Help With 60Hz Hum PLEASE

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.

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?

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.

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? 
 

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.

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, 

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.

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 

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. 

jea48,

I bought the ADCOM used. One channel was not working, and it would not turn on at all when first purchased. The tech was not very forthcoming on what exactly he replace. He did mention the bridge rectifier however he never confirmed if he replaced it. I have tried to contact him several times and have not received a response......Dunno whats up with that. There are no traditional fuses on this unit. It has had some mod completed by ADCOM that uses some other sort of safety.

YES, I listened to the two links and it sounds just like the 60hz buzz! I mean its dead on with the recording.

I do have a diagram that shows the DC power supply and I will post it in the shared dropbox folder.

I want to point out that the transformer itself produces an audible 60 hz buzz that can be herd while standing next to the unit. I have read this is normal.

Using my multi meter I checked for continuity between the chases and the #1 pin on the XLR jack and yes, there is continuity. There is also continuity between the chases and the outer shell of the RCA jack.

I went doen to Stereotypes in Daytona Beach, FL and they were nice enough to allow me to borrow a set of TARA LABS XLR IC for a small deposit.

I plugged in the Tara Labs cables and the noise was still there! Rats....it was worth a try.

almarg, the 7800 series uses the same amp boards for the GFA-7805/7807. You will see the same markings for the power supply schematics. Link to service manual below.

https://www.dropbox.com/sh/p7w1zmad9dwhx3o/AAC1ZY5kCxocLwKCn_nfTgBNa?dl=0

NEWS. Dead silence....AT LAST!

I will post what I did to fix the problem later. Right now I am trying to put my system back together and confirm it still works after its all back in the rack.

THANKS SO MUCH

Especially to jea48 and almarg. You pointed me in the right direction. Thanks!

GOOD EVENING,

I have been busy all day, but I stayed up late last night putting everything together. Here is what I found works....not 100% sure I understand why yet, but I think I understand what has happened.

jea48, The link you provided to www.rane.com coupled with discussions about grounding and ground loops really helped solve this. Also, some dumb luck played a part.

After spending an hour reading through www.rane.com/note110.html and subsequent pages I began to understand the difficulties manufactures face with using balanced and unbalanced connections on the same unit.

I ended up modifying all of my XLR interconnects to match "cable 1" at www.rane.com/note110.html. I did this to one cable first, and after doing so the noise that was being produced changed greatly. Not is was much louder. It also sounded more like a 120hz hmm instead of the 60 cycle buzz.

It was good to have something different and right away I thought to now chases ground the two units together. Since the amp and pre-amp were so far apart, and I was in a hurry to test my theory. I just plugged an RCA cable into the unbalanced connection point above the XLR IC on the amp and then touched the outer ring against the chases of the Marantz. The following silence was only broken from my cheering. No more buzz or hum. Just a very soft hiss that I find to be common in systems.

Right after this I posted the success and then went to work reinstalling my system.

After installing all my components and plugging the amp and pre-amp into the power source, I checked to verify the noise was still gone. I made a custom lead to go from the frame of my amp to the frame of the pre-amp. Hooked up just one speaker fired it up and.....BZZZZZZ. "What the heck?" I think to myself.

Taking a step back and reviewing the changes the main thing that has changed, other than the proximity of the components, is where I am grounding the two components together.

Grabbing an old RCA IC I cut it apart and plug into the amp unbalanced input, and connect the shield wire to the frame of the Marantz. For some reason there is still a 60 cycle buzz.

"Wait", I think to myself. I have plugged into a different channel than what channel is hooked up to the speaker. So I switch the RCA plug to the same channel that the speaker is hooked up to and voila. The noise is completely gone again.

What I ended up doing is jumping all of the RCA outer rings together and then linking that to chassis of the Marantz.

Keep in mind I am using the XLR ICs for my sound path. The RCA outer ring is just for grounding to the Marantz.

I think by doing this I have bonded all of the signal and chassis grounds in the amp and joined the Marantz eliminating any kind of ground loop effect.

The one thing that is still present is a pop or clicking sound when I turn on the system or mute the pre-amp. Don’t know why.

My system has been running all day, and it has never sounded better.

Thank you all again for your help! Especially jea48 and almarg! Your awesome!

P.S. My back is just fine.

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!

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. 

So, summing this up quick. Heeellllll NO! (Im not taking my AMP out again for some time, I hope)

I spoke with the local stereo shop and the sales man there told me they had a similar experience with Sherborne AMP.  Sherborne told them to do the same thing I did to my Adcom. This statement was followed by the salesman slamming both companies saying "why can't they build a true balanced system." He went on to say that the amps were not truly balanced and so on with some other things I forget because I tuned him out realizing he has never studied the circuits of either amps and thusly not in a position to make an educated statement.

On to some good news. I purchased my Sony XBR75X850C today! I am so excited to receive it. I ordered it online.

So, time to start saving for my OPPO-105D........any one got one for sale at a reasonable price?   

So it has been a couple weeks and everything is running great!

Thank you all for your help again!