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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
53 responses Add your response
dog_or_man OP
68 posts
 
Just a quick bump to this thread -- with some new info to report:

1) My electrician-friend thinks grounding issues will be easier to check than dc-offset, which suggests he doesn't have the equipment to check the latter at his disposal.

2) The breaking-IC connections and re-establishing them turns out to be a red herring: It's the *POWER* connections that have to be disconnected and reestablished, only.

3) The CD-player transformer doesn't just get extremely hot, it also has an audible hum which I'd never noticed before this most recent round of tests. So the amp and the CD-player are both humming from inside their respective chassis.

Follow-up thoughts are welcome and appreciated as always.
almarg's avatar
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almarg
9,670 posts
 
Thanks for the update. I don't think there is anything in what you've reported which changes my basic recommendation -- step one is to have all of the ac wiring, grounding, and voltages thoroughly checked out.

My instinct would be that dc offset is much less likely to be the cause of the problems than a miswire or a missing wire would be.

Regards,
-- Al
ua100k
32 posts
 
hi,

I was looking for something else and stumbled across your post.

I am an electronic Engineer. Your modulation is a slow build up of waves going back and forth, building up much like a bridge collapsing or tsunami building up, wave over wave. You probably are starting with less then 1 hz - you cannot hear this, then increasing until audible range.

I have designed high frequency circuits and networking etc. The signal reflections are causing this and they are caused by "mirrors" in the signal path.

You only bet is to change out each item in your system until you find it. The amp, pre-amp, speaker cable, Interconnect, source etc.

You could try to isolate this by turning on just the amp and speakers, leave it on for 1 day. Try it with just the pre-amp, amp, speaker. Then 1 source, pre-amp, amp, speaker, then another source, pre-amp, amp, speaker until you figure out where in the chain the reflection is.

If you have the reflection jumping across or around the components, then you have a very unique situation - you should write this up. IT is hard, not impossible, for reflections to go backwards through components, it is typically within or between 2 components.

Also, not possible to bench measure, the power supply of one of the units has the slow modulation, so you have to open all the units and measure which unit is creating this modulation when you hear the sound. You will need a scope to see this.

All of this is a lot of work. It might be a lot more fun just to change everything out and start fresh. Unless you type A and have to solve this for enjoyment.
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