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JBL L100t Crossover Rebuild

Wayniac

Wayniac

Active Member
I am the original owner of a pair of L100ts. I purchased them at the Yokota Air Base exchange back in the mid eighties. The serial numbers are quite low, in the 700's and had the original point-to-point style crossovers. The photo below is not mine, but my crossovers look like this.
 

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I wanted to copy the later design, which incorporated a printed circuit board. Again, this photo is not mine but borrowed from the guys over at Lansing Heritage forums.
 

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I opened the solder side photo with Microsoft Paint. Widened, stretched the PCB and mapped the traces. I modified the overall layout a bit to better suit my needs.
 

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Heat transferred to copper clad boards. Etched with ferric chloride.
 

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Drilled and stuffed with Dayton and Solen capacitors, new resistors and original coils. Done.
 

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Very nice work.:thmbsp:

Good to see some one still etching their own circuit boards.

Thanks for the post and the pictures.:yes:
 
Nice!

Can you post an image of the mask (or whatever it is called) for future reference? I doubt I'll ever need it someone will.
 
I got to say I just love this It gave me some insight as to how to get a project off the ground.

Thanks Borus
 
All else being equal, how does the circuit board represent an improvement over the one with the terminal strips?
 
Mr. dB said:
All else being equal, how does the circuit board represent an improvement over the one with the terminal strips?
Click to expand...

IME, it doesn't. At least not from a sonic standpoint In every case I've heard a difference, point-to-point wiring has sounded better than a printed circuit board.

Point-to-point wiring generally will have higher gauge wire (usually), less interference due to non-parallel wiring (point-to-point is generally non-parallel in all THREE dimensions, whereas printed circuits always have at least ONE parallel direction) and wider spacing between wires, and if done right, lower point-to-point distances. It can also have better grounding (true "star" grounds) and better nodal configuration in general (if you need to connect 5 or more things at one low-impedance point- just route them to the same POINT, on a terminal. Can't do that on a PC board... at least not easily)...

Also, point-to-point is generally more reliable (no boards to crack or delaminate/track-lift), and easier to service, should anything actually GO wrong...

IMHO, the only advantage of a PC board is lower cost of production and assembly. There's no performance advantage to use one in an audio circuit, from my perspective...
 
donprice said:
Nice!

Can you post an image of the mask (or whatever it is called) for future reference? I doubt I'll ever need it someone will.
Click to expand...

Sure, I'll post it. I will make a couple of small changes though. Close examination of my finished board will reveal the resistors are not lined up perfectly. I etched the PCB before I had the resistors in my hand. I can easily adjust the traces to facilitate perfect alignment.

All else being equal, how does the circuit board represent an improvement over the one with the terminal strips?
Click to expand...

Sonically, none at all. I bought these speakers new for about $1300, 1985 dollars. Back then, that was a lot of money. As part of my maintenance routine, I would rotate the bass drivers once or twice a year. I was a bit torqued when I first removed a bass driver and layed eyes upon the shoddy workmanship of these crossovers. This has aggravated me every time I rotated the bass drivers.

L100ts in 1985...............................................$1300.00
New crossover parts.......................................$100.00
Peace of mind after 26 years of aggravation.........Priceless
 
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riker1384 said:
By later design, do you mean you copied the L100t3 crossover?
Click to expand...

No, I rebuilt to original L100t specs. I read many posts regarding the T vs T3. Schematically, the T and the T3 are virtually identical (the T3 has an additional resistor) with small changes to the passive component values. My new PCB can be either. I did look around a bit for new inductors with T3 values and was unsuccessful. I have been watching that auction site for some T3 crossovers to pop up. I'll eventually try the T3 formula.............
 
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