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    Hum reduction quest - solved !

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    LeGrace

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    Hum reduction quest - solved !

    Post by LeGrace on Thu Aug 03, 2017 4:32 pm

    Alongside redplate gremlin lives his nasty cousin hum gremlin. These dumbkofs have got to go! Made a list as follows:

    1) Re-tension and clean power tube and rectifier sockets
    2) Upgrade RCA connectors
    3) Improve wire management
    4) Evaluate different front driver tubes

    Item 1 is complete, used electronics grade alcohol. Item 2 I have all copper RCA's on the way to replace the original stock brass (presumably) connectors which are a bit under-size, in that all my cables fit too loosely. When I install them will also do item 3, esp wrt isolating power transformer wires using wire fasteners. Invite suggestions for item 4), as well as additional items I should be adding to my list? Thanks!
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    deepee99

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    Re: Hum reduction quest - solved !

    Post by deepee99 on Thu Aug 03, 2017 7:01 pm

    LeGrace wrote:Alongside redplate gremlin lives his nasty cousin hum gremlin. These dumbkofs have got to go! Made a list as follows:

    1) Re-tension and clean power tube and rectifier sockets
    2) Upgrade RCA connectors
    3) Improve wire management
    4) Evaluate different front driver tubes

    Item 1 is complete, used electronics grade alcohol. Item 2 I have all copper RCA's on the way to replace the original stock brass (presumably) connectors which are a bit under-size, in that all my cables fit too loosely. When I install them will also do item 3, esp wrt isolating power transformer wires using wire fasteners. Invite suggestions for item 4), as well as additional items I should be adding to my list? Thanks!





    A major source of hum comes from AC lines and signal lines running in parallel close together. If they have to be near each other cross them at right-angles. Maybe you did that in Step 3 but if not, do so. Phonograph lines are particularly sensitive to to this as the signal lines run at such low volts.
    Is this a system-wide hum, or specific to one component? If system-wide, I would guess your problem is in the interconnects between the pre-amp and power amp(s). If they're running horizontal, make sure any AC power cords nearby run vertically. That would be my SWAG, anyways.
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    LeGrace

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    Re: Hum reduction quest - solved !

    Post by LeGrace on Thu Aug 03, 2017 7:11 pm

    Thanks, appreciate the advice. Will check that. I am also waiting on delivery of higher quality IC's (Siltech cables) that incorporate better shielding then the local hardware store stuff I'm currently using.
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    Peter W.

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    Re: Hum reduction quest - solved !

    Post by Peter W. on Fri Aug 04, 2017 8:01 am

    Actual AC hum comes in two basic flavors, and understanding the difference between them is critical to 'fixing' it.

    Flavor A: 60 HZ Hum - primary source is induction from a 60 HZ AC source. This can be an AC line running too close to line carrying signal, transformer induction and any of several similar sources. In one case in my experience, even a little Neon pilot light not properly shielded.

    Flavor B: 120 HZ Hum - Primary source is induction from chopped DC. Primary source of chopped DC is poor filtration, an unshielded choke and any of several similar sources.

    Flavor X: Hum that is neither 60 nor 120 HZ - Not common, and not always true HUMmmmm, but often noise, static, hash and so forth. Typically from outside sources such as ignition transformers (oil burning furnaces or boilers), dimmers, unsuppressed motors and similar. Also may be rF noise on exactly those loose connections you are curing with better jacks and plugs.

    The first is typically cured by physical means. Isolating the AC supply system and components from the DC side. Either with shielding, shielded connectors, wire management, or other means. When one sees neatly bundled-and-bound wiring and lots of right-angles in mil-spec. equipment, that is as much to avoid hum issues as it is for appearance. Sloppy wiring, even if 'correct' connection-by-connection is problematic. Shortest-path *does not* necessarily mean *shortest-wire* either. If one has the correct tools, one may set the wire path before cutting and stripping the second end. Makes life much easier.

    The second is cured by using a good rectifier - one that does not pass any AC - proper filtration, if a choke is used, it should be placed properly, pretty basic stuff. Whenever I am  "done" with a re-cap or similar, I look for any AC on the DC side of the power-supply. More than a very few MV, and back to the beginning.

    Now, for the last! Again, you are doing the right things - tight connections, proper shielding, and did I mention tight connections? No need for boutique cables, just competently made cables of adequate capacity using decent materials. Keep in mind that induced noise is as baffled by aluminum or steel shielding as it is by OFC (oxygen-free-copper), gold plating, silver or anything other metal. And, of course, a noisy power source. If it is well-and-truly bad, a power/line-conditioner is in the cards. Well-and-truly bad power, by the way, is incredibly rare these days. As is outside source RF stuff. Unless you or your  neighbor plays with a bunch of Jacob's Ladders, or uses a coherer transmitter, uses vintage vacuum cleaners, or similar, this will not be an issue.

    Aside: I once had a receiver that would "oscillate" to CB channel 22. Turned out to be corrosion salts on the phono input. Did I mention tight connections? And *NOT* just the shield shell on an RCA jack.

    Best of luck to you. But be sure as you start in on whether you are dealing with 60, 120, other, one, two, or all three.
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    arledgsc

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    Re: Hum reduction quest - solved !

    Post by arledgsc on Fri Aug 04, 2017 8:54 am

    Power everything from the same AC source. The reference ground for all your equipment must be the same potential.
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    bluemeanies

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    Re: Hum reduction quest - solved !

    Post by bluemeanies on Fri Aug 04, 2017 10:41 am

    arledgsc wrote:Power everything from the same AC source.  The reference ground for all your equipment must be the same potential.

    Agree...you guys know your stuff...little for me to add.
    My hum (speaker) came from a bad ground.
    I also at a different time, when introducing tubes, had a SLIGHT HISS coming from my tweeters. I had also had introduced a new pre amp for my 2channel which was connected into my Furman. The hiss from the speakers could only be heard if you were literally a foot away. I connected my preamp to a wall outlet and the hiss flew away.
    At this time I have my m125's connected to a kill O watt which is connected to a Variac for different reasons.
    Everything now is connected to two manual line fault interruptors and and my system is dead quiet.

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    deepee99

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    Re: Hum reduction quest - solved !

    Post by deepee99 on Fri Aug 04, 2017 11:26 am

    Again (sorry to sound like a broken record here), dedicating a line directly from the circuit-breaker panel directly to the wall outlet you use for your audio system -- whether solid-state or tube -- gets rid of a lot of racket from fluorescent lights, computers, dimmers, electric motors, etc., etc.
    I did have a pre-amp tube once that gave intermittent 120-cycle hum that drove me nuts tracking down. I was sure it was in the power supply or there was some intermittent RF burst from elsewhere like a CB or a Ham getting at the system. It wasn't until I swapped in new tubes in the pre-amp just to try them out that it went away. Never occurred to me a tube could do that, but . . . tubes are like that. Good luck and let us know what the final fix was.
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    jfine

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    Re: Hum reduction quest - solved !

    Post by jfine on Sat Aug 05, 2017 12:32 am

    My M125's had a slight hum, upgraded front driver tubes and it's quite as a mouse now. Bob actually nailed that one.
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    deepee99

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    Re: Hum reduction quest - solved !

    Post by deepee99 on Sat Aug 05, 2017 12:59 am

    jfine wrote:My M125's had a slight hum, upgraded front driver tubes and it's quite as a mouse now. Bob actually nailed that one.
    I even covered my outdoor power meter with tin-foil, thinking it was coming from the new transmitters they had installed so they just read the meter driving by. Boy, did I get laughed at about that!
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    LeGrace

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    Re: Hum reduction quest - solved !

    Post by LeGrace on Sat Aug 05, 2017 6:54 am

    jfine wrote:My M125's had a slight hum, upgraded front driver tubes and it's quite as a mouse now. Bob actually nailed that one.

    What replacement did you go with? Really would like to put this issue to bed.
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    arledgsc

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    Re: Hum reduction quest - solved !

    Post by arledgsc on Sat Aug 05, 2017 9:55 am

    Are you having the same issue with two M-125s? I had a front end tube once that induced a lot of hum for some reason.

    But if you are having issue with only one M-125 swap the tubes to see if anything follows. Would be just a process of elimination at this point.
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    LeGrace

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    Re: Hum reduction quest - solved !

    Post by LeGrace on Sat Aug 05, 2017 10:40 am

    arledgsc wrote:Are you having the same issue with two M-125s?   I had a front end tube once that induced a lot of hum for some reason.  

    But if you are having issue with only one M-125 swap the tubes to see if anything follows.  Would be just a process of elimination at this point.

    The hum now appears to be associated mainly with one amp, but in a way I dont get yet. First to reiterate hum emits from both speakers at exactly the same level when both amps are on. Intensity is constant, does not change with volume adjustment.  But I just made an interesting discovery as I was playing around with my RCA cables to try and get a tighter connection, ie by squeezing the collars a bit.

    I do the first amp and turn it on, the familiar hum emerges. OK on to the next one. I reach around to the back of the second amp (which is currently off) and remove its RCA cable to tighten it. The hum from the speaker connected to the powered amp instantly and completely disappears! I mean its now dead quiet. I reattach the RCA on the non powered amp and the hum on the speaker attached to the powered amp instantly reappears. Cable off, no hum, cable back on, hum. The part that puzzles me is the amp is not even turned on!! Reverse the procedure and amp 2 hums irregardless. So a little progress,  narrows down the problem a bit.  

    Would seem to point a finger at a grounding related issue vs tube related?
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    arledgsc

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    Re: Hum reduction quest - solved !

    Post by arledgsc on Sat Aug 05, 2017 10:52 am

    Are both amps connected to the same AC plug?   You could be just experiencing a ground loop issue when you connect and disconnect the cold amp phono plugs.

    Is chassis ground connected via the IEC AC connector?   If not sounds like a classic ground loop issue where connecting the cold amp causes hum in the other amp.  I would check that in both amps.
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    deepee99

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    Re: Hum reduction quest - solved !

    Post by deepee99 on Sat Aug 05, 2017 11:31 am

    arledgsc wrote:Are both amps connected to the same AC plug?   You could be just experiencing a ground loop issue when you connect and disconnect the cold amp phono plugs.

    Is chassis ground connected via the IEC AC connector?   If not sounds like a classic ground loop issue where connecting the cold amp causes hum in the other amp.  I would check that in both amps.

    Good point, arledgsc. LeGrace, I know "cheater plugs" that eliminate the ground are not legal in Canada, but I'm sure there's a black market for them. If not, I'll be happy to send you one for $1 plus smuggling and postage fees. Smile
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    LeGrace

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    Re: Hum reduction quest - solved !

    Post by LeGrace on Sat Aug 05, 2017 4:50 pm

    I physically relocated one of the M125's so that I could in turn connect all amps into a common plug. Hum is reduced by ~90%. There is a tiny residue, but I now have to place my ear within 1-2 inches of the speaker to hear it. I can live with that.  Very Happy And I have yet to install the new RCA plugs or shielded IC's. But why should this have made such a difference when the two wall plugs I'm using for all my components are on the same breaker? They are about 10 feet apart with my stereo situated in between.
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    deepee99

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    Re: Hum reduction quest - solved !

    Post by deepee99 on Sat Aug 05, 2017 5:34 pm

    What else is on that breaker?
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    LeGrace

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    Re: Hum reduction quest - solved !

    Post by LeGrace on Sat Aug 05, 2017 7:13 pm

    deepee99 wrote:What else is on that breaker?

    Just a dehumidifier, but I unplugged it this morning....oh wait.. Suspect
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    deepee99

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    Re: Hum reduction quest - solved !

    Post by deepee99 on Sat Aug 05, 2017 7:15 pm

    If it's got a motor in it (prolly) that would explain a lot.
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    j beede

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    Re: Hum reduction quest - solved !

    Post by j beede on Sat Aug 05, 2017 8:48 pm

    Are your interconnect cables directional? If not you might try making them so by opening the shield connection at the destination end. This may break your apparent ground loop.
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    jfine

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    Re: Hum reduction quest - solved !

    Post by jfine on Sat Aug 05, 2017 9:32 pm

    LeGrace wrote:I physically relocated one of the M125's so that I could in turn connect all amps into a common plug. Hum is reduced by ~90%.

    Exact thing happened to me with some mac gear, they had to be on the same single outlet, even though the 2 outlets on that wall were on the same circuit. If I plugged one component to one outlet, the other to the other outlet, hum city.

    Forgot to mention I did use cheater plugs on my M125's besides replacing the driver tubes, there's some who believe stuff sounds better that way anyhow, so I left them on. Those plugs also helped a sub amp I used to use on that same wall, the cheater plug made hum go away on that as well. Makes sense I guess since there's no 3rd prong to create *some* ground loop issues.
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    LeGrace

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    Re: Hum reduction quest - solved !

    Post by LeGrace on Sun Aug 06, 2017 5:48 am

    jfine wrote:
    LeGrace wrote:I physically relocated one of the M125's so that I could in turn connect all amps into a common plug. Hum is reduced by ~90%.

    Exact thing happened to me with some mac gear, they had to be on the same single outlet, even though the 2 outlets on that wall were on the same circuit. If I plugged one component to one outlet, the other to the other outlet, hum city.

    Forgot to mention I did use cheater plugs on my M125's besides replacing the driver tubes, there's some who believe stuff sounds better that way anyhow, so I left them on. Those plugs also helped a sub amp I used to use on that same wall, the cheater plug made hum go away on that as well. Makes sense I guess since there's no 3rd prong to create *some* ground loop issues.

    Thanks for sharing this. Even though situation has improved I would still prefer zero hum as opposed to tolerable level hum. Sounds like those plugs could provide an answer. Do you know where I could order some? Are they called something else by any chance?
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    arledgsc

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    Re: Hum reduction quest - solved !

    Post by arledgsc on Sun Aug 06, 2017 8:55 am

    They are called "grounding adapter" so Google search that. Target has a 2-pack for $1.99. But most hardware stores carry these.
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    LeGrace

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    Re: Hum reduction quest - solved !

    Post by LeGrace on Sun Aug 06, 2017 12:54 pm

    arledgsc wrote:They are called "grounding adapter" so Google search that.  Target has a 2-pack for $1.99.  But most hardware stores carry these.  

    Thanks! Ordered some online, local hw shops dont carry anything like that.
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    LeGrace

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    Re: Hum reduction quest - solved !

    Post by LeGrace on Sun Aug 06, 2017 3:43 pm

    One step forward, two back. Today hum is back close to where I started. Sad Sure hope those adapter plugs or maybe the new shielded cables bring some relief. Really getting tired of this issue.
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    deepee99

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    Re: Hum reduction quest - solved !

    Post by deepee99 on Sun Aug 06, 2017 3:51 pm

    LeGrace wrote:One step forward, two back. Today hum is back close to where I started. Sad  Sure hope those adapter plugs or maybe the new shielded cables bring some relief. Really getting tired of this issue.      
    Just use one plug. Otherwise you're just doubling-down on the ground isolation problem.

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