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Help with Sonus Faber Extrema issue

I have a pair of Sonus Faber Extremas hooked up to a pair of Parasound JC1 monoblocks.  One of the speakers periodically will exhibit signicantly lower volume (down to almost no volume) in the middle of a listening session.  It seems to occur when during more dynamic passages and also when the amps have been on for a while.  If I turn everything off for a few minutes, the problem usually goes away.  I reversed the speaker cables at the speakers and the same speaker still exhibited the issue, so the issue is with the speaker.  What could cause this problem?  Could it be a bad connection somewhere in the speaker?  Could it be that crossover parts need to be changed due to age?
wcheng2
georgehifi's avatar
georgehifi
10,312 posts
 

Awesome combination btw, JC1’s and Extremas, best Esotar dynamic tweeter with the high bias setting on the JC1 should sound absolutely maaaaaaaagic!!!

Hope it’s not the speaker. See if you can try another amp, before pulling the speakers apart.

There is nothing to the xover to really do what your saying, the inductor across the mid/bass unit either works or doesn’t the resistor the same, can’t really go semi faulty, and the cap on the tweeter would knock out the highs if open.
http://www.stereophile.com/images/archivesart/sfefigB.jpg

Cheers George
gs5556
1,235 posts
 
I agree with the crossover problem. There is a power resistor in series with the tweeter. If it is failing, the resistance rises with temperature and the signal voltage is converted to heat instead of music.

Explains why it's only one speaker, happens after it running and returning to normal when cool.
georgehifi's avatar
georgehifi
10,312 posts
 
I agree with the crossover problem. There is a power resistor in series with the tweeter. If it is failing, the resistance rises with temperature and the signal voltage is converted to heat instead of music.
It wouldn’t cause this explanation, just muted high frequencies, he would still have all the bass and midrange.
" will exhibit significantly lower volume (down to almost no volume)"

Try another amp first, as these Extremas are put together like a Swiss watch, it would be a shame to break/damage all the seals to find out they’re fine.

Cheers George
gs5556
1,235 posts
 
I hear you, George, but it happens with two amps. I guess the way to be certain is to repeat the failure mode, turn off both amps and immediately measure the resistance across both speaker's terminals and compare. If one is way higher than the other then it's the resistor. If both are the same it's something else. (The only other thing to check is to swap cables at the speaker terminals instead of the amps to rule out a flaky cable connection).
wcheng2 OP
40 posts
 
How would I measure resistance across the speaker terminals?
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