The 2405

[mantisory]

Hi everyone.
I am a newbie to the whole world of JBL, Altec, and SET. I recently purchased a pair of speakers using the 4560 cabinet using the E145 driver, along with a 511B using a 2426 compression driver.
The thing is, I generally have to heavily EQ this setup because the 2426 driver rolls off way too quickly, to my ears anyway.
So I am purchasing the JBL 2405 to handle high frequencies, but am unsure how to set it up. Tri-amping, for now at least, is out of the question. So I will be looking at some sort of passive arrangement with resistors and an L-Pad or something? I am unsure how to determine what parts to use...
Thanks for any suggestions you can help me out with.
Byron
p.s. - also, any suggestions on what might be causing big hum with the JBL crossover?

[hjames]

Doesn't sound like you have much of a crossover at present, at least, you didn't list one, so not sure how you blame the hum on "the JBL crossover" ... (if so, what model #?)

Hum is often a difference in ground between gear - so what active gear (amp/preamp/EQ) is currently in your system?

Also, what are you using for a sound-source - Vinyl, cd, iPod, live band?
DO you have the TV/Projector or cableTV connected in any way?
CATV is a big HUM villain in many home theatre systems ...

Hi everyone.
I am a newbie to the whole world of JBL, Altec, and SET. I recently purchased a pair of speakers using the 4560 cabinet using the E145 driver, along with a 511B using a 2426 compression driver.
The thing is, I generally have to heavily EQ this setup because the 2426 driver rolls off way too quickly, to my ears anyway.
So I am purchasing the JBL 2405 to handle high frequencies, but am unsure how to set it up. Tri-amping, for now at least, is out of the question. So I will be looking at some sort of passive arrangement with resistors and an L-Pad or something? I am unsure how to determine what parts to use...
Thanks for any suggestions you can help me out with.
Byron
p.s. - also, any suggestions on what might be causing big hum with the JBL crossover?

[mantisory]

Thanks for the reply..
The crossover is a jbl crossover with 800 hz card installed. Source is typical audio gear only, with a tube preamp.
I have several crossovers including a behringer, rane, and dod..but liked the jbl best until it all of a sudden started humming.
Byron

[hjames]

Thanks for the reply..
The crossover is a jbl crossover with 800 hz card installed. Source is typical audio gear only, with a tube preamp.
I have several crossovers including a behringer, rane, and dod..but liked the jbl best until it all of a sudden started humming.
Byron

Ah, so you are using the JBL/UREI crossover with preset cards ... kind of a biamp configuration?
Perhaps a JBL 5234? If needed, the manual is here:
http://www.jblproservice.com/pdf/Vin...-5233_5234.pdf

I used the user-adjustable M552 crossover for a year or so, until I swapped it out for a newer Ashley XR1001 -
you can find them used for about $100 or so these days. I even have a spare one now, if it goes bad.

Anyway, its very hard to say exactly why it started humming,
I have a sometimes intermittent hum in my system - the devil to find!
Reseating all the XR cables or swapping out your 1/4 inch phone cables may help.
If you are using adapters - one of them may be bad - take time and swap them out on a 1 by 1 basis.
If the hum present on all your drivers? Or just part of the system?

If its the crossover, maybe a capacitor has aged and dropped out of spec, or some kind of a power supply problem ...
That's to be expected with older used gear ... find a good bench tech and have them scope it out -

Most of our audio circle here in northern VA have found a shop we can trust to work on our older Adcom amps and such ...
You may have fiends in Toronto who could recommend a local shop?

[Earl K]

,,,,, snip,,,,You may have fiends in Toronto who could recommend a local shop?

( Heh, I've been described that way more than once in my life-time ) .

So Mantisory, for a repair to your ( 5234a ? ) crossover ???

- Well,,, it may not be worth fixing ( due to labour costs ) .

- I'd suggest that you exhaust every possibility of simple user error / before involving those who charge for their diagnostic time .
- ( ie; people change things in systems all the time with out mentally logging the process / & then only "notice" the consequences after it's much too late to make the necessary associations for effective backtracking ) .


- If you remain convinced there's a problem with your crossover ( & want to fix it ) , you can try Audio Operations ( Ltd ) .
- They are ( or used to be ) a JBL Pro dealer .

They're out in Mississauga ( 905 629-1722 ).

Located at ; 600 Orwell Street , Unit 29 .


<> EarlK

PS : Closed Saturday & Sunday . FWIW, ( unless they've gotten better ) they can be fairly slack at responding to the ringing telephone when they're fully occupied with one of their AV installs .

[Audiobeer]

Ah, I used the user-adjustable M552 crossover for a year or so, until I swapped it out for a newer Ashley XR1001 -
you can find them used for about $100 or so these days. I even have a spare one now, if it goes bad.

At that price you stole them Heather!

[Mr. Widget]

So I am purchasing the JBL 2405 to handle high frequencies, but am unsure how to set it up. Tri-amping, for now at least, is out of the question. So I will be looking at some sort of passive arrangement with resistors and an L-Pad or something? I am unsure how to determine what parts to use...
Thanks for any suggestions you can help me out with.

Many in the SET world will have you simply parallel the 2405 onto the mid driver and use a simple cap to filter the lower frequencies from the 2405... this will work, i.e. it will add brightness to the system.

I would use a proper network. A very good starting point would be to try the LP section of the mid horn and the HF section from one of the JBL studio monitor crossovers that use these components.


Widget

[mantisory]

Many in the SET world will have you simply parallel the 2405 onto the mid driver and use a simple cap to filter the lower frequencies from the 2405... this will work, i.e. it will add brightness to the system.

I would use a proper network. A very good starting point would be to try the LP section of the mid horn and the HF section from one of the JBL studio monitor crossovers that use these components.


Widget

Thanks for the information! I think I may use a proper network, but perhaps just doing a paralleled cap to begin with until I figure out the passive crossover network - I am thinking maybe around 2uf or so (I think that should give me around a 10k crossover)...
I can play with that and I dunno, I will likely use the Behringer x-over I have along with the dbx2496 until I build a complete passive network.

Thanks for the help by the way!
Cheers, and happy Canada/Indepedance day!
Byron

[mantisory]

Hi everyone,
I just wanted to see if the ideas I have regarding a passive network for these drivers are okay.
Both are 8 Ohm drivers, but there is an efficiency difference between the two - the 2426 is 107dB and the 2405 is 105dB (from the JBL site anyway)
I am thinking I would like the crossover point to be around 10k or so, since without the 2405, the 2426 starts rolling off around there.
My main question is, do you think I can get away with just putting a crossover on the 2405 (a simple 2nd order L-R with 1uF / .25mH ), and just let the 2426 roll off naturally? Or should I build the "same" R-L crossover for the 2426?
I am also thinking that the 2dB difference between the drivers may or may not be enough to hear, but if it is I imagine I could just put an L-Pad on the 2426 to knock it down a couple dB?
Thanks for any help or suggestions you may have
Regards,
Byron

[toddalin]

JBL 3106 network was designed to do what you want to do. The schematic is available online.

[Chas]

Maybe it is humming because it forgot the lyrics, I do that sometimes!

If you are local to SE Mississauga I might be able to assist....drop me a PM