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Quad 909 heat and hum

I am very happy with my Quad set-up. I recently came into some issues that I discussed with Quad USA, but I want to get the opinion of other owners out there.
I have it hooked to a Quad 99 pre-amp with the supplied Ampbus or with regular interconnects, and into a pair of Usher CP 6311's via Audioquest Slate cables, all plugged into a PS Audio Duet with the stock cords. Using a Sony 705ES CDP for now.
First thing I noticed is that when in stand-by (stand-by mode of the preamp, led on the amp goes red, everything goes quiet), it continues to get very warm. I could have sworn it was not this way from the beginning, but Quad technical team insists that ought to be the case, and the standby mode is nothing but a fancy muting button. Anyone else noticed how warm it is in this mode?
I wouldn't have gone looking for trouble, but what prompted this was an annoying humming noice into the tweeter in this stand-by mode. It is not there with a different amp into the same cables and speakers. Swapping the power cord with the better one that came with the pre-amp did not change it one bit. With the pre-amp off completely and disconnected it is still there. Quad's explanation was that the amp is more sensitive than others to interference from the power grid etc. Anyone else have this problem? How do you deal with it?
Should I be worried about downstream components if something was indeed wrong? For now I have it connected with regular interconnects, and fully on all the time (Quad USA distributor advice again).
Thanks a bunch.
roc_doc
roc_doc OP
55 posts
 
Thanks Digsmithd. Mine doesn't seem to change with time of day. It's one of the reasons I am concern about this being more than AC or DC or RF interference - I would expect those to fluctuate some.
I found an interesting thread on Audioasylum, someone found that the bolt holding the transformer in place on the case was loose, and tightening it in place solved the problem. Others seem to report some noise as well though, so I don't know if I should escalate this or not.
Any other experiences?
Thanks
roc_doc OP
55 posts
 
Here's an interesting bit I just found. First, it does not sound like 60 Hz, it's a tad higher, and in fact coming from the tweeter. Second, it now seems to disappear when I turn on the pre-amp. What can this mean? How can having the pre-amp connected make it better?
Thanks again
roc_doc OP
55 posts
 
I think I figured it out. Does not fully compute in my relatively non-technical head, but here is what transpired: On the assumption that it might be a ground loop harmonic, and given that on occasion I did also hear a 60 Hz hum, I started playing with interconnects between the pre-amp and amp. My brother gave me his old HomeGrown Audio connects to try. These are grounded. Hook them up, and boom, terrible, loud buzzing, same as before, but way louder! Next I took them out and replaced with the AQ Sidewinder I was using with the tuner. No ground pin with these. Hooked them up, and the system is now dead quiet. I just realized in retrospect that all my interconnect play had been with grounded ones. Never tried this one pair that was just sitting there.
Does this make sense to anyone? Recall, the buzz was there even with the amp as a stand-alone, not connected to anything! Could the input binders be generating loops by themselves, and now putting ungrounded interconnects over them solves it? I do not get it, but I don't much care!! Happy to have everything nice and quiet once more!
Any Quad 909 owners with similar issues, take note.
Thanks everyone.
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