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back to ask again long sorry

If you recognize the user-ID, then you know the problem I'm about to describe because I've been yapping about it in these forums, on and off, for *years*. I'm only in here to try again because everything I've done so far to try to fix it has resulted in just more credit-card bills.

The sound is perfect for the first twenty or thirty minutes -- always has been, and I always think I've fixed whatever's wrong -- and then, gradually, the sound becomes reedy and increasingly sibilant in the upper midrange and apparently "over-modulated" right around the midrange-tweeter crossover.

If I shut everything off and reconnect everything, the problem often goes away for another twenty or thirty minutes, but not always.

It can't be a problem with components or speakers because everything in the chain has been repeatedly replaced, and many configurations have been sent off for service and returned with clean bills of health.

I don't think it's RF pollution because I've encountered the problem at a friend's house, and fixed it doing the same thing, over there: reconnected everything and had great sound for... twenty minutes.

I don't think it's a cracked RCA input socket because the problem has spanned several configurations of equipment.

I don't think it's a bad interconnect because the problem has spanned several configurations of cabling.

I don't think I'm delusional because non-audiophile listeners have commented on both the unpleasantness of the sound before reconnection, and the improvement afterward.

At all events, something seems to be "building up" in the signal path, somewhere, and the act of severing all the connections seems to cause whatever that build-up is, to be dissipated.

Lately I've been trying to fix this by... well... *reading* -- about everything from PS-Audio Humbusters to Audience Adept Response power conditioners and back to the XDC power filters by Channel Islands Audio. Trouble is, I'm cleaned-out financially and I just really don't feel like spending any more money before knowing with a bit more certainty that more dollars spent will point me more definitively toward getting to the bottom of this. Are there professionals who can help to diagnose the problem, and who are then also knowledgeable enough about the industry to recommend the proper fix?

Current system configuration: (many, many others have been tried!)

McCormack MAP-1 and DNA-HT5, connected directly to dedicated AC circuit via Signal Cable power cords

Arcam FMJ-CD23 connected directly to nearby, undedicated AC circuit, via signal cable digital power cord

Sony BDP-S550 blu-ray player and Panasonic TX50 plasma TV, connected to APC H-15 power supply, which is in turn connected to the undedicated AC circuit via Harmony power cord

Salk Songtower QWT speakers, front L and R, Linn Trikan center channel, Totem Mite-T rear L and R.

signal cable interconnects, element cable cross-connected speaker cables.

Thanks again, everybody.

Dave O'Gorman
Gainesville, Florida
dog_or_man
cyclonicman
693 posts
 
Since you fixed everything and it even occurs at your friends house, maybe it's the quality of electricity being delivered to your community, voltage fluctuations, etc.
unclejeff
1,313 posts
 
Heat. I had a Saturn Car that would just stop running after 20 minutes of city driving, but never on the freeway. As it turned out the fuel pump had a contact that started to arc when the engine got really hot.

20 minutes. Something in system gets to a certain temperature and then goes 'off'.

That's the best I can do for you. i don't want to talk about how many mechanics and dollars were involved with tracing this problem/
dog_or_man OP
68 posts
 
Sns: Do you mean to suggest that I should connect the preamp, poweramp, and cdp to the same line conditioner and thence to a single outlet on the dedicated line?

Almarg: How do I "use a multimeter to check if one of the AC runs is miswired"? And how do I "orient" a two-prong plug? How do I diagnose, and what do I do about, an "open AC neutral run"?

Ghosthouse: The problem was "fixed" when we did a quick break-and-reconnect at the friend's house, and did not recur until I was back home, but it seemed unlikely to me that it would have happened at the friend's house in the first place, if the problem was in my home. Thoughts? Could the whole thing be attributable to the fact that my central AC and furnace air-handler are located about 28" away from the left speaker, on the other side of a thin plaster wall?

Uru975: Can I give specific instructions to an aftermarket tech, that will reduce the likelihood of a "false negative"? The Arcam CDP, in particular, gets *really* hot after it's been running for awhile, and other owners have said that theirs don't.

Mrderrick: Listener fatigue is certainly possible -- anything's possible -- but would that fatigue "reset" after such a short interval of time needed to break and reestablish the ic connections? Sometimes the problem has been "fixed" in as little as two minutes.

Cyclonicman: How do I "check the quality of electricity being delivered to the community, voltage fluctuations, etc." and what do I do when the results turn out to be bad? I've been thinking this could be it: We have a municipal power company here in Gainesville, Florida, and they... well... s*ck, frankly.
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almarg
9,670 posts
 
How do I "use a multimeter to check if one of the AC runs is miswired"? And how do I "orient" a two-prong plug? How do I diagnose, and what do I do about, an "open AC neutral run"?

Set the multimeter to read ac volts, on a scale that is greater than 120V, such as the scale that many multimeters have that reads 0 to 300VAC. Then for each outlet measure the voltage between hot and neutral, hot and safety ground, and safety ground and neutral.

How to orient a two-prong plug, if any, I explained in my earlier post. I'm referring to the fact that if the two prongs are not polarized (i.e., one is not wider than the other), they can be plugged in with two possible orientations.

If an ac neutral run is open, it should become apparent by performing the multimeter measurements described immediately above (i.e., you will not see any voltage between hot and neutral).

If you don't have a multimeter, or other ac voltmeter, or you don't feel comfortable doing these things, try my other suggestions first and if they don't lead anywhere perhaps you know someone nearby who has experience making electrical measurements.

One more possibility occurs to me: Somehow either a large dc offset or an ultrasonic oscillation may be being sent into the speakers (both would be inaudible), causing speaker driver or crossover elements to heat up excessively, producing the audible symptoms after the 20 minute period. Not sure what might cause that, given that you've apparently tried multiple amplifiers, and I'm not sure how a dc offset would affect the midrange-tweeter part of the spectrum, but I thought I'd mention these possibilities in case they trigger some further thoughts.

Regards,
-- Al
dog_or_man OP
68 posts
 
I should tell everybody one more thing.

Sorry this is coming out in dribs and drabs, but I have a hunch that this might be an important detail: I started shoveling money at my stereo in the first place because an old configuration of gear and speakers developed this *bizarre* characteristic that several different techies were unable to recreate on their own benches: After extended listening, the left channel would develop a "whooshy" kind of noise, almost like the sound your ear makes when it has water in it, and would attenuate in volume, eventually to zero.

If I went to the back of the stack and wiggled the left-channel IC between the pre- and power amps, I'd hear a series of loud pops in that channel, and then everything would work just fine again, for awhile. As I say, it was for this reason that I started swapping-out gear in the first place, but what the ancient problem and the current one seem to have in common is a tendency for "build-up" to be dissipated by mechanical processes at the back of the stack.

Does this shed any new light?
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