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Heres a question, has anyone rebuilt their factory N1200 crossovers? I was just listening to my 001 system and was wondering if a rebuild would enhance their sound? I thought I could google and a million topics would pop up about people modifying/rebuilding the xovers but notta. So I figured I would ask? Like the saying says "Curiosity killed the cat" :p
Is the later pro 3120 the same schematic? I think so, not positive. Certainly very close. But, I have experimented with the 3120 - tried a Solen in place of the 13.5uF "high pass" cap along with .01 by-pass caps on all three caps. Sounded pretty good to me - smoother, more open, natural. But, it is easy to work on - you can snip off the leads and just clip in the experimental cap with alligator clips. If you don't like it, go back to std. One test is worth 1000 expert opinions! I'd say the .01 by-pass caps are a "given." Could try that first. Barron 030 here on the site has done a lot of stuff with the old stuff as well - might 'search' his name. Mike
P.S. I have yet to find a failed / degraded cap in these old JBL crossovers (I measure 'em after I replace them). So if yours sound good, they probably are good. But the newer polyprop, etc. caps do sound somewhat different. It's an experiment and you are the chief engineer.
Hi Cooljjay
Well I never owned a 001 system. So, I don’t have any first hand experience working with a N1200 network. But, that is not to say that I can’t come up with some suggestions. In looking over the schematic and surmising how JBL would build the network. I could see a few areas where there could be some improvements. Replacing and by-passing the caps would make a noticeable improvement. Since, a 13.5uf and the 16.5uf cap values are not very common.
You could use a 12uf cap and a 1.5uf cap wired in parallel for the 13.5uf cap value.
And for the 15uf cap and a 1.5uf cap wired in parallel for the 16.5uf cap value. And Solan or Jantzan CrossCap would be a good choice for brands, without spending a lot.
The other area where there could be some improvement would be replacing 1.4mH coil (L1) with either a higher power rated iron-core coil or possibly a heavy gauge air-core coil. The bass will sound cleaner at higher power levels with a higher quality coil. But, there are two issues that you are going to run into.
1. After checking a part express catalog, a 1.4mH coil does not appear to a stock value.
So, this would require purchasing a 1.5mH coil and remove a few turns to get the correct 1.4mH value. And this is not something that should be attempted unless you have some test equipment. A simple LCR meter is required. If you don’t have the test equipment then maybe a local LH member could help you out with the modification for a beer.
:cheers:
2. And finding a new 1.4mH coil that would physically fit inside the case. Alternatively, the aluminum back cover plate could be replaced with a fiberglass board and the coil could be mounted outside of the case with nylon wire ties. (McMaster-Carr # 8549K44 is a source for fiberglass board)
Since, there are no stock replacements for the 1.1mH (L2) tapped-coil there is no way of improving its performance without hand winding a replacement coil from scratch. So, I would handle that part with extreme care during any network overhaul. If you do plan on overhauling your N1200 networks and you have access to an LCR meter. Please measure the inductance values of the L2 coil are all of its tap points and post the results here. To my knowledge, the exact inductance values have never been posted here and the schematic does not list them.
And considering, the small size of L2 coil it could be possible to hand wind a tapped coil without a lot of expense, if you were to start with an “Erse I Core” coil as a base. It would just take a lot of time to make.
Link to the schematic: http://www.jblproservice.com/pdf/Net...tics/N1200.pdf
Baron030:)
Hi Cooljay,
I rebuilt my N1200's when I noticed a difference between my 2 Harkness cabs. After melting through the wax and testing the caps, some were almost twice the stated capacitance.
Baron's suggestion is a good one, the results for me were quite noticeable and worth the time. My only suggestion would be to build up the new crossover on a new mounting plate and preserve the original, I kind of wished I had done that, you wouldn't have to deal with the wax.
Good luck
For the benefit of anyone wanting to make a new network from scratch, here is an option for making the networks circuit boards. It called a “Turret Board” and it is something that I am thinking of using for my next project. The following link has very detailed instructions for making a “Turret Board” and the link also has all of the parts required. Actually, these instructions are for building a tube amp circuit board. But the techniques described still apply to all circuit boards. And I have also included a few other sources for parts.
Turret Board Instructions (PDF file): http://www.tubedepot.com/boards.html
Fiberglass Boards: McMaster-Carr # 8549K44 (other larger sizes are available)
Keystone 1540-4 Turrets: Mouser part# 534-1540-4
In the case of the N1200 network, the big thing that is holding people back from building their own N1200 networks is the L2 auto-former coil and possibly the S1 rotary switch as well. And I think that if someone digs deep enough, Mouser probably has an exact replacement part for the S1 switch.
Actually, the cost of test equipment has come down over the years. I currently use have a Parts Express DMM and LCR meter (# 390-513) and it is more then accurate enough for just about any project. And the reason why I can attest the accuracy of this relatively cheap LCR meter is that I have done direct impedance measurement comparisons using Cliowin 7.13 lite software. And the results are well within 1% of each other.
Baron030:)