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 Post subject: Altec Lansing A7-500W
PostPosted: 25 Jul 2017, 17:08 
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Joined: 04 Jun 2008, 20:59
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Location: Arizona, USA
Hi Everyone, my current project. Restoring a pair of vintage (ca 1972) Altec Lansing A7-500W. It is a studio variation of the Voice of the Theater. Much more suitable for homes even if it is huge. I have had the enclosures for a while, but now have ordered new production drivers from Great Plains Audio and with a bit of advice from another enthusiast I'm bringing them back to essentially original condition. GPA is a long time refurbisher and small scale manufacturer for Altec products. Not the current crop of junk, but the vintage gear. Their site has a interesting portion on the history of Altec Lansing as well. Beware any potential builders that want to do what I am doing...the components are not cheap. More to follow as the project unfolds.

Good listening
Bruce
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Altec Lansing Magnificent.jpg


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PostPosted: 28 Jul 2017, 21:30 
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The woofers came yesterday....beasts, roughly 25 pounds each. I'll do photos later. The high freq drivers are due next week and they are about 10 pounds each. I'll need a crane to move the cabinets. I figure they will be close to 250 pounds each when finished. I can't wait to hear them. The woofers (in these enclosures) will respond from 34 to nearly 2000 HZ with only 0.32 db of ripple. My program came up with the same number. Supposed to be some of the best around. Just you need a huge box...about 200 liters.

Good listening
Bruce

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PostPosted: 28 Jul 2017, 23:17 
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Location: Chilliwack, BC
OI!
I need my back pills just reading this :eek: :D

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PostPosted: 01 Aug 2017, 22:29 
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Location: Winnipeg, CANADA
I've seen a couple of Altec rebuilds by GPA and they do very nice work. Bruce, are you replacing both the horn tweeters and the woofers with new production?

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PostPosted: 02 Aug 2017, 16:36 
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Hi, yes all new components. I have been following guidance from a speaker enthusiast who has recommended not using the Altec horn or tweeter, but use 15 inch SEOS horns and Radian 475PB drivers. The combination is supposed to be much smoother than the originals. The GPA woofer is by all accounts really special and one of the very smoothest in existence. I will know in a few days as everything except the Radians have arrived. One advantage is that I don't have to find a pair of the horns. GPA does have tweeters though. I'm taking lots of photos so I will post them when it is done. Someone could duplicate the build if they are good with wood, but beware this is not an inexpensive build.

Good listening
Bruce

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PostPosted: 09 Aug 2017, 21:27 
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Hi, An update. The speaker systems are up and running. A little more tweaking is in order, but I can say now that these really sing. The Radian drivers on the SEOS horns really deliver. As a long time ESL lover (still am) these drivers are as fast and clean as the ESLs. The GPA woofers are everything claimed of them. All in all a really fine sounding system. It is now my main one. The sound differences between the ESLs and the Altecs are pretty much how the sound field is delivered. For want of a better way to describe it I would say the ESls present a diffuse field and envelop the room. The Altecs are more defined and kind of locked in place like a sound stage would be. Some of the differences are certainly due to how I must locate the speakers. The Altecs have to go into corners on either side of the fireplace. They are too huge to go anywhere else. The ESLs can not function in corners at all and need to be about 4 feet from the walls both sides and rear. Effectively the listener distance is 1/2 of that to the Altecs. Still the Altecs are a bit better overall. I love both, but for now the Martin Logans go into storage. I attached a few photos. I have more if someone needs details on the build. The crossover has gotten better resistors since the photos as well. I had to pad down the Radians by 12 db and use a "L" pad (set at about -6 more) to get them to match the woofers (not slouches either at 95-96 dbw). Crossover is in the 1600HZ range. More to follow.

Good listening
Bruce
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Room with Altecs.jpg
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Altec1.jpg
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Altec 3.jpg


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PostPosted: 10 Aug 2017, 20:28 
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Hi Bruce. Looks real good. In the XO, the power rating of the resistors seems small. I would have thought that something closer to 10W would be used.

What is the estimated overall sensitivity of the loudspeaker system?

Cheers

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PostPosted: 11 Aug 2017, 10:26 
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Hi Gio, they were just to test it. 10 watters are what will eventually be there. Funny thing is though they may be just fine as is (1 watt MO resistors). The sensitivity of the Radians is 111 db/w so I highly doubt that they are actually seeing anywhere near a tenth of a watt and the resistors certainly no more than that. I do suspect that the first resistor has to handle more as it must bleed off much of the input power. Efficiency does makes life easier sometimes. With everything in place the overall sensitivity is 96 db/w. Since I am using it with my original KT88 project amps (updated with all current mods) I can easily drive a person out of the room with loudness. I still have work to do on the enclosures. Another diyer and I have been conferring on this and he has provided detailed drawings to strengthen the enclosure. As he put it, its not bad now, but it can be even better. A few chunks of wood and a metal brace is all that is required. I am really surprised by the Radians on the SEOS horns. No "honk", no odd peaks etc. Smooth and fast. I used some by Eminence a while back and the crossover had to take care of a number of peaks and dips. Not these guys.

Good listening
Bruce

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PostPosted: 21 Aug 2017, 19:36 
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I first heard voice of the theatre boxes with a couple of 15" when I was 19 years
of age, and still remember it today. they wer playing an Avery Fisher test record.
there were several events on the test record, but when the broken glass came up,
that was the most real to life sound, I have ever heard, never heard it like that,
again. those speakers cost big money, but I tell you, they are worth it.


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PostPosted: 22 Aug 2017, 20:58 
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Hi, They used a variation of mine in small theaters. I remember hearing a pair when I worked for a theater company. We played music through them. Stunning, clean and loud. Ones in original condition are quite costly now. Seems to be in the over $5000 range for a pair. I'm not into it that much, but about $1300 in components as I already had the enclosures. I got them (empty) at a thrift store for $80 for the pair a while back. I have adjusted the crossover a little and it is now not perfectly symmetrical up and down (1650 HZ center) as the woofer does not roll off until around 3KHZ. So I had to artificially help it to do that a little. The tweeter is padded down 16 db to match the woofer. It has a sensitivity of 111db/w and the woofer only 95 (as installed in the enclosure). Really nice sound. Clean, clear, no horn artifacts (the Radian on the SEOS horn are sweet) and plenty loud with a system efficiency of 95 db/w. Feeding it with my personal pair of KT120 Oddblocks is overkill, but they are really clean in the 0-10 watt range (under 0.5% distortion there) and super clean (under 0.1%) in the one watt range. This is where most of the listening is done. One watt will do 95 db, I like my ears 8-) and see no need to reach the huge levels that the amps and speakers can reach.

Good listening
Bruce

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