL of your tweeters are blown?  The way I read this is you could lose one or a couple and they all go out.  Of the 16 not working you could have as many as 12 good ones.

Adams