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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
dog_or_man OP
68 posts
 
These are great action-items to checklist my way down. I'll try to get my electrician friend to come over and look into the earth ground and the DC-offset first, and then maybe take things from there in the direction of an isolation transformer. ...Yes?
almarg's avatar
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almarg
9,670 posts
 
Ok, that's great that you have a friend who is an electrician.

An isolation transformer would eliminate problems with dc offsets, assuming the offset was not so severe that it would cause the transformer itself to overheat or have other problems. But I don't think an isolation transformer would be relevant to the other possible causes that have been mentioned.

Re UncleJeff's comment, yes, undoubtedly something is misbehaving after warming up for 20 minutes or so. But considering the history of similar problems with multiple components over the years, it would seem that something else (such as problems with the ac wiring or grounding) is causing damage to some part or parts, and that damage is in turn resulting in the misbehavior after warmup.

Regards,
-- Al
dog_or_man OP
68 posts
 
I agree: the trouble seems partly due to contagious failure whose root-cause has never been identified. I always write too much on these things and my OP was *way* out of hand, but at this moment the most relevant points seem to be:

1) Similar problem years ago with Parasound stuff, couldn't be verified on three separate benches

2) Similar problem regardless of assorted gear-swaps in the meantime

3) Audible transformer hum in usually stone-silent McCormack amp, both through the front apron and down the speaker wires, and

4) Breaking and re-establishing the interconnect connections seems to fix everything for a while.

...It would seem that we're pointing squarely in the direction of either inadequate grounding or excessive dc-offset or both, as root causes of other things that aren't otherwise scientifically explicable.

Anyone think that conclusion, in the wake of the four salient points listed, isn't justified, or importantly overlooks other possibilities that should be addressed first?
sns
3,003 posts
 
All the power related stuff sounds reasonable. I don't get the breaking and re-establishing IC thing, this has nothing to do with power issues.

I don't recall if this has already been mentioned, but it sounds like you may have an over-voltage situation as well, this causes hum in my isolation transformer. Other than the hum, I haven't had any other issues.

Proper grounding of dedicated circuits is absolutely critical as well. As I previously mentioned, you should get all equipment off the non-dedicated lines, all kinds of crap rides in on shared grounds and mains. Digital will benefit most from clean AC, all your video equipment should be on seperate lines from audio equipment.

You should have 3 dedicated lines, one for amp, most likely straight into wall, another for CDP and preamp, a third for video components. You'll never get to the bottem of anything until you do this.

Next, get a quality power conditioner for digital and preamp, maybe amp. At this point you'll be able to make a correct diagnosis as to possible issues with the sonic palatte of audio components.
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almarg
9,670 posts
 
I don't get the breaking and re-establishing IC thing, this has nothing to do with power issues.

Sns, there are two possible relations that I can envision, albeit somewhat vaguely:

-- If a ground is missing somewhere, a component by itself (not connected to anything else except power) would tend to have its chassis and signal ground "float" to a voltage level that is determined by small leakage currents in its power transformer, or elsewhere in its internal circuitry. Connection to other components via interconnects would change that, because the interconnect shields tie together the chassis (and consequently the signal grounds) of the connected components. If multiple components are not properly grounded, they will "want" to float to different levels, but the interconnects between them will prevent that. Temporarily breaking the interconnections will allow the chassis of each component to return to the level that is determined its own internal leakage paths.

-- If the proper ground paths and ac return paths are not present (especially if ac neutral is open somewhere), return currents could be flowing through roundabout paths that may include or be affected by the presence of the interconnects. That conceivably could be causing something, such as a power transformer, to overheat and cause the audible symptoms after a warmup period. For instance, if ac neutral is open, the leakage path through a power transformer to ac safety ground could be breaking down and serving as part of the return path (for a component with a 3-prong plug), which would definitely overheat the transformer. For a component with a 2-prong plug, the return path in the absence of ac neutral could be via interconnect shields to other components and through them to safety ground.

Or something like that; I obviously can't formulate all of this precisely, but my point is that a relation between disconnecting the interconnects and a power problem is very conceivable.

Good point about the overvoltage possibility. Re your suggestions about multiple dedicated lines, etc., those are all excellent suggestions for optimizing sound quality, but I think that what we are dealing with here is a basic functionality and reliability problem, which needs to be resolved first.

Regards,
-- Al
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