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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
ddrave44
146 posts
 
Do you have a cable box anywhere in the house? From what I've seen, it doesn't need to be physically connected to the preamp/receiver to put the hum into the system. A ground loop isolator on the cable line worked for me. I used a TII 220 by TII Network Technologies that I got for about $21. You bring the cable line to the isolator and then connect the isolator to the cable box. For me the hum disappeared immediately. 

Long story, but I have a tube amp that is very sensitive to hum. I noticed that when I unplugged the cable line from the cable box the hum went away. Same when the amp was at a family member's house. The cheater plug did work, but I wasn't so comfortable with that solution, as I think the grounding is there for a safety reason (I don't have a background in electronics, but it seems logical). Anyway, by then I had bought the ground loop isolator so went back to the grounded plug.

Good luck.
jea48
4,424 posts
 

A special note on “hum:” When there is a low-volume “hum” audible throughout your speakers, even with the main

volume turned all the way down, you have a common phenomenon known as a “ground loop.” A ground loop is basically

a difference in ground voltages between two or more components which are connected electrically and which creates

multiple current paths where there must only be one. This difference in potentials creates a 60Hz low-level sound

(approximately a low A), that seems to “hum.”

It can be caused by adding new components to your system, but that does not imply there is anything electrically

wrong with any new component. With the advent of audio/video and home theater systems, the problem has become

commonplace. Generally, the cause is the Cable-TV incoming signal line. This new incoming line may add an additional

ground at a different potential to the AC line ground of your other equipment (refer to Note I and 2, to troubleshoot

a hum problem).

Note 1: Cable TV systems can sometimes contribute to ground loop problems which cause “hum.” To determine if your

cable system is the contributing factor, disconnect the Cable-TV incoming signal line (round, 75Ω) at the wall, or the first

component the cable is connected to (i.e. the cable box, or VCR). If the hum is no longer present, you must insert a “75Ω

Ground Loop Isolator” before reconnecting the line. You should check with your ADCOM Dealer to obtain one. If the “75Ω

Ground Loop Isolator” works only partially or not at all, then please read Note 2 to complete the troubleshooting procedure.

Note 2: Make sure that the power amplifier is at least 6” from the Preamp and/or Processor. Usually putting another

component between them is sufficient to minimize the hum. If this does not reduce the hum, turn the system off and

disconnect all Inputs from the amplifier. If the hum still persists, then your Dealer or Service Center must examine the

amplifier. If the hum disappears, try another set of RCA cables. Connect one RCA cable at a time to see if one specific

cable is responsible. If any or all cables cause the hum to appear, then the preamp or processor should be evaluated for

proper operation by your Dealer or Authorized Service Center.

12


GFA 7805 Owner Manual (PDF)
http://www.google.com/url?sa=t&rct=j&q=&esrc=s&source=web&cd=12&ved=0ahUKEwi...


Note #2) above. Picky little burger isn’t it? Maybe it just doesn’t like being in the same room as the Marantz 8801.



http://www.stereophile.com/content/adcom-gfa-7805-five-channel-power-amplifier-measurements#gJ5bG65z...



http://www.stereophile.com/content/adcom-gfa-7805-five-channel-power-amplifier-cable-issues#QSojSble...


jo3533,

Will you please acknowledge if the Adcom 7805 has a 3 wire grounded plug or a two wire plug.

jo3533 OP
18 posts
 
Jea48,

My Adcom has a 3 wire grounded plug.

Thanks all for taking the time to post on this. I still have not figured out the problem.

Does anyone have any input on the mystery center channel that was repaired not having the noise? I think they replaced the bridge rectifier. Can bridge rectifiers that are old or going bad allow noise through? Thought that the capacitors would help smooth that out. At any rate I plan to move the amp out of the same area as the pre-amp and see if that helps. If not I am going to borrow an oscilloscope and see if I can track down the noise. 

Thoughts?
jo3533 OP
18 posts
 
Ok, so I was mistaken. The noise is just as bad on the center channel. I took apart my XLR cables today and looked for the dreaded "pin 1" problem and I thought I had found the issue. But after clipping the shielding wire same result.

This is driving me crazy. Next I am buying longer interconnects and moving the amp farther from the pre-amp. Ill let everyone know the results.


noromance's avatar
noromance
9,769 posts
 
Try moving everything off your current outlet to just one. Use an extension cord and multi-gang outlet adapter. Take the conditioner out too. Try a few different outlets on different circuits.
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