[Wayner]

That's right! This is the EVIL topic that no-one really wants to talk about. The problem is, many don't know what to do about it, or even determine what really is the true source of the beast. Hum can destroy the musical experience. It is very elusive.

I'm hoping with the collective knowledge of this bunch, we should be able to identify the sources, take action and cure the problems collectively. I know this can be an ugly topic, so keep it civil. The truth is, we all have a hum issue somewhere in our systems, right?

Well, I'll start it off. What is hum? Scouring the internet we find several causes. The simplest explanation is the old ground loop situation. This is a confusing topic from the get-go. To make the description simple, let's just say it's electron movement in a zero based ground plane, induced by uneven ground potentials of connected systems. If there is the slightest difference in potential, current will flow.

The other effect that causes hum is Electro-magnetic-fields. This is energy transmitted through the air. It can come from the windings of a near-by motor or transformer, it can come from fluorescent lamps and many other annoying sources.

What problems have you had? Have you been able to fix it? Have you just given up? Do you blame a particular component?

Wayner

[S Clark]

The transformer in my Moscode 300 has a mechanical hummmm.  After talking to George Kaye, my options were to replace it or cut a stick to shove down between it and the case.  The stick along with some neoprene added to the case for damping worked fairly well, and sticks are cheaper than transformers.  One day I'll get around to replacing the vibrating transformer, but not for now.

[ebag4]

Wayner,
This is a timely topic for me as last night I was able to track down a source of hum that I have had for a couple of weeks.  I recently installed a USB DAC into my system.  I did not have any hum originally, my system is in my home office and I was using my laptop to run foobar2k and Xlobby to play flac files.  I upgrade what I call my server machine (which resides downstairs below my office) so it could run these programs and connected it via USB to my DAC, this way the PC is not in my listening space.  Once I did that I noticed that I had a slight hum issue that would increase with the volume control.  I tried a cheater plug on both the DAC and the PC but neither took care of the issue even when they both had cheater plugs.  BTW, all I had to do to create the hum was to make certain the grounded casing of the USB cable was touching the USB port on the DAC and the grounded connection of the RCAs from the DAC to the integrated amp were touching the grounded casing of the RCA input to the amp.  I checked it out again using the in room laptop and viola, no hum.  It was at this point a lightbulb went on.  I took 2 cheater plugs down to the PC (nothing was using a cheater at this point) and used one for the PC and the other for the .....wait for it.....monitor.  That ended my hum problem.  At this point I am hum free with a cheater plug on the PC and monitor with the DAC plugged straight into the wall.

Sorry for the long drawn out description but maybe it will help someone else out.

Great topic!

Best,
Ed

[bummrush]

hum comes out of my counterpoint if a toaster oven is on in the kitchen,otherwise not a speck of hum anywhere.

[OldCoder]

I was having an unusual hum issue with my Ultra 550 a few weeks ago.  The transformer itself was humming, the hum did not enter the audio circuit.

It turned out that my audio power circuit, a non-dedicated houshold circuit, was being shared by a halogen lamp in the living room upstairs.  When the lamp was on, it put enough trash on the power line to induce the transformer vibration.

The problem doesn't exist if I make sure that lamp is turned off before I go downstairs to listen.

[TomW16]

I have experienced a hum when a DC power cord was too close to an unsheilded interconnect.  The hum was eliminated by separating the power cord and interconnect.

Cheers,
Tom

[avahifi]

Hum

Sometimes its just because the unit does not know the words. 

Frank

Seriously, it is often caused because wires are not zero resistance, chassis can pick up electomagnetic radiated noise, and of course that hellifweknow issue too.

Ground loops occur when there is more than one ground path with a real resistance between them causing current to flow where it is not supposed to flow - such as with three wire AC grounded audio components mixed with two wire ones.  There are now two ground paths, one between the equipment through the audio cable grounds, the other between chassis grounds through the power cords.  Finding and fixing all these issues in new design is a real headache, even when you think you are obeying all the "rules" of good design.

If only wires all were zero resistance our work would be easier.

Regards again,

Frank Van Alstine

[Wayner]

Good morning Frank.

Older style (not torridail) transformers are made with an internal 2 coil bobbin (with the primary and secondary windings) and a steel laminate case. This case is made up of layers sheet steel that are usually bolted, or sometimes welded together. If you hear a mechanical hum (not in the circuit), it is from these laminates. In some area, 2 adjacent laminates are being induced by the magnetic field (60 cycle) to vibrate (the laminates are loose). HID light fixtures often have this problem. If you are outside at night and have a street light or farm light humming, this is the cause. It goes away when the sheets are forced to stop slapping each other.

Wall warts are an evil source as well. There is a transformer in there and it has a magnetic field that certainly can penetrate cables. Good points, all.

[HAL]

DC on the AC line will cause toroidal transformers to hum.  The DC saturates the toroidal core.

One cause of this is older switching power supplies from desktop PC's or laptops on the same circuit as the audio system. 

Using an isolation transformer will break the DC connection and stop the hum.  Other units are now available to stop DC.

Light dimmers are another big source of noise that can be put back on the AC line.  Usually the worst noise level at mid level dimmer settings.  This is a buzz source more than a hum source.  Turning them up to full or zero output stops the AC line noise as the dimmer is no longer fuctioning. 

[Brown]

DC on the AC line will cause toroidal transformers to hum.  The DC saturates the toroidal core.

One cause of this is older switching power supplies from desktop PC's or laptops on the same circuit as the audio system. 

Using an isolation transformer will break the DC connection and stop the hum.  Other units are now available to stop DC.

Light dimmers are another big source of noise that can be put back on the AC line.  Usually the worst noise level at mid level dimmer settings.  This is a buzz source more than a hum source.  Turning them up to full or zero output stops the AC line noise as the dimmer is no longer functioning. 

Great post. Thanks. Just put a isolation transformer in the line for my computer and plasma set up. It appears my CDP for main system located on another room was on the same circuit as the pooter and TV.  I'll be dammed. The buzz and hum is now GONE GONE GONE.

Thanks again. 30 years plus at this game and still learning. Thanks again.

[ArthurDent]

Hum

Sometimes its just because the unit does not know the words. 

Frank

    Thanks for the morning chuckle Frank. 

[avahifi]

Anyone know of a good source of 1 to 1 isolation transformers suitable for a big power amp (15 amp at 120V AC) at a reasonable price?

I would like to have something to recommend to clients who may have that DC on the AC line issue.

Regards,

Frank Van Alstine

[oneinthepipe]

Anyone know of a good source of 1 to 1 isolation transformers suitable for a big power amp (15 amp at 120V AC) at a reasonable price?

I would like to have something to recommend to clients who may have that DC on the AC line issue.

Regards,

Frank Van Alstine

Wouldn't DC on the AC also affect a preamp?  I have a hum that disappears when the preamp is turned off.

[charmerci]

If only wires all were zero resistance our work would be easier.

Frank Van Alstine



So, does anyone know which audio companies are planning on using superconducting wire in their components?

I guess the question is, what company will come out with the first superconducting speaker cable and interconnects?

[modular747]

So, does anyone know which audio companies are planning on using superconducting wire in their components?

Keep your liquid helium well chilled until they do...

[stereocilia]

I had a Plinius amp that hummed like a sonofabi*!h -- electrical hum that is, not mechanical.  I used a cheater plug until I sold the amp and replaced it with AVA.  I purchased it used; it turns out it was the actual amp reviewed in Stereophile.  I know because the serial number matched, and yes, the hum was mentioned.  I think the review is still available for free on line.

Anyway, I also enjoy the band Hum.  ("She thinks she missed the train to Mars...") One of my favorite concert memories is the free outdoor concert in Champaign, IL.

[HAL]

The companies that are doing balanced isolation transformers are Equi=Tech, Furman Sound and Balanced Power Technologies.   Equi=Tech and Plitron also make the bare toroidal transformers. 

[TerryWI]

I had a lovely hum whenever I switched on my turntable and chose the phono input on my integrated amp.  It was not audible with music playing, but I expect it was doing harm to the sound.  I tried reseating cables, moving the turntable, moving the external phono amp, switching phono amps, using cheater plugs, plugging in directly to the outlets, using different outlets, using surge protectors, etc.  But nothing ever cured or even changed the hum.  I chalked it up to the talked about Grado hum problem with certain turntables.

A number of years later I read a post where a fellow suggested moving your turntable ground from the external phono stage to the ground post on the integrated amp.   Why not, never tried that and didn't even realize that was a proper hookup.  So after making the change I fired everything back up and sure enough, my hum was now gone.  The answer was right before me all those years.  How humbling, but what relief!   

[Brett Buck]

What problems have you had? Have you been able to fix it? Have you just given up? Do you blame a particular component?

   The best tool I have found for tracing down hum is a set of RCA jack shorting plugs. Just short out various preamp inputs until the hum goes away, then you have found the source. I also short the unused inputs. The vast majority of issues I have found were related to hum induced from the sources. Of course the phono input is notorious for picking hum, but sometimes the isolation between inputs is not perfect, and hum on one input appears when another is selected.

      I did have one hum issue I never really diagnosed, although I fixed it. I had a mechanical hum that was coming from the power transformer on my Omegastar 260. I didn't appear on the output, just a hum/buzz from the transformer itself. After some futzing around, I found that there was one location and orientation that just caused a hum. I moved it 12" and rotated it 90 degrees, and the hum went away. There's something about that spot that is just bad, but I have no idea what it might be.


      Brett

[satfrat]

I'm hoping with the collective knowledge of this bunch, we should be able to identify the sources, take action and cure the problems collectively. I know this can be an ugly topic, so keep it civil. The truth is, we all have a hum issue somewhere in our systems, right?

Wayner

Sorry Wayner but I've never had hum in my system since I instituted power conditioning in the form of my BPT balanced power conditioning, concocting a grounded dedicated circuit for my system and using shielded power cords. My system is dead quiet and that is the truth for me in my system. So hopefully your thread will address humming for those folks who actually do have this issue but I'm wondering if it's really that big an issue a for a lot of folks?

Cheers,
Robin