Replace entire network or re-cap 40-yr old Showco S-200 crossover?

[psarahtonen]

I've got a good one for you esteemed audiophiles...

These are EXTREMELY rare and obscure but beautiful sounding speakers made by Showco, the arena rock sound system pioneers. Showco circa 1978 took one of their patents for folded horn speaker design and made a handful of studio monitors they called the S-200 and also the legendary "Disco Pyramid" speakers.

I am the proud owner of one pair of the approximately 400 speakers they manufactured before losing interest in studio and disco equipment. I've reconditioned everything in the 4-way towers except the crossovers. Google can't find any of the capacitor codes I see in the rather ugly over network. One other owner gave me a spec sheet, perhaps the only documentation on the S-200, which states the following specs:

4-way 8-Ohms
28-18kHz (+/- 1 dB)
120 watt RMS
91.5 dB efficiency
12" "Bass" (pyramid horn)
8" mid-bass (pyramid horn)
4" midrange
1" dual tweeters

Crossover points: 200Hz, 800Hz, 5000Hz

Please help me find replacement capacitors or suggest an entire passive crossover network. I would prefer to just upgrade the caps to preserve the legacy and value of the speakers. Here are the codes:

cap #1
TSI-7814
PXA5LR50
5 uF 50VAC

cap #2
TSI-7811
PXB15LP50
15 uF 50VAC

cap #3
TSI-7814
PXB24LP50
24 uF 50VAC

cap #4
TSI-7814
PXA5LR50
5 uF 50VAC

cap #5
TSI-7818
PXC_?_00NV5_?_ (I'm assuming the blanks are "1" and "0")
100 uF 50VAC

Any help you can give me to preserve these treasures would be... well... helpful.

Then I just need to figure out how to get to the dang things! The crossovers are glued underneath the mid-bass horn just behind the 4" mid speaker (see photo #2) and is only accessible through the bass speaker mount on the floor pyramid (see photo #4)... Please see the photos

 

[roger2]

Hello psarahtonen. Welcome to AK

IMO, replace the caps only. Do not replace the entire network, for two reasons:

1) Coils do not degrade with time or use. Some types of capacitors do. Have a look at this thread, in particular posts 2, 5, 6, and 11.

2) Most importantly, the crossover network in a well designed speaker is highly specific to the particular drivers used and is tailored to the actual impedance characteristics of those drivers. Off-the-shelf crossovers, based off of nominal impedances, would be a mismatch resulting in (possibly horrendous) gaps or spikes (even worse than gaps, spikes result in harshness) in the overall frequency response. Just say no, even though it may seem that everyone online does it.


If your crossover networks have any level controls, those should receive a good cleaning. Inspect carefully for any bad solder joints or any type of corrosion in the network or connections to the drivers.

Nice speakers. Good luck with your project.



EDIT: TBH, I thought these were mylar (polyester film) caps. But based on BinaryMike's comments I may have been mistaken. In any case they should be replaced.

 

[BinaryMike]

I generally get standard non-polarized electrolytics like these from Parts Express. You will find that some values have to be made up by paralleling smaller caps. Just try to get the total well within 5% of the target value and you'll be fine. You could replace the smaller ones with plastic film caps instead, but there's a good chance that performance will change because plastic caps have much lower ESR than vintage electrolytic types.

 

[psarahtonen]

I first must decode the values from what is imprinted on the caps. I can't figure out the alphas... PXA? LR? They don't really correlate to any of the charts I've seen.

Parts Express says that the only thing that matters are the micro-farad numbers on covers... is that true? I could buy ANY 5, 15, 24, and 100 uf capacitor and it would work as well as these?

 

[BinaryMike]

Anything with equal microfarads and equal or higher voltage rating will work. The ones Parts Express sells are probably better than the originals, but you don't really have much choice about that. All currently available caps designed for use in speaker crossovers are likely better than the originals. In theory, you could get closer to original cap characteristics by adding a small amount of series resistance at each one. In practice, you need the original cap's ESR spec to determine the right amount of resistance to add, and that's rarely available. Most of us just replace 'em with modern caps and call it good.

 

[westend]

I'd suggest to build a new crossover network and disconnect the originals, leaving them in place. The most costly part of this effort will be the inductors and with the values used in the originals (printed on sides of covers), won't be a bank-buster. I like to use Axon True caps from Parts Connexion. They are good film caps with decent pricing.
If you do it like this, it will be as close to retaining the originals as possible. You could go back to the original network at any time.

 

[psarahtonen]

Chris at Parts Connexion was little confused about the speakers as well. I made this wiring diagram based on what I see in the messy crossover (see below). I ordered a combination of ClarityCap and Axon caps and I think I'm within the 5% tolerance of the originals. SO now I'm thinking about pulling all the ugly stuff out and rebuilding the whole thing. Are there 4 way circuit boards out there or should I just buy a raw Radio Shack 4 x 6?

Thanks for all of your help!