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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
whyland

Showing 5 responses by timlub

timlub
2,043 posts
 
Hi Whyland,
Yes John Bau tested every woofer and built crossover parts to each matched pair... This is still not a problem. Most manufactures,even high end manufactures match parts to plus or minus 10%. I have always done the same as John building my own product, but if you have an LCR meter and wind or unwind your coils to the inductance stated on your schematic, you should be within 2% tolerance and will yield very good results. I would replace the coils in both speakers and good air core coils can be expensive. Check Zalytron, Parts Express and Madisound, one of them will give very tight tolerences on their better coil lines.
I hope this helps,
Tim
timlub
2,043 posts
 
Whyland,
Don't you have both speakers? And aren't the crossovers in tact on the second speaker? Everyone is making this much too difficult. These are matched pairs. Remove the coils from the good crossover, measure them, then buy new ones for both at the same value.
Tim
timlub
2,043 posts
 
I believe Bill does surrounds, recones and diaphram replacements only.... but the call is free, worth checking out.
timlub
2,043 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
2,043 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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