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?
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?
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
"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
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.
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?
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?
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?
"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.
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.
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.
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?
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