I would like to clone a pair of crossovers for my JBL L55 speakers. The current crossovers have what appears to be inductors with two center taps. I would like to replicate them with discrete components. I suppose I could measure the inductors to determine the values of the taps but my LCR meter for some reason does not do L or C. The x-over in question is the LX15 which only gives one value for the inductor. The LX4-1 controls the same drivers but in a smaller enclosure, the schematic for it has a little more info on the center taps ( -3 and -6) but I'm unsure of its meaning. Help please.
I think what you have there are autotransformers. Perhaps you could leave them out and find another way to attenuate the signal.
While there can be different reasons for using these, I suspect this one has been because the designer of the crossover was trying to avoid using series resistance.
If I omit the autotransformer and resistors in the attenuation circuit, should I also eliminate the first 8uF capacitor?
No. Keep that capacitor and the RLC next to the driver. This way it is one of the valid original configurations (notwithstanding what you choose to do about attenuating the tweeter).
I also have a pair of JBL LX4-2 from the L77 speakers, I opened the crossovers and they have what looks like tiny transformers, although without center taps.
Is this also an "autotransformer" rather than an inductor?
Is this also an "autotransformer" rather than an inductor?
Based on the schematic, that's an inductor. The shell core is irrelevant in that respect.
Thank you.
I'm curious about the second autotransformer, it's listed as 3mH with two taps, one labeled -3 the other -6.
A couple of dumb questions......
What does the -3 and -6 designate?
Can it be replicated with three discrete autotransformers?
I'm curious about the second autotransformer, it's listed as 3mH with two taps, one labeled -3 the other -6.
A couple of dumb questions......
What does the -3 and -6 designate?
Can it be replicated with three discrete autotransformers?
I am going to guess the -3 and -6 are DB of attenuation by looking at the taps.
You would not need an autoformer if you only use the 0 setting.
The advantage of the autoformer is you get the same behavior as an L pad without adding series impedance.
Adding series impedance can cause compression drivers to not sound as good.
You would not need an autoformer if you only use the 0 setting.
The advantage of the autoformer is you get the same behavior as an L pad without adding series impedance.
Adding series impedance can cause compression drivers to not sound as good.
What are you meaning by discrete components in this case? Just getting rid of the switch, or do you mean something else?
I'm new to electronics so I may not be using the correct terminology.
The autotransformer appears to be custom made with 3 distinct settings. Can I replace it with two or three off the shelf components to replicate the original circuit?
The autotransformer appears to be custom made with 3 distinct settings. Can I replace it with two or three off the shelf components to replicate the original circuit?
They need to be coupled so you cannot replace the autoformer with three inductors.
If you do not ever plan to use the -3 and -6 settings, you could use a 3 MH inductor.
The first post shows the total inductance of the autoformer to be 3 mH, so it is a 2nd order high pass with the 8 microfarad and 3 mH.
The 5 ohm + 8 microfarad + 2.5 mH in series in the first post are meant to counter the resonance of the HF driver. The crossover will ot be as accurate without it.
If you want to completely replicate the circuit, you would need to hand wind/rewind using a new 3 ferrite cored choke.
You need a working inductance meter to do this. Not so many turns of wire are involved so it is not so hard to do.
If you do not ever plan to use the -3 and -6 settings, you could use a 3 MH inductor.
The first post shows the total inductance of the autoformer to be 3 mH, so it is a 2nd order high pass with the 8 microfarad and 3 mH.
The 5 ohm + 8 microfarad + 2.5 mH in series in the first post are meant to counter the resonance of the HF driver. The crossover will ot be as accurate without it.
If you want to completely replicate the circuit, you would need to hand wind/rewind using a new 3 ferrite cored choke.
You need a working inductance meter to do this. Not so many turns of wire are involved so it is not so hard to do.
IMHO- no, the part is labeled "3.0mH", total inductance seems to be critical. Do math. The 8uFd against 3.0mH is around 1kHz, so is the crossover!! If you leave the choke out, more bass gets in tweeter, distorts and burns. (The 8uFd is a first-order bass-cut, but this speaker was meant to play loud, it needs the second-order bass-cut of a C-L network.)
The full-tweet equivalent circuit is this:
I have no idea why a JBL choke would ever go bad?? Even gross rust on the iron is negligible. In salt-water atmosphere the copper could turn green and go open.