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Spica TC-50 crossover repair

Recently got a pair of Spica TC-50 speakers in a trade. Nice looking speaker that from all accounts is a nice sounding set as well. Original boxes and original stands. Problem is one of the speakers has a crossover that was in the process of being repaired and is missing the three coils. My question is: is this worth the time and effort to repair or should I give up the dream? I have a schematic that lists the parts required, but the web site I got this information has a caveat that reads "Spica carefully graded and tested each woofer. Then based on those parameters a service code was assigned and paired with a matching crossover. For this reason, it is unlikely that your components will match these exactly" I assume if I were to replace the coils in one crossover, they should also be replaced in the other (complete) crossover. However, this statement leads me to believe it may never be completely "right". Or will difference likely be negligible? Lastly, are any electrical DIYers out there that can tell me any relatively easy ways to test the woofers as Spica did in order to select the proper coils to rehab these speakers. What is the opinion out there? Thanks, Whyland
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timlub
2,042 posts
 
I believe Bill does surrounds, recones and diaphram replacements only.... but the call is free, worth checking out.
jeallen
3 posts
 
Wow, lots of good advise here. I have the spicaspeakers site and thought I should weigh in. Ponnie and John B are friends and can be a big help.

Suggestions:
1) If you alter the coils (to air coils) you will alter the time alignment, which is in my opinion is key to the character of these speakers.
2) The coils didn't change with the services code. The service code was done to adjust the crossover to match the peak characteristics of the woofer and to remove a hump in the freq. response (not the actaual crossover points). To accomplish this only a couple(?) of caps and resistor (or two) was altered. The schematics are on my site.
timlub
2,042 posts
 
The time alignment is mostly due to the reactive impedance of the inductor. It is possible that in impedance compensation circuits that it could make a difference but only if the coil resistance is needed. Coil resistance can easily be changed with the gauge the coil is wound in.
A very simple fix all around would be to measure the resistance of the cored coil and get enough larger gauge air core coil to have the same resistance as the original iron core coil. Overall results would then be improved over the original design, but more costly.
I recommend that if all possible to use an air coil at least on the tweeter.
Jeallen, can you give me your site address.
timlub
2,042 posts
 
I just went to spicaspeaker.com and found the crossover. This one of the most simple circuits as far as building, but extremely difficult to match. Some real genius for its time when we couldn't model with computers like we do today. John used a quasi butterworth/bessel slopes. Easy to build, but John taylored every crossover individually. The good news is that the tweeter is 6db per octave and no coil in its crossover circuit, but he does have compensation on the tweeter and that uses a coil. The crossover does not dictate whether he used a iron core or air core, but Jeallen is correct, that if he used a core, it will effect your compensation circuitry. You will need to come as close as you can to replacing with the same type and gauge of coil and replace the pair. He also uses electrolytics all over the place, Electrolytics are cheap and many have improved, I would replace a few with good film, but many of those will need to stay electrolytic or you will risk changing the original character of the speaker. Either way at this age of the speaker, I would replace them.
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whyland OP
16 posts
 
I greatly appreciate all the good advise here. I recently received an email from someone who had an extra crossover they were parting out (from TC-50) and they volunteered to send the inductor coils that they did not require for their project. I will use these in the repair of my crossover that is missing this element. I appreciate jeallen letting me know about the fact that the coils were not where these were changed for factory specs. BTW, I found your site very helpful in this project. Also, while all the caps visually appear to be in nice condition on both of my crossovers, should they be replaced due to age regardless? If so, I was advised to use same value electrolitic ones? Is this the common wisdom on the matter? Thanks again for everyones help.
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