Hello,
After few month I had collected all drivers for 4 way: 2235H - 2121H - LE85+H91(Blue) - 077. May I follow below schematic or need to modify something for 2121H and LE85. I think 077 can take 2405 cross of 4344 is fine. I will built cabinet 4344 because we have very detail drawing in this forum.
Attachment 77274
I recommend that you bi amp your project
This will significantly reduce complexity and cost of the passive crossover and improve the dynamic performance of the loudspeaker
Concerning the schematic that particular version of the circuit is the 4344/4345.
This version has component values and voltage drives optimised for the 2122H mid cone.
I will investigate what revision of the original 3143 factory was applicable for the 2121 midrange driver.
The 2122H driver is now NLA and people are either making a driver using a 2123 or E110 basket with an after market recone kit.
Okay,
I spent a while looking at some old threads on the subject of the 4343 3143 network.
At the time (2003-2005) most people were interested in restoring old 4343 or upgrading to the 4344 model.
The 2121 driver used in the 4343 is known for some break up modes and at the time it was felt that most people would benefit from a new equivalent crossover to incorporate the improved 2122 driver as used in the 4344-4345.
The crossover schematic you posted is the charge coupled network for the 2122 as used on the 4344 and 4345.
An updated schematic for the 4343 was not investigated and those who decided to keep the 2121 driver simply updated or re built the 3143 network or they used the 4340 schematic which is bi amp only.
Suggest you check the condition of the 2121 foam surrounds. There is nothing wrong with the 2121 driver, the 2122 driver is a refinement.
The 4341 was the passive only version.
So you have some decisions:
Use the 2121 driver Y/N
If "Y" build a 3143 or 3140 network (can be charge coupled)
DO NOT attempt to cut and past parts of the original 3143 network with the updated 2122 network as you will find yourself in a huge mess based on recent feedback.. The voltage drives are not compatible.
If "N" investigate a 2122 driver but very hard to find or the 2123 (but requires a specific network)
See this post
http://www.audioheritage.org/vbullet...ll=1#post66931
Thank Ian,
here is my 2121H foam surrounds condition :crying: it not so nice but I will keep and re-foam therefore I chosen "Y" and go for 3143 cross as you advised. I don't seen charge coupler for 3143 yet and I will try to find.
Attachment 77295
I'm wonder why 3143 with 52uF filter but 3140 wasn't. The inductor 2.9mH are necessary or not because it also not appearance on 3140.
Attachment 77296
All your questions are highly relevant and frequently whenever the 3143 network enquiry comes up.Quote:
Originally Posted by hpham
Firstly, visit this thread on re foaming if your intend to attempt it yourself.
Otherwise I recommend a qualified technician to avoid damage to the cone and voice coil.
There is some debate on the authenticity of after market re cone kits in terms of obtaining the drivers original specifications.
Look carefully before you purchase your re foam OR re-cone kit.
It may be possible to buy the JBL 2121 recone kit.
Pm member (Edgewound to confirm this)
http://www.audioheritage.org/vbullet...d-Step-by-step
Secondly, There is no charge coupled network so I will post a schematic given you plan to use the 2121.
Can I confirm you intend to run your project full passive OR Biamp?
In relation to the 52 uf capacitor this question also comes up with the 3143 network.
For clarity the 3140 network was the bi-amp only version for the 4340 monitor.
The 3143 network was designed for switchable operation from passive to bi amp mode in the stock factory.
It was later found that this switch was at the request of the marketing department and is a departure from the most direct and pure signal path.
Because the biamp high pass filter for the 2121 is done actively in the then 5234A active crossover the 52 uf capacitor and then 2.9 mh inductor is not required.
To improve protection of the HF and UHF drivers from amplifier turn on thump the signal is taken after the 52 uf capacitor in passive mode. (It took a while to understand why JBL did that)
Simplified 3143 charge coupled schematic
I can provide you more detailed information on how to build this.
Send me a pm
Simplified 3143 charge coupled schematic (simulation Linearx LEAP Crossover Shop)
I can provide you more detailed information on how to build this.
This should be rather good in charge coupled configuration
I might even build this myself
Send me a pm
As a side note while I was looking through some old threads a member wrote he found some new old stock grey 4343s and set them up at home.
Apparently they absolutely killed his Klipschorns.
But they were stock 4343s so if he still around he might be interested in this.
Ian
An often overlooked but critical factor in crossover network design & implementation is the DCR of the inductors, which directly determines th " Q ", and therefore the steepness of the slope of the pole in which it is used.
A crossover section, which is an electrical filter, is made up of a number of poles connected to each other in order to approximate the desired steepness of slope and passband characteristics.
So if your intent is to copy the performance of the original network based on its electrical design and its interaction with the connected drivers, you must know the original inductors' DCR and incorporate this resistance value into the clone inductors' total series DC resistance.
For example, I had some 3107 networks, that each had two 1.8 mH inductors which in conjunction with the capacitors used made up a 12 db/octave network which controlled the response of the 4350 Studio Montor's 2202 midbass and 2440 midrange drivers.
The 1.8 mH inductors each had a DCR of 3.5 ohms, far higher than you would expect in a typical OEM coil which tend to be of low resistance.
A high quality non-inductive resistor of the proper wattage can be added in series with an inductor whose DCR is less than that of the original unit, to achieve the needed total series resistance.
Some of the less mathematically challenged than I members here might elaborate on this basic premise.
I hope this helps in you project. Regards, - D _ E -
You are correct
That is why JBL published voltage drives into the standard test jig are useful and this has been the key in all the equivalent schematics to date.
What is interesting is the stock network is not unlike my own diy network l did back in 1979. That system has been legendary.
But there's always room for improvement so l plan to put in a charge coupled network
The John Eargle book Handbook of Recording Engineering has much of JBLs thinking on crossover network of that era and that was the basis of my original network
The posted simplified schematic is a primer.