I'm afraid it's the amp. Probably a bad filter capacitor. Get it repaired or buy a different one.
If your system can take it, switch to 240V can help.
If your system can take it, switch to 240V can help.
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
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
78 responses Add your response
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? |
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 |
I suppose a Faraday Cage effect is a possible explanation, but a couple of factors seem to suggest otherwise. First, the problem didn't seem to be sensitive to the positions of the components, which lessens the likelihood that EMI pickup (that would be prevented or minimized by a Faraday Cage) was responsible. Second, a similar shielding effect was apparently present all along, since the two chassis had always been interconnected via the shield of the XLR cables. The shields of the cables having apparently been connected to the chassis of each component both via pin 1 and via the jumpers in the cable which connected pin 1 to the shells of the connectors. Putting my previous speculation in more general terms, I suspect basically that the grounding approaches in the two components, possibly in combination with some condition-related issue (such as a leaky line filter capacitor), somehow caused an interaction between the two components resulting in small (and perhaps expectable) amounts of AC leakage to chassis in one of the components (perhaps occurring via stray capacitances in a power transformer or via a leaky line filter capacitor) to be seen by the amp as signal. Best regards, -- Al |
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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. |
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.Your guess is as good as mine, Jim. Although I'll add that if the modules in the Adcom conform to the photo you supplied (as opposed to the schematic), as we said earlier it would appear that the Adcom's analog ground (which is common with the ground sleeves of the RCA connectors) is connected to XLR pin 1 through a thermistor. And if that is the case then the solution Joe arrived at resulted in a reduction of the impedance between the Adcom's analog ground and the chassis of the Marantz Pre/Pro (which you had indicated is common with the signal ground of the Marantz), from whatever impedance the thermistor has during normal operation to essentially zero. The introduction of that more direct connection between the signal grounds of the two units would seem consistent with a reduction or elimination of hum, that might have been caused by small amounts of AC leakage to chassis in either component. In any event, considered purely from an intuitive standpoint it seems to me to be very plausible that what Joe did would result in a solution. Best regards, -- Al |
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 |
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! |
Great news indeed, Joe! We provided some thoughts and leads, and you did an exemplary job of following up on them in a thorough manner, and taking them further. Truly a collaborative effort, on a difficult problem (as grounding and hum problems often are). Regarding the popping issue, all I can suggest is what I said in my post dated 2-7-16, which raised the possibility that it might be resolved by a firmware update, if one is available. As I indicated in that post, someone had reported elsewhere a few years ago that what sounds like the same problem was **introduced** by a firmware update. Which suggests the possibility that the issue may have been addressed in a subsequent update. Aside from that possibility, I would suspect that the popping is being caused by a hardware problem, perhaps a faulty capacitor or relay, or a diode associated with a relay. Enjoy! Best regards, -- Al |
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 |
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. |
I would try the cable fix . They ran the power and cable through the same hole in my house . I had a 20k new system and there was a slight hum . I took some speaker wire , strip the ends and twisted it around the cable splitter and connected the other end to a water pipe with vise grips . Problem solved . |
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 |
Good call! Yes, it appears that it could be a thermistor. Ironically, though, I believe that the symbol for R55 shown nearby on the schematic (connecting digital ground to chassis) is one of the symbols that are used to represent thermistors, yet R55 appears in the photo to be just a jumper. Also, I don’t see any listing at all for R55 in the parts list. So if the photo is considered to be gospel, as opposed to the schematic and the parts list, it appears that XLR pin 1 is connected directly to chassis (via the R49 jumper); digital ground is also connected to chassis; and analog ground is connected to those points through a thermistor. Given the flexibility that is provided by the board design for how these circuit points are utilized I doubt that there would have been a reason for them to modify the related circuit traces under or within the board. But given the inconsistencies between the various documents it’s all hard to figure. Best regards, -- Al |
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 |
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Good find, Jim. Consistent with your comment, very close to that clip are a couple of locations that appear likely to be designed and designated for resistors, but appear to have jumpers installed. (I expanded the photo to 200% to be able to see that better). My guess (which appears to be confirmed by the diagram you referred to in the service manual) is that one of them is R49, and that there is a connection within the board from one of the R49 pads to the pad the clip is attached to. With the other end of the clip being physically connected to chassis. Although as you indicated it appears nearby that there is an actual resistor installed at what the service manual diagram depicts as R47 (the pin 1 to analog ground connection). So the parts list and the photo are inconsistent. Best regards, -- Al |
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 |
Hi Jim, Although we can’t be completely certain, I’m thinking that R49 and R47, which are explicitly noted in the parts list in the service manual as being "jumpers," are most likely just short lengths of wire. And I’m envisioning that during the design process the 1/4 watt 0R00 designations were just used by the electrical designers to specify to the mechanical designers that the corresponding holes and pads in the printed circuit board should be spaced and sized such that they would be suitable for insertion of 1/4 watt resistors. The intent being to provide the flexibility of being able to install 1/4 watt low value resistors later in the development process, if it proved to be necessary. Best regards, -- Al |
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 |
Wow! Congratulations! Can’t wait to hear what the solution was. Jim, sorry for not responding to your post of yesterday morning sooner. It’s a busy weekend here. Your points were well taken, IMO, and as you’ve seen Joe subsequently confirmed that continuity existed per your suggestion. I would highlight, though, that R49 and R47 are jumpers, not resistors, as indicated by the zero ohm value noted on the schematic ("0R00"), and as stated explicitly in the parts list in the service manual. So analog signal ground and chassis/safety ground are connected directly together in this design, rather than through a low value resistor (which would lessen the chances of ground loop issues, as Atmasphere has stated in a number of past threads here). Also, as indicated in the Rane paper you linked to earlier, ideally XLR pin 1 should be connected to chassis ground and NOT to signal ground, although in this case that is probably a moot point since both grounds are jumpered together. So although the design is not ideal in a couple of respects, in ways that could conceivably contribute to hum problems depending in part on how grounds are handled in the component the amp is connected to, and perhaps also depending on whether XLR or RCA interconnections are used, my understanding (consistent with what is said in the Rane paper) is that lots of other designs are similarly flawed. But we’ll soon see what the upshot is in this case. Best regards, -- Al |
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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 |
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 |
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. |
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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. |
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 |
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’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." |
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 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 |
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 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 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 |
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 |
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 |
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 |
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 |
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. |
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. |
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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