L100 Century polarity

[B. Schafer]

My father has given me a lovely pair of L100's circa 1972. The speakers are aligned in a vertical array. I would guess that the black is + and the red is - on this speaker, since it is a JBL of this vintage. Can anyone confirm this? The 9 volt test scares me, whether it should or not. Thanks!

[Rex Mills]

I believe you are correct on the polarity, cone should move forwaed with a positive signal at the black terminal. If the 9 volts scares you, try any 1.5 volt battery, such as AA or AAA.

[boputnam]

The 9-volt test won't damage the L100's. It is indeed a brute-force level of test, but the large transducers (123A woofer) can handle this, and it won't get through the crossover.


I am fairly confident the L100 cabinet is positive. But, you can run the test easily enough. It is important, however, that you test the cabinet through the binding posts. The wiring to/from the crossover can reverse the action of the transducers. If the battery posts don't align for a simple connection directly to the speaker posts, grab a small length of lamp cord to shunt the two posts (+ to red).

The 123A is positive (cone excursion out on positive signal) which is quite anomalous for it's vintage. It may be JBL designed this transducer positive for its pedestrian use. The similar vintage 4312 is cross-wired so that the 2213H woofer (which is negative) runs positive.

email with questions.

[4313B]

Here's a little cheat sheet for the L100/4310

[boputnam]

Giskard...

You have a simply stunning and vast wealth of JBL knowledge. Incredible. I have JBL Envy!

I picture you surrounded by exotic transducers, jars of Aquaplas and long-lost mass rings, woofer brackets and compression drivers, walls lined with ring binders stuffed with network schematics and T-S parameters.

Wow.

Here's me:



Ha! (I hope that's nobody on this thread!)

[boputnam]

But a bit more seriously...

That cheat-sheet is real interesting. Do you have (in that vast resource of JBL-ness of yours) schematics for the C533, L100, L100A, and 4310? Or Links to same?

Thanks.

[4313B]

Yeah, I have schematics, but I've never gotten around to scanning them into a computer. The schematics are on the cheat sheet anyway, 13.5 uF S = 13.5 uF in series, 1.0 mH P = 1.0 mH in parallel, so you can sketch them up easy enough. :)

[boputnam]

Yea, true enough. I was intested in seeing the signal path, because with the 123A being positive, the LF cone excursions as noted are not what I expected.

Thanks, as always.

[4313B]

So, if you pull the LE10H out of the 4313 and put the positive terminal of a 1.5V or 9V battery to the LE10H's red terminal you get inward cone motion and if you do the same thing with your 123A you get outward cone motion? Which 123A do you have? -1? -3? or is it a 2212? What model loudspeaker is this out of?

[boputnam]

LE10H moves in.
123A-1 moves out.
As I posted here, 18 April.
http://www.audioheritage.org/vbulletin/showthread.php?s=&threadid=9

It is not a 2212.

The 123A-1 was from an L100 (not mine...)

[4313B]

Well that's goofy then, fortunately the 2212 is the only cone kit available for the 123A-1 so as those drivers are reconed they will be corrected. The schematics are based on the fact that all JBL transducers exhibited forward cone motion when positive voltage was applied to the black terminal.

Fortunately the L100/4310 sounds so terrible I'm quite sure whichever way you wire the LF will have no bearing on sound quality unless you're thinking "lesser of two evils".

ROFLOL, OMG I crack myself up! :p :p :p

According to recent events on ebay, if I hadn't tossed those four pair I ran across a few years ago into the trash I would be $4,000 ahead of the game :rolleyes:

[boputnam]

I peed myself when I read that...!

Especially the line..."as those drivers are reconed they will be corrected."

Negative is good!!

;-p