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advice re: hum and passive distribution bars.

Need some advice from the experts please. I've got two dedicated 20 amp lines installed ( on circuits 1 and 3 on the same side of my electrical panel , hopefully in phase?) they travel across my garage into my living room ending with 4 available power points. When I use both lines(normally one for the cd the other for the amps. see system for more details) I have a very very low level hum only heard with ears near to speakers. However when I connect all my system to just one of the dedicated lines using a two way adaptor to help accommodate the three pieces in my system. I have no hum . Any ideas to what I should get my electrician to change with regards to the two lines installed ( for example. widen the cable runs further apart or twist them together? , change earthing at circuit box? ) which will allow me to use both of them with no hum. Lifting the ground (tried on the cd or pre but didn't try on amp) which I'd rather not do anyway didn't help. I use XLR cables throughout and don't have any tv's/ cable boxes in the same room. Also what are your thoughts on the possible advantages or not on using a high quality passive power distribution bars such as, but randomly selected,Supra, ESP, Nordost ( thor) or Acoustic revive (RTP-4) which always get rave reviews where one is only using a single electrical output but obviously mixing digital and analogue components on it. As compared to using the separate dedicated lines. Thanks.
128x128pcoombs
pcoombs's avatar
pcoombs OP
84 posts
 
Ok, heres the update, tested lines with volt meter. Definitely both circuits on same leg. which is good .All screws in outlets where fully tight. I tried all three components on one circuit only, both with and without cheater plugs throughout with same results, no audible hum. ( just a super faint sense of some noise compared to nothingness when I de-mute my line stage , which I'm presuming is perfectly normal) I've also put two components, for example amp and cd on one line and the line-stage with a cheater plug on the other line , again no hum. So the hum which is, I should stress very very low in nature can only be heard when I use both circuits without any cheater plugs being used. I went up into my garage loft to look at the cable runs. they are stabled together along various joists There is in the middle of the loft floor possibly the garage a door opener power supply/transformer? sticking up which the cables run to about 6 " at its closest . Would it be worth spreading the cables apart from each other and further away from whatever that is? Even if i manage to somehow remove the last vestige of hum from when using both lines I'm still wondering if I should focus on only using one anyway along with a quality distribution bar.
jea48
4,313 posts
 
One other thing you might try.....

I assume the two dedicated circuits and duplex receptacles are somewhat next to one another. A few feet apart at most.

You will need a length of bare #12 or #14 copper wire.
(Bare solid wire from a piece of Romex would do the job.)
The wire needs to be long enough to run from one duplex receptacle to the other.

* Turn off both circuits at the electrical panel.

* Pull the cover plates from the duplex receptacles.

* Loosen the 6/32 screws that fasten each duplex receptacle to the rough-in boxes. Bottom screws more so.

* Bend a hook on each end of the solid bare wire.

* Install the hook of the wire behind the duplex receptacle supporting strap, (bottom of recept.)

* Tighten back down the 6/32 screws making sure the bare solid wire exits down from the duplex receptacle supporting strap.

Basically you are tying the safety equipment grounds of each dedicated branch circuit together. Creating a closer star ground point ahead of your audio equipment.
Same thing Kirkus was describing in one of his posts

* Reinstall duplex cover plates and turn back on the two circuit breakers.

* Re-check for hum....

If the Hum is gone..... best you call back your electrician and have him tie the two safety grounding conductors of the branch circuits together in a more permanent concealed manner.

pcoombs's avatar
pcoombs OP
84 posts
 
Thanks for the advice Jea48 I'm going to try it. Just to be certain I understand the bare wire should attach between and connect to both the receptacles by just pressure after (tightening back down) onto the bottom metal body work ( supporting straps) that has the holes used to screw duplex into wall. Rather than the actual earth wire screw that are located on bottom left of each receptacle. At least as a temporary test method. Thanks again Philip.
jea48
4,313 posts
 
Just to be certain I understand the bare wire should attach between and connect to both the receptacles by just pressure after (tightening back down) onto the bottom metal body work ( supporting straps) that has the holes used to screw duplex into wall. Rather than the actual earth wire screw that are located on bottom left of each receptacle. At least as a temporary test method.

Pcoombs,

Correct.
But to be a little clearer. The hook, or open eye, of the solid wire will hook, hang, on the 6/32 mounting screw behind the strap of the receptacle.
The wire will be sandwiched between the strap and the receptacle rough-in box.
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