Living with unsolvable hum - Any audio detectives out there?
For over a year I have put up with a hum in my system, coming through the speakers (not chassis hum). I cannot make it go away. It seems to be related to the preamp because it stops when I replace the preamp. But I had my local tech hook up the preamp on his bench and it is quiet as a mouse. I've also corresponded with its designer, David Berning, who has been very responsive and helpful. But no luck solving it. I thought it may be related to the separate power supply's umbilical but David Berning said likely not. Earlier this year I even bought a star grounding component from Granite Audio and connected everything to it. Didn't work. After trying everything the engineer at Granite could think of (he was great), he was stumped too. These people have forgotten more than I'll ever know about the subject, so I gave up at that point and just lived with it. I had also tried everything they and a few knowledgeable friends have suggested (see below). But now I would like to take another swing at solving it. Any ideas? What kills me is that now I can't recall when it started, which would be very helpful to diagnose. The system sounds as good as I've ever had it now, and I LOVE the Berning preamp. So replacing it or other major components is not an attractive proposition for me.
For any intrepid detectives, here are the facts:
- Hum is typical 60 cycle sound- both channels equal volume of hum- loud enough to hear at the listening position, but just barely. Quite noticeable when standing at the rack. - Hums with any source, not volume dependent, still hums with no source components attached (I even tried unplugged them from the wall too). But the hum stops if preamp is disconnected from amps. - System plugs into a dedicated 20 amp line with eight plugs. Nothing else is on this circuit except my audio system. I had an electrician verify and tighten all the ground connections. The service is a relatively new 200 amp service. The electrician tested and found no ground issues or noise in the dedicated line. - Tried shutting down all breakers in the house except my dedicated audio line. No effect, surprisingly. I had high hopes for that one! - Tried cheater plug on everything including the preamp. No effect. - Tried different interconnects between pre and power amps... No effect. - Replaced all linestage tubes. No effect. - Moved components around, moved the power supply, even used long interconnects to move the preamp three feet in front of the rack. No effect. - Tried an extension cord to plug the preamp into a different AC circuit. No effect. -The only thing I know of that could try, but have not tried, is replacing the power supply tubes, but I didn't bother because on the bench it made no noise for my tech.
My system: - Power: Temporarily I'm using a Shunyata T6000 distributor (the hum existed prior to this, and the Shunyata didn't solve it). All Cardas Golden Ref or Golden power cords, except T6000 is plugged into the wall with Shunyata Sigma HC cord. Analog: Koetsu Rosewood Signature Platinum, Jelco TK-850, Cardas Golden Cross phono cable Digital: CEC transport and Audio Logic DAC, Golden Cross interconnect. Preamp: Custom Berning Octal tube preamp with separate tube rectified switching power supply, built-in Jensen transformer MC stage at 24x gain (on the high side, I know, but it sounds amazing compared to other winding options) -Power amps: Quicksilver v4 monos with KT150 tubes -Two REL G2 subs (hum existed before them, and persists when they are disconnected and unplugged) Somehow the interaction between the preamp and other components seems to be creating the problem. Source components don't seem to matter, but amps are Quicksilver v4 monos. Speakers are Verity Audio Parsifals. Interconnects, speaker cables and power cables are Cardas Golden Cross. Speakers: Verity Audio Parsifal Encores. No surround sound or home theater.
You're looking under the wrong rock:It is not an electrical hum problem, it is mechanical and coming from your preamp power supply. The S:N test of your preamp found no problem. You hear it next to your rack. Use an old mechanic's (weight doesn't matter) trick to imitate a stethiscope. Take a screwdriver. Place the plastic handle at your ear and touch the chassis of your preamp power supply to see if you hear the hum. If so, then the problem is there; probably due to a poor orientation of a toroidal transformer, or possibly bad rectifier tubes.
I looked at the advice in the posts here, both good and bad. So far, there is no mention of trying a line level audio transformer inline with either the output of your pre amp or (one at a time with all other inputs-Disconnected) with one of the inputs. This is mostly to discover where the source of the problem lies, but might actually be a good enough fix sonically as to keep it in place. Sorry, I do not have a lead on who makes a fine quality unit for this. It will however isolate either the input or output of your unit.
oldears "You’re looking under the wrong rock:It is not an electrical hum problem, it is mechanical and coming from your preamp power supply. The S:N test of your preamp found no problem. You hear it next to your rack."
montaldo "But I had my local tech hook up the preamp on his bench and it is quiet as a mouse."
Stu - Assumed montaldo gave his local tech both the pre amp and the pre amp power supply....but I could be completely wrong.
Could be worth a try, but! Only difference with your situation is your hum transfers to speakers. My amp has ten power rectifiers for dealing with design inherent or dirty-power before signal output which shut the problem down. That said the amplifier hum was a real problem until I inserted a holton dc blocker. Various mains power conditioners just didn't work! I learnt that once you get up to certain sized toridal transformers mains power can become a significant problem. My amp has a 400va pair of transformers. As per its' instructions the mains distributor is fed from the blocker unit, which is mains plugged to the wall. This reduced the hum to negligible audibility. I also got an acoustic advantage across the dynamic range with particular reduction in the high frequency band. Hope this offers solution, cheers
I had a very similar issue years ago, and it drove me crazy for a while. The fix was to properly ground the cable splitter at the point of ingress to my home. The inbound cable and electric services entered my garage at the same place. Grounding the splitter solved my hum completely and permanently. I'm not suggesting this is definitely your problem, but it's a simple fix to try.
backtothe80s. "The fix was to properly ground the cable splitter at the point of ingress to my home."
montaldo. "Earlier this year I even bought a star grounding component from Granite Audio and connected everything to it. Didn't work. After trying everything the engineer at Granite could think of (he was great), he was stumped too"
I left a message with Chris at https://www.kf7p.com/KF7P/Welcome.html and will be chatting with him to see if he has any other customers that experienced similar challenges.
I have as much interest as Montaldo to solve this similar issue.
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For my grounding, I have two 6 foot copper rods driven into the ground and wired these only to the D100A. This did not solve my issue.
And recall, I recently had the D100A power supply filters caps replaced (past year) and no 60 cycle noise on tech's bench similar to Montaldo.
I have an email in to Scott Frankland to talk about ground loops.
I had this same problem years ago with a BAT VK30. I tried everything in your list, Drove me crazy. I called the BATmeister who replied "my preamps don't hum", and hung up. I even bought a PS Audio Humbuster which changed nothing.So I left it with a very good audio tech. He called me back and said he had put it on his test bench and it was better than spec. I responded that the sound seemed to come mostly from the area of the right channel toroid transformer. He said, "ah so, I know about that kind of problem, let me call you back". He called back 10' later and said it was fixed and I could pick it up. He loosened the fixing bolt and rotated the transformer on axis for minimum hum and checked the left channel also. I picked it up and put it in the system... dead quiet.
After 40 yrs in the communication business, there are 2 main sources of 'hum'. The first obvious one is an extraneous ground. The 2nd and most difficult one is an unbalance line load. All of the suggestions here are very good ones indeed. I read most of them and don't recall a suggestion or simply running a temporary power supply from the initial termination (from the power company) directly to your equipment. Make it as short as possible. Shielded wiring just laying on the ground if necessary, as short as possible. That would eliminate beaucoup possibilities. Doesn't take much resistance to duplicate your problem. Secondly, just a minute amount of carbon build-up on a selector switch can also duplicate your trouble. Don't recall how old your preamp is, but clean, clean, clean. Again, I apologize if these are duplicate suggestions, I did not completely read all postings. Simplify the power path. If you have performed most of these suggestions and resolved nothing, plz see oldhvymec suggestion, take a toke and just hum along...good luck. AB
OP before I read through this, did you pull the valves tighten the pin pockets and swap the rect valves? Did you pull the fuse and inspect the fuse pocket, clean it and replace the fuse. Did you replace the PC? Just asking?
I have not checked/cleaned the preamp fuse. Will do that first, as well as disconnecting wifi and other simple tests suggested, such as trying a backup amp to see if the interaction with my amps is a problem. Then check pre tube pins seatings. Then will see if I can take it to a friend's house. if it hums at friend's, maybe replace power supply tubes. Then will embark on other ideas mentioned.
Can't thank all you guys enough for your time and ideas!
A common wiring arrangement in pro audio to stop ground loops is to lift the ground of interconnect cables at one end. We did it all the time building amp racks and outbound racks. We would lift the ground on the inputs to the power amps when linking them together and from the outputs of the crossover/processer. Easy to do with balanced XLR connectors. We always did it on the input end of the cable. We also never lifted power grounds, it was forbiden by my boss at the time. I have never done it with unbalanced RCA cables but it is worth a try.
Lifting the signal ground is a fine idea, when there are multiple signal wires.
These are mono amps, so I would suggest the OP try cheater plugs on one or the other amp first, and if that works, get a hum buster (or whatever they are called). Actually, the OP should unplug 1 mono amp from the power completely, and see if this doesn't fix it.
Ok before you go out and buy anything, do this first!
Take a good look behind your equipment. Look at all the power and signal cables. Make sure all of them cross each other at about 90 degrees. No parallel cables should be touching or near each other.
Anything running parallel should be at least 12" apart...better if it is 18".
To some degree, reorganize your components to accommodate better cable management.
Undo looping cable. Use shorter and longer power cables to tailor to the need.
If you need, use small blocks of wood or zip ties or velcro to create separation and organization.
Also get rid of wall warts and non audio equipment connected to the line.
Separate the analog stuff from the digital stuff. They should not share the same line.
This worked for me...and I have 2 dedicated audio lines. The noise appeared when I quickly and carelessly changed out my power conditioner for another. The noise is most likely coming from your own equipment.
Look inside any point to point wired preamp or amp...everything crosses at 90 for this same reason.
Pulled Audio Research D100A out of rack. Put amp into my garage workbench away from all RF devices. Plugged amp right into wall outlet. No donut between amp and wall outlet. Plugged speakers right into amp. Zero 60 hertz cycle. Amp is fine as Scott mentioned.
Test 2:
Plugged my old iphone 6 into patch cable with 1/4 inch to RCAs. Plugged RCAs right into amp. Before turning on iphone, checked speakers with amp. Zero 60 hertz cycle.
Test 3:
Turned on iphone with no music at low volume level. Checked speakers with amp. Zero 60 hertz cycle. Turned iphone volume to max. Zero 60 hertz cycle.
Test 4:
Turned on iphone with music...listened specifically between music gaps = zero 60 hertz cycle.
Results
Amp is quiet when it is by itself and NOT near equipment. Using garage wall outlet power and no line conditioner / regenerator. Using no donut toroid. This is baseline for the amp in an isolated environment so I don't need to further test/discuss the amp power supply, caps, transformer, etc. in my situation. DONE.
Next Step For Ground Loop Tests
Perform lifted ground technique per Scott. Lifted ground = all equipment in stereo rack plugged into wall outlet WITHOUT ground = insert a small 3 prong to 2 prong (plus wire for ground)
into ALL stereo / related devices in rack EXCEPT for the most sensitive pickup device. In this case, this would be my phono tube amp. Phono tube amp is plugged directly into wall outlet WITH normal 3 prong ground = only ONE source for ground across all equipment to baseline all equipment. Listen for 60 hertz cycle.
If 60 hertz cycle through speakers....then probably not a ground loop issue and a local proximity 60 hertz transmission being picked up by the phono power cord. If this occurs, then I will purchase clamp on ferrite and place on the amp.
If no 60 hertz cycle through speakers with single ground source (phono amp), then systematically begin removing the 3 to 2 power connectors. Remove one at a time. Remove from the most sensitive to least sensitive gear. In my case I would then remove line amp 3 to 2 connector, since that is next in the chain after the phono amp, which plugs into line amp. Test for 60 cycle, and continue proceeding.
If 60 cycle surfaces, then that device "may" be the one or one of several contributing noise generators.
I have a ground loop problem....at the very end of the system chain and NOT caused by other equipment (the other gear were very good shiny object distractions).
Performed systematic changes as previously described.
As soon as I got to the D100A amp with and without the 3 to 2 power cord convertor....60 cycle speaker buzz gone/appears.
* Using same existing wall outlets as before; no changes for scientific method approach. * No donut / toroid in the mix * Amp plugged straight into wall outlet with no conditioners/regenerators.
I cannot confirm (and I don't feel like sleuthing this deep), but my music room wall shares a wall with the garage. Even though all garage outlets use a separate and dedicated fuses, I am wondering if the wall mounted Electric Vehicle transformer on that shared wall, the garage refrigerator along that shared wall, or the tankless water heater along that shared wall are tapping into the same ground.
Regardless....I have zero 60 cycle hum from my speakers when I lift the ground for the D100A.
Montaldo, my hunting is done. I have given you one process / approach.
Hum is frustrating !!! Nothing worse than hearing that during a quiet passage. A while back I had a problem where it was not a constant hum. It was intermittent. Well after doing all the usual tests and remedies ,it turned out to be one of those Glade plug in air fresheners. Threw those in the trash and problem solved.
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