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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
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almarg
9,670 posts
 
Thanks for providing the documents, Joe.  After looking at the schematic I withdraw my suggestion of RCA shorting plugs.  Consistent with your earlier comment it shows the center pin of the RCA connector being wired directly to pin 2 of the XLR connector.  Some unusual things that are done with various resistors account for the unusual differences in input impedance and gain between balanced and unbalanced input modes.

I'm assuming, btw, that the schematic you provided, which is for a GFA-7800, represents the circuitry for each of the five channels of your GFA-7805.

I don't know if the fact that the cables you are using connect pin 1 to the shells of the XLR connectors might factor into the problem.  But in any event I would suggest ordering the Mogami cables I referenced earlier, as I suspect they will sound at least a little bit better than what you are using even if changing to them doesn't help the problem. 
With the XLR cables disconnected from pre-amp. (NO NOISE)
This is different than before.  Perhaps when you tried this previously, with noise resulting, most of the length of the cable was closer to the amp than in the present arrangement that is shown in the photos, resulting in the unterminated cable picking up EMI from the amp itself (as I speculated earlier).

Not sure what else to suggest at this point.

Regards,
-- Al
 

jea48
4,424 posts
 

Al,

From jo3533 first posted message.

Quote:
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)
End of quote

>>>>>>>>>>>>>>>>>>>>>>>>>>>>

Al,

Number 5 & 6.
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)


>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>

2-22-2016

jo3533 said: 

Quote:
So with the iPhone plugged in with RCA connectors there is no 60hz hmm. So I decided to go ahead and plug in the xlr cable into the same channel that the RCA cable is plugged into. NOTE: the XLR cables were not connected to anything for this test, they were plugged into the amp only. The noise was back, although much softer. So then I flipped the "Balanced/Unbalanced" switch to "Balanced" and the noise was back. Unplugged the xor cable and the noise is gone.

Bottom line. Every time I plug in the xlr cables the noise comes back. Even if they are not connected to anything on the other end.

End of quote

"So then I flipped the Balanced/unbalanced" switch to "Balanced" and the noise was back."

>>>>>>>>>>>>>>>>>>

From his last post:

Quote:

With everything plugged in and the amp on, pre-amp off. (NOISE)
With Amp on and pre amp on. (NOISE)

With the XLR cables disconnected from pre-amp. (NO NOISE)

With the pre-amp not plugged into the wall at all, and with the XLR ICs connected. (NOISE)

End of quote.

>>>>>>>>>>>>>>

I think jo3533 has been fighting this thing for so long he is getting confused with the some of the results from all the tests.

I think his first posted message and his last post are probably what he found to be the case.  Just a guess his post on 2-22-2016 was in error. We won't know for sure until he posts back.


It's late that's it for tonight.

Jim



lp2cd
101 posts
 
I’m sorry, but I haven’t perused every word of this thread, so I may have missed some things. One often very effective, and rather expensive, cure for 60 Hz hum in a system is to use balanced AC power. Typically, balanced AC will reduce system hum by at least 10-15 dB, and possibly more. Balanced AC is a pro move, and you will find that most high-end recording studios use balanced AC throughout for good reasons. It does need to be approached with some care and understanding, as well as an adequate budget, but it will pay big sonic dividends in almost any system, and is overall much more effective than other types of "power conditioning." Google "Equi=Tech" and "Son of Q."
jea48
4,424 posts
 

Hi Al,

Disregard my last post.


https://www.dropbox.com/sh/1rdxqg82pw3ecq9/AAATCANt3v5Vc3kMZ0taSa1na?dl=0

Look at picture #3 of the OP’s Link of the XLR connector. Notice that jumper wire from pin 1 to pin 3? Could that be the problem?


>>>>>>>>>>>>>>

Found this doing a search for the wiring of an XLR connector.
http://www.scotaudio.com/wiring.htm

Quote from Link:

"How to wire an XLR connector (unbalanced)

The unbalanced system is used for high impedance microphones over short distances, and is not recommended for professional use due to susceptability to any RF noise - such as lighting sources, taxi radios etc.

Pin 1 is shorted to pin 3, at either end of the cable"

End of Quote.

>>>>>>>>>>>>>>>>>

Here is another Link.
http://www.rane.com/note110.html


Al,

Me thinks this could be jo3533 noise problem. What say you?

All he would need to do is clip the jumper wire that is connected from pin1 to pin 3.

He would need to check the connectors at both ends of the cable for the jumper.

He could start with just one cable and clip the jumpers and then try the cable in his system and check for the hum/buzz.


Jim


almarg's avatar
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almarg
9,670 posts
 
Hi Jim,

When I first looked at that photo last night I interpreted it the same way as you did, that two pins (probably 1 and 3) were jumpered together. But after noting Joe’s statement that:
I took the XLR cable apart on both ends and both end have pin 1 connected to the shield ground of the plug itself. You can see it in the photos.
... and after looking at the photo a little further, I concluded that pin 1 is most likely not connected to pin 3, but rather to a lug which in turn connects to the shell of the XLR connector. Which was the reason I said in my last post that:
I don’t know if the fact that the cables you are using connect pin 1 to the shells of the XLR connectors might factor into the problem. But in any event I would suggest ordering the Mogami cables I referenced earlier....
But I agree that it can’t hurt, and could conceivably help, to clip that jumper at both ends of the cable and see what happens.

Best regards,
-- Al

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