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Old 23rd August 2013, 06:12 AM   #31
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I have a box sitting in my basement with all of the parts & plans as procured from David Lucas. Simply never got around to building these, especially after ( briefly ) looking over the quality of the parts supplied. Seeing this thread has got me wondering now..... Sean
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Old 23rd August 2013, 03:53 PM   #32
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Aw_Dee_O: you only live once...go ahead and build them. Mine have lasted more than 16 years. Don't expect full-range response though. They should be crossed over around 300-350 hz with an active Xover for best results otherwise they won't play very loud. Good luck.
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Old 23rd August 2013, 04:05 PM   #33
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Here is a schematic I drew up of the Lucas "Interface." Lucas claimed this circuit allowed the amp to see an 8 ohm load constantly, and by adjusting the capacitor value you could "adjust the EQ for more or less bass." The toggle switch also allowed for "more or less bass," but you had to determine which setting was "better" by listening. Lucas wasn't specific. Hope this helps, and any info re: how/if the circuit works would be most informative.
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Old 23rd August 2013, 05:03 PM   #34
tyu is offline tyu  United States
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Wow.............thanks for the pic........an info on this.........i well try this on my Acoustat 121 interfaces an we well see...............Mr Pass told me years ago ......a transfourmer is a Transfourmer...is a tra....you get it.......an that i should use one ...in one of his Class a Diy Amps....insted of the res. that i keep smokin......Trany.worket great........... an never even go hot
thanks for all an any info on ESL........setups.
Long live Acoustats......

Last edited by tyu; 23rd August 2013 at 05:07 PM.
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Old 23rd August 2013, 08:45 PM   #35
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Quote:
Originally Posted by waldtraut View Post
Here is a schematic I drew up of the Lucas "Interface." ...Hope this helps, and any info re: how/if the circuit works would be most informative.
The schematic is most informative and is what I had suspected....one Lucas "mystery" solved
It is the patented Audiostatic Mirror drive circuit which provides a +6dB or more bass boost for equalizing the dipole roll-off of full rang dipole ESLs.

Audiostatic used a large AT(autotransformer) with a center tap, Lucas is using the center-tapped 12volt secondary for the same purpose but with less power handling capability. With the switch in the down position the boost would be +6dB. The results with the switch in the up position would depend on the phasing of windings...either more or less boost.

Basically it works by sending high frequencies directly to the step up transformer thru the coupling capacitor connected to the top of the AT winding, but sends low frequencies to the center tap of the AT which then doubles the voltage at the top of the winding. This creates a shelving network with LF boost of +6dB.

For further details, see the attached Peters US patent.
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Last edited by bolserst; 23rd August 2013 at 08:49 PM.
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Old 23rd August 2013, 10:22 PM   #36
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Bolserst: I raise my glass (of Weyerbacher Eighteen, a weizenbock) to you for solving this mystery. I like knowing how stuff works. Thanks.
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Old 23rd August 2013, 11:31 PM   #37
Pyramid is offline Pyramid  United States
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Default ESL power supply

I built a set of ESLs with the kit I purchased from David Lucas in the late 90's. Threw most of it away and built them using my own parts as most of it was junk, especially the power supply design. I think I ended up using a 555 and LM386 driving a low voltage transformer then multiplier. Worked OK for awhile, but when one of the panels failed, I started over from scratch. Came up with an interesting design based on a low cost CCFL xfmr that is self excited. CADed the boards in the attached photo and they have been working great ever since. Runs from a 9V wall wart and produces about 3KV.

Also found some great double sided tape to use for spacers: 3M VHB in .063" thickness. They use it to replace screws it bonds so strong. Went with steel stators instead of alum, much stiffer and less prone to damage.
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File Type: jpg DSCN0642.jpg (433.3 KB, 133 views)
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Old 24th August 2013, 04:40 AM   #38
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Very Cool, Nice Build !!

jer
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Old 24th August 2013, 08:52 AM   #39
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Default David Lucas Equalizer

Waldtraut,
Just confirming that the Lucas EQ unit that I discovered was a Radio Shack 25.2 volt center-tapped power transformer, is wired as the group has surmised: the yellow/black/yellow wires on one side of the unit are the transformer's center tapped secondary, and the two black wires coming out of the unit are the 120V primary wires. The xfmr was potted by inserting it into blue electrical box and filling with white sand, then potting with about 1/2" of white potting compound on top of that, so digging one out is no problem at all.

I should mention that the Lucas $99 EI step up transformer has the ID number "RE 90823" printed on the case, the dimensions are: 2.7" wide, 3.2 " high, and 3.3" deep, and the laminated core looks to be about: 2.6" wide, 3.1" high, and 1.5" deep. Wires on one side are: Orange/brown/red, and wires on other side are:white/blue/tan(yellow?),purple/green. The green, white, and purple wires were not used by Lucas. I have tried searching for this tranny in all the major US transformer catalogs, but no luck with that number and dimensions (if anybody is interested, or just curious). BTW, the overall dimensions include the can covers on both sides. It is painted black, and might weigh a couple of pounds at the most.

I still have my 2x3 curved lincane panels, but have not used them for some years, and my wife wants me to get rid of them. In my opinion, aluminum lincane at .020" thickness, is not very strong for ESL use, unless it were backed with some form of reinforcing grid. Curving them helped with rigidity, but they were still not that rigid.

Just another of my 2 cents if Lucas info (my contact there was a guy named Tim, FWIW, so I am not even sure if a David Lucas ever existed in the company.
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Old 24th August 2013, 12:36 PM   #40
tyu is offline tyu  United States
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THanks Waldtraut............Bolerst.....an others.......
David Lucas ........who was this guy?
well i gess we may never know..............but there was a lot of Adds in a lot of Audio Mags...for sure......... frount an back covers,.full pages..............i was in the Audio bizz at the time an called...got the info sent to me,far as i went....oh well

Last edited by tyu; 24th August 2013 at 12:40 PM.
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