Info on the Yamaha JA-6681 compression driver - Page 3 - diyAudio
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Old 7th April 2010, 05:44 PM   #21
djn is offline djn  United States
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I just happen to ask a friend if he had any old stuff, speaker wise, I could use to build up a pair of speakers for an unemployeed friend and the Yamaha is what he drug out of his garage. I bet if you have a prosound guy near you that has been around for a while, he might have them.
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Old 7th April 2010, 06:51 PM   #22
Radian is offline Radian  Germany
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Quote:
Originally Posted by winslow View Post
Where are you guys finding the Yamaha drivers?
They are getting really rare. Five six years ago the poped up on ebay more often.
Meyer Sound used them in many of their products that had 1.4" drivers.
It is the MS-1401a - the 1401b is based on the Radian 1" driver.

I stand by what I said in the other thread, that the Radian 850PB is very
close to the Yamaha JA-6681. About equal in the mid range and better from
10k up. But it will not do 250hz like the Yamaha. I see no point in using a
driver that low as the radiation pattern suffers allot with big tractrix or
LeCleach horns.
If the back chamer of the Radian is made bigger and some absorbent material
is used to get rid of the crazy reflections in the stock Radian, I am quite sure
it will hold it's own against the Yamaha.
The Yamaha will not do without a Tweeter as it falls off rapidly above 12khz

Greets,
Klaus
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Old 12th April 2010, 05:29 PM   #23
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Hi,
I am the lucky owner of the JA6604 of the ebay auction stated above.
Or should I say unlucky, the magnets were decentered and one diaphragm broke during shipping.
I also own a good pair of JA6603, one of JA6681B and one of MS1401A.
The ring tweeter used is the JA4281B, and I have some JA4205 (again one with shifted magnet because of shipping ...)
I reckon the larger drivers have the same magnetic assembly and the same phase plug as the smaller ja6603 ones.
All of those drivers sound fantastic (and I owned the JBL 2431h wich were not bad drivers ...)
I will be very interested in any info, I will also try to share the data I gathered about yamaha pro speakers ...
Lagroute
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Old 12th April 2010, 05:58 PM   #24
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hi Lagroute

what is the difference, soundwise, between the JA6681B, and the 6604 ?
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Old 12th April 2010, 08:15 PM   #25
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None to my ears, as those are basically the same drivers. most of the small differences were because of the horns (1.4 inch for the 6681 and 1 inch for the 6604).
In fact, you can consider that the 6604 is the same driver as the 6681 if taken with a 1" 1.4" adapter. And with a less beautiful casing.
The problem is, the 6604 is maybye even more rare than the 6681. Never seen one on the internet, except those I bought.
The 6604 shares all the mechanical parts with the 6603, only the diaphragm is different. The 6603 sounds extremely good, and I think that it is an underrated driver. It is as good as the JBL and Altec phenolic horn drivers, for a fraction of the price (considerig you can grab a pair on ebay for less than 150$ when it shows up).
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Old 12th April 2010, 11:38 PM   #26
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How is the diaphragm different?

Any chance of jpegs of the back end looking at the diaphragms?

_-_-bear
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Old 13th April 2010, 06:32 AM   #27
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JA6604 : the same aluminium with copper berylium fingers as the 6681
JA6603 : phenolic diaphragm
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Old 13th April 2010, 09:38 AM   #28
Radian is offline Radian  Germany
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Quote:
Originally Posted by bear View Post
How is the diaphragm different?

Any chance of jpegs of the back end looking at the diaphragms?

_-_-bear
The 6603 diaphragm is phenolic and goes only up to 8000hz and dies out
gracefully without any breakups. Perfect if one, like me, can't stand
tweeter-less horn setups.
The 6681 diaphragm is aluminum with a uniqe surround. It goes up to
12000hz and falls off quickly after that. For some classical and club music
it can be used without a tweeter, but that's not my cup of tea.

As has been pointed out before, the whole 6603 motor is identical to the
6681 but most of the time can only be found with shifted magnets.
Mine was shifted to the point that the coil was clamped in. With a plastic
hamer and a measuring tool to adjust engine valves it can be precisely
realigned. BTW the whole Standard-Line (raw aluminum) had the shifted
magnet problem. One of my bass drivers out of the 5115H cabinets
was also rubbing because of this problem. It seems that Yamaha used
inferior glue, to hold the magnets in place. Actually they might just have
used screws to clamp in the magnets, as I see two screws close to the
6603 drivers exit that I do not remember having seen on the 6681 when
I had them apart. My bass drivers have those two screws also.

Greets,
Klaus

Last edited by Radian; 13th April 2010 at 09:45 AM.
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Old 13th April 2010, 11:17 AM   #29
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I had a problem of broken magnets (yes broken) on 2 jA3882 15' woofers and on one of the 6604 ... maybye the ferrite used was not that great also ?
Anyways, they must have done a really good job to make such good sounding drivers with not so great materials.
All the horn drivers were intended for use with ja4205 / ja4281 ring tweeters. Those are the best tweeters I know. I made comparisons of ja4281b against JBL2405 2402h and fostex ft96h, the yamaha were the smoothest and the more natural sounding. the others sounded agressive and the JBL were agressive AND less detailed.
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Old 13th April 2010, 12:37 PM   #30
Radian is offline Radian  Germany
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Funny that Yamaha and Emilar ceramic drivers can reach the sonics of those
expensive Alnico Beryllium drivers.

As for tweeters, I never understood why people pay so much money to get
a pair of JBL tweeters. The Fane ST5020/22 walkes all over them.
Have you compared the ja4205 to the ja4281?
My ja 4205 could not reach the smoothness, airiness and detail of my Fanes.
Sad that Fane stopped producing the ST5020/22. It was the best bang for
buck tweeter out there. When crossed wrong they sound agressiv too
though.

Greets,
Klaus
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