I recently bought this nice set of Sony SS 3700 speakers from Supergrand.
They are very nice is every way but the one tweeter had a "raspy/hoarse"sound to it. I first suspected capacitors in the cross-over but after swopping the tweeters I was sure its the tweeter itself thats not 100%.
Running the tweeter on the oscillator confirmed my findings and this evening I scraped the courage together to open the tweeter up.
Now this is an aluminum dome tweeter and it has a nice protective grill (also doubles as a Helmholz resonator) on the front. It is glued in place and removing it looked like it was going to be trouble. But a bit of nail-polish remover, dripped around the grill edge, softened the glue and it came loose without a hitch. Not even the paint or plastic was damaged (there is a slight haze mark on the plastic plate but nothing to worry about.
Next the three magnet screws were carefully loosened and the magnet pried away - with great care of course.
What did I find? At first I thought it was the lead wire that was fractured where it runs over the "surround"part of the dome (a common spot of failure in old tweeters). But when I took a close look it was a bit more nasty than antispated.
The voice-coil itself must have sustained a period of high power which caused it to heat up just enough to expand and loosen itself from the former (but also because of the heat the glue lost its grip and the former was toasted a bit). These are "dry" tweeters with no ferro-fluid in the magnetic gap.
Now the question is... what to do? Try and carefully rewind it? Or prop back the coil and secure it with a few coats of laquer?
Not at all am I stressed out about this. These speakers are 40 years olf after all and I got them for a great price.
Another option that I am concidering would be to get a set of generic dome tweeters and rebuild the domes onto the ULM magnets... to keep the look and hopefully the sound. These are true 1"(25.5 mm) voic-coil diameter tweeters.
Here is some photos for your amusement:
Copper clad tweeter pole-piece - nice!
They are very nice is every way but the one tweeter had a "raspy/hoarse"sound to it. I first suspected capacitors in the cross-over but after swopping the tweeters I was sure its the tweeter itself thats not 100%.
Running the tweeter on the oscillator confirmed my findings and this evening I scraped the courage together to open the tweeter up.
Now this is an aluminum dome tweeter and it has a nice protective grill (also doubles as a Helmholz resonator) on the front. It is glued in place and removing it looked like it was going to be trouble. But a bit of nail-polish remover, dripped around the grill edge, softened the glue and it came loose without a hitch. Not even the paint or plastic was damaged (there is a slight haze mark on the plastic plate but nothing to worry about.
Next the three magnet screws were carefully loosened and the magnet pried away - with great care of course.
What did I find? At first I thought it was the lead wire that was fractured where it runs over the "surround"part of the dome (a common spot of failure in old tweeters). But when I took a close look it was a bit more nasty than antispated.
The voice-coil itself must have sustained a period of high power which caused it to heat up just enough to expand and loosen itself from the former (but also because of the heat the glue lost its grip and the former was toasted a bit). These are "dry" tweeters with no ferro-fluid in the magnetic gap.
Now the question is... what to do? Try and carefully rewind it? Or prop back the coil and secure it with a few coats of laquer?
Not at all am I stressed out about this. These speakers are 40 years olf after all and I got them for a great price.
Another option that I am concidering would be to get a set of generic dome tweeters and rebuild the domes onto the ULM magnets... to keep the look and hopefully the sound. These are true 1"(25.5 mm) voic-coil diameter tweeters.
Here is some photos for your amusement:
Copper clad tweeter pole-piece - nice!
