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Old 12th February 2003, 03:21 PM   #1
Cobra2 is offline Cobra2  Norway
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Default JBL - L300 mods/updating?

Hello! - please help:

My friend have a pair of the big, old JBL - L300...
and wonder if they can be made "up to date" with
small / careful modifications ???
If you have any experience with these,
please post here!
(and, will it be difficult splitting the filter, for bi-wiring?)

Arne K
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Old 12th February 2003, 08:17 PM   #2
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Hi Arne,

You donít have to split the filter. This is what I would do. Make a new or get a used xover between the LE-85ís and the 077ís and run the woofer right from the amp. I would run a electronic xover for the woofer to horn transition, but you donít have to.

Cross the LE-85 to the 077ís at about 8kHz or higher if possible. You can frequently find N7000 xovers on ebay, but the N8000 is kind of rare. It may be easier just to make a new xover with premium parts. If you donít use the premium parts, at least bi-pass the cap with good audio grade caps.

Cover the baffle around the mid-horn and the 077ís with 7mm foam or felt (remove the lens first so the foam goes right to the edge of the horn). Cut strips of the same foam and wedge them between the fins on the rear of the lens, but not more then 10mm in from the back edge. There should be a round area open to the horn mouth. This will help to control any baffle diffraction as the sound wave travels through the lens. Wrap the mid-horn very tightly with some heavy rubber or neoprene. You can use large wire ties to hold the rubber tight around the horn, the more the better.

In the photo, you can see the foam on the baffle and wedged into the back of the fins. You can also see the N7000 which I totally rebuilt with Solen coils and caps. I may eventually replace the L-Pad with fixed value Caddocks.

Email me if you have any questions.

Rodd Yamashita
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Old 12th February 2003, 09:17 PM   #3
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Your friend is a lucky man; the 300's are IMO the greatest effort JBL has ever made in loudspeakers. I once tried to buy the raw drivers and the tweeters (o77 ring radiator) were unobtainable and over $600 ea. I still have one of the original brochures of this speaker.
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Old 13th February 2003, 06:39 AM   #4
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As well as rubber & duct-tape like Rodd has used, duct-seal works a charm for damping horns and speaker baskets.

dave
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Old 13th February 2003, 06:43 AM   #5
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Quote:
Originally posted by planet10
As well as rubber & duct-tape like Rodd has used, duct-seal works a charm for damping horns and speaker baskets.

dave
I know you can't see it in the photo, but there also are a number of muffler clamps under the duct tape

Rodd Yamashita
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Old 13th February 2003, 06:56 AM   #6
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Arne,

Try this JBL link for information about the crossover;

http://www.jblproservice.com/navigat...chematics.html

This will give you a diagram/schematic of the design if you care to update say the capacitors which would improve resolution. Or bi pass the existing caps.

The equivelant in the JBL Pro monitor was the 4333/4333A/4333B.

The latter two versions were biamp version with a switchable crossover. The drivers are identical to the 300, the crossover is number 3133.

I would image the Aleph (Aleph 3 or 5) amplifier on the horn and Slot if biamped would be magic, I currently use the Aleph 2 on my diy 4345 JBL 4 way wth a passive crossoover, its very smooth.

regards

Ian
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Old 13th February 2003, 08:40 AM   #7
Norbert is offline Norbert  Europe
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Arne,

you will find lots of information about JBL speakers and also about the L300 or 4333 Monitor here:

Lansing Heritage
Lansing Heritage Library
Lansing Heritage Forum
L300 Summit

Best regards,

Norbert
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Old 14th February 2003, 05:43 AM   #8
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Default RE:...

Thanx all !

Arne K
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Old 14th February 2003, 10:45 AM   #9
Doug is offline Doug  Canada
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Default JBL L-300

If you get or have access to audioXpress magazine, in the September 2001 there is article called " Resurrecting a Vintage JBL Classic " featuring the L-300. They do a complete rebuild on it.

I have been wanting to get a pair myself to rebuild. A friend of mine back in 1976 bought a pair and they made a lasting impression on me, very quick and powerfull bass. I could never afford a pair back then. If I remember correctly they cost approx $2500.00 per pair Canadian, a lot of cash back then.

DOUG
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Old 4th March 2003, 06:31 PM   #10
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I've got the L65, the L300's little brother, with the same tweeter.
About the crossover, I must say that replacing the stock caps with mundorf or audyn caps gives a much better, smoother and more detailed sound than simply bypassing the caps, especially to get the grains of the tweeter and the mids.
Also replace the stock inductor on the horn which is probably iron-coiled with a decend aircoil or if you got the money, a tritec or so.
Greets
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