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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
jea48
4,424 posts
 

Ok, so I hooked up an old Koss CD player to my amp. fired up the CD player and then the amp. One note about this unit is that it only has a two prong plug much like my Marantz.

The noise was GREATLY reduced. I could still hear it, but is was very faint.

Just out of curiosity. Would better xlr cables help clean up some of this noise? I am using an inexpensive cable set currently.

jo3533,

Sounds good.

You could still hear the faint noise, jmho, because the Adcom is rated at 300 watts per channel. Jmho, that’s probably the best an RCA singled ended ICs, interconnects, will do. You need to go with balanced ICs.

Hopefully Al, (almarg) is still following this thread when someone posts on it and will hopefully chime in. Al can tell you the whys you will need balanced cables over single ended for the lowest noise floor possible.


I take it you have not bought any new 1 meter or longer XRL balanced cables yet? For a test just pick up 1 pair for now. Try them between the Marantz and the Adcom amp. Connect them to the front left and right channel outs on the Marantz to the front left and right channel inputs on the Adcom amp.

Don’t forget you have to / need to separate the two from one another. I would try to get the Marantz at least 18" to 24" away from the Adcom amp.


Quote:
Adcom GFA 7805 specs:
Continuous power: 300Wx5 into 8 ohms (24.8dBW), 450Wx5 into 4 ohms (23.5dBW); both at <1% THD, 20Hz-20kHz. Input sensitivity for full output: 1.61V RMS. Voltage gain: 29.67dB. Input impedance: 500k ohms (RCA), 10k ohms (XLR). THD+noise (typical): <0.135% (8 ohms), <0.3% (4 ohms). Frequency response: 10Hz-20kHz, +0/-0.25dB at 1W, 8 ohms. Power bandwidth: 3Hz-130kHz, -3dB.Signal/noise: >112dB, A-weighted. Damping factor: >500.

Read more at http://www.stereophile.com/content/adcom-gfa-7805-five-channel-power-amplifier-specifications#jVM8Mi...

almarg's avatar
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almarg
9,670 posts
 
Al can tell you the whys you will need balanced cables over single ended for the lowest noise floor possible.
A properly designed balanced interface will reject nearly all noise that is present equally on its two signal lines, since a balanced receiver circuit responds essentially just to the difference between the voltages on those two lines. An unbalanced interface has only one signal line, of course, so it will not do that. Also, a **properly designed** balanced interface will be less susceptible to ground loop-related hum and noise than an unbalanced interface, since a properly designed balanced interface will not put signal current through the ground connection in the cable. Although as was said earlier it appears in this case that a ground loop is not responsible for the problem.

A suggestion that occurs to me at this point, although it is just a hunch: In addition to obtaining longer XLR cables, purchase some RCA shorting plugs and insert them into the amp’s RCA input connectors, while connecting the amp to the preamp with the XLRs. Just a hunch, as I say, taking into account that both the specs for the amp and the Stereophile measurements at the link Jim provided make it clear that the amp’s RCA and XLR inputs are received by separate and independent input stages. (If that were not the case shorting plugs on the RCA inputs would probably short out one of the two signals in the balanced signal pair).

You can find a number of sellers at eBay offering inexpensive RCA shorting plugs.

Regards,
-- Al
jo3533 OP
18 posts
 
jea48,

I was and still am using XLR IC's. I only ran RCA interconnects for the above test, and it still does not answer my initial question. Even now with my ADCOM on the floor and longer XLR cables with plenty of room between the two components there is the dreaded humm.

It seems I only get the humm when connecting between the Marantz and the Adcom? I have to test this further to confirm.

Thank You for the help thus far.


Almarg, I don't know if the statement that the XLR and RCA inputs are received by separate and independent input stages is true. I have the schematic for the unit and to me it looks like they are on a shared circuit. If I can figure out how I will link the schematics to this thread.

Thank you both very much. Any suggestions for a QUALITY XLR IC that will not break the bank? I am looking at Audioquest Columbia XLR Cables. Thoughts?
jea48
4,424 posts
 

I was and still am using XLR IC’s. I only ran RCA interconnects for the above test, and it still does not answer my initial question.

Yes I understood you were going to use XLR ICs. I just don’t remember reading in one of your previous posts you had bought the longer cables yet.


Even now with my ADCOM on the floor and longer XLR cables with plenty of room between the two components there is the dreaded hum.

With absolutely nothing connected to any of the inputs on the Marantz? The only two components powered up is the Marantz and the Adcom? And you have the hum?

That just doesn’t make any sense......

.

Just grabbing at straws, what mode do you have the Marantz set to?

Try setting the mode to stereo. Just the front right and left channels.

Did you try my test using only one pair of XLR cables connected to the front/main right and left channels only? Baby steps first.

.

.


Al,

 For what’s it worth the Marantz balanced output XRL male connector pin out is,

Looking at the connector

Upper left pin #1 (ground)

Upper right pin #2 (Hot +)

Bottom center pin #3 (cold -)

Polarity probably is reversed with respect to the Adcom, but that wouldn’t/shouldn’t case a hum/buzz problem. Correct?

I can’t believe the Marantz would be outputting any DC. If it is where would you measure it, from what pin to what pin? Would even the smallest amount of DC cause a hum on an input of a 300 watt power amp?

There can’t be any AC difference of potential, voltage, (ground loop) from the chassis of the Marantz to the chassis of the Adcom. The Marantz uses a 2 wire cord and plug. AC wiring inside is double insulated. Unless the Marantz has a power transformer with an above normal primary to secondary coupling capacitance. Not sure that would even do it. If jo3533 disconnected all ICs between the Marantz and Adcom, powered up both units, and then checked with an AC volt meter for an AC voltage from one chassis to the other chassis he should measure zero AC volts, Correct?

Jim


http://us.marantz.com/us/products/pages/ZoomImage.aspx?img=/Assets/images/products/AV8801/XL_av8801_...



http://us.marantz.com/us/products/pages/ProductDetails.aspx?CatId=avseparates&ProductId=AV8801





jo3533 OP
18 posts
 
Jea48, 

With just the XLR cables hooked up to the amp and absolutely nothing else. There is the humm. Even while using the same outlet or separate outlets, and even with the same configuration as tested with the Koss cd player. 

These test have been completed in STEREO mode and I have flipped flopped to 5 channel music to see if there was any difference. None noted. But, since I only have 2 longer XLR ICs current test have only been done in stereo.

I did my homework for XLR pin out configuration on the Marantz and Adcom and they look to be identical.

I purchased cheap XLR cables and I am wondering if that is causing my problems. Thats why I keep asking about better cables......

Soon I will be borrowing an oscilloscope. I plan to use this to track down the noise source. Hopefully.

I am about to bring in an EE to help the ME out LOL.



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