Topic: Please advice! Hum issues!

[Boxerfan88]

use a 240v-240v isolation transformer?


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[terfyo]

i do have a balanced transformer which i have custom made by Koba in Chinatown.
the transformer helps with approximately -200mV from the reading purely from the socket.
Any ways to kinda like, remove this problem of the AC?

[AndrewC]

...
oh btw, i have recently bought the EMI Power Line Tester from an MO and realized that when my airconditioner is not turned on, the reading shows 450mV there about. However, when my AC is turned on, with the compressor cut in, the reading is 1,500mV.
...
Anybody got any ideas on how to reduce the noise injection into the power line when the AC is running?

You've got a classic case of ground loop caused by leakage current into your home's ground by a high-powered appliance.

(A=Your Air-conditioning system. C1=Your Pre-Amp. C2=Your Amp)

If you look at the picture, it also explains why lifting your Pre-Amp's ground won't solve the problem, but lifting the Amp's ground does (breaks "I" current flow). Instead if lifting the power-Amp's ground, a safer option would be a signal isolation transformer for your 2 channels. Something like ;


 
An AC isolation transformer for your entire sound system would be a good (albeit bandaid) solution. Addressing the root-cause would mean getting an electrician to re-wire your Air-conditioning power cables so that it doesn't leak/induce stray currents into the ground.   

Good luck! 

[aero88]

Hi Andrew,

Well said. But just curious will the hum isolation module affect the sound quality?

[AndrewC]

... But just curious will the hum isolation module affect the sound quality?

I’ve never had to use one myself personally, but I'm pretty sure it will impact the sound quality. How significantly kind of depends on the rest of the system.

In the case of the pictured isolator I posted, it’s from Radio Design Labs. According to the specs, it has a THD+N of <0.5% (30Hz-20kH), and Cross-talk of <60dB…. I bet the Thread Starter’s Amp/PreAmp have better specs than that, in other words, this ‘Hum Killer” will add distortion and cross-talk into the audio chain. 

[comfortablynumb]

I have hum issue in my system too
After investing in power conditioners, the problem persisted
 Finally found the root cause of the him.
One of my ceiling fans electrical switch was tapping on my AV system power source.

So each time I play my AV system, I will not switch on that particular fan
Problem solved.

Just troubleshoot 1st. Determine what appliances are in use when using yr AV system and try to isolate the culprit appliance

[terfyo]

Ar. This i have tried already.
I actually switched off all the breakers, leaving only the hifi breaker on (when no one is at home of course), the hum still persist.
I've bought a few pieces of ferrite core clips from Koba last weekend, yet to confirm if the hum persists.

[HiFi]

Does it work with the ferrite core clips?

[terfyo]

Does it work with the ferrite core clips?

Nope. It doesn't work..
That only takes a little EMI out of the equation. I think it has something to do with the ground loop.

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