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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
almarg's avatar
almarg
9,670 posts
 
Great news indeed, Joe!

We provided some thoughts and leads, and you did an exemplary job of following up on them in a thorough manner, and taking them further. Truly a collaborative effort, on a difficult problem (as grounding and hum problems often are).

Regarding the popping issue, all I can suggest is what I said in my post dated 2-7-16, which raised the possibility that it might be resolved by a firmware update, if one is available. As I indicated in that post, someone had reported elsewhere a few years ago that what sounds like the same problem was **introduced** by a firmware update. Which suggests the possibility that the issue may have been addressed in a subsequent update. Aside from that possibility, I would suspect that the popping is being caused by a hardware problem, perhaps a faulty capacitor or relay, or a diode associated with a relay.

Enjoy! Best regards,
-- Al

jo3533 OP
18 posts
 
Darn Cats......Why are they curious again? 

So, I was extremely hesitant to pull my rack out of my wall again to try this, but curiosity got the best of me also. However, I had a hunch what was going to happen, and that turned out to be correct.

Grounding to the chassis of the amp the 60hz. buzz came back in full effect. 

I promptly changed it back and pushed my rack back into my wall where it will stay until I purchase my Oppo-105D. At which point I will also make a relay circuit to control the on/off cycle of some muffin fans I am running. (right now I have them on a switch I must turn on and off) 

Just in case you wanted to know. My next, and last, comports for a while will be the Oppo-105D (I have to save for a bit for this) and the Sony xbr75x850c (I have been saving for this, almost there!)

Other than that I do not plan to do anything to the system for a good long while except enjoy it!
jea48
4,795 posts
 

Joe, (jo3533),

Thanks for doing the test for me. Had I known you had to pull out the rack I would not not have asked you to try it. Thanks again.


AL,

Looking at the Adcom Amp schematic wiring diagram again, trying to figure out why when all the outer contacts of the RCA jacks of the 5 amps of the Adcom are connected together and then connected to the Marantz chassis by an extended wire, the hum/buzz is eliminated.

Wiring diagram.
https://www.dropbox.com/sh/p7w1zmad9dwhx3o/AABK0x1GA9mMJZ_-hz-V--a1a/GFA7800AMP_REV082.pdf?dl=0

Without the added wire connected to the Marantz chassis, (connected signal ground), to the signal grounds of the Adcom’s 5 separate amplifiers, the XLR cables/circuitry (either at the Marantz or the Adcom), the signal grounds of the two pieces of equipment are not connected together by the XLR cables alone.

Am I right?

So when the two pieces of equipment’s signal grounds were not bonded, connected, together, (by the added wire connection circuit), why was the sound, hum/buzz 60Hz?

Jim

almarg's avatar
almarg
9,670 posts
 
Looking at the Adcom Amp schematic wiring diagram again, trying to figure out why when all the outer contacts of the RCA jacks of the 5 amps of the Adcom are connected together and then connected to the Marantz chassis by an extended wire, the hum/buzz is eliminated.
Your guess is as good as mine, Jim.  Although I'll add that if the modules in the Adcom conform to the photo you supplied (as opposed to the schematic), as we said earlier it would appear that the Adcom's analog ground (which is common with the ground sleeves of the RCA connectors) is connected to XLR pin 1 through a thermistor.  And if that is the case then the solution Joe arrived at resulted in a reduction of the impedance between the Adcom's analog ground and the chassis of the Marantz Pre/Pro (which you had indicated is common with the signal ground of the Marantz), from whatever impedance the thermistor has during normal operation to essentially zero.  The introduction of that more direct connection between the signal grounds of the two units would seem consistent with a reduction or elimination of hum, that might have been caused by small amounts of AC leakage to chassis in either component.

In any event, considered purely from an intuitive standpoint it seems to me to be very plausible that what Joe did would result in a solution.

Best regards,
-- Al
 
jo3533 OP
18 posts
 
My thought comes down to two words. Faraday Cage.

I believe what I created was a EMF cage around both the Adcom and Marants. That is why the noise comes back when I only connect to the chassis of the Adcom.

I could be completely wrong, but its what I think is going on. Again I am a mechanical engineer not a electrical engineer. I leave that stuff to the smart people. 
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