250Ti Jubilee happy unhappy
Hello JBL Lovers,
since one month my youth dream comes true: I´m an owner of a pair of 250Ti Jubilee. I love them. No WAF needle at all. At school days in my youth I heard the Original 250Ti in an HIFI exhibition in Düsseldorf (Germany) amplified with the extraorinary Harman Kardon Citation XX monster. They played fine songs and when listening to the climax drum solo from Saga ("a brief case") I got tears in my eyes. I swore myself that one day I will get these huge babies.
Well, I read in this forum quite a lot but still have some questions, perhaps Giskard is the right guru :applaud: to answer but I´m happy for any answers/suggestions/infos etc.
In my 250Ti Jubilee a (expensive! bought by my predecessor) network is used made completely by Mundorf (unbiased)wich gaves too little heights and middle, that I would like to compare once against the biased original (which I also get had of the salesman). There is a -4dB reduction for UHF and -2dB reduction for the HF, which I (hopefully) will change to +- 0 dB this weekend. And another failure was made in taking the wrong value for Resistor R6 (1Ohm instead of 9.1Ohm, how does this result "in the ear", giskard?)
I have read already almost all threads in the forum belonging to this and have some points in the original network schematics that perhaps are false? (e.g. the LE14H-1 with pos. (+) marking in the network schematic stands for "outward cone movement with pos. voltage to red input terminal". My LE14H-1 moves inward in this scenario!
I also read the JBL convention on polarity (for the old chassis), where black in JBL sense is always plus instead of black in the rest of the world. But at some time this was changed to agree with other manufacturers. But when?
The cabling for MidFrequency Chassis (MF) and woofer (Low frequency, LF) are made of "strip and tin" while the others uses male/female connectors to make sure not plugging wrong.
I know simply not certainly which cabling poles to chassis obtains the best results. A/B hearings are not easy but possibly (Phases switch to single chassis like Dr. Electron has told). Sometimes it´s the willing of the designer (G.T.) that single Chassis are plugged in reverse in order to minimize the joint area of frequency through phases rotation.
Who knows which cable connects to which port of any chassis connection originally?
Other hints/success moments? Assembly hint experiences? Questions?
All is wellcome. All listeners are wellcome to hear here...
Hope this text is not too long/too bad english or boring too much:blink:.
Pictures can be send if some wanted.
Thank you very much in advance and sincere greetings out of Ebringen (in Freiburg, D)
Mike. :bouncy:
Low Tweeter Output & Polarity Reverses
Filigran,
- Did Mundorf actually build this replacement network for your 250 Jubilee ?
- It would be helpful to others who may want to help you , if you posted a picture of the schematic for this (converted) network . JPGs , .gifs, and pdfs are easily posted here ( among a few other file types ) .
- Since the Mundorf network isn't "biased" and the original Jubilee is ( biased ) , something may have gone wrong with the value conversions for the passives .
There is a file size limitation for attachements , as well as a limitation on any images' width & height. These guidelines are speced out by the Administrator in the Information Forum .
- Also , your first post contained a reference to "R6" , being a value of;
Quote:
(1Ohm instead of 9.1Ohm, how does this result "in the ear", giskard?)
- Is that what you actually meant ? 1. Ohm vs 9.1 Ohm , or is the above, just a mistake in typing ( ie; missing the "0" in 10 Ohms ) ?
Quote:
Unfortunatelly there is no systematic [(+)/(-) vs. red/black] how the polarity is to the single chassis
- Does this mean that your replacement Mundorf network is internally wired utilizing 4 pairs of red & black wires ?
- Or, does the internal wiring in your replacement network follow the same color code conventions as the original Jubilee network ?
- Are you experienced at tracing ( or tracking-down or identifying ) which wires are the ground wires in a multiway passive crossover ?
Quote:
Who knows which cable connects to which port of any chassis connection originally?
- The designer determines which polarities for the various drivers gives the best acoustical summation through the 3 distinct crossover areas .
- All the various 250 networks do indicate whether or not a driver will "suck-air"/ or rarify/ move backwards ( when connected according to the diagram ) or if the driver will "blow-air" or compress/move forwards ( when connected according to the diagram ) . What's most important to observe ( IMO ) is the various polarity relationships that exist between the 4 drivers .
Quote:
The cabling for MidFrequency Chassis (MF) and woofer (Low frequency, LF) are made of "strip and tin" while the others uses male/female connectors to make sure not plugging wrong.
- Your focus is too narrow & likely too simplistic/naîve . You need to broaden it to hopefully find the full magnitude of any possible polarity problems built into your custom network .
(1) For instance ; Just because someone installed "sexed" connectors on the colored wires in your replacement network doesn't mean those "sexed" connectors are on the right wires .
(2) I'd suggest you; Go back & do the 1.5V battery test of the 3 coned drivers. Note which color of terminal or shape of tab gives an outward movement when you apply a positive DC voltage.
- Remove one tweeter and then see if it has identifying "+" & "-" markings .
- I'm not sure if the battery test is wise to apply to a tweeter like this ( maybe someone can enlighten us ) . I'm also not sure if you would see any diaphagm movement if you did apply 1.5 volts DC.
(3) Once "you" know which terminal gives outward cone movement on each of your 4 drivers "&" once "you" know which wires on your crossver represent the common/negative/ or drain wire of the replacement crossover,,,,, then ,,, you'll can get some meaningfull advice on how to wire it up properly according to the intended polarities of that network .
Some House-Keeping Tips
- If you are going to add your replies inside of my entire "quoted" post , then will you please make it easier to differentiate your text from mine. There are a bunch of ways to do that.
ie; Colorizing your text is an easy way to do this .
- colorizing is accomplished by surrounding the chosen text with ["color=blue] & [/color]. Leave out the " in the first bracket .
- to italicize ( outside of a quoted post ) one would add ["i] & [/] around the text to be italized ( again, leave out the " sign within the first bracket ).
- so to colorize and italize "this Example !" , you would write :
["color=blue]["i]this Example ![/i][/color] - Now leaving out the two " characters it becomes : this Example !
Which is much easier to spot and focus on in a sea of black ink !
:) - Thanks !
Missing db in the HF & UHF areas ?
Hi filigran
As far as I see it , if you are missing output strength in the HF & UHF areas, the reason(s) must be from one ( or a combinations of ) the following three possibilities .
(1) The custom crossover you are using was made with the incorrect value resistors.
- You can easily determine if this is the case by comparing the value of the present resistors to the values speced for the N250Ti Jubilee.
(2) Your custom crossover may have inductors that have higher than speced DCR values .
- Again, You can easily determine if this is the case by checking the DCR values of the present inductors to the values speced for the Jubilee network.
(3) The usage of Mundorf capacitors has drastically changed the "voicing" of a system that was voiced for "bypassed" , "DC-biased", "electrolytic capacitors".
- This is a possible explanation and not as far fetched as it may appear , though it relies on accepting a phenomenon that's not talked about much ( at least not around here ) . Since I've never heard Mundorf caps / I can't speak with any first hand experience on how they might effect the overall voicing of your 250ti system.
- I have found in my own studies on caps , that as caps get smoother & deeper sounding / there can be a perceived level-drop to the UHF area . I haven't found it to be measurable / but subjectively the effect is very real . I've even taken to bypassing smooth sounding networks with sharper sounding caps - just to restore a sense of "loudness" to the UHF area . Also, I find that smooth/deep sounding network legs ( a compression driver circuit in my case ) must be turned up a bit to restore subjective balance ( when balanced against woofers ) . This increase is usually confined to the neighbourhood of a fraction of a db ( maybe .5 db ).
- The Mundorfs just might be subjecting you to this effect .
- You will need to reduce the resistive padding on these 2 network legs to test out this idea .
- A problem in attempting to change the amount of tweeter padding ? One needs to know the AC impedance curves for the 2 top-end drivers to reasonably alter the values of the padding resistors.
- I don't have those curves to give you / maybe someone else does and can post them.
- Without them, you will most likely change the circuits' working impedance in that area. The preceeding LC components are set to work to a specific impedance. A change in working circuit impedance will result in a shift to the crossover points. Not a good thing .
:)
