Model 19 Crossover Rebuild Schematic Question

[sburke]

Hello All,

I have a question regarding the Model 19 crossover. This is based on the schematic that is available elsewhere within these posts.

I decided to rebuild my crossovers using upgraded components of the same values. Due to the size of some of these components (Goertz 12awg inductors, ASC Motor Run caps), the new crossovers will be external in their own box. So far, so good. I've added new binding posts to the rear of the cabinets, a pair for LF and a pair for HF, with 14awg solid core straight to the LF driver and 18awg solid core straight to the HF driver. Currently the new crossover retains one input from the amp and two outputs for the associated drivers. I will be using the L-Pads. In this configuration I can either use the new passive crossover or go to an active crossover at some point in the future. So that's the history. Now to the question.

I'd would like to separate the LF and HF within the crossover network so that I would have two inputs at the crossover, one for LF and one for HF. My thoughts in doing this are to have the ability to use two amps. One for LF and one for HF. In the schematic, it appears that L1 is being shared by both drivers. Am I correct in assuming that to decouple the drivers through the crossover network that I would require another .3 inductor for the HF driver? Or could I simply run another ground and a new input from the center tap of the 8ohm L-Pad?

As you may have noticed, I'm not very familiar with crossover networks. I've got enough knowledge to read and build from a schematic though.

Any assistance or ideas would be greatly appreciated.

Thanks much,

Steve

[sburke]

Richard,

Thank you very much. This is exactly what I needed to know.

Steve

[Richard C.]

Steve,

Did you take one of your controls apart yet? They are both exactly the same L-pad, only wired using the two different wirewound elements. L-pads are "normally" wired with all three connections (shared common). As one increases, the other one decreases which maintains a somewhat constant impedance on the input side.

I thought about doing the same thing as you with my 19's. I could bi-amp them using the two sets of terminals, and if I had to go back to one amp; I could just parallel the LF & HF terminals.

I would also like to know if you could get those motor run caps in a close tolerance or do you measure and hand pick? I use the Dayton or Solen metallized polypropylene caps from Parts Express.

Richard C.

[Richard C.]

Hello,
The .3mH inductor is only used for the HF. The LF signal passes thru unchanged. Just break the connection between L1 & L2 and connect your new LF input to L2. Make the original input (white wire), your new HF input. You can also break apart the two different (- BLK) circuits if you want to isolate both sections.
Richard C.

[sburke]

Richard,

I also noticed that both L-Pads are the same just wired differently. I've left the stocks in place because I found a source for new one's at a very good price. Same measurements. Basically the same L-Pad, just newer.

Yes, the motor run caps that I purchased are within 2% or so of their ratings, though in place of 8, 16,& 21 I used 7.5, 15 & 20. With the tolerance threshold of older caps I figured I'd be ok with these values. I did not specify that they be matched though I was keeping my fingers crossed.

Going back to the schematic and your idea of paralleling to revert from two amps back to one. How might that be accomplished best while keeping LF and HF separate? Is it simply adding a jumper between both positives and a jumper between both negatives of the inputs?

Steve

[Richard C.]

Steve,

Since you are changing parts on your crossovers, it should be easy to isolate the LF & HF sections and wire each to it's own set of input terminals. Yes, just parallel the two Red & the two Blk terminals, and it will work just like original.

BUT, I am sure that most people would tell you to bypass the passive crossover when you bi-amp - nothing between your amp and the drivers. If your new crossover is external, you can experiment.

Richard C.

[sburke]

Excellent! Yes, this will certainly give me more freedom to experiment. Richard, thanks so much for the clarification and assistance.

Steve