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

[RoyC]

16 hours ago, Aadams said:

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

The LST essentially has two pairs of tweeters, with the tweeters of each pair connected in series. The pairs are connected in parallel. The resulting tweeter impedance is the same as a single AR-3a/LST tweeter. The LST crossover's tweeter cap value is the same as the 3a (6uf).

Roy

[Jeff_C]

To elucidate the point RoyC and Aadams makes, if one tweeter in the 'series' wired section of the LST is blown (goes open circuit) then its partner tweeter wired in series with it will also cease to produce audio, as it has no complete circuit. The parallel wired pair of tweeters should still work.  Taking this a step further, if two tweeters go open circuit, then depending on which two , there could none of the four tweeters producing audio or two tweeters producing audio.

I believe it would take a minimum of 8 tweeters to go open circuit to prevent all 16 tweeters producing audio. But conversely the 'right' combination of 8 blown tweeters could leave 8 producing audio.

[mike tarelli]

22 hours ago, djcheung said:

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.

Hello David,

Thanks to Klaus I know the fuses are available at RS Components Ltd GB. They may also have the holders.

Mike

[xmas111]

1 hour ago, Jeff_C said:

To elucidate the point RoyC and Aadams makes, if one tweeter in the 'series' wired section of the LST is blown (goes open circuit) then its partner tweeter wired in series with it will also cease to produce audio, as it has no complete circuit.

Looking at the schematic it looks like a single tweeter can open and the other three will still function.   I'm not sure what the impedance would be with three tweeters, didn't look that deep into it.   Then again I might be reading the schematic incorrectly.

[ra.ra]

4 hours ago, xmas111 said:

Looking at the schematic it looks like a single tweeter can open and the other three will still function.

That's exactly what I thought when I looked at the tweeter wiring. Doesn't that center wire shown here ensure that three tweeters remain active if one goes mute?  

[Glitch]

4 hours ago, xmas111 said:

Looking at the schematic it looks like a single tweeter can open and the other three will still function.   I'm not sure what the impedance would be with three tweeters, didn't look that deep into it.   Then again I might be reading the schematic incorrectly.

xmas111:  I believe that you are correct about the schematic.  With one blown tweeter, the others will still function, but with an unequal sound output.  The total impedance of the remaining three drivers would be 1.5 times that of a single driver.

[Glitch]

I'm a bit confused by the discussion of blown tweeters in Frank's LST's.  I don't recall him saying that his current tweeters weren't working.  Did I miss something?

There was a comment about needing to make cabinet modifications to try back wired tweeters.  Wouldn't the connections to the back wired tweeters be made inside the cabinet?

Frank:  I forgot that you have three pairs of LST's.  If this was my project, I would pick the "worst" pair and experiment on them.  This way you could try your modifications, do the A/B testing, and track your progress without taking down your main system.  I concur with the others that suggested that you try to make the modifications in such a way that everything is reversible.  There are many really good suggestions about how you should proceed.  You have lots of options.  In the end, you'll have to decide for yourself if the modifications are an improvement.  Unfortunately, the very nature of sound perception makes it impossible for somebody else to predict what you'll interpret as an improvement in sound quality.

[RoyC]

1 hour ago, ra.ra said:

That's exactly what I thought when I looked at the tweeter wiring. Doesn't that center wire shown here ensure that three tweeters remain active if one goes mute?  

Thanks for posting the schematic, Robert. I haven't looked at it in a long while. I agree with you guys. Even though the thought of a series connection suggests otherwise, the schematic clearly shows one tweeter won't take out another...and, in retrospect, I don't recall any other tweeters or mids in an LST cabinet being mute due to a bad one.

Things do change in terms of impedance, crossover point, and tweeter balance when inserting a non-original tweeter into the mix. In lieu of having original replacement tweeters, all of the tweeters would have to be replaced with the same model to maintain optimal balance. Although the original tweeter's response is not shaped by a parallel coil, later type tweeters (ie AR-9,11, ABT, Midwest, HiVi, etc) would require a coil of an undetermined value across the whole array to retain something similar to the original high frequency response characteristics. It would be placed across the tweeters in the same manner as the #6/1.35mh parallel coil is across the mid array.

Roy

[ra.ra]

1 hour ago, Glitch said:

I don't recall him saying that his current tweeters weren't working.

I had that same thought before my previous post and then re-read Frank's original post, and this is correct, he has not ID'd any dead original tweeters.

1 hour ago, Glitch said:

Wouldn't the connections to the back wired tweeters be made inside the cabinet?

IMO, this is always ideal, but since Frank has not posted pics of his speakers sans grille covers, we're left guessing if he has front or rear-wired mid and tweet drivers. He does make a comment about drilling the tweeter face plates, so we can assume he has exposed front panel terminals that he's planning to connect to the tweeter rear terminals. I have a strong personal dislike for those front-exposed tinsel wires, so whenever I've encountered this type of situation with a driver replacement, I try to make efforts to abandon the front terminals altogether and keep all the wiring inside the cabinet. I totally agree with your thought.   

59 minutes ago, RoyC said:

Things do change in terms of impedance, crossover point, and tweeter balance when inserting a non-original tweeter into the mix. In lieu of having original replacement tweeters, all of the tweeters would have to be replaced with the same model to maintain optimal balance. Although the original tweeter's response is not shaped by a parallel coil, later type tweeters (ie AR-9,11, ABT, Midwest, HiVi, etc) would require a coil of an undetermined value across the whole array to retain something similar to the original high frequency response characteristics. It would be placed across the tweeters in the same manner as the #6/1.35mh parallel coil is across the mid array.

Roy, this is just another great set of tips for how to conceptually approach this type of tweeter replacement.

Good call on the LST x-o schematic by xmas111.

[Aadams]

3 hours ago, Glitch said:

m a bit confused by the discussion of blown tweeters in Frank's LST's.  I don't recall him saying that his current tweeters weren't working.  Did I miss something?

It was disclosed in another LST thread about 2 years ago in a discussion with Owlspace.  You have to keep up:)

Aadams

[frankmarsi]

5-2-18   7:31P.M.

Before I get my panties into a bunch let me simply state that my AR-LST’s are early issues and their S/N’s only have three digits starting with S/N 612 and consecutively numbered thereafter.

These LST’s have front wired tweeters and midranges along with the standard AR 12 woofer. From their first issue they had front wired drivers like all AR speakers did and within a year’s time or so, they sported rear wiring as all AR speakers newly did.

Because I’ve elected to improve my system in some ways like better interconnects, better tonearms and cartridges, I feel it’s high time I get the LST’s in total order with-out having any thoughts of incompleteness for the rest of my listening days.

These 90 lb. boxes are not easily moved or worked on in a living room setting. And although someone here suggested bringing them down the basement to work on, I’m afraid not. They’re simply too heavy and awkward to move around, position or anything else besides actually listening to them.

Now that I’ve got the bug to replace tweeters and the cabinets will be moved this one time only, I’m ready to move forward.

FM

[ar_pro]

Realizing, Frank, that you haven't exactly solicited an opinion, in the spirit of AR-brotherhood, I'm inclined to give one.

Considering the quality of the equipment that you own, as well as the time & energy devoted to bringing this excellent audio system into being, it would seem that the most straightforward, effective, and long-term solution would be to by-God first get ONE PAIR of AR-LST speakers into 100%, full-spec, no-shortcuts, working order.  

It's wonderful that you'be been blessed with multiple LST's but it's also a little bit of a curse, in that the inclination is to never give up the stack, and to keep everything "functioning". The perfect being the enemy of the good, you now find yourself with multiple AR-9 tweeters, and add-on Microstatics as part of the solution to keep things rolling.  From a distance, it looks as if you're maybe not thinking this through, since - and as has already been noted - member Chris1 can repair AR LST tweeters! 

The stack can wait - in my humble opinion, one restored & perfectly-functioning set of LST's  might be the true gold standard.

 

 

[Jeff_C]

On ‎02‎/‎05‎/‎2018 at 11:59 AM, xmas111 said:

Looking at the schematic it looks like a single tweeter can open and the other three will still function.   I'm not sure what the impedance would be with three tweeters, didn't look that deep into it.   Then again I might be reading the schematic incorrectly.

You (and others) are right, I was commenting about a usual series/parallel arrangement. I should have looked at the schematic.

[frankmarsi]

5-16-18

I have been sitting on eggshells listening for the noises I reported initially. Every time I listened, I sat in fear of whatever could happen. Either a amplifier explosion, or a woofer flying out of its metal basket and cabinet grill cloth.

When I read from member “Chris1this1” I thought his suggestion was a possibility but,  doubtful as being the cause. A week ago I sheepishly walked up to the speaker I thought was the noise maker (only rarely and not  continuously) , and I turned the transformer’s control several times back and forth while quietly hoping this might be a solution as Chris suggested it might be. Chris’s suggestion reminded me of the possibility of oxidation, dirt or fiber-glass particles working their way into those contacts of the transformer. I haven’t heard the offending noise ever since.

So, all’s well that ends well, I hope. My fear was that perhaps it might have been a dying capacitor and the chance that it’s still not up to spec and is a required repair but, there are no audible noises or indications that are audible.

It may have been the speaker’s ‘caps’ or transformer's contacts or,  it maybe an amplifier problem still looming but, either way I’m not hearing the noises any longer so,  fingers are crossed.

I have held-off on the installation of any tweeters until the problem is resolved completely because I'm not willing to blow the 16 expensive used AR-9 tweeters that are slated for these four LSTs.

Any knowledgeable opinions? 

FM

P.S. Is Chris becoming our tweeter hero and more?

[ra.ra]

On 5/1/2018 at 7:44 AM, djcheung said:

The fuse holder on one of the speakers is broken. Any idea where I can get a replacement?

David, those black LST's really look great, and I'm sure they will sound terrific once you get them restored. I would think that any place that sells the fuses would also sell the corresponding holding clips. Just yesterday I was in a local hardware store and spotted a variety of these devices in parts drawers  - - - surely you need a specific size but not sure about the proper metal alloy.

[djcheung]

Thanks ra.ra,

I have managed to get some fuse Bussmann FNM-2 on ebay, £3.75 for 2 - new old stock.

I have seen the fuse clips on Mouser and just checking which one I should get. They are £0.45 each but almost £13 shipping charges. I still yet to remove the old broken fuse clips to double check before ordering. Due to the advances of online shopping, local shops here in the UK only carry normal standard main stream parts. Anything unusual always presents a challenge ! 

I still need to get some stands for them to lift them off the floor. 

After that, I will need to decide which pair of speakers I should keep in the same room. Currently I have AR9 and AR3a in the same room. With the AR-LST ..........

The woofers have been refoamed and will listen for a while before deciding anything I need to do with them.

I have a few pairs of AR but this is in another league that I haven't experienced before.

Best regards,

David

[JKent]

David,

I may have fuse blocks. Will check and let you know but shipping may be an issue. Cheapest looks like about $14 USD or £10.40 GBP so not much of a savings.

-Kent

[djcheung]

Hi Kent,

Thanks very for the offer. I think I might just get a few more from Mouser to justify the high shipping charges. So have spares if the others break. I am really looking forward to getting it set up properly. I am new to this sophisticated level of design. I am sure will ask for more of your expert advice as I go along on the road of discovery.

Best regards,

David. 

[JKent]

David

The fuse blocks I have are Ferraz-Shawmut part # 30311.

Looking through ebay I see some in the UK: 5 pieces for 14.68 GBP. Search ebay for "5 x 30311 Gould Ferraz Shawmut Mersen fuse block 30A 600V"

What is the part # you're looking at on Mouser?

-Kent