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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
imhififan's avatar
imhififan
2,217 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. 
almarg's avatar
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almarg
9,670 posts
 
Bgoeller, note the most recent post above by Jea48. I agree with him that the findings stated so far are not consistent with the problem being caused by a ground loop.

Good suggestion by Imhififan to see if the 8801 produces a hum when connected to the sub.

One note about muting. When I do use mute there is a "pop" whenever I mute or un-mute the system. Is something I should be concerned about?
Not sure that any of us can answer that, and of course it would depend on how severe it is. I wouldn’t be totally surprised, though, if the underlying cause turns out to be the same as whatever is causing the hum problem.

But on the other hand take a look at this thread, starting with post no. 245. That poster also had a popping problem with an 8801, which occurred at power on/off, mute on/off, and Audyssey on/off. Some posts later he incorrectly concluded that it was due to an interchange in the 8801’s design of the signals on XLR pins 2 and 3 relative to the USA convention of pin 2 hot and pin 3 cold, which of course would not be responsible for that kind of problem. (At most it would result in a polarity inversion, which on most recordings would be audibly insignificant, and which in any event can be compensated for by interchanging + and - at the speakers or the amp outputs. And if an XLR input and an XLR output are being used it wouldn’t result in a polarity inversion at all, since the two inversions would cancel out). Later in the thread, though, it appears that the popping problem remained, and no resolution was indicated.

Finally, FWIW, in post no. 245 that poster linked to a post by someone else who had a popping problem with an 8801 at power on/off and mute on/off, which arose only after a firmware update had been incorporated in the unit. Apparently no resolution was indicated there either. But that would seem to suggest that if perchance any firmware updates were released subsequent to whatever version is in your unit, updating to the latest firmware MIGHT cure the popping.

Regards,
-- Al

ddrave44
148 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
4,649 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.

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