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 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.
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!
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.
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) http://www.audioresearch.com/ContentsFiles/VT50_SchemPL.pdf
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.
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.
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.)
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.
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.
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.
"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."
(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.
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 .
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!
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.
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!
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.
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?
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.
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.
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.
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.
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.
Al said: 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.
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.
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?
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