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Crossovers


Supercooper188

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The Chicago Industrial Condenser capacitors used in early AR systems are generally extremely reliable, but they have been known to drift over the years. The biggest problem with the crossovers is actually not the crossover itself, but the tweeter adjustment controls. The un plated brass contacts on the inside get corroded, and need to be polished. I have found that cleaning the original level controls yields the best performance, however you can replace them with L-pads.

I own several pairs of AR speakers, and I have only experienced a bad capacitor in one of them. One of my AR-4x's has lower tweeter output than the other, and I found the problem was with the capacitor. I really hate to replace it, because I love the sound of those old caps, but I really see no other option. And if I do it in one speaker, I need to do it in the other. They really do sound different than the poly caps of today.

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Capacitance is not the only parameter needed to specify a cap's performance. I have measured the Dissipation Factor in several of the Chicago Industrial units of the 60's and 70's and found it to be has high as 0.82 at 1 kHz. DF = ESR/reactance. With time, water vapor permeates inward along the wire/wax surfaces. On another thread, it was shown that Callins npe capacitors of the mid-70s to early 80s can leak causing water to exit and C and DF to increase.

The old capacitors whose sound you may enjoy today did not produce that same sound when they were new.

Other members have reported finding cold solder joints. (Solder which is jiggled or bumped during cooling to the solid phase will form a high resistance polycrystalline network instead of a low resistance alloy.) Perhaps the assembler was distracted by something more interesting than building crossovers?

Capacitor aging, potentiometer corrosion, and cold solder joints can all be issues in 30-to-45-year-old crossovers.

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