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.
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
11 responses Add your response
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. |
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. |
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. |
Hi Whyland Another resource to help with your Spica TC-50 repair could be the Skiing Ninja. I've read good things about his cross over mods for different speaker manufacturers. SkiingNinja Good luck. |
Hi Ponnie, I may have some of the inductors here. Problem is, the value of one of the inductors is dependent on the service code, and I can't find that chart! But we can probably get him close. It would help if I had the service code and a photo of the other speaker's xover. No promises, but we'll give it a try. I'm out of town all day tomorrow. John If you want to forward me the photos and service codes I will forward it to John Bau. If you can furnish me an email address I will have him send you the information you need. my email is pjs3805a@hotmail.com |
Also, check Spica enthusiast site .spicaspeakers.com . If you want to email me and I will ask John Bau for you the questions you have. pjs3805a@hotmail.com or search for me by the name and send the email direct to me. I have an active ad or two running right now. Include your active email address and I will send it the moment he responds. I don't know what speakers you have had in the past but, Spicas are special. TC50's and TC60's. |
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 |