Pioneer CS-88a Rebuild Part 2 - Crossover Rebuild

As mentioned in Part 1 of this series, the pair of Pioneer CS-88a speakers I was fostering required a crossover recap as well, read on for some thoughts on that process.




In comparison to refoaming the tweeters, recapping the crossover is fairly simple and not nearly as time consuming. If you haven't already, completely remove all of the drivers (marking the leads so you can put it all back together again) to get yourself some working space to remove the crossover (it unscrews from the inside), then unscrew the 10 screws securing the crossover to the cabinet (taking care not to strip the heads of the ones that are overtightened...).

The crossover itself isn't hugely exciting, it's a handful of capacitors, resistors, and inductors, with knobs you can turn to make the speakers sound ever so slightly worse. The resistors are very nice wire-wound pieces, and shouldn't ever need replacement unless physically damaged. Same goes for the inductors.

Capacitors however never get better with age. You could unsolder them all and test them, but you've already come this far, you might as well replace them.

On my crossovers, the capacitors are are labeled with their value in uF, but if you want, you can look at the schematic yourself over at AudioKarma. C1 is 50 uF, C2 is 30 uF, C3 is 5 uF, C4 is 3 uF, and C5 is 1 uF. As is typical with 'vintage' (and probably modern, though I haven't rebuilt one), the right capacitors aren't readily available, so combining values is required.

The links to the capacitors I used from Parts-Express are unfortunately broken. I've provided supplementary links below, but they may not be the exact capacitors I used. But I used non-polarized electrolytic capacitors, similar to those originally used in the crossover. The voltage rating on the capacitors I used was 100V.

Since the exact values were not available, I combined capacitors in parallel (capacitance adds in parallel) to achieve the required values.

For C1, a single 50 uF capacitor was used.

For C2, two 15 uF capacitors were used.

For C3, a 1 uF and a 4 uF were combined.

For C4, two, 1.5 uF capacitors were combined.

For C5, a 1 uF capacitor was used.

So, to fully recap two crossovers, you need:

• 2x 50 uF
• 4x 15 uF
• 2x 4 uF
• 4x 1.5 uF
• 4x 1 uF

I tend to order one extra of everything in case I screw up.

With parts ordered, it's time to start on disassembly of the crossover. Disassemble the binding posts to make things easier to work with, pull off the plastic back plate, and mark the solder joints for each of the capacitors (note that there may already be quality control marks in place [the red marks in these images]).

With the joints all marked, cut the leads to each capacitor. Take a razor blade, scalpel, or whatever reasonably precise sharp cutting tool you have available, and cut through the glue under each capacitor. This should loosen each capacitor enough you can break it off by rocking it back and forth with a pliers. If you can't, reapply the cutting tool, and try rocking again. It may take several iterations of this to free the capacitors.

I then removed the majority of the solder from each marked joint using my soldering iron and a 'manual desoldering tool' (spring loaded desoldering vac). Once the majority of leftover solder was removed, I grabbed the leftover capacitor lead with a pliers, and tugged while applying heat with the iron to remove the remaining capacitor leads.

In an ideal world, at this point we would remove the leftover glue that held on the caps we removed. Unfortunately, the ancient glue seems resistant to any chemical solvent I had available and was much too solid to easily remove by hand. Instead, I just took my cutting tool and scraped myself out a decent enough surface to glue the new capacitors to.

Once that's done, hose down the multiposition switches with some contact cleaner, work them back and forth several times (you may want to press the knob back on for this) and let the whole mess dry.

Reassembly is basically the reverse of disassembly. In the cases where you are using two capacitors to replace one, you may find the holes aren't quite large enough for both leads. In these cases, I wrapped the leads of one capacitor as near as possible to where the leads of the other capacitor entered the body, wrapped the leads once or twice, soldering them together, and then cut the leftover lead such that only one capacitor lead remained.

Now, apply some glue to the capacitors (I used Liquid Nails, in the past I've used Shoe-Goo, use whatever slightly rubbery adhesive you have available) and poke the leads through the holes (the capacitors aren't polarized) making sure to put the right capacitors in the right places. I try to keep the values visible to help whoever gets stuck rebuilding these again in 20 years.

Flip the crossover, and solder the capacitors in place. Once all capacitors are soldered, clip any excess leads, and wait at least an hour for the glue to dry before reinstalling the crossovers.

Once the glue is dry, and the solder has cooled, you can start reassembling the speakers. Snap the plastic back plate on the crossover, and put the binding posts back together. Install the crossover in the speaker enclosure (making sure all the writing comes up right side up). Then rebuild the speakers in the reverse order you took everything apart (following the labels you put on each lead).

At this point, you should be good to connect them to a system and try them out. Feel free to congratulate yourself on a job well done.