5235 Input Transformers

[John W]

After looking at a few recent threads on the 5235 crossover, I noticed that mine is a little different from both the schematic and the other pictures that have been posted.
The crossover has a pair of Jensen JT-11P input transformers used for isolation and converting the unbalanced inputs to balanced (I suppose).

Does anyone know if this was something added at the factory, or is it a modification by a previous owner? Anyone else have these in theirs?

[JBL 4645]

I just highlighted a few words what you said hear and added a few and did a quick search on Google main web page and found this.

http://www.audioheritage.org/vbulletin/showthread.php?t=659 (http://www.audioheritage.org/vbulletin/showthread.php?t=659)

http://audioheritage.csdco.com/vbulletin/printthread.php?t=1388&pp=1000 (http://audioheritage.csdco.com/vbulletin/printthread.php?t=1388&pp=1000)

http://www.film-tech.com/warehouse/index.php?category=2 (http://www.film-tech.com/warehouse/index.php?category=2)

Something is up with my pdf, so you’ll have to scowl down the page and look for (JBL model 5235 crossover) under SOUND EQUIPMENT.

Then again you can sift though Google.
http://www.google.co.uk/search?sourceid=navclient&hl=en-GB&ie=UTF-8&rlz=1T4ADBF_en-GBGB246GB246&q=JBL+5235+crossover+modifications (http://www.google.co.uk/search?sourceid=navclient&hl=en-GB&ie=UTF-8&rlz=1T4ADBF_en-GBGB246GB246&q=JBL+5235+crossover+modifications)


Crossover schematic (http://www.jblproservice.com/pdf/Network%20Schematics/3143%20Network.pdf)
Peace.

:xmas:

[subwoof]

Those were a customer / user addition. Typically they were added when the xover / amp rack is in a remote location that has AC ground issues.

By isolating the inputs with transformers, no ground loop can occur unless the installer really screws it up.

The pair of those on ebay would sell for more than the crossover..:o)

sub

[boputnam]

Those were a customer / user addition. Typically they were added when the xover / amp rack is in a remote location that has AC ground issues. 'zactly.


The crossover has a pair of Jensen JT-11P input transformers used for isolation and converting the unbalanced inputs to balanced (I suppose).I don't believe this modifcation would have balanced the inputs - I think all it did was insert the isolation transformer for the obvious need.

My grab is, if you don't have a GL issue in your system, remove them.


...unless the installer really screws it up.
This does concern me - I hate to see undocumented fiddling with my stuff... :biting:

[John W]

Thanks for the info.

I don't really need them for isolation and it looks like an easy process putting them back to original.

[Mr. Widget]

Thanks for the info.

I don't really need them for isolation and it looks like an easy process putting them back to original.Don't toss 'em! Those are excellent isolation transformers. Who ever did it, spent money on the good stuff instead of using a cheapo box outside of the crossover.

If you ever need them, they can come in real handy.


Widget

[boputnam]

Don't toss 'em! Those are excellent isolation transformers. 'zactly!

Aas subwoof said, they arie indeed very pricy. Whomever did the mods, knew quality, that's for sure!

[jblbgw_man]

Don't know if I am missing something here, :dont-know but the 5235 inputs are balanced anyway, it is only the outputs that are single ended. The only difference adding the transformers would make is to increase the CMR from the basic opamp configuration.:xmas:

[Zilch]

And provide isolation, no?

[jblbgw_man]

And provide isolation, no?

If the drain or earth wire is only connected at one end then I still fail to see the advantage if already electronically balanced. (unless each source leg is of differing impedance OR if the balanced input is using a simple single op amp resulting in differing input impedances between the inverting and non inverting inputs which the 5235 is not) The transformer will tolerate this better without adversely effecting CMR unlike its op amp counterpart. Yes true there will be physical electrical isolation between windings, for? What purpose. :dont-know Unless you are expecting induced high voltage common mode surges on the line higher than the op amp can tolerate but never (in my sheltered life) in studio or live installations with properly (star) earthed mains supply have I ever had the necessity to use one and certainly not for home use.

Instances where I would and have used an iso transformer are where I might expect to find this high common mode voltage surge, say connecting signal between Studios and Transmitter site atop a mountain in a lightening prone area or between Link Hut and Transmitter site. Even in these instances the earthing (star) between these buildings are generally substantial and tied well together so still unlikely to find this high common mode voltage induced warranting an iso transformer, well not for audio, video being unbalanced well maybe.

In the same instances above but where the earthing is separate and not tied together or not star earthed then it would be more likely to be exposed to this and hence the use of iso transformers would be good engineering practise. I’m not sure but am I still missing something here? if so :banghead:

In summary, use an iso transformer for converting unbalanced to balanced input/outputs, improving CMR of crappy designed and cheap electronically balanced inputs and outputs where input and source impedances are not equal or where you are expecting high common mode voltage spikes and if using for the later then make sure the insulation of the transformer will handle the expected high voltage spikes otherwise there is no point to it.

So my bet in this instance is that they have been installed into this 5235 to improve CMR ......... NOW time for a beer !!!!!

[jblbgw_man]

Amendment to previous post .............. on checking the specs for the Jensen Transformer it would seem that what I have outlined in the second paragraph about lightening and long transmission lines is what this particular model transformer is intended for, even including gas discharge suppression. Therefore the conclusion for the inclusion of these transformers in the 5235 is that it must have been used some distance from or used on a separate earthing system/power circuit to the rest of the audio/PA system. http://www.jensen-transformers.com/as/as005.pdf (http://www.jensen-transformers.com/as/as005.pdf) with the benifit of improving CMR :p

:cheers:

[JBL 4645]

jblbgw_man

Lighting, gas discharge, good grief the guy is only using this in the home, isn’t he?:D

I know (ISO) stands for international standards organisation.

So what does (CMR) stand for?

Peace.:)

:tree:

[subwoof]

it's CMRR actually. someone misspelled it

Common mode rejection ratio.

Essentially it means the measure of how well a signal that is inducted on BOTH the hot and cold wires of a balanced line ( transformered or not ) is rejected at the receiving end.

You know - how many times you get rejected with the first line on ladies night divided by the number of consumed beers and multiplied by the cylinders in your car.

Big / high quality transformer / johnson means all your problems are solved....

Simple.

sub

[John W]

Don't toss 'em! Those are excellent isolation transformers. Who ever did it, spent money on the good stuff instead of using a cheapo box outside of the crossover.

If you ever need them, they can come in real handy.


Widget

Thanks for heads up.
I was actually researching these transformers seperately to provide balanced inputs on a couple of homemade amplifiers that are currently un-balanced only. After seeing the pictures on the Jensen sight, I remembered seeing them somewhere before.:)

[boputnam]

...the 5235 inputs are balanced ... only the outputs that are single ended (unbalanced). And, gentle readers note that the 5235 is Pin3 hot (+).

There's been much posted about the 5235 - good stuff in the 5235 Crossover- XLR to RCA adaptors thread...

[jblbgw_man]

Ok well I am waayyy tooo busy to learn how to multi quote for this reply but I will respond ....:banghead:

JBL4645 ... I agree, a distinct overkill for home use, I was just outlining an example or examples where this type of transformer would be useful, certainly not for home use.

ISO in this sense is short for ISOlation Transformer. (industry term)

CMR = Common Mode Rejection

Subwoof .... CMR is not a typo, the term CMRR is used only to quote a figure or performance if you like of a piece of equipment in dB's, WHAT I refer to is the act of Common Mode Rejection in general without quoting figures, hence CMR is a more appropriate terminology.:duel:

John W .... you will probably find a cheaper transformer for what you want to do without having gas discharge suppression inbuilt.:applaud: but if you have them you might as well use them.

Merry Christmas to all :sleigh:

[4343]

Back in Feb of '06 I bought the last two 5235's from jbl4ever, both have these same transformers in them. The install looks like a professional install, mine are almost identical to the photo above... I've done a lot of rework, so I know what a good job looks like.

[johnaec]

OK - I just opened up two 5235 crossovers here to pull the cards and both have the *exact* same transformer setup as the original post, transformer orientation and position, etc., down to the little drop of glue holding the wires to the board between the transformers! They had to be a JBL mod/option, or else someone did a whole bunch of them at the same time, to crossovers that ended up all over the place...

Actually, there might be some truth to that last statement. These were from a batch of about a dozen that someone was selling on here some time back. Maybe all these mentioned were from that batch. :dont-know

John