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
Did you try using RCA connections from 8801 to 7805?
The 7805 has very low input impedance on Xlr.

2.   Unplugged any non essential item leaving just the pre-amp and amp plugged in (NO CHANGE, NOISE PRESENT)

To be clear, you had nothing connected to any of the line inputs on the Marantz A/V preamp? (All the input jacks were empty of Interconnect cables?) Volume control set to minimum.

The only interconnects connections were from the outputs of the Marantz to the Adcom power amp. Is that correct? 


Do you have Cable TV, or a Dish, connected to the MARANTZ 8801? 

If you have a cable TV connection to your audio system, it is probably this. I've had hum problems with my phono preamp that was corrected by re-orienting the equipment to a different location.

Try using a "cheater plug" (2 prong plug) on your preamp. You may have a ground-loop coming thru the interconnect.
This test will make the amp the grounded component, and isolate the preamp.

As you said, you're using cheap XLR cables, so they may not be properly grounded.

"Try using a "cheater plug" (2 prong plug) on your preamp. You may have a ground-loop coming thru the interconnect.
This test will make the amp the grounded component, and isolate the preamp."


I believe the preamp is already using a 2 prong plug. So, if the amp has a 3 prong plug, then try the cheater plug on the amp. IMHO, it is best when both the preamp and the amp are the same. Hopefully, someone else will respond to this.


Wow a lot of feed back here. Thanks.

So currently the only components I have hooked up are listed in the original post. I have no TV, cable, satellite hooked up.

UNBALANCED CONNECTIONS are RCA connections. When I hooked them up the noise was worse.

Since this post I have tried using a cheater plug (no grounding pin) and there was no change.

Please read through my original post carefully as it has listed everything that is hooked up in the system, and I have not left anything out. If I have it, its listed

Any comments about the amp and amp repair? Might my fist thoughts been correct? What about a higher quality XLR cable? 

Thanks.
Did the system always suffer this noise problem, or is it a recent manifestation?
What happens to the hum if the Marantz is muted, with the mute function set to "full" rather than the other attenuation settings that are provided for that function?

Regards,
-- Al
 
When I mute the Marantz 8801 the noise is still coming through the speakers.

This condition was present when I was running my Rotel RSX-1067 as well. In fact I think this condition has been there ever since I got my amp. Running separates is new to me.

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?
Post removed 

To all,

The Marantz 8801 has double insulated AC power wiring. The IEC power inlet connector on the back has only the hot and neutral contact blades. Safety equipment ground is not used.

The signal ground of the Marantz 8801 is bonded, connected, to the chassis though.

From what I can tell the 5 channel Adcom amp has a captive power cord. I assume the power cord is 3 wire and the plug has the ground pin and therefore the amp chassis uses the wall receptacle safety equipment ground.

//

IF, big if, I understand the OPs check list correctly,

SO if the 2 wire cord and plug powered Marantz 8801 is coupled to the 3 wire cord and plug equipment grounded, 5 channel power amp by >> interconnects >>, and absolutely nothing is connected to any of the inputs on the Marantz, I see no circuit path for a ground loop to exist from the grounded AC power system. The hum is being caused by something else, jmho.




try using a wire and touching it to the source to preamp, preamp to amp, etc.  to see if the hum is eliminated

"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
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. 
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

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.

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.

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?
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.


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.


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.

You never said how long the XLR cables are. I assume they are at least 1 meter.


That should be plenty long for a temporary equipment set up test. It may require moving the heavy Adcom amp though. (You will probably need put the Adcom on the floor. If the floor covering is carpet you may need to either sit the amp on a hard surface or slightly elevate the amp above the carpet if the amp has air vents on the underside of the amp.) (You will need to reconnect, solder, the shield back on the XLR connector)

.


Set up:

Rearrange the Adcom so you can place the Marantz 8801 on the floor directly behind the amp. The rear panels of the two will be facing one another. Space the two as far as possible from one another limited only be the XLR cables.

For this test plug the Adcom and Marantz directly into the wall duplex receptacle 20 amp dedicated circuit. Unplug the Furman power condition from the AC power. You do not want anything AC powered near the Adcom or Marantz equipment.

Do not connect anything to the inputs of the Marantz 8801.

Isolate the Adcom speaker wires as they leave the amp as far as possible from the Marantz 8801 as well. Basically you want the Adcom and Marantz 8801 setting all alone by themselves on the floor.

Make sure the AC power cords of the two units are kept away from the XLR cables.

Turn on/power up the Marantz 8801. Mute the 8801.

Next power up the Adcom amp.

Check for hum.



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...

Jea48,


My XLR cables are very short. 1 foot only. I ordered some loser cables and when they come in I will be doing this test and let you know the results.

Thanks!
OK.....so I never made it all of the way to the testing sequence as stated above. I started to set up for the test, but when I get the 100lb. amp out of the equipment rack and set it on the floor. I decided to try a couple of things before I removed the rest of my equipment.

In order to shorten this a bit I will cut to what I did the gave me a reason to pause and reflect.

For this the amp is plugged into a dedicated outlet with NOTHING else attached.

I ended up plugging in my iPhone directly into the amp using 1/8" to RCA adapter. Voila, no noise at ALL!. 

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.

I am now, more than ever, thinking the problem is within the amp.

Any thoughts? Any suggestions? 
 

jo3533,

You cannot connect the XRL cables to the amp without the other ends of the cables connected to a load/source.

If they are not connected to a load, like a preamp, and are just laying there open ended you basically have 5 antennas picking up RFI and sending the noise to the inputs of 5 power amps.

If you have the amp on the floor that’s is definitely the hard part of the job.

The Marantz 8801 is considerably lighter.


But, before you pull the Marantz out of the rack do you by chance have an old DVD player? Or you could use your Sony multidisc player.

For a test connect a pair of RCA interconnects from the audio out of the player to the front right and left channels RCA jacks on the Adcom amp.

With the Adcom amp turned OFF,

Plug in the power cord of the player and turn it on.

You will not be playing any music through the player. DO NOT press start to play.(If you are using an old DVD player don’t put a disc in it.) By chance if a disc is in the player and you were to press play the music would be loud but not ear deafening. I still would not try it!

Next flip the toggle switches on the back of the Adcom for the front right and left channel amps to single ended. Turn on the amp.

Just a guess you will not hear the dreaded hum.

Unlike when you were using the iPhone for a test which is battery powered, the player is 120V AC powered. The player is the termination for the single ended RCA interconnect cables. Both pieces of equipment are powered from your house’s 120V mains power.


Post back your findings.

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.


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...

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
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?

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





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.



jo3533,

I am at a loss.

Starting from ground zero with no ICs connected to the Adcom Amp there is no hum.

When you connected the DVD player to the Adcom amp using single ended ICs there was just a faint hum. Which Al explained the reason for the faint hum quite well.

In earlier posts you tried just having one pair of XLR balanced cables hooked up from the Marantz to the Adcom with the Marantz power cord unplugged from the AC power. Absolutely nothing was connected to the Marantz except the pair of XRL cables to the Adcom amp. That eliminates any chance of a feed through ground loop current path through the Marantz signal ground chassis to the Adcom amp. So at that point the Marantz is strictly a termination device for the ends of the two XLR cables that connect to the Adcom.The Marantz would be nothing more than one expensive XLR cable terminator. A boat anchor.

Just for the heck of it would you try just one XLR connected to the Marantz and the Adcom. Marantz dead, power cord unplugged from AC power. Nothing connected to the back panel of the Marantz except the one lonely XRL cable. Check for hum at the speaker fed by this channel of the Adcom.

If it is the XLR cable picking up air born RFI you must have something in your house or close to your house generating a lot of RFI. Try wrapping some tin foil the entire length of the outer jacket of the XLR cable. Stop short at one end by a couple of inches. Check for hum.

JO3533, yes by all means try to somehow post or link to the schematic you have for the amp. I’ve tried to find one online and have not been able to.

Jim, a couple of your recent statements have touched upon what I’ve been thinking that led me to suggest putting shorting plugs on the RCA inputs. Without a schematic I’m shooting in the dark to some extent, but here is my speculation:

First, even if there is some commonality between the input circuitry for the RCA inputs and the XLR inputs, given that the input impedance of the RCA inputs is vastly higher than it is for the XLR inputs, and given that per JA’s measurements the gain of the RCA inputs is even significantly higher than for the XLR inputs, I can’t envision a scenario in which putting shorting plugs on the RCA inputs would adversely affect the signals on the XLR inputs. (In contrast to the design approach that is used by many amps providing XLR and RCA inputs, in which the center pin of the RCA connector is connected directly to pin 2 of the XLR connector, with the balanced/unbalanced switch simply grounding pin 3 of the XLR connector when the switch is set to unbalanced).

Second, I would discount as irrelevant all of the findings in which hum occurred when an unterminated XLR cable was connected, and when an XLR cable was connected to the AVR while the AVR was unplugged from AC power (which probably also represents an essentially unterminated condition).

Third, what I’m envisioning relates to Jim’s comment that:
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?
I’m envisioning that the Marantz AVR has significant AC leakage to its chassis and its signal ground (which Jim had indicated earlier are common with each other), the leakage occurring either in its power transformer or perhaps as a result of a leaky line filter capacitor. As long as the leakage is within reason, it won’t cause a problem under **most** circumstances.

Now imagine hypothetically that the amp has an infinite input impedance. Since the AVR has a two-wire power cord, the amp would then see the input signals it receives as "floating" relative to its own safety ground and signal ground. Meaning that the two signals in each balanced signal pair would both be seen as riding up and down over a significant voltage range at a 60 Hz rate. In other words, a significant amount of 60 Hz "common mode" noise would be present.  The finite (and relatively low) input impedance of the amp’s XLR inputs will then greatly reduce that range, but I’m envisioning that there may still be enough 60 Hz common mode noise on the signals, relative to safety ground and to the amp’s signal ground (which is probably connected to safety ground through a low impedance) to cause the issue. And conceivably it could be causing the issue by coupling into the very high impedance of the RCA input circuitry (although other pathways are possible as well). Which is why I am suggesting the shorting plugs, assuming I am correct in thinking that they will not affect the signals received via the XLR connector.

To respond to some other questions that have been raised: The polarities of pins 2 and 3 on the XLR connectors of the components have no relevance to the issue. I wouldn’t expect a DC offset in the AVR’s outputs to be relevant either. For relatively low-priced but high quality XLR cables I suggest Mogami Gold Studio, in either a 6 foot length or a 3 foot length. Mogami Gold Studio is the de facto cable of choice in most recording studios and other pro audio applications, and has been used in home audio applications and recommended here by me and many others in the past. Although as is usually the case among audiophiles opinions about it are not unanimous.

Good luck. Regards,
-- Al

Al,

Thanks for the response.


Second, I would discount as irrelevant all of the findings in which hum occurred when an unterminated XLR cable was connected, and when an XLR cable was connected to the AVR while the AVR was unplugged from AC power (which probably also represents an essentially unterminated condition).


Please explain your reasoning for when connected to a preamp that is powered off being the same as the cable not connected to anything, open ended.

I have had instances when a power amp was left powered up and the preamp was turned off. There was not any hum/buzz coming from the speakers. Of course I have never owned a 300 watt per channel amp either.


I still can’t wrap my head around that the Adcom amp is quiet when nothing is connected to any of it’s inputs, but when an XLR balanced cable is connected to the amp it hums/buzzes. I have been assuming the hum/buzz is only from the speaker connected to that channel of the amp.

Jim

Please explain your reasoning for when connected to a preamp that is powered off being the same as the cable not connected to anything, open ended.
Hi Jim,

While the output impedance of an unpowered solid state component is probably unpredictable in most cases, especially without detailed knowledge of its design, I would expect that in general it would be very high. Very high output impedance = essentially no termination at that end of the cable.
I have had instances when a power amp was left powered up and the preamp was turned off. There was not any hum/buzz coming from the speakers. Of course I have never owned a 300 watt per channel amp either.
Not relevant; different components.  And chances are those preamps had 3-wire power cords, as opposed to the OP's AVR (see the comments in my first post of today about "floating").
I still can’t wrap my head around that the Adcom amp is quiet when nothing is connected to any of it’s inputs, but when an XLR balanced cable is connected to the amp it hums/buzzes. I have been assuming the hum/buzz is only from the speaker connected to that channel of the amp.
If the unterminated cable is not picking up radiation from some external source of EMI, perhaps it is picking up such radiation from some part of the amp itself. And if so, that pickup would probably not be an issue when the input end of the cable is terminated by the very low output impedance of the powered up AVR. I would expect that the very low output impedance of the powered up AVR would load down and "kill" any such pickup.

Best regards,
-- Al

jea48 said:
I have had instances when a power amp was left powered up and the preamp was turned off. There was not any hum/buzz coming from the speakers. Of course I have never owned a 300 watt per channel amp either.


Not relevant; different components. And chances are those preamps had 3-wire power cords, as opposed to the OP's AVR (see the comments in my first post of today about "floating").

Hi Al,

The safety equipment ground would not have any relevance as its' purpose is to provide a low resistive path for ground fault current to return to the source.

Two things happened immediately when the Marantz was connected to the Adcom by a wire IC.

 The Signal ground of the Adcom was extended through the IC to the chassis/signal ground of the Marantz.

Second, assuming the signal ground of the Adcom is connected to the chassis of the Adcom then the safety equipment ground is connected to the Marantz chassis as well.

Jim


Hi Jim,

Please consider the paragraph in my first post of today in which I used the word "floating."  And in doing so, re your comment that:
... the Signal ground of the Adcom was extended through the IC to the chassis/signal ground of the Marantz.
consider that the Adcom amp may connect pin 1 of its XLR connectors to chassis, rather than to its signal ground (the former, in fact, generally being best practice).  And its signal ground and chassis may be connected together through a significant impedance (that also generally being best practice).

My point being that the amp may not "see" the balanced pair of signals it is receiving as being tightly referenced to its own signal ground.  Resulting in the possibility that the amp might see those signals as having some degree of 60 Hz common mode noise riding on them, that may in turn somehow couple into its signal path to a degree that results in hum.

Best regards,
-- Al
 

Thanks Al for the response. Hopefully jo3533 will pick up some RCA shorting plugs.


jo3533,

Does the hum sound like one of these?

60 Hz.
https://www.youtube.com/watch?v=E_Sf7rSOU78


120Hz.
https://www.youtube.com/watch?v=pC4Uzt0qm2E




Here is a link to some photos of the following testing, and the schematics of the ADCOM 7805. 

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

As you can see in the photos I pulled the units out of the rack and set them up as far apart as I could get them. Plugged them into separate outlets, and used XLR ICs.

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)

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.

Ok, thats all I can do for tonight. I worked 13.5 hours today and its time to just sit and eat.

Thank you all for so much help and input........soon I hope to get little feedback on my thought of cheap cables causing the problem?

I need to check chassis current and a grounding wire between the two (although I have done the grounding wire before) but I just can't bring myself to complete it tonight.

Thanks Again 

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
 

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



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."

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


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

Al,

Just looked at the picture again. I think you are correct.


Jim

I think my post about XLR cables not being plugged in and there being noise was an error.

CONFIRMED With the amp connected but not the per-amp there is no noise. Checked it twice tonight.

I am going to sleep on this tonight and figure out what I am going to do tomorrow.

Thanks again for the support. Sorry about the confusion. 


Post removed 
Post removed 
I think my post about XLR cables not being plugged in and there being noise was an error.

CONFIRMED With the amp connected but not the per-amp there is no noise. Checked it twice tonight.

That makes more sense why it doesn’t matter if the Marantz is powered on or powered off with the power cord disconnected from the power outlet.

jo3533,

Did you buy the Adcom amp new or used?

I believe you said in a previous post the amp always had the hum since you have owned it. Is that correct?

Did you click on the two links I provided for the sound of 60Hz and 120hz? Does the hum/buzz sound you hear sound like either one of them?

Is it actually a hum or a buzzing sound?

I looked at the schematic wiring diagram you provide in your last post. Do you have a diagram that shows the power transformer and DC power supply?

You said in an earlier post you had the amp worked on because the center channel had went out.

You said:


"I think they replaced the bridge rectifier. Can bridge rectifiers that are old or going bad allow noise through?"


Did the service tech say anything about if anything in the rectifier circuitry had shorted to the metal chassis or anything like that?

Was any fuses blown?

The reason I ask if you look at the schematic wiring drawing, look at the XRL connector pinouts. Look at pin #1 ground and follow the line down the page and you come to R49 a 1/4 watt resistor which is in series with the line. Follow the line on down the page where it ends at the earth ground symbol. This is the circuit that connects the signal ground to the metal chassis of the amp.

By chance was this 1/4 watt resistor blown because of a B+ short to the chassis?

If the connection of the signal ground to the metal chassis is open, not made, then the outer metal case/chassis could cause noise problems.

If the signal ground is floating above the chassis I wonder what that does to the input sensitivity of the input circuit of each channel of the amp.

Do you have a multimeter?

If so I would be curious if there is continuity from pin 1 on any XLR input connector to the metal chassis of the amp.

I would first check for DC voltage from Pin 1 to the chassis. Amp powered on. If the 1/4 resistor is good you should read zero DC volts. (Just guessing the value of the resistor is 10 ohms or less.)

If that is the case turn off the amp. Unplug it from the AC power wall outlet. Then check for continuity from Pin 1 to the metal chassis of the amp.


Al,

If by chance you are reading this post I would appreciate your thoughts.

Jim

jo3533,

Here is a quote from Charles Hansen.

The only way that the case can provide any shielding for the audio circuitry is if it is connected to the signal ground. In addition, if it is left unconnected from the signal ground, then it will create unwanted capacitive feedback loops (both positive and negative) between various parts of the circuitry. Refer to Morrison’s books for additional details.

http://www.audioasylum.com/audio/general/messages/52/525622.html