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HUM dilemma Can anyone solve This one?

Hi bob - read your posts on hum and hope you can help my dilemma. I have lexicon dc-1 preamp, krell kav250a, ead powermaster 500 and all b&w nautilus speakers. i have a continuous hum, as long as the amps are on. The preamp can be powered off, have satellite only, and if that wire is unscrewed from the wall, the hum is still there. Use a Monster HTS conditioner, all shielded interconnects, and everything is plugged into one outlet. Had three dimmers associated with the same circuit, and switched all of them for top-of-the line lutron dimmers (at $70/each!), switching every dimmer on the circuit. In fact, I ran everything by high grade extension cord to a different outlet on a different circuit - none of which changed a darn thing! The only thing that changes the tone of the hum is increasing or decreasing the degree of dimming on the dimmers - any of them. They are all grounded properly and have the latest RF suppression according to Lutron. The other difference I notice is that the speakers powered by the EAD Powermaster 500 tend to emit a slightly louder hum than the two mains attached to the krell. but when one listens, I still hear the hum in the mains as well. I will try cheater plugs, but dont want the expensive equipment at risk, but what else can i do? the last thing i should note is that i have six halogen bulbs in the dimmer switches, all of which hum similarly when dimmed. i am told this is acceptable, but the loudness of the dimmed bulbs is quite noticeable. Any ideas? This is a real dilemma for me! When sitting in the room with everything off (lights, preamp, tv, all lights, everything except the two amps [which are always powered on]), I still hear the hum! It's just audible enough that it makes sitting in what should be a quiet room kind of annoying. One last note - just to let you know I'm not crazy - even my girlfriend has noticed the hum and she doesn't know much about audio at all. She even jokes how her $200 system has less hum than my $25k system! Please help!!

In need,
Baz
bazmataz
the_lanman
27 posts
 
Had a similar hum problem with my combination HT and audio system. Turned out to be the Krell 500 3 prong plug. Try a 3 prong to 2 prong “cheater plug” on the Krell. Worked for me…
mrderrick
292 posts
 
I'll make some assumptions and some suggestions. I assume that you you do not have a dedicated circuit since you mentioned the dimmers are on the same circuit. A dedicated circuit (or 2) might help. Have you checked the polarity of your wall outlets? Have you gone to your electrical panel and turned all of the circuits off, one at a time, to see if another load on the system is causing the hum? Is the circuit for you gear run from a sub panel? If it is, you need to check that the grounds are bonded to the box and the neutrals are seperate and not bonded to ground. (the neutrals and grounds are only bonded together at the main AC entrance, from there out, they need to be apart) I strongly advise against "cheater" plugs. If this turns out to be a persistant problem, you may want to try a power conditioner with balanced 120V output.(60V+60V)
djsuperstring
2 posts
 
Kinsekd, I have a Krell KAV-500i that I am soon going to sell (I love it, but I no longer have a use for it). At the moment I am using it as a pre-amp only. I have noticed that when the "theatre throughput" button is engaged, there is a very distinct hum. This is on a two-channel system, I am not attempting to use it for surround applications. When that button is not engaged, the whole system is dead quiet..........
bazmataz OP
43 posts
 
I don't have a dedicated circuit, and was going to try a cheater plug to see if it works. Why do people advise against it? The polarity checks as normal with the three pronged polarity checker. No reverse, adequate ground. Am I guessing that cheater plugs or a $1000 power conditioner are the only things that are going to help?

Can anyone explain why the dimmer switches still affect the hum to such a great degree even though they are supposed to provide superior RF suppression? Is it safe to say this is not RFI related? Thanks again... Baz
glen's avatar
glen
714 posts
 
Mixing lighting and plugs on the same circuit is an industry no no.(Electrical construction) Who ever wired your house was not very bright. You may have a grounding problem at the panel itself. Or somewhere in the circuit. An unbalanced neutral or a neutral balanced on two hots can have an adverse effect. (This is a common practice in house wiring) Ballests in light fixtures create a lot of noise in circuits if applicable. A cheater plug defeats the ground completly. If there is ever a short to metal on your unit guess who becomes the ground wire. Think of your ground as a life jacket and never take it off. A good start is a dedicated circuit or two each with a dedicated neutral and isolated ground attached to an IG recptacle.
Glen
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