[Hap]

Would appreciate any advice on how to solve a low level hum that is present on all audio gear throughout the home.
It is a constant hum; say above 100Hz with some high frequency that is heard in everything from my main audio system, PC speakers, and A/V systems in all rooms.
The hum does not increase with gain.

The hum is present on my main audio system even if I cut all other circuit breakers off at the main panel and unplug everything else.
Same goes for my Video system, which is on a separate breaker from my audio.

Am 99.999% certain that it is not a CATV ground loop problem, as the hum does not change whether the CATV cable is connected or not.
I also have a ground loop isolation transformer connected to the CATV input line which did nothing to solve this.
 
I live in a high-rise building right in the city, so I don't know if that is the basis of my problem.
The N to G in the AC line has a very small amount of voltage, like .025vac, but I was told that is normal.

Things I have tried to date:

PLC's multiple brands and configurations throughout the apartment; APC, Monster, OneAC, Chang, etc.

Plug in line filters; high-end, low-end, DIY, in-line capacitors, etc., mostly for the L to N lines.

Have several N to G filters throughout the house.

Upgraded power cords; some with and without filters.

Checked or upgraded all power outlets throughout the apartment and confirmed all connections are correct with earth ground attached.

Everything that is plugged into a wall socket has been checked for correct polarity.

Main audio system has a single point grounding configuration.

Thank you to anyone that is kind enough to take the time and share some advice.

Cheers All!

[TomS]

Sounds like a real puzzler here, so it will be interesting to see who solves it first

It may be a radiated field rather than something that's transmitted through the power lines themselves if those measures had no effect.

Since you're in a high rise is there a mechanical room close, with perhaps an elevator controller, pumps, or large power transformers for distribution within the building?  Anything big like power lines somewhere close?

Tom

[Wayner]

Have you stripped everything off of the system except for speakers, amp and pre-amp? Does the hum occur even at the minimal connection level? Maybe I'd even start with just the pre-amp and a pair of headphones and start re-connecting from there.

Because you live in an apartment building, there are all kinds of suspects, from neighbors to the mechanical room of the building. How about noise on a good ole AM/FM portable radio (battery operated), then if there is no noise, plug it in and see if that starts something.

That's all I got for now.

Wayner

[Hap]

Hey TomS and Wayner,
Thanks for the replies.

My unit is about 20 ft from the elevator shafts, separated by two concrete walls and a room for the storage lockers.
The building also has central air conditioning, but the hum is there even if I shut off the a/c power off to my unit.

Wayner,
I have tried the radio test and it is confirmed that the noise is being generated though my AC lines.
The hum will be audible on all of the outlets I have tried connecting an audio source to; kitchen, bathrooms, bedrooms, patio...
As for my main audio system, I can get the hum diminished if I hook up minimal connections just as you pointed out; say just my CD player with headphones, or direct connected to a power amp.
Running any source through the preamp then into the power amps makes the hum more noticeable.

But anything that has speakers which is connected to an AC power source (PC speakers) has the hum present at idle.

[Speedskater]

What do they call it?
Large building that have 3 phase power. 3rd harmonic noise on the neutral.

[Wayner]

I call it ground loop.

[ctviggen]

Main audio system has a single point grounding configuration.

What does this mean?  If it means that all audio components are plugged into a single device or outlet, that's good.  If it means that you've taken an external wire and run between components, that's bad.  You've just created your own ground loop. 

Do you have a battery backup you could use/borrow?  Even if it's meant for a computer, if you hook the preamp and amp up to the battery backup and then play through there (with the backup disconnected from the wall), what happens?  If you still get hum, I'd say one of your components is causing the hum.  By the way, don't connect a source to the preamp. 

[Wayner]

ctviggen makes a good point. Only one component (usually the pre-amp, or amp should be grounded via the 3-prong plug (if yours has one). That component will bleed off all of the others thru the interconnect shields, where the ground loop is coming from. If you have a CD player, for example, with a 3-prong plug, put a cheater on that. It will be safe (unless you're on wet concrete, barefoot holding the device).

Wayner  aa

[Hap]

Much thanks for the great pointers...

Sorry, but I should retract my comment about having  a "single point ground config." in my audio system.
All the components of my audio system are plugged into a single AC line; thus the 3 PLC's used in this system share the same AC line.
I do not have an external wire that is used to connect all the components to earth ground.

I'll find a buddy that has a UPS big enough to power up my preamp and one amp and try that suggestion out to see if that helps.

My preamp is a CJ PV12, and does not have the earth ground connected.  Sources are a CD player and VPI TT, which also do not have an earth ground.  Three SS amps with an electronic x-over that runs on 9v battery power.

I have tried running just the CD player directly into the x-over, then into one Acurus 250 amp; the low level hum does get softer by about 50% with this configuration, but is not completely eliminated.

Also, even if I completely disconnect everything in my audio system; and all appliances for that matter from the AC sockets, I will still get the hum through my PC speakers, which is in one of the bedrooms.

[fly_fish_nz]

You've probably already thought of these, but any dimmer switches, fluorescent lighting, or computer power supplies on the same circuits?  Each can cause noise with some components - my laptop power supply causes noise even when the laptop is not attached.

[Hap]

fly_fish_nz,
Thanks for the suggestion.
No dimmers or fluorescent lighting on the same circuit at the audio system, but do have these in the apartment.
I can cut the power at the breaker box to all of these, and still have the low level hum; same goes for any wall warts.

This may a little bit off topic, but I took a look inside a high dollar power cable last night, and noticed there is a very small gauge (28-30) wire that is attached to the earth ground on the component socket end, and is wound around the outside of the jacket (1 turn per 3-4") and stops in the middle of the cable run.
Guessing this is supposed to suppress RFI or other hash around the power cable and shunt it to earth ground?

[andyr]

ctviggen makes a good point. Only one component (usually the pre-amp, or amp should be grounded via the 3-prong plug (if yours has one). That component will bleed off all of the others thru the interconnect shields, where the ground loop is coming from. If you have a CD player, for example, with a 3-prong plug, put a cheater on that. It will be safe (unless you're on wet concrete, barefoot holding the device).

Wayner  aa

Wayner, I'm afraid I disagree totally with what you say.     I believe "my" way is:
a) based on safe electrical standards, and
b) good engineering practices

... unfortunately, many components where the mfrs save a few pennies by using 2-wire mains cables (ie. without the ground wire) do not meet the above.  Certainly all my gear does.

I believe many people get confused about mains electrical "earth" vs "signal earth", so I will attempt to lay out my argument to avoid any confusion.

I'll also relate to you 2 instances of "hum" problems which I've had to solve recently (and one wasn't an earth loop!  ).

Firstly, for basic safety, mains electrical wiring should be 3-core throughout.  IE. the 3rd prong on each mains plug connects to the mains "earth" wire.  In Australia, anyway, this is tied to the "Neutral" block back at the Consumer Unit, as well as a copper ground stake outside the house.

Secondly, all components should have a 3-core mains cable; and the earth tag inside the IEC socket on the case should be tied to the case via an earth bolt.  Thus if the live mains core accidentally touches the case, it will short to mains earth and trip the fuse/MCB or the RCD.

Thirdly, all parts of the signal path and the PSes should not touch the case - this means speaker BPs, input RCAs etc..

Thus RCA "grounds" connect the signal ground planes of successive components together but they have no connection to mains earth.

Fourthly, to minimise noise it is good practice to decouple signal "ground" from PS '"ground" by means of a 10ohm res.  This keeps noise from heavy currents associated with PS filter caps charging/discharging, from polluting the signal ground plane.

As an example of why this is good practice, I have had a longstanding hum coming from the main speakers in one of my hifi systems when I connect a powered sub.  A mate with the same amplifier and sub did not experience any hum!  After racking my brains and trying lots of "fixes", I finally realised my mate's preamp certainly did have signal ground lifted from PS ground (as he has the same preamp which I use in my main system) ... so I inspected the preamp I was using in that system and found that it did not separate signal earth from PS earth.  So I inserted a 10ohm res between the two ... and solved the hum problem!  Hooray!   

The second example of a hum problem which I've had to deal with recently was not in fact an earth loop!      I recently changed an amp in my main system for a very wide bandwidth amp and found I was getting a 100Hz "hum" from the bass panels of my Magneplanars.  After 3 weeks of getting more and more frustrated when different things I tried failed to have an affect, I finally (very accidentally!  ) found what was causing this hum!

No ground loops ... a 2nF cap across the speaker BPs cured the problem!  It would seem that Magneplanar drivers act as very good RF antennae ... this enters the amp via the BPs and if it is a very wide bandwidth amp (in this case up to 150Khz), it will negatively interact with the circuit!     (The old amp was not wide bandwidth.)

The cap shorts out the RF signal before it can get into the amp!

Regards,

Andy

[Hap]

andyr,

Thank you for your input on this subject.
Am currently experimenting with neutral to earth ground filters, and will probably try your 10ohm resistor and/or 2nf cap mods at some point in my quest to kill the hum problems.
Will also check to see that my IC grounds have no connection to the earth grounds.

Someone here suggested that I get an electrician to take a look at the wiring and breaker box in my apartment to get an idea of how the building was wired.
I got a buddy to look at this a few days ago, and he confirmed that the point of service where the Neutral and Earth Ground is bonded is not at my breaker box, or connected to the wiring coming into my apartment..
The building does not have sub-metered electrical service to each unit, so he said the point of service could be located in a number of areas throughout the building.
This could be a potential cause of the hum problem, since the AC lines in my unit does not have a true earth ground connection to tie into. (I'm on the 12th floor)

Please excuse me if I explained any of this incorrectly, as I am not very proficient in this field.

Another issue my electrician pointed out is that my hum problems may not be confined to the AC mains; as he picked up some airborne RF noise in the master bedroom, which he said could be coming from a TV or Radio station transmitter tower located near my building.

In any case, any suggestions or comments will be much appreciated.

Cheers to all!

[andyr]

Another issue my electrician pointed out is that my hum problems may not be confined to the AC mains; as he picked up some airborne RF noise in the master bedroom, which he said could be coming from a TV or Radio station transmitter tower located near my building.

In any case, any suggestions or comments will be much appreciated.

Cheers to all!

Hi Hap,

If your electrician suggests that there's a nearby transmitter tower then maybe you are experiencing the same RF-induced hum that I've just solved with a cap across the amp's speaker BPs?

Get hold of some 1nF metallised polyprop or film caps and connect them across the amp's BPs.  If 1nF doesn't do much ... try 2nF.  That's what cured my RF-induced hum (caused by the amp having an extended bandwidth)! 

One related point.  As well as this hum, are you experiencing "tizzing" (ie. distortion) on bass transients?  If so then it is undoubtedly an RF-induced problem.

Regards,

Andy

[Hap]

andyr,

Just to confirm your suggestion; I should try and place a 2nf (.002uf) metalized polypropylene cap between the + and - power amp Binding Post terminals on the L and R channel outputs.
Can you please clarify what amp BP's stand for.

Are the voltage ratings for these caps critical....I got some .001uf 600vdc film caps; would these work as a trial basis.

Thanks for your assistance.
Hap

[andyr]

andyr,

Just to confirm your suggestion; I should try and place a 2nf (.002uf) metalized polypropylene cap between the + and - power amp Binding Post terminals on the L and R channel outputs.
Can you please clarify what amp BP's stand for.

Are the voltage ratings for these caps critical....I got some .001uf 600vdc film caps; would these work as a trial basis.

Thanks for your assistance.
Hap

Hi Hap,

Yes, "BPs" are the ouput speaker Binding Posts. 

OK, the actual value - if it solves your problem - will depend on how much bandwidth your amp has.  As I said, my new bass-panel amp goes up to 150Khz and 2nF solves the problem.  If your amp doesn't go quite as high then maybe 1nF will do?

The voltage must be anything over 100v - so the 600v caps you mentioned will be fine.  I could only get 1nF/1000v film caps (better than needed!) so that's what I used. 

As it's a PITA soldering one then two caps to 2 pairs of banana plugs or spades, and then connecting them up to see the result ... maybe you can use some crocodile clips to connect the caps, while you're experimenting?

Good luck,

Andy

[Hap]

andyr,

Thanks for the prompt reply.

Will try your cap mod on a pair of Acurus A250 SS amps that  power my mids and subs.
Do you think the .001uf or .002uf 600vdc metalized polypropylene caps will work between the BP's of the outputs of this amp.

Any suggestions or cautionary tips you know off hand with this amp.

Regards,
Hap

[andyr]

andyr,

Thanks for the prompt reply.

Will try your cap mod on a pair of Acurus A250 SS amps that  power my mids and subs.
Do you think the .001uf or .002uf 600vdc metalized polypropylene caps will work between the BP's of the outputs of this amp.

Any suggestions or cautionary tips you know off hand with this amp.

Regards,

Hap

Hi Hap,

Sorry, I have absolutely no knowledge of Acurus amps.  Now, some amps are "sensitive to" (ie. do not like!) too much capacitance on their output BPs.  How much "too much" is ... is a question for the amp mfr.  (My own amps can take up to about 5nF without sweating!     And my speaker cables are less than a ft long - as my XO/amp box sits directly behind each speaker!)

This capacitance on the output BPs can be created by putting a cap straight across them ... or by having speaker cables which are either very long or very high capacitance (like braided cables).

That's why I suggest trying 1nF first ... this shouldn't put a bad load on the amp, however, if you have either very long speaker cables or are using very high capacitance cables, you should ask Acurus what is the max capacitance they recommend.

Regards,

Andy

[Occam]

ctviggen makes a good point. Only one component (usually the pre-amp, or amp should be grounded via the 3-prong plug (if yours has one). That component will bleed off all of the others thru the interconnect shields, where the ground loop is coming from. If you have a CD player, for example, with a 3-prong plug, put a cheater on that. It will be safe (unless you're on wet concrete, barefoot holding the device).

Wayner  aa

Wayner - I agree with the points andyr made....
and now I'm going to speak as the Facilitator of the Lab Circle -

DON'T YOU EVER POST SUCH A DANGEROUS, STUPID RECOMMENDATION TO DISABLE THE SAFETY GROUND ON A MAINS GROUNDED COMPONENT IN THE LAB CIRCLE, EVER!!!

For careful testing, yes, but it MUST be reconnected for normal use. Until such time that NEC approves of alternative safety procedures/methodologies for Class I components, that rule stands.

If you cannot abide by that rule, do not post in the Lab Circle.