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Help With 60Hz Hum PLEASE

Greetings,

I am having some issues with noise coming through my speakers at low volume. The noise sounds like a 60hz cycle hum, and can be heard clearly when the volume is all the way down. I have tried several things to quiet down this noise, but nothing has worked so far.

Before I give details of action items I have tried, let me inform you of the components I am running.

My system consist of:

·     AV PRE/PRO MARANTZ 8801

·     AMP ADCOM GFA-7805

·     SONY 300 DISC CD CHANGER

·     SPEAKERS B&W CDM9NT/CDM CNT/CDM1NT

·     SUB VELODYNE SPL1000 SERIES II (NOT HOOKED UP AT THIS TIME)

·     USING XLR INTERCONNECTS BETWEEN PRE-AMP AND AMP (MONO PRICE)

·     DEDICATED OUTLET CONNECTED TO 20AMP CIRCUIT BREAKER

·     FURMAN POWER CONDITIONER (EVERYTHING PLUGS INTO THIS)

·     I SEGREGATE OUT THE AC POWER LINES FROM THE SIGNAL AND SPEAKER CABLES


So this is what I have done to check the system so far.

1.   First off I separated all of the components power sources, plugging each component into its own outlet with the amp plugged into the dedicated outlet. (NO CHANGE, NOISE PRESENT)

2.   Unplugged any no essential item leaving just the pre-amp and amp plugged in (NO CHANGE, NOISE PRESENT)

3.   Removed the amp from the system, plugged in single source and speaker set (NOISE IS COMPLETELY GONE!!!)

a.   FOR ABOVE TEST I USED MY IPHONE WITH A SET OF RCA INTERCONNECTS STRAIGHT TO THE AMP.

                                              i.   I really suspected the amp at first because about a year ago I had the unit repaired for a standby condition. The repair center I used also repaired the CENTER CHANNEL BOARD while they had the unit. I noticed that the center channel has almost no noise coming through, but after the previous findings I decided this might be a symptom not the cause of the noise.

4.   Hooked back up system and tested (CRAP, THE NOISE IS BACK)

5.   Unplugged all of the XLR interconnects from pre-amp side (NOISE IS GONE, YEAH!)

6.   Plugged in one interconnect into pre-amp (noise comes through that channel)

7.   Switched between XLR and UNBALANCED (THE UNBALANCED CONNECTION WAS A BIT WORSE)


My conclusion is that something is happening between my pre-amp and amp that is allowing this 60hz signal though. I am wondering if it could be the interconnects themselves because I am not using a high quality interconnect. All I am using is Mono Price XLR cables. Although, why would there be no noise when the cable is plugged into the amp and not the pre-amp? Might the Marantz 8801 be the culprit due to the fact that when I plug in the cable into the pre-amp is when the noise comes through? Or maybe my first instinct was correct in that the amp is the problem?

Any help figuring this out is appreciated.

Thank You Kindly,

Joe

jo3533
Post removed 
jea48
4,678 posts
 

To all,

The Marantz 8801 has double insulated AC power wiring. The IEC power inlet connector on the back has only the hot and neutral contact blades. Safety equipment ground is not used.

The signal ground of the Marantz 8801 is bonded, connected, to the chassis though.

From what I can tell the 5 channel Adcom amp has a captive power cord. I assume the power cord is 3 wire and the plug has the ground pin and therefore the amp chassis uses the wall receptacle safety equipment ground.

//

IF, big if, I understand the OPs check list correctly,

SO if the 2 wire cord and plug powered Marantz 8801 is coupled to the 3 wire cord and plug equipment grounded, 5 channel power amp by >> interconnects >>, and absolutely nothing is connected to any of the inputs on the Marantz, I see no circuit path for a ground loop to exist from the grounded AC power system. The hum is being caused by something else, jmho.




bigkidz
3,415 posts
 
try using a wire and touching it to the source to preamp, preamp to amp, etc.  to see if the hum is eliminated

imhififan's avatar
imhififan
2,218 posts
 
"7.   Switched between XLR and UNBALANCED (THE UNBALANCED CONNECTION WAS A BIT WORSE)"
I missed this line, my bad.
THE UNBALANCED CONNECTION WAS A BIT WORSE because of the 7805 has higher gain on unbalanced input.
You have a noisy 8801?
Disconnect all input and output from the 8801, using the VELODYNE connect to one of the 8801 output channel and see if the sub pickup any hum
bgoeller
73 posts
 
Go get an Ebtech HumX ($50-ish) and try it on each component starting at the front and moving towards the amp until you find the offending device. 

Then an you can either leave the HumX in the chain, problem solved. Or, figure out why the ground loop exists with that device/interface, at the risk of your sanity. 
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