Can I safely do this to a passive crossover?

[mixsit]

I have a JBL D-120/075/N2400 passive monitor.

What I want to do is move the 12" speaker connections from the low-out of the crossover to the full-range x-over input terminals. This would leave the low freq. terminals disconnected (and un-loaded?) and allow me to dial the 075 in or out as needed.

This could be a nice fix for a switchover from electric to acoustic guitar cab duties -if it's feasible. And I like my JBL's -don't want to let the smoke out you know...
Thanks in advance.
Wayne Smith

[edgewound]

Yes...that'll work fine.

[mixsit]

Yes...that'll work fine.

Excellent! (and fast too. ) We're ramping up to back up a friend this weekend and when I decided both guitars would be nice in the set, I started fishing for a quick fix you see.
So thank you very much.
Wayne

[edgewound]

Excellent! (and fast too. ) We're ramping up to back up a friend this weekend and when I decided both guitars would be nice in the set, I started fishing for a quick fix you see.
So thank you very much.
Wayne

Glad to help, Wayne....welcome to the forum. Just beware though....answers don't always come that quickly...lol

[mixsit]

10-4.
Wayne

[Zilch]

http://www.jblproservice.com/pdf/Net...tics/N2400.pdf

Note mandatory upgrade (2) there.

Then, go here: http://www.bcae1.com/

Click on #91 at the right and scroll down for "Open Crossover Output Warning."

I've never smoked anything doing it, but the potential is there, apparently, and I herewith retract my earlier opinion that it was not a problem.

Answer: A "dummy" load resistor across the LF output, but that's going to dissipate amplifier power.

Better: Disconnect the LF inductor from the input with a switch.

[GordonW]

Better: Disconnect the LF inductor from the input with a switch.

Yep... and here's a further exploration of that idea: Take a DPDT switch, and you can rig a bypass, where one throw of the switch will USE the factory lowpass section, and the other will BYPASS the lowpass, completely. Here's the same JBL schematic, only modified to show where the switch would wire in (BTW: UNLESS there is a DOT at the intersection, crossing wires DO NOT connect!):

[mixsit]

http://www.jblproservice.com/pdf/Network%20Schematics/N2400.pdf

Note mandatory upgrade (2) there.

Then, go here: http://www.bcae1.com/

Click on #91 at the right and scroll down for "Open Crossover Output Warning."

Better: Disconnect the LF inductor from the input with a switch.

Ok. I see the difference using the switch. Is this the correct refrence to the open-circuit issue? It seems to apply to when there is no LF load connected.

"You may damage your amplifier if you drive a second (or higher) order crossover when the speaker's voice coil is open (the speaker is blown) or if no speaker is connected to the crossover's output. "

I do recall the fairly high wattage resisters in there but I haven't opened them in years and may have been advised to remove them (for pa work at the time) -for more level.
Wayne
By the way, I ran it last night with the D-120 full range, the 075 dialed off, and I was surprised to find I still had tons of top end for the acoustic/electric. Quite a speaker.

[Zilch]

Ok. I see the difference using the switch. Is this the correct refrence to the open-circuit issue? It seems to apply to when there is no LF load connected.

Yup, that's the problem. You cant' leave that inductor and capacitor in the circuit without a speaker load; the impedance drops to zero at the crossover frequency, and you risk damage to your amp.

If those two 5-Ohm resistors are in your crossover, I'd leave them there, and if they're not there, I'd install them. Their purpose is prevent overdriving the 075. Yeah, you'll get higher output without them, but blowing the HF driver was enough of a problem that JBL made the upgrade "Mandatory." You assert you have plenty of HF output, anyway.

I'd use Gordon's clever switching scheme above to accomplish your objective. You'll ultimately want the extra "sizzle" the 075 provides....

[mixsit]

Oops. I see it now. The speaker in parallel with zero ohms.. is still trouble.

[edgewound]

Rather than modify your N2400...why not just build a simple Hi-Pass network w ith an L-Pad for your 075?

[GordonW]

I thought he wanted to be able to keep the low-pass for the D120, for certain occasions.

As an alternative, it may actually BE easier to just BUILD a "clone" of the N2400, including my switch mod, as opposed to having to go into an N2400 and modify it.

I mean, this is the whole parts list:

2- 6uF capacitors
1- 1.1 mH inductor
2- 5 ohm 15 watt (I'd upgrade from the spec'd 11 watt) resistors
1- 8-ohm 30-50 watt L-pad
1- DPDT non-center-off switch

Couldn't be THAT hard to just build one, on a board the right size to fit in where the original N2400 bolts in...

Regards,
Gordon.

[Baron030]

Hi Mixsit



I found a link to the best possible x-over circuit for your application.



http://www.jblproservice.com/pdf/Cabaret%20Series/4602B.pdf



But, the only down side of this design is having to make a tapped 0.4 mH coil.



Maybe it might be worth contacting JBL to see if they have any NOS (New Old Stock) crossover networks for 4602B - you just never know.

Then again hand winding a tapped 0.4 mH coil can't be all that much work considering how little actual wire is in 0.4 mH coil.