Back (again) by popular demand:  This listing is for ONE PAIR (two) of UNPOPULATED crossover PCBs (printed-circuit boards) for JBL L300 Summit and JBL 433X three-way loudspeakers.  Your purchase will also include detailed instructions, layout photos and a parts list to build these boards into complete crossovers.  The purchase does NOT include the electronic components (capacitors, resistors, coils, etc.) to build the crossovers.  The photographs showing these components are for illustrative purposes only; you will have to buy the electrical parts separately.

These crossover boards use a circuit inspired by legendary engineer Nelson Pass's improved design for the JBL L300.  (No claim is made to Mr. Pass's intellectual property or design.)  The schematic takes Mr. Pass's basic approach and charge-couples it to introduce a small bias current into the capacitors to reduce hysteresis distortion and improve resolution. 

There is no need for batteries in this design; rather, inspired by JBL's latest charge-coupled networks (see, e.g., JBL's model 4365), this approach uses diodes and resistors to supply a small amount of direct current from the input signal, to the capacitors.

I've used these crossovers in my own restored L300s (shown in photos) and they sound terrific; very smooth, clear and non-fatiguing, with great detail and imaging.

These boards include wiring eyelets to let you use the stock L-pads, and they are set up to allow you to amplify the woofers separately, should you so desire, or jumper the inputs for a single input. 

The boards mount in the base on the L300 cabinet using the existing mounting screw locations.  I have not fitted them into 4333 cabinets, but per other users they're be easy to locate.  They measure about 8 ¼" by 13 ¾".   (They are 208mm x 350mm; thickness is 1.6 mm, 2 Layers, Finished Copper: 1 oz.)

The total cost of the completed boards, including the recommended components (again, not supplied) is less than the price that the old JBL OEM networks typically command on eBay (around $650 / pair, from what I've seen).  To populate BOTH boards with standard components that I suggest was about $310, plus shipping at the time I first created this listing (March 2018), and I include shopping-cart screenshots for those parts at Parts Express and Parts Connexion.  I have already sold several dozen pairs to rave reviews.

My user name on audiokarma and Lansing Heritage is the same as here on eBay.

Thanks for looking!