Now, on precisely the day after my biggest audio DIY project in 35 years--replacing the Low Frequency transformer in the Right Acoustat--I find that it probably wasn't necessary to do so.
I did all the required experiments beforehand, and they all came out the way that showed the LF transformer replacement. But, in retrospect, it was all apparently coincidence. The devil in the machine, the machine of my entire system--or perhaps just the Krell FPB 300--had me fooled.
It appears that the capacitor replacement was the "real" fix to the right speaker--the fix that stopped the fairly regular amplifier shutdowns. I did that fix on Christmas Day, and then enjoyed the system without further shutdown incidents so far.
However, just after New Year's day, I observed a new problem. The right channel of the amplifier, which normally runs 10F cooler, was running up to 15F hotter than the left channel, and reaching the highest temperatures I've ever seen on the Krell, just playing FM radio at moderate levels (actually, in retrospect, they were "moderately high" levels).
I then tried running the speaker with the LF transformer disconnected, so it was only playing the circuit in which I had replaced the capacitor. At first, I did notice that the amplifier was drawing more than the expected wattage at startup in the morning. I was thinking "aha, there is still a problem with the HF circuit after all." But, then the wattage went back to the normal levels (630W average long term, playing FM radio, both channels playing apparently at plateau level "2"). And normal behavior was then observed for two days.
So I switched back to the LF circuit, by plugging it back in, and disconnecting the HF circuit, by clipping the wire from the capacitors feeding the variable resistor.
With this change (and also, I wasn't noticing, the warmer weather) the right channel of the amplifier started "overheating" again, running hotter and hotter each day until Friday I was seeing 194F again, just as I had just after New Years, when the left channel was the typical (for it) 169F.
To follow up the capacitor replacement I did on Christmas Day, the next day I had re-cabled the Krell (and the Hafler 9300) to run through my modified QSC ABX amplifier switching box. And for that purpose, I had twisted all new speaker cables for each amplifier to feed the ABX box, and hooked up the old Canare 4S11 cables to run from the ABX box to the speakers.
It occurred to me that the new (and old) cables, and switching box, might be causing some kind of amplifier parasitics. So, I did the test for that, I ran my old low cap twisted pair Teflon speaker cables, bypassing the ABX box and the 4S11. That did not help, I was still getting the high temperatures on the right side.
So, I switched the cable over to the other speaker, so I was powering the left speaker with the right amplifier channel (while the other channel had shorting input plugs and was disconnected from speaker cables). Now, there was no overheating problem in the right amplifier channel all day Sunday.
So I had all the evidence I needed, from a perfectly consistent and complete set of experiments, to show that the problem was being caused by the LF circuit in the left speaker.
After I did the replacement on Monday, I proceded to play both speakers on their normal respective channels, and noticed the right channel of the amplifier was running about equally warm as the left, but not getting above 170F. Perhaps this was just because I am now running both speakers full range.
So, even the "experiment" after the transformer replacement showed I had done the correct thing.
So all was well, until Tuesday morning. Then, over the course of 3 hours, the right amplifier channel heated up to 190F all over again, while the left channel was loafing around at about 160F. On the way to 190F, however, sometimes the left channel seemed "normal" at 160F or so, then other times it was in the 170's.
Monitoring the amplifier wattage (around 730W) at idle, I tried various things, including disconnecting the speaker connections from the amplifier altogether and plugging the shorting input plug into the right amplifier channel. Nothing seemed to help. I ultimately let the amplifier idle for 3 hours, and it fell only slightly to 630W (with the left channel at 120F and the right channel at 170F, this suggests correct idle "level 1" in the right channel and "level 3" plateau in the left).
Now this "overheating" problem seems to be some malfunction in the Krell itself, and something I've seen long before, mostly in the left channel. As long as the amplifier doesn't actually shut down, perhaps the best thing is to just let it do it's own thing. Perhaps the cold weather affected some sensor in the Krell and it's temporarily or not so temporarily misbehaving. But sounding great!
At this point, apparently the thing to do is just let the system play.
I did all the required experiments beforehand, and they all came out the way that showed the LF transformer replacement. But, in retrospect, it was all apparently coincidence. The devil in the machine, the machine of my entire system--or perhaps just the Krell FPB 300--had me fooled.
It appears that the capacitor replacement was the "real" fix to the right speaker--the fix that stopped the fairly regular amplifier shutdowns. I did that fix on Christmas Day, and then enjoyed the system without further shutdown incidents so far.
However, just after New Year's day, I observed a new problem. The right channel of the amplifier, which normally runs 10F cooler, was running up to 15F hotter than the left channel, and reaching the highest temperatures I've ever seen on the Krell, just playing FM radio at moderate levels (actually, in retrospect, they were "moderately high" levels).
I then tried running the speaker with the LF transformer disconnected, so it was only playing the circuit in which I had replaced the capacitor. At first, I did notice that the amplifier was drawing more than the expected wattage at startup in the morning. I was thinking "aha, there is still a problem with the HF circuit after all." But, then the wattage went back to the normal levels (630W average long term, playing FM radio, both channels playing apparently at plateau level "2"). And normal behavior was then observed for two days.
So I switched back to the LF circuit, by plugging it back in, and disconnecting the HF circuit, by clipping the wire from the capacitors feeding the variable resistor.
With this change (and also, I wasn't noticing, the warmer weather) the right channel of the amplifier started "overheating" again, running hotter and hotter each day until Friday I was seeing 194F again, just as I had just after New Years, when the left channel was the typical (for it) 169F.
To follow up the capacitor replacement I did on Christmas Day, the next day I had re-cabled the Krell (and the Hafler 9300) to run through my modified QSC ABX amplifier switching box. And for that purpose, I had twisted all new speaker cables for each amplifier to feed the ABX box, and hooked up the old Canare 4S11 cables to run from the ABX box to the speakers.
It occurred to me that the new (and old) cables, and switching box, might be causing some kind of amplifier parasitics. So, I did the test for that, I ran my old low cap twisted pair Teflon speaker cables, bypassing the ABX box and the 4S11. That did not help, I was still getting the high temperatures on the right side.
So, I switched the cable over to the other speaker, so I was powering the left speaker with the right amplifier channel (while the other channel had shorting input plugs and was disconnected from speaker cables). Now, there was no overheating problem in the right amplifier channel all day Sunday.
So I had all the evidence I needed, from a perfectly consistent and complete set of experiments, to show that the problem was being caused by the LF circuit in the left speaker.
After I did the replacement on Monday, I proceded to play both speakers on their normal respective channels, and noticed the right channel of the amplifier was running about equally warm as the left, but not getting above 170F. Perhaps this was just because I am now running both speakers full range.
So, even the "experiment" after the transformer replacement showed I had done the correct thing.
So all was well, until Tuesday morning. Then, over the course of 3 hours, the right amplifier channel heated up to 190F all over again, while the left channel was loafing around at about 160F. On the way to 190F, however, sometimes the left channel seemed "normal" at 160F or so, then other times it was in the 170's.
Monitoring the amplifier wattage (around 730W) at idle, I tried various things, including disconnecting the speaker connections from the amplifier altogether and plugging the shorting input plug into the right amplifier channel. Nothing seemed to help. I ultimately let the amplifier idle for 3 hours, and it fell only slightly to 630W (with the left channel at 120F and the right channel at 170F, this suggests correct idle "level 1" in the right channel and "level 3" plateau in the left).
Now this "overheating" problem seems to be some malfunction in the Krell itself, and something I've seen long before, mostly in the left channel. As long as the amplifier doesn't actually shut down, perhaps the best thing is to just let it do it's own thing. Perhaps the cold weather affected some sensor in the Krell and it's temporarily or not so temporarily misbehaving. But sounding great!
At this point, apparently the thing to do is just let the system play.
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