Black LST's

[KlausDK]

Dear All

As far as I can see, there are no pictures of a black painted LST here at the CSP. Since I have just finished restoring the last of my LST's I thought I would post a picture for reference. Notice that the logo plate is aluminium and not brass as the other classical AR speakers, is that normal for LST's? My LST's have serial numbers just above 500.

I have also posted two pictures of the Cross-over, before and after upgrade. I have replaced the capacitors with new polypropylene for the midrange and the tweeter and a (green) electrolytic for the woofer bypass cap (notice the hugh difference in size!!). The tweeter has a 5.6 myF polypropylene paralleled by a .47 myF Jensen polystyrene by-pass cap (the yellow cap).

I have experimented with by-pass caps, and I found polystyrene to be the best for my ears and likings. These are old stock film caps made by Jensen in the late 60's. Jensen have both old polycarbonate and polystyrene film caps 100 and 200 Volt on stock. Polycarbonate film gives a warmer sound, but polystyrene film gives the most precise soundstage/picture. Polycarbonate and polystyrene caps, like polypropylene, don't dry out as electrolytic and paper/oil caps do.

The two big blue 5000 myF/60 Volt in series (equals 2500 myF/120 Volt) has been by-passed by a Jensen paper/oil 1 myF cap to reduce ESR in the high range (the orange cap). I have left the original wax-caps in place for now, but if I had removed them, I would have had room for the second 5000 myF cap on the cross-over board.

I have not replaced the resistor, but I plan to do so. I have also experimented with resistors and found that there is an immense influence on sound from resistors in series with drivers (tweeters and midrange). This goes from producing a directly harsh unpleasant sound to a mere reduced soundstage, but still a clear reduction in sound quality. basically no component is introduced in the signal path without an effect on the sound, good or bad.

Notice that the midrange 40 myF cap was constructed of a 30 myF electrolytic cap and a 10 myF wax-cap in parallel. Notice also the very thin cabling used for these high power speakers. I have replaced some but not all, may-bee some other time.

So how do the upgraded speakers sound compared to the old worn-out(?) electrolytic/wax caps? Nothing laid back here, more through-put in the midrange and especially in the high-range. Generally a more transparent sound picture.

BRgds Klaus

[dynaco_dan]

Hi Klaus;

Yes, the plates were aluminum, not brass.

Speaker look great.

Great write-up.

Nice photos, Klaus, thank you.

[ar_pro]

Very nice - a fresh, modern-looking appearance for the LST. Excellent job!

Have you ever considered running your crossovers outboard? It would certainly make any changes or mods an easier job.

[roundhome]

I haver one black lst in bad shape shipping dicided that it was supposed to be a wood project. as in you asamlble.

but it will get put back together

[frankmarsi]

O.K. , where'd you get those name-plates? I need four and would even pay for them even though I just blew so much on my woofers. Please pity me, why don't cha, I’m an AR addict much like all those poor souls out there who refuse to admit it! I'm a starving AR victim of the 'love' of loving music. Or is that reversed

Hey, and now that I mentioned it, can Larry at vintage AR make these for me and others? Sorry to put you on the spot Larry, but we could use a little provocation, as long as it's peaceful. AR name plates in silver would give a new look to old AR speakers, affording mass acceptance to the un-worthy who know nothing about such 'old-speakers', they'd love them this way. Sometimes small changes can make big differences.

FM

frankmarsi@verizon.net

verizon.net

[KlausDK]

Due to the "back-door" access to the LST crossover board, I have not thought of moving the cross-over out of these speakers, but I plan to do it on my AR-90's, that is a real hazard to work on.

BRgds Klaus

[KlausDK]

Hi Frank

The aluminium LST name-plates are the original ones that came with the speakers. I haven't seen replicas of LST logo plates. But while Larry is at it, I need 8 sets of AR-6 logo plates, but ordinary brass plates thanks.

BRgds Klaus

[frankmarsi]

>Hi Frank

>

>The aluminium LST name-plates are the original ones that came

>with the speakers. I haven't seen replicas of LST logo plates.

>But while Larry is at it, I need 8 sets of AR-6 logo plates,

>but ordinary brass plates thanks.

>

>BRgds Klaus

Thanks for the reply, as I thought, these obviously were a 'special' order. Although I never heard of LSTs' in black I sure do like 'em.

I bet Larry at "vintageAR" does have just what you're looking for, find his page on the Bay.

P.S. why do you have so many AR-6s? What are you some kind of nut about this hobby?(just being playful here)

Or are you just as ill as I am with my collection that any AR lover would be high for life with? And I just imagine there are some individuals out there even more crazed that you and I? Funny thing is when I 'acquired' my LSTs', I was informed that they were running in sync with many AR-6's also. I didn't acquire the AR6's but I was happy to get the LSTs'. I was told they were all used in a theater, imagine that.

FM

[frankmarsi]

>Due to the "back-door" access to the LST crossover

>board, I have not thought of moving the cross-over out of

>these speakers, but I plan to do it on my AR-90's, that is a

>real hazard to work on.

>

>BRgds Klaus

Dear Klaus, my LST's also have the rear panel 'hatch' and I was thinking that it would be better to remove that door to do all of the X-over work I am dreading, but need to do. Do you recommend this 'rear-approach' if you will, or is it more common practice to enter from the front?

Now I know there are many people out there attaching a sexual notation to my question, but I personally feel the 'rear' entrance is less problematic,not that I can't face the music mind you, I love women's faces like any other man, but are there any 'tricks' or special notes you can pass along in going for the 'rear-approach'?.

Straight as an arrow, Frank Marsi

[KlausDK]

Dear Frank

What can I say? Yes and No.

And regarding the LST cross-over, the back entrance is by far to prefer, since the cross over components in the LST is mounted on a print board and soldered on the back, you need to unscrew the print board to unsolder/solder components, that will be a real hazard though the woofer hole. I would wish AR had chosen this solution for more models of their speakers, but there is probably a high price tag associated with this solution.

The problem I encountered was that the gasket that seals the back plate, after many years of compression, has grown bigger than the hole it should fit in. Therefore I fastened the gasket in the recess on the back of the speaker (with a moderate amount of glue from a glue stick), and then it is smooth sailing to put the back plate back in place.

Brgds Klaus

PS: The soft black finish was a listed option and not a special delivery as you can see from this letter from LST section in the library:

http://www.classicspeakerpages.net/IP.Board/uploads/monthly_03_2013/post-100160-0-94762000-1363188811.jpg

PPS: LST's were used in the Covent Garden Opera in London and both AR-6's and LST's were used in the Royal Opera House in Copenhagen, as you can see in this thread:

http://www.classicspeakerpages.net/dc/dcbo...ing_type=search

[KlausDK]

After some serious listening, I was not completely satisfied with the quality of the high range, it was kind of disharmonic some how. North Creek has a sale on some of their caps, among them the 6 myF Crescendo cap, and I have ordered 4 pcs. I decided to replace the metalized polypropylene tweeter cap with the film and foil wound Crescendo cap bypassed with a 0.1 myF polystyrene cap.

This sounds much better, maybe the 0.47 myF bypass cap was too big compared to the total tweeter cap value of 6 myF. I also used the opportunity to fasten the tweeter cap properly on the printboard. Now all I need is a 50-60 hours or so of loud music playing, to get the caps to settle in.

New cross-over print picture enlosed.

BRgds Klaus

[KlausDK]

After even more critical listening, I wasn't completely satisfied with the midrange either, I found it too closed, so I decided to go for the resistors. I changed the .47 Ohm resistor in series with the midrange to an audiophile non-inductive.

Furthermore I decided to try to install the 10 Ohm bypass resistor over the giant caps, as they are used in the 10Pi as well as in the LST-2 and as rumour has it, was also used in LST at some point in time.

Furthermore, I decided to change the Solen 40 myF cap for the midrange with a Jantzen Cross-cap as I use in my 10Pi and 11, since they are very open and nice sounding in the midrange.

With all three changes installed in one speaker, I A/B'ed them and I heard a significant improvement in the upgraded speaker in the mid-range, voices more open, sound more out of the speaker. A/B'ed with my 10Pi, they are still not as open, but much better than before the upgrade.

Just to be sure that I was not biased I had an audiophile friend doing a "blind" test between the two LST speakers as well, and he came to the same conclusion, the sound were much better balanced in the updated speaker.

Was there any changes to the high or the low? Maybe the woofer got a little more lively after the upgrade, but I am not 100% on that, no changes detected in the tweeter area

New cross over photo enclosed.

BRgds Klaus

[KlausDK]

I have twisted a little more on the caps, here is an adjusted schematic and list of Capacitors used in the restauration:

C1: 6 myF Crescendo Cap from North Creek and a 221 nF Polystyrene film bypass cap from Jensen.

C2: 39 myF Cross Cap from Jantzen and a 470 nF Polystyrene film bypass cap from Jensen.

C3: 150 myF/100V electrolytic bipolar Capacitor

C4: 1 myF/100V paper oil capacitor from Jensen

C5: 200 myF/100V Zen cap from North Creek

C6: 5000 myF/60V electrolytic bipolar capacitor

C7: 5000 myF/60V electrolytic bipolar capacitor

C6 and C7 are coupled in series and is therefore effectively a 2.500 myF/120 Volt cap. The two "smaller" 1 myF and 200 myF bypass caps are used to improve the sound in mid- and high-range.

The resistors are 10watt RSS resistors from Jantzen

BRgds Klaus

http://www.classicspeakerpages.net/dc/user_files/2623.jpg

[KlausDK]

Furthermore I decided to try to install the 10 Ohm bypass resistor over the giant caps, as they are used in the 10Pi as well as in the LST-2 and as rumour has it, was also used in LST at some point in time.

I happened to stumble over an old (unnamed) post dated back in December 2002, in which there is a mention of a set of LST's with a 10 Ohm resistor like the 10Pi setup, under the heading "EV vs. HK Design Philosophy":

"BTW, my AR-LST crossover network is slightly different from the schematic shown on this site and what is also shown in the original AR-LST manual. I seem to have a later produced AR-LST (mid 1970's?) with the tweeters and midranges that are "back wired" instead of directly on the front baffle boards. They switched the 5000ufd series capacitance bank and replaced it with one single non-polar 2500ufd paralleled with a 10 ohm resistor. Was this supposed to be an improvement or just a mod so that it would present a less harsh load on some cheaper solid state amps of the time, I wonder. I am wondering if I should put the crossover circuit back to using only a series 5000 ufd value to get the lower octave bass notes through to the woofer better. Any AR-LST experts out there? I know what I am doing technically and engineering wise, but I am just curious to hear if anyone knows why this modification was made to later AR-LST's. Perhaps cost cutting? A 10 ohm resistor is much cheaper than another 2500ufd 60VDC non-polar capacitor for sure."

So this setup was used in the latest backwired version of the LST.

BRgds Klaus

XOver3.pdf