Slight hum in my amp. Is this normal?

I have an Anthem A5 and when I turn it on there is a slight "hum" if you put your ear close to it. From 3 feet away it’s unnoticeable. It's in the amp, not in the speakers.
Is this normal?
Just some transformer hum not unusual. Is the amp new or new to you? Or if you've had it a while is this noise new?
I would not say it is "normal" but it is pretty common.  Both my Acurus amps emit a slight hum that is only audible at close distances.  Most likely transformer hum(vibrations) in the majority of cases.

Having spoken to a couple of manufacturers about their amps it seems that the use of low or zero negative feedback can leave an amp vulnerable to slight hum. 
Use a balanced power source and it'll go away.  A Furman, Euqitec, Tourous etc.  

Good Listening

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I bought a now discontinued PS Audio Humbuster III to solve that issue and it did. Those things show up for sale here and there and something like that should be made by somebody else, but I’m not sure if that exists. Maybe as part of a good power conditioner.
I don’t recall ever hearing it before. When I moved into a new home, the right surround was dead. I took it to an authorized Anthem service center, the only one in the USA, they couldn’t find any problem so as a preventative measure, they disassembled it and reseated everything. When I powered it up is when I noticed. Note this home was built in 1941 and still has "knob and wire" electrical. It looks like everything is grounded but electrical is not my specialty. I’m purchasing a Torus TOT MAX tomorrow so I wonder if that will help. I'm not sure if everything is sharing the same ground. If it were a grounding issue, wouldn't I hear it in the speakers? This is not coming from the speakers, only the amp.
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I've always experienced power transformer hum and HF hiss until my current ARC and Hegel H30 amps.  Both dead quiet so I guess it's design dependent.
Question for oldschool...if you've got 'knob & tube', I can only assume you don't have the 3rd prong 'direct ground' wiring.  That could be an issue, even if it's all wired correctly.  In order to use those wall plugs which Should be 2 prong only, you'd be forced to either use a 'dead man' 3>2 plug adapter at each connection for such, or been doing some 'plug surgery' and snipping off the 3rd prong.

In the first case, the 3rd is just hooked up to the normal ground.  In the second, you just 'sidestep' it, which does eliminate any common grounding between any and all chassis ground connections.

The 3rd dedicated ground exists solely for short-circuit safety issues, and it's what a GFCI depends upon in the modern kitchen and protect you from grounding yourself out if you come in contact with water if using a faulted device.  By extension it works for the balance of the home if, by chance, you're operating a faulty appliance or spill your drink on some device.

Now....given your situation, if there's no hum exhibited from any other device, within your system or without (a fluorescent lamp or some other device being run concurrently when you've powered up), and it ONLY exists from the one device that you've had refurb'ed, I'd look at a interconnect cable going into AND out of the amp.

I chased a 'hum' gremlin in my system not long ago, swapping power cords, power sources, interconnects on All components, hunting down a somewhat loud hum.  It finally came down to One faulty cable of a pair, which had either a bad RCA plug or a fault in the wire itself.

Viola', it worked.  To be honest, there is a slight residual hum from the amp if I crank it up with no program.  And a power conditioner may or may not minimize that, depending on (as noted) the design and parts used in your amp and other segments in the signal chain.

While I'm being long-winded and pontificating *G*, you might try hooking up the amp into a 'bare bones' setup....different speakers, one source, something really minimalist.  See if it still hums at you.  Dig out the 'orphans' in the attic, closet, or garage...hit up a buddy for an afternoon 'test', you spring for the lunch and libations...

Not that I'm not telling you to buy a power conditioner, but it'll save you the WTH response if it doesn't make a difference....;)  The last could be cheaper and maybe more fun and educational. *S*
Thank you everyone for the great intell. I bought a Torus TOT MAX yesterday at a killer price and the dreaded hum is still there. I'm convinced its internal in the amp and something isn't right. This morning real early I powered it up with no input. Nothing else was on and I could hear a ver faint hum from 10 ft away.
I've sent an email to the local Anthem authorized service center, who told me this is normal, and we'll see what they say. As I mentioned before, there has never been a detectable noise (hum) from this unit until they disassembled and re assembled it. Worst case, I bite the bullet and ship it to Anthem factory at a hefty shipping cost.
I once had a subwoofer that had an internal hum.  It was actually more of a very faint buzz, but audible when it was quiet.  The manufacturer of the sub acknowledged that some of their transformers were noisier than others and they sent me some parts to install around the transformer that physically isolated it from the cabinet and the noise went away.  If in your case the service involved "disassembled and reseated everything" then I suppose it's possible that what you are hearing is resonance from vibration.  They would need to loosen and retighten the fasteners holding the transformer in place such that it doesn't resonate quite as loudly.  I just thought I'd share my experience since the solution for my issue was a physical one rather than electrical.
jc4659, my guess is either you hit the nail on the head or it's a faulty component. Your suggestion is about the most logical given the history. Another thing I'd like to add, this unit replaced an Integra 50.3 AVR that was dead quiet. I don't believe this "hum" is normal and definitely not acceptable. I'll report the service centers response tomorrow. I believe they are a top notch shop however it's my assumption the tech may have missed something. Whatever the case it's gonna be fixed even at the cost of shipping from Los Angeles to Anthem in Canada and back.
Watching this post with interest. I have a Prima Luna integrated making hum. If you are successful getting your fixed, I'll send mine in (under warranty) to see if it is fixable.

The Torus TOT MAX you bought is certainly a nice power isolation transformer. Thing is though, in the case of hum, that can very well be caused by DC on the line, and I don’t believe the Torus has a filter for that. For another $120 you might as well get an Emotiva CMX-2.

I have one. It does work and even if it doesn’t in your particular case, it cant hurt. So essentially what I’m suggesting is use both the Torus and CMX-2. Torus plugged into CMX-2 of course.

wolf_garcia recommended a PS Audio Humbuster III. Same concept/functionality. That too would be good if you can find one, but is likely more expensive than the Emotiva.

I like the concept of what you and wolf_garcia suggest. Here is Los Angeles we typically don't have the same power issues one would have in other parts of the country however it couldn't hurt. Reviewing the chain of events, I seriously think it's a component issue and I know it's in the amp as it is not coming through the speakers. I'm going to exhaust that possibility first and then add the Emotiva. I like Emotiva products. I have one of their HDMI cables, a couple interconnects, and a power cable (AWG 12).

Here is a more detailed description of the events leading up to my evaluation. I posted this in another forum explaining its wording:

Yesterday I purchased a Torus TOT MAX. WOW, what an improvement it made to audio quality however, the "hum" is still there. This morning I got up extra early as it was very quiet in the room and outside so I figured it would be a great time to see to what degree this "hum" was. As luck would have it, I could hear the "hum" in my seating position 10 ft away from the A5, and it was running through the Torus. Correct me if I'm wrong but the Torus should have corrected the problem if it were a grounding issue. Here are the sequence of events leading to this problem.
-Bought as a used unit, damaged in shipping
-Took it to the only authorized Anthem repair facility in the US here in Los Angeles
-Repaired successfully and ran beautifully until
-Moved to a new home and the right surround was dead
-Brought it back to the service center and they found no issues
-Then they completely dismantled it and re assembled finding no issues
-As soon as I got it home, I noticed the dreaded "hum"
-I returned to the service center the following week and they plugged it in with no interconnects, only the AC power. We heard the hum. Of course we had to put our ears relatively close to the unit to hear. Problem was, there was ambient noise in the room so it wasn't as easy to hear. They said what I was hearing was perfectly normal. The skeptic that I am and never hearing this before, I had my doubts.
Now that I've tested it with the Torus, heard the same hum as before at home and at the service center and the fact I never heard it before, tells me there's something not right.
Today I sent an email to the service center asking what he suggests. Worst case scenario, I send it to Anthem Canada and get it corrected once and for all. They can expect a telephone call from me tomorrow discussing this and their suggestions. I know they are going to suggest sending it in, of course! They like the business. I don't mind the service bill, it's the shipping I have an issue with since its not exactly small or light weight.


Is this what the inside of the amp looks like?

If so notice the two toroidal transformers on each side. Pull the top off the amp and check the center mounting bolt and nut for tightness. Make sure the round top plate is seated properly on the top of the transformers. Maybe one of them is loose.

After checking them, to make sure they are secure, power up the amp and listen to the two transformers. If the hum/vibration is still there listen to each transformer individually the best you can. First verify the hum is coming from one or both of the transformers. Is one louder than the other? If so recheck the mounting bolt and nut. Make sure the round top plate is seated properly on top of the transformer.

I was unaware (until I heard about it here and looked the damn things up) of the Emotiva CMX stuff, but it IS less expensive than the Humbuster III, and actually obtainable. Cool.
What jea48 said.  I just didn't want to be an accomplice if you touched the wrong place with your screwdriver.  Let us know what the solution was.

Today I dropped it off at the local authorized service center who has been the only company to work on my amp. Interesting thing, without opening the cover, I put my ear real close to the vents adjacent to the transformers, there are two, one on the left and one on the right just behind the front panel. I could swear the hum sounds slightly louder from the right side making the right side transformer suspect. I used an analog decibel meter using fast and slow response, and it's hard to tell with the slightest ambient sound pressure. It measured approximately 55 dB with the right side maybe 1/2 - 1 dB higher. Are my ears that good? the proof will be in the pudden when the shop gets into it. The owner said he would get in early when it's dead quiet and listen for the hum.
I told him today that the hum is loudest when power is initially applied then quiets down however, I can still hear the hum from 10 ft away when the room is quiet. Of course when a program is playing, the speakers drown it out so It's inaudible. My Integra DTR-50.3 AVR, $700.00 retail has always been dead quiet. Certainly a $4000.00 retail Anthem A5 amp should be as well.
Lets see what they say in a couple days. Stay tuned!
Wow, I thought it was bad hearing hum from my Klipsch speakers from 12 feet. I'd be pissed if I could hear the actual transformers! I have an Emotive  CMX-2 ($127 w/tax) coming tomorrow. I'll report on its efficacy.
Wow, I thought it was bad hearing hum from my Klipsch speakers from 12 feet. I'd be pissed if I could hear the actual transformers! I have an Emotive CMX-2 ($127 w/tax) coming tomorrow. I'll report on its efficacy.

If the cause of the hum is DC on the line, it certainly should work. It can't hurt in any case, unless one considers the two blue status indicators to be "active" and thus draw some minuscule amount of current.

You can have DC on the line and oddly enough, it can be passed through transformers. It could also be considered a 2nd harmonic as basically its caused by loading on 1/2 of the AC line and so the AC waveform can be offset slightly just as if it were riding on a slight amount of DC. The resulting asymmetry could be interpreted as a 2nd harmonic.

Its easy to correct with a DC blocker which is a simple and inexpensive device. DC on the line can cause the core of the transformer to saturate, causing it to rattle or hum. It can vary from one transformer to the next even with parts from the same construction run.

Grounding in the house has nothing to do with this problem even if its not DC on the line. So the age of the wiring isn’t the problem.

Transformers can be mechanically noisy on their own despite the best of intentions. Tightening a noisy part down won’t help and might make it worse. But sometime the part is causing something else in the chassis (like a cover) to resonate and it might be possible to damp that part. If you can only hear the problem when you are within 6 inches of the amp its not a problem. IME, most audiophiles listen to their gear considerably further from the amp they are playing :)

Getting quiet transformers is always an on-going challenge. Transformer manufacturers often don’t understand how important it is for the part to be silent and might sometimes skimp on a few core laminations or the like thinking they can save a buck. In the process they might loose the entire run as reject parts!

Good Luck!


You can have DC on the line and oddly enough, it can be passed through transformers.
Please explain.
@jea48 , I thought I did. One more try:

DC on the line occurs when 1/2 of the AC line (for example, positive going portion of the AC waveform) is loaded while the other half is not.

Space heaters or hair dryers on half power do just exactly that. So one half of the AC line can have lower amplitude due to the loading as a result.

But its still an AC waveform and so can travel through a transformer. But the output will still be asymmetrical. The asymmetry can be filtered out by a DC blocker which is a simple circuit consisting of 2 or 4 diodes that are bypassed by some large capacity electrolytic caps.

Go under chassis, remove the transformer screws, apply some blue tac or similar substance to the holes and re-tighten the screws. It will lower transformer noise.
Received the Emotiva  CMX-2 which made no difference in suppressing the 60 Hz hum (clearly heard thru my KEF Q1 monitors 12 inches away).
No source was connected, hum did not vary with volume and mute button made no difference. I've given up hope of using this integrated with my Klipsch LaScalla IIs. I'll be content using my BAT VK-300se 150 wpc integrated which is dead silent. Sometimes you get what you pay for...
It's a beautiful unit and extremely well made (big, beefy power cord). I don't need it so may try to return. Thanks for the heads-up!

But its still an AC waveform and so can travel through a transformer. But the output will still be asymmetrical.
Is it really DC in the true sense/meaning of the word? Does it build to a DC voltage and then fall to zero at each half of the waveform cycle? If so then I could see how it would pass though from the primary to the secondary winding of an isolation transformer.

Sorry for my ignorance. I am just trying to better understand what is going on.
I do know there are people that say that an isolation transformer will block DC offset on the AC mains from the secondary of the transformer. I personally do not have any personal experience whether it will or not.
I believe you when you say it will not. I also believe that to be the case from actual bench testing which you have done.

I know AC and DC can both travel in a circuit at the same time. And yes I know the DC can be blocked using a DC blocker allowing only the AC to pass though the circuit or another circuit.

I know a pulsating DC voltage source, such as a battery, can be transformed, for lack of a better word, but constant DC voltage cannot. (As long as the applied voltage is constant.) If a constant DC voltage could pass through a transformer then an output transformer on a tube power amp would pass DC to the speakers.

Atmasphere 5-24-2017
DC on the line occurs when 1/2 of the AC line (for example, positive going portion of the AC waveform) is loaded while the other half is not.

Space heaters or hair dryers on half power do just exactly that. So one half of the AC line can have lower amplitude due to the loading as a result.

But its still an AC waveform and so can travel through a transformer. But the output will still be asymmetrical. The asymmetry can be filtered out by a DC blocker which is a simple circuit consisting of 2 or 4 diodes that are bypassed by some large capacity electrolytic caps.
Ralph, I share Jim’s puzzlement about that. If a waveform that is asymmetrical above and below zero volts is sent into a transformer, I would expect that what would emerge from the output winding of the transformer is a waveform that looks similar (assuming that the frequency components other than DC are within the transformer’s bandwidth), but that has been offset up or down such that the zero Hz (DC) component is eliminated.

Best regards,
-- Al
@almarg , that's true, and if you look at my initial post I mentioned that DC on the line can also be interpreted as a 2nd harmonic. Its pretty clear that filtering using a transformer is an inefficient method; a DC blocker is a lot cheaper!

FWIW, most of the time the reason for DC on the line is an issue that is pretty closely associated with the local AC situation. For example, if there is a distribution transformer serving five houses, only one house might be running a space heater at half power, but all five houses would experience DC on the line.

Thanks, Ralph. To be clear, though, am I correct in believing that to the extent the asymmetry of the waveform corresponds to a 2nd harmonic component, neither a DC blocker nor a transformer would eliminate it?

Best regards,
-- Al

^^ Yes- and that is what we are dealing with when the power transformer in most audio equipment is involved. Its best to block the DC prior to a transformer- otherwise you have to use a very sophisticated power conditioner!
Is your system set up for pure stereo?  Or, are you connected to some video theatre stuff too?

If so....disconnect all the inputs from sources leaving only one source at a, phono...etc.

I'm thinking you need to rule out groundloop.

I had the same problem to my Constellation Mono amp.  Amp checked and find nothing at the Constellation repairing center.  Checked with Shunyata Research, I used quite a lot electrical products from them, they said probably a DC on the main.  With a reasonable low cost for a try, I tailor-made 2 DC blockers (one for each channel), to which to ensure sufficient current serving the Mono amp.   No hum from amp anymore, and more importantly that would not affect the sonic performance. 
My amp has been at the shop since Wednesday and the owner called me this morning at 7:00 am when the shop was dead quiet. Said he did agree the transformer on the right was a bit louder than the left however it was a normal hum. I explained again that it was loudest when you first power it up then the hum diminishes after a few seconds but is still audible. He wants to keep power applied to it and observe.
Another thing I just remembered and haven't mentioned, since the hum began, it has been running a bit warm even at low listening levels when it was in my system. Another thing is this whole thing only began when I moved into this house with knob & wire electrical. It is on a 20 amp circuit.
All of these things suggest DC in the line. Just to review; all of the problems began when I moved in this house. First thing was the surround right channel was dead. The shop found no malfunction indicating a loose connection that suddenly worked when I delivered it to the shop. As a precautionary measure, they disassembled it reseated everything. When I brought it home is when I noticed the hum. After bringing it back to the shop, being told it was normal, brought it home and noticed it running warmer than normal and of course the hum was still there. Since I refuse to accept that its operating normally, its back to the shop.
Again with everything I've read, this smells of DC. Even a Torus TOT MAX made no difference. I just ordered an Emotiva CMX-2. I plan to call the shop tomorrow for status.
Anyone care to guess what the problem is?
My guess is; 1- there's a bad connection, 2- a faulty component (transformer), or 3- DC in the line.
There are two issues being discussed in this thread:  the original issue of a transformer hum and hum coming out of speakers.  They are two separate issues.  The transformer hum is mechanical, the speaker hum is electrical.  Hum out of the speakers is caused by one or more ground loops in the system.
Mechanical hum is caused by other issues, typically:  a DC offset in the AC line; electrical noise in the AC line; a poorly designed or implemented transformer; or an old transformer. 
I have three essentially identical amps that are about 25 years old.  The transformers in them did not hum, at least audibly, when they were new.  Now I can hear them from across the room.  Everything I read indicated that since the noise was constant and occurred with no fluorescent lights on and no motors running that it was caused by DC on the AC line.  As it happens, I built these amps at a company I used to own.  I consulted with my ex-partner, the design engineer and he said he doubted there was DC on the line and that the transformers, which are toroidal, were probably just old and the windings had loosened slightly.  I decided to build a DC blocker anyway.  It didn't help.  I tried an isolation transformer.  It didn't help.  I then built a fixture to measure any DC offset on the line.  What do you know, it was zero.
In the end, I moved the amps to the room behind the front listening room wall.  All's quiet on the listening room front.
oldschool1 - I suspect the right transformer in your amp is humming louder because the bias on the right channel is slightly higher.
I had the same problem with an Ayre V3 amp. I first built a DC blocker and that did not help so i removed the transformers that were humming and took them to a motor shop. They were dipped in that special winding varnish and when i reinstalled them they were dead quiet. What happens is that one or more loops of wire loosen up and then the magnetics cause the loose wire to vibrate. By locking them all back together it solves the issue.
have experience with this one.  DC is in your line.  It not only can cause hum from the transformer, it can damage it (AND WARRANTY will not cover it) if you use it like this over time.  Bought a DC filter from EMOTIVA,  around $100 as I recall.  works like a champ!!!
SILENCE.   My humble opinion.  a great product for the money
 I was having the same problem a little while ago where my amp started humming. I tried multiple things without success but later I found that the problem was being caused by a potable heater connected somewhere else in the house.

if you ground is not isolated everything that is connected to the house is picked up by some of your components.

in my case that's all it took to get it fixed.

Hope this helps.


I have a modwright integrated KWI-200 that developed a hum that got louder over time. I finally had to send it to them and they replaced the transformer.
if this is a new problem since you moved, I don't believe in coincidences. 
I explained again that it was loudest when you first power it up then the hum diminishes after a few seconds but is still audible. He wants to keep power applied to it and observe.
Another thing I just remembered and haven't mentioned, since the hum began, it has been running a bit warm even at low listening levels when it was in my system.
Its 100% normal for any toroid to make a bit of noise on startup. This is because the core of the transformer can become magnetized when the unit is turned off. The next time its turned on, the magnetic field causes saturation in the core and the transformer rattles until the magnetic field is degaussed by the alternating current.

The second paragraph above suggests that the bias of the amplifier is high- which could account for the additional mechanical noise.
Picked up my amp today and at the shop it seemed dead quiet however, there's ambient noise in the shop. According to the owner, early in the morning he heard nothing. It was dead quiet. After getting it home I spent the evening re configuring all my wiring taking care no power came in contact with any signal wire. here are my results as I emailed the shop owner:

Hello Morris,
It’s about 10:20 pm and everything sounds great however….
Remember I said that the “hum” could be heard from 10 ft away? Well I just unplugged and powered everything off one thing at a time and here’s my findings; What I can hear from 10 ft away is coming from the speakers. Yes there is a very slight “hum” in the amp and it’s also coming from the speakers. If I disconnected the interconnects from the preamp, no change. Of course since the power is off on the preamp and no signal feeding to the amp. Then I disconnected all the speaker cables and yes there is a “hum” or “buzz” in the amp. It has to be very quiet in the room to hear it.
This “hum” or “buzz” is not only in the amp but sending it through to all 5 channels. this explains why I can hear it from my listening position. I have a surround sound “hum” or “buzz”. So yes, the “hum” or “buzz” is in the amp and the amp also sends this noise to the speakers, all 5 channels. Could it be a bad ground causing this? Again if its the ONLY component with power connected, how could that be? Btw, there is no other electrical device on in the house other than an incandescent lamp for light. I tried powering it straight from the wall, using the Torus TOT MAX, and straight from the wall with a Emotiva CMX-2 Precision AC Line Restoration and Common Mode Filter System without the Torus.
I can only suspect it’s a component in the amp that is defective common to all 5 channels.

Any ideas anyone?
As a last resort, I will send it to Anthem in Canada. Being a current item, they will have all the components to trouble shoot with. It's just expensive to ship from California to Ontario, Canada. May be my last and only option.
oldschool1, I can't remember.  Did you ever try a cheater plug just to see if it eliminates the hum from the speakers?  Not to use permanently, but to narrow your investigation?  In any case good luck in finding the issue.
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I tried a different power cord. If it were a ground issue, wouldn’t running it through a power conditioner such as the Torus correct it? Also, the Torus is plugged into the outlet by the left channel and I tried plugging directly to the outlet by the right channel. And the electrical connection is a two wire AC connection to the power source.