Help With 60Hz Hum PLEASE
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? |
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. |
GFA 7805 Owner Manual (PDF) Note #2) above. Picky little burger isn’t it? Maybe it just doesn’t like being in the same room as the Marantz 8801. jo3533, Will you please acknowledge if the Adcom 7805 has a 3 wire grounded plug or a two wire plug. |
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:
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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. |
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: |
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. |
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
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Al, Thanks for the response.
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 |
jea48 said:
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 |
Al, From jo3533 first posted message. Quote: >>>>>>>>>>>>>>>>>>>>>>>>>>>> Al, Number 5 & 6. >>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>> 2-22-2016 jo3533 said: Quote: 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) 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 |
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. 120Hz. |
Hi Al, Disregard my last post.
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. 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. 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 |
I think my post about XLR cables not being plugged in and there being noise was an error. 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, Here is a quote from Charles Hansen.
http://www.audioasylum.com/audio/general/messages/52/525622.html |
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:
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 |
Al,
(Note: I quit using the Agon insert quote feature. Half the time the thing doesn’t work or doesn’t work right! Maybe it’s my old Windows 7.) You are correct R55 location on the picture of the amp is a jumper wire. As for R55 not being on the parts list, I couldn’t find it listed either. It could be the Adcom 7807 is not built exactly as the 7805. One may have come before the other. Edit: And we don't know how many times the schematic wiring diagram, jo3533 supplied, may have been revised. Where do you suppose Joe, (jo3533) is? I sure hope he didn’t throw his back out, or worse, trying to put the Adcom amp back in the rack. Jim |
Hi Al, Interesting comments regarding the R49. At the time of my post Joe had not posted the service manual PDF. I wonder what component R49 is actually made of? It’s not a fuse and technically it is not a jumper. "R" usually designates a resistor. But as you pointed out it does not have a resistance value. What ever it is made of it is rated for 1/4 watt. I assume that if a DC B+ voltage fault to chassis event happened the 1/4 watt device would blow open. (Note R47 connection is upstream of R49. R49 is the gate keeper to the chassis connection.) ARC uses an actual 10 ohm 1/4 watt resistor to connect the power supply neg DC rail on one channel to the metal chassis. Another 10 ohm 1/4 watt resistor is used to connect pin 1 to the chassis. (ARC VT50) Even though when Joe checked for continuity from pin 1 to chassis and he posted he measured there is, I was still going to suggest he still run a jumper from pin 1 of one of the amp’s XLR female connectors to the chassis. I first wanted to look at the other PDFs he supplied last night. Jim |
Al, Yes, I found it in the parts list of the service manual.
Thanks. While waiting for Joe to post how he fixed the hum problem I have been looking at the other PDFs he posted last night. I also found a picture, (I believe), of one of the five channels used in the amp. The clip seen on the top left side of the board, do think that is used to bond, connect, the signal ground to the chassis? Or do you think a bonding jumper wire was used? Note the jumper wire in the R49 spot? Note the little guy in the R47 spot? (Look at the service manual PDF of the channel amp's parts/components layout.) Jim |
Al, R47 looks like a thermistor to me. Puzzling to me though it is installed in the R47 circuit board location instead of the R49 location. Unless the circuit trace on the underside of the board was changed before the actual circuit board production putting it in series with the chassis bonding, connection, grounding clip. Picture of amp board Circuit PDF Jim |
Jo3533, Great news! I am glad to hear the dreaded hum/buzz is finally gone. With that said,...... Curiosity killed the cat. Would you try one more test for me? Would you disconnect the wire that you connected to the Marantz chassis and instead connect it to the metal chassis of the Adcom amp. Post back the results. Jim |
Joe, (jo3533), Thanks for doing the test for me. Had I known you had to pull out the rack I would not not have asked you to try it. Thanks again. AL, Looking at the Adcom Amp schematic wiring diagram again, trying to figure out why when all the outer contacts of the RCA jacks of the 5 amps of the Adcom are connected together and then connected to the Marantz chassis by an extended wire, the hum/buzz is eliminated. Wiring diagram. Without the added wire connected to the Marantz chassis, (connected signal ground), to the signal grounds of the Adcom’s 5 separate amplifiers, the XLR cables/circuitry (either at the Marantz or the Adcom), the signal grounds of the two pieces of equipment are not connected together by the XLR cables alone. Am I right? So when the two pieces of equipment’s signal grounds were not bonded, connected, together, (by the added wire connection circuit), why was the sound, hum/buzz 60Hz? Jim |
That was my thought several posts ago. But then if that was the case Joe would have heard a 120Hz hum wouldn’t he have? And connecting the signals grounds of the Adcom to the chassis of the Marantz would not have stopped the hum, imo. I think your response in your previous post is more likely the reason for the hum/buzz problem and the fix Joe came up with. The only thing I might add is we don’t know if Joe tried every separate channel of the Adcom to see if every one had the hum when connected to the Marantz. Joe bought the Adcom used in a non working condition. If I remember Joe said the whole Adcom amp was dead. He had the amp repaired and the repair tech told Joe the center channel was the problem. Joe remembers the tech said he replaced the bridge rectifier in the power supply of the center channel. We really don’t know the full extent of the damage to the center channel. We do know all of the 5 channels of the amp are fed by a common power transformer. Just a guess the center channel fault event caused the primary of the power transformer to overload and caused the overload protection of the amp to open. I would like to know if any of the thermistors were damaged or blown open by the center channel fault event.
So I guess the only way to find out for sure is for Joe to pull the Adcom back out of the rack and check for the thermistor in position R47 on each of the 5 channels and check if they show conductivity. LOL, good luck with that happening anytime soon. Cheers, Jim |
