View Full Version : 4312 and L100 Restoration

04-27-2005, 09:14 PM
I found this forum after looking for speaker restoration tips. What a help. I'm the original owner of two L-100's I bought in 1976, and two 4312's I bought in the mid 80's.

I have a few questions which everyone could help me with.

1. In replacing the foam insert in the cover, there is a fine mesh cloth underneath. Unforetunately in the pre-internet days I used a hot melt to place non-oem foam in the walnut trimmed cover. I'm slowly getting all of that crap out in prep for a replacement either with the cloth used in later L-100's or modern foam.
However, I haven't seen any posts on what folks have used to replace this mesh cloth. In using cloth, are folks cutting 1/4" oak plywood to match the speaker pattern, and wrapping it with the blue cloth. If I dont use foam, what is the preferred method for mounting the cloth? Can anyone offer any help.

2.Is the blue OEM JBL type cloth available, or will there be another buy in the near future; where I could get enough to do 3-4 pairs of speakers? Where was that cloth bought, and can we just buy smaller amounts ourselves?

3.In my 4312's the crossovers sound "scratchy" when adjusted. What can I do to fix these? Can anyone suggest a reliable way to rebuild those to the original spec?

4. Like others, my wife used to look at my L-100's and say--Wow what a great place for a plant. Is there amu sure fire way to remove water stains, or do I just dry sand?

Unforetuantely I'm a chemist not a EE, so figuring out the design of the crossovers go over my head, however I have access to several EE's at work who'd be glad to help me rebuild them; if I can get the schematics for them. Either that or I'd go for having them rebuilt after I've finidhed the cabinet work.

Thanks for the help, I'm glad I found this forum. Over the years I've steadfastly resisted buying any of the smaller (so the sales guys say "better") modern speakers. I've always been quick to point out that in several movie theatre's I seen 4312 control monitors used for THX applications; but I've never seen these midget speakers used like that.

Thanks for the forum and the help in advance, JBL rocks.

Don C
04-27-2005, 09:51 PM
(1) Window screen. Velcro.
(2) Parts Express has good grille cloth.
(3) Replace the L-pads.
(4) Schematics (http://www.jblproservice.com/pdf/Studio%20Monitor%20Series/4312LR.pdf)

04-27-2005, 10:23 PM
I did a search, so whats the L-Pad?
I was going to replace the speaker wiring posts in the rebuild to accept larger wires. Should the x over and speaker connections be wired with larger guage wire.

When used in my final home theatre setup; I was going to go with a high end Denon amp, so I dont want any connection problems with an amp that'll push 170W. When I popped open the L-100s and 4312's I couldn't believe what was used for hookup wire. Looks like pre-monster wire days for sure.

I was also hoping that more of the cloth discribed here was available.

04-27-2005, 11:05 PM
1) Fiberglass window screen.
2) I am buying a bulk lot of JBL Monitor Blue grille cloth. It'll be 8 to 10 weeks before it gets here. Send me a PM with your eMail address to get on the list for notification.
3) Parts Express has L-Pads. They're the two level controls there.
4) You'll have to lightly sand and re-oil. Search the forum for refinishing threads.
5) As long as you can get 16 Ga. speaker wire in the terminals, don't bother replacing them.
6) The internal wiring of the speakers is fine, and doesn't matter one whit. Ask your EE friends about the wire hype you've been listening to.

04-28-2005, 11:17 AM
You can also just try cleaning the L-pads. Spray some de-oxifier into the vents and move the knobs around a bit. This will clean them up and may be all that is needed.

04-28-2005, 12:36 PM
...if I can get the schematics for them. Not knowing which iteration of the 4312 you have, here's all the schematics for the entire series. Note that:

The first 4312 ("3112") has a LF polarity reverse that of later 4312 iterations ("3112A, A&B, C")
The major network evolution in later issues is the 0.01 uF bypass caps.

04-28-2005, 12:39 PM

04-28-2005, 07:36 PM
I assume you are speaking of the cloth on the grille frames for the L100s. I make exact foam grille replacements for the L100s and can either help you in replacing the cloth on the frames or better, if you send the frames to me, I can repair/replace, and install new foam grilles. More information and pictures of my work are on this forum site (see info on L100 raffle held recently).

04-29-2005, 04:15 PM
I assume you are speaking of the cloth on the grille frames for the L100s. I make exact foam grille replacements for the L100s

Can we assume that you are set up and making exact Quadrex grilles?

04-29-2005, 06:03 PM
Pls send me a PM, or email me at lgvenable@charter.net about the grills, and we'll work out the details as to which way I go