For clarity can you advise if you are modifying a stock 3143 network?
Not quite. The network I am rebuilding is one I built to the JBL design using "replacement parts I bought from JBL I did not buy the parts for the high pass of the 10 inch or low pass of the 15 inch so no switch was needed. I just go in where the switch would have allowed me to enter for a biamp setup.
Or do you plan to build your own network?
I plan to build the JBL 3143 but using higher grade caps and inductors and resistors, but only the components aabove the 15 inch driver circuits. It will be as if I used their switch.
I do not plan to change any values. I will be widening the baffle of the 10 inch and horns to the JBL 4343 width.
I have a 6 cubic ft cabinet containing the 15 inch which lies on one side. By turning it over I will get the 18 inch spacing of 10 to 15 inch driver centers in the 4343 within a quarter inch.
The stock 3143 has been arranged to provide a smooth transition between all the drivers allowing for their locations on the front baffle.
The network also provides the option of internal passive or external bi amping with a multi pole rotary switch. The switch isolates the woofer from the LF filter elements on the woofer and the HP elements on the mid cone driver.
I never installed these or the switch.
It should be noted the voltage drive for the active crossover of the woofer and mid cone in the 4343 has been specifically tailored for these particular drivers and their location on the baffle.
You will NOT get the correct results with other than the designated voltage drive. A simple search will locate these elsewhere on the forums.
I may have a problem here as I am going to use a Marchand 24/octave crossover for the 10 to 15 inch transition. I have gotten two cards set at 300 cps and 2 set at 400 cos to allow me to try different combinations including some overlap. I know JBL did some things like mating 6 with 18 dB/octave slopes. I was trying more for time alignment than necessarily purely flat responce. I miss the sound I used to get from the L300 which covered most of the bass and lower midrange with the 15 inch.
Refer to the 5234/35 Pdf manuals for the active filter RC values. It should be possible for Marchland to provide a customised card. If you get this
right the active mode will be subjectively better with the Amber amp on the mid/top end. No question of that. Get it wrong and you will spend a lifetime wondering why it sounds not quite right.
I recommend you build new networks rather than attempt to upgrade the stock 3143. The reason is the bi amp switch will hinder any gains and replacing parts in the stock network will be difficult.
You will also need to be very careful with all the phasing on the drivers. Again, I have no switchand never did. TIT has been biamped from the time I bought the 2121 midranges. I currently have the unit biamped at 300 cps with a Marchard X1 set (24/octave). I had tried variations of 6 and 12 db/octave with a heathkit active but the 24 seems better. It is not too bad but I wanted to be able to play a little with overlap to see if I could get it a little flatter and also wanted to upgrade resistors, caps and inductors. I already purchased the caps and resistors I think will be good, but am still looking as to how closely I need to match air core to iron core inductor DC resistance. I know it has to be an external series non inductive of 0.I ohm or less. The inductors come within a tenths of an ohm of one another for the 0.16 and 0.25uF but am off by 0.1 ohm in the 1.0 and 1.7. I only have a meter sreadout to the nearest tenth of an ohm so I cannot measure closer than about the nearest 0.05 ohm. I was trying to learn if that is significant or not. The DCR 's range from about 0.2 ohms to 0.5 ohms among the 4 iron core units from JBL but are about 0.1 ohm lower in the air core ribbon inductors I was considering for the 1.7 and 1uF inductors. Also the replacements are 16 gage which is probably a heavier gage than in the JBL, at least by micrometer diameter measurement on the JBL coil wire. What I don't know is how meaningful that diffeerence is. The ones with the big difference have padding of 2 to 4 ohms to back lower the driver efficiency to match the horns in the circuit, not just the L pads The L-pads for the horn and 10 inch are 16 ohm, again stock JBL replacement parts.
If it were me I would write to Giskard nicely and arrange a pair 2122H to replace the 2121 and get new diamond surround aluminium diaphragms for the compression driver and get on the list for V 3 of the 3145 equivalent network. You stand to gain light years more from this approach than merely putting in better parts.
As a side note, I do have a second set of horn drivers I got a while back. They are the pro designator units with the diamond surrounds, not visually similar to the LE85's. Instead of big and black cylinder shaped magnetic assemblies, they are gray and angular in the magetic region and I think they had the rubber rings on them. I have them in a second set of cabinets with another set of 15's for the TV and used the old longer horns and the L200 JBL crossovers. Should I be swapping out the magnetic compression drivers??? Rightly or wrongly I always thought the design change was for use of the ferrite magnets since alnico became tough to get due to commerce on the nickel from Africa because of so much political turmoil. Not as good, but available and with some design changes could simulate the quality of the alnicos.
I am really trying to avoid changing out the 10 inch drivers. If I do that, it will set me on another project looking for a way to use them somewhere. I am one of those nuts who does not like to see things go to waste.
What is starting to worry me is that using the 24/0ctave instead of the passive network or JBL 12/0ctave active unit may cause a problem. I know they like 12/octave with flipped polarity. Second order seems to be a standard for a lot of pro gear so I thought that is the reason they used it and 24 should be better, but if they have something else in their active circuit that is designed to overcome some impedance peaks in the drivers, using the 24 in standard polarity could be a problem. I don't know how to search the forums easily. I get moved around to a lot of different threads and wind up reading them oll only to find I learned something but not what I needed. I already have my new caps and resistors in hand (and paid for) so I would hate to start over. The caps were not like I bought Mundorf Silver gold or the like (I got Clarity Caps and 1% Dayton 0.1uF polypropllene and some 0.009uF polystyrenes for jumpers) but still I have a couple of hundred bucks in them. I really don't want to start over. I still have another Nak ZX7 and 682 ZX to get fixed as well as a neat McIntosh 240 amp to have repaired. I just retired so I am not broke but have to be a little cautious. Time for new windows this spring too! In addition, my earing in the HF range is lousy at my age. I think it is down about 80 dB above about 8k. Even have trouble hearing vocal sybillants. Stuck an 075 bullet in my center speaker for the TV so I can understand speach.
Now that I bled for a while, can you tell me two things (I know, all tell me to go a different route and I cannot seem to hear them)
1) how close do DCR's have to match if I go to air cores? Should I add some 0.1 ohm series resistors to the air cores to better match them? I cannot get much closer than around 0.05 ohms since I don't have a meter that reads past 0.1 ohm.
2) with a 24/octave between the 10 and 15, is there a phasing/time alignment problem using the stock JBL baffle layout?
As a side note I had considered inserting a second active and using the McIntosh for one or both horns. Just taking this a step at a time for now though.
And Ian, thanks for the help. If you get a chance take a peek at http://sheneskillies.com My other bigger hobby.
Ian