Monday, January 1, 2018

Have I finally fixed the Acoustats???

It's now been 6 days since I replaced the electrolytic capacitor in my right Acoustat with a new 50uF 100V capacitor from Madisound.  There have been no failures so far.  Alas, it appears both my subwoofers are now defunct, so I've been playing the Acoustats full range, which I concede has virtues, including being a more complete test of the speakers...  Sound has been marvelous, though I also realize now some of the excess bass reverberation in DJ voices in NOT because of my subwoofers.

Months of previous testing suggested the problem with that speaker was not in the Low Frequency circuit, which has the LF transformer, where failures are often said to "usually" occur.

I had been thinking, therefore, for quite some time that the failure might be in the HF transformer.  But Andy Szabo, the AcoustatAnswerMan says that is so rare he has never seen a failed HF transformer.

Then I had also been thinking the failure might be in the resistor.  But unlike the resistor in the left speaker, this one does not have a hairline crack in the visible wire contact.  So I had not suspected a fault in the right resistor.  (The "cracked" left resistor seems to be fine according to all tests done so far.)

But it did seem to me, even when my first interface failed in 2010, that a likely failure point might be the electrolytic capacitor.

Although it seems at first blush a failure in the 47uF capacitor wouldn't cause the amplifier to detect a "short" (in fact, the load would be considerably reduced) I reasoned earlier this year that any such intermittant failure might cause a kind of "flyback" phenomenon when connection is restored that temporarily stored energy is then reflected back at the amplifier in an instantaneous transient, causing the amplifier to "see" what looks like a short for the briefest of durations, such as 10 msec.  The Krell might be able to decide to shutdown in less time than that.  This was my reasoning why the cracked resistor might be causing a problem (although, it could cause OTHER problems if the crack was in the portion going to ground).  And the same reasoning would apply to the electrolytic capacitor.

That is now what I now think was happening with the right speaker.  A momentary failure in the capacitor was being seen as a short by the amplifier.

The left speaker was fixed two months ago by connecting the LF transformer to the correct winding for 1+1 operation, suggesting there might be a fault in 2+2 tap I had connected to.   I didn't really think that changing this would fix the problem, but so far it seems to have done so.

So, six months wondering in the deepest audio desert may have come to an end.  Now, among other things, I need to get the subwoofer plate amplifiers replaced.  A second time in left subwoofer...however that might be fixed by replacing the fuse which I haven't tried yet.

Now, many previous times, I thought I had fixed the Acoustats, not so much by fixing the acoustats but by changing something, like putting the subwoofers on a different circuit, only to find later that each such change didn't prevent another amplifier shutdown a week later.  I'm only 6 days into testing the speakers with the present level of changes, so there's still some possibility of a failure.  But because this has been a holiday vacation week for me, I've done enough testing now, the cure seems pretty well established.

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