JBL N1200/N8000 Crossover Upgrade - diyAudio
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Old 30th March 2015, 07:23 PM   #1
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Default JBL N1200/N8000 Crossover Upgrade

Hi.
Looking to replace my JBL crossovers with a single 3-way crossover. Inspired by the upgrade of the JBL L300 crossover by Nelson Pass. I will be using most of the elements of the original design, but the challenge will be to replace the 1.1mh tapped inductor with an equivalent circuit. It has been suggested i use a 3 ohm series resistor after the parallel 1.1mh coil. Nelson Pass used a 8 ohm series resistor after the series capacitor in his redesign. So, my question is, do i put the 3 ohm series resistor after the series capacitor or after the parallel coil or does it matter?
Thanks, Barry
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Old 31st March 2015, 08:48 AM   #2
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Old 31st March 2015, 12:08 PM   #3
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Drivers are: JBL 130A woofer, LE175 compression driver on a 1217-1290 horn/lense and a 077 slot tweeter.
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Old 31st March 2015, 12:24 PM   #4
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Quote:
Originally Posted by zenbar View Post
Hi.
So, my question is, do i put the 3 ohm series resistor after the series capacitor or after the parallel coil or does it matter?
Thanks, Barry
There will be a subtle difference. As with all tweeter filters, if you pad with a resistor at the back end of the filter you are essentially increasing the load resistance and the corner Q of the filter will sharpen. If you put a resistor at the front of the circuit (and before or after the capacitor doesn't make any difference, it is before the inductor) then the corner Q will soften.

Note that these early JBL crossovers are very generic and you can do much better designing a crossover for your specific system.

Regards,
David
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Old 31st March 2015, 02:28 PM   #5
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Anyone have a better crossover design for this set of drivers? I can solder up a crossover from a schematic, but crossover design is beyond me. Any suggestions on how to improve these old JBL crossovers? Cabinets are ported 6 cu. ft., similar in size and shape to the JBL L220 and tuned to 45 hz.
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Old 22nd May 2015, 08:21 AM   #6
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I have built similar systems with Elliot active crossovers and bi or tri-amping the system. The frequencies are 1200Hz and 8000Hz.

To design active crossovers takes quite a bit of research, unless you just want to throw something together. Parts-Express has a three-way 12db pcb. You can estimate a crossover, but it is better to get a zobel network and L-pad attenuator in there.
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Old 22nd May 2015, 08:37 AM   #7
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A second thought, most likely only the capacitors would degrade. You could replace them, even though you may have to use parallel caps to get the closest values; but anything within 20% would be adequate. Dayton audio has polypropylene at 12uF, 12 + 1.5, and 15 + 1.5 to get very close values at better than 5%.
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