View Full Version : N2600 crossover
05-08-2007, 07:01 PM
I have very limited experience with speaker building and circuits in general and have just inherited pair of c38 cabinets with a system 30 (d130; 075; n2600 16 ohm) configuration. Should the L-Pads be 'stepped' at the 1,2,3,4 settings? Mine turns smoothly about 330 degrees before stopping? Should I need to replace it with a new one (partexpress), do i order a 8 ohm or 16 ohm? The crossover and speakers are labeled 16 ohm, but a N2600 spec I have indicates an 8 ohm L-Pad. The N2600 spec indicates that the crossover is 8 ohm. Do I have the wrong spec...I'm a little confused http://www.jblproservice.com/pdf/Network%20Schematics/N2600.pdf
05-09-2007, 05:27 PM
After looking at the N2600 network service bulletin, I can understand your confusion. The N2600 specification really does not indicate that the network has an 8 ohm impedance. Instead it indicates is what the network's correct frequency response should be, when the network is being tested with a "Standard Test Fixture". It is the "Standard Test Fixture" that has 8 ohms impedance, and not the network's impedance. The N2600 is really designed as a 16 or 32 ohm crossover network. But, you should be aware that JBL has not been completely honest about their driver impedances. So, your 16 ohms 075s are actually more like about 10 ohms. And it is for that reason, that JBL uses an 8 ohm L-Pad in the N2600 network.
If you are currently having problems with your N2600's L-Pads, you may not need to replace them. I would recommend that you try cleaning them with a contact cleaner first. Since, the N2600 network uses the same L-Pad as the N2400 network; here is a link to some cleaning tips: http://audioheritage.org/vbulletin/showthread.php?t=15974
You also have a question about setting the 075ís L-Pad output level. Don't rely on the knob's number setting. Someone could have used an Allen wrench and reset the knob's position relative to the L-Pads position. So, recommending a number setting would be absolutely meaningless. But, I would compare the two networks against each other just to make sure that knob positions match when the L-Pad are set to either their minimum or maximum values. And if they don't match, then use an Allen wrench and reset one of the knob's position, until they do. The reason for this minor knob adjustment is so that you can get the 075s levels to match in a stereo system easily.
The 030 system's 075 L-Pad output level is really adjusted by ears alone. If the 075's output level is set too low, then the system will sound muddy. And if it's set too high then the system sounds too bright and harsh. Personally, I find a music track that has a female artist with a nice clear voice as a good source for adjusting the 075s output level. The vocal harmonics will transverse across the crossover point and itís real easy to tell if the level is set right or not. My current favorite artist for system balance checks is Mary Chapin Carpenter. If her voice sounds nice and sweet, then chances are the level is adjusted right.
There are few other minor fine points that I should bring up. In the N2400 network, JBL made a minor modification to include two 5 ohm 11 watt resistors to create a -8.5db fixed L-Pad between the high pass capacitor and the 8 ohm L-Pad. This modification was made to prevent any chance of the 075 from being over driven, should someone set the L-Pad to its maximum output level. It is not likely that your N2600 network has these additional resistors. So, I would be careful not to make your level adjustments at a high volume level. Personally, I would not bother in making any modifications to the N2600. Just be aware that there is a risk to the 075 when the L-Pad is set to its maximum output level.
And if you should find yourself having to re-coning your 16 ohm D-130s as 8 ohm E-130s at some point in the future. Just be aware that it is no big deal to modify the network to convert it to an 8 ohm, N2400 network.
05-09-2007, 06:09 PM
Thanks Baron! I appreciate your input. These are beautiful speakers with 'a lot of family history'.
I just posted a new thread inquiring about DCR specs. I'm wondering if these speakers are really 8 ohm?
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