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Dedicated Line Noise Filter?

I don’t know if what I’m seeking exists, so I’m asking the experts.
I have 2 dedicated lines installed; one for analogue, one for digital. They originate at a sub-panel off the main circuit box. The sub-panel is connected by the hot lead and has it’s own ground including a second grounding rod. There is a home surge protector installed at the main circuit box.

I have passive conditioning on both lines for the components, yet I’m still hearing noise thru the speakers (from about two feet away). I live in a city and I suppose it could be dirty power from the grid.
Now to my question; is there a noise filter that can be installed at the site of the circuit panels? My electrician offered a surge protector with noise filtering (plus EMI/RFI), but was very expensive. So, is there a device that can be installed upstream to lower the noise floor?
Many thanks.
128x128lowrider57
lak's avatar
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lak
3,516 posts
 
Probably not what you are looking for however I thought I'd mentioned it:
Somewhere after the sub-panel but before the AC outlet you might consider the installation of an isolation transformer 5 KVA each per dedicated line. This would be dependent upon your logistics because the isolation transformers will generate some heat and 60 dB of hum. 
In my basement, I had two isolation transformers in-between my main panel and sub-panel (feeding my sub-pannel) which gave me eight dedicated lines.
yakbob
162 posts
 
Have you tried or considered a Jensen line transformer between your source and pre or between your pre and power amp? I realize inserting such a device is taboo on this site because its installed "in the chain", but the Jensen devices are high quality, and inexpensive enough that you're not out much money if you decide it's not working.


winoguy17
592 posts
 
 Are you positive the noise isnt being generated by one of your components?
lowrider57's avatar
lowrider57 OP
3,018 posts
 
@winoguy17 , that's a good thought. My SS amp has high gain and was boosting the noise level previously on a shared dedicated line. Since I moved my system to a subpanel with a line dedicated to analogue, the noise floor has been greatly reduced.
As a test, I hooked up an old Kenwood amp with much lower power and the noise from the mains was still present.

@yakbob , I tried a Jensen transformer between preamp and amp, but I have an Atma-Sphere OTL pre and the transformer ruined the sonics. I've seen some comments by Ralph(atmasphere) where he says putting a transformer inline with an OTL device can have unpredictable or negative results.

@lak , I like the concept of the iso transformers and looked at how you've implemented them. That type of setup would work in my basement, but cost is a consideration. I will ask my electrician about it and show him your pics, thanks.
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gdnrbob
2,421 posts
 
@lowrider57 
How expensive was the surge protector with noise filtering? It would seem to be the right way to go, in my opinion.
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