|analogic||3/13/2018 3:33 PM|
|Why is my amp humming?|
Hey guys I'm new to the forum.
So I've got an audio amplifier from Cambridge Audio called Azur 340A SE integrated amplifier which has started to produce a humming sound which is very noticable when not listening to anything. It's a budget amplifier that I got new over 7 years ago, and other than the humming it has always, and is still working flawlessly. If I move either the 3.5 mm input cables around, or the speaker cables, I can make the humming sound cancel out almost completely. Also if I touch the chassi of the amplifier the humming gets noticeably reduced. Googling my problem has led me to believe that the problem is due to some capacitor going bad, so I opened it up to take a look but I cannot find leakage or any other sign of component failure. I will add some pictures.
Hope you guys can point me in the right direction!
|The Dude||3/13/2018 3:53 PM|
|Welcome to the place!|
Does the amp hum with no input (nothing plugged into the inputs- not just input turned down)? If it does not, the problem is more likely input connections. Cracked solder on input jacks, corrosion (cleaning), bad cables, etc. If caps were bad, it would hum even with no input.
|bob p||3/13/2018 8:52 PM|
|Are you talking about 60 cycle humming or 120 cycle buzzing? Specifying which one is important as it narrows down where to look.|
|E biddy||3/13/2018 9:22 PM|
|Because it doesn't know the words?|
Sorry, I couldn't help myself.
|Enzo||3/13/2018 9:26 PM|
|E biddy, everyone!!! He'll be here all week. Try the veal.|
|bob p||3/13/2018 9:48 PM|
|I see that you guys from Lansing, Michigan stick together. Hmmm.|
|Mick Bailey||3/14/2018 3:04 AM|
|No.1 reason for hi-fi amps humming is ground loops or other grounding issues. The fact that you can reduce or eliminate the hum by touching the chassis or a low-impedance path to ground (speaker leads) suggests that your problem isn't the capacitors - when these fail you get constant hum regardless.|
Firstly, what is your complete setup with the amp? Secondly, there's often a screw terminal with an earth symbol on the back of the amp. Is this connected? (usually by a flying lead to a similar terminal on connected equipment). Also, is your mains lead in good condition?
|analogic||3/14/2018 5:58 AM|
|Thanks for all the answers guys!|
Could it be that I'm using a very long 3.5 mm cable? It's 5 meters long maybe it is acting like an antenna? But in that case, wouldnt the noise be affected by the volume knob? And why would it be reduced by touching the chassi?
|Mick Bailey||3/14/2018 9:01 AM|
|The screw terminal is not present on your amp. It's there in some amps to provide a separate ground to (say) a record deck.|
To test if you have a ground loop problem try using your setup with a battery-powered device that is not connected to the mains. See if it still hums.
|Jazz P Bass||3/14/2018 10:12 AM|
|If you have another amplifier setup, try using the Record Out to that amp.|
Or the Record Monitor.
|Chuck H||3/14/2018 11:28 AM|
|I'm with Mick. I think it's a ground loop. VERY common in multi amp systems. Since you have no hum with nothing plugged in and the hum level is constant when your computer is plugged in I have to conclude that there is a ground in the power amp of one or both amplifiers that is shared with the input ground of one or both amplifiers. If this is the case, ground lifting one amp may help. Try using an AC ground lift adapter first with the sub. If that doesn't help try it with the 340A, but do not ground lift both because that could leave the only safety ground connection through that long cable to your computer (bad). If ground lifting doesn't fix it the next easiest solution might be to make a custom input cable that is shield isolated on one end.|
|bob p||3/14/2018 1:26 PM|
|Component stereo can be an a$$pain (there go those dollar signs again) when it comes to ground noise.|
Me? I'd do the custom interconnect before I'd ever lift a ground on a piece of AC powered gear. Lifting grounds has safety repercussions and is best avoided.
When you pay for those expensive "directional" HiFi cables, you're getting what Chuck mentioned -- they have the ground lifted at the send side of the cable.
Sometimes you can use a low power rated "fusible link" resistor to elevate chassis ground over earth ground to address ground loops. I'd rather do that than lift the chassis ground entirely. It's just not safe.
|Chuck H||3/14/2018 1:38 PM|
|Absolutely right. I didn't even consider directional cables (because I've never used them). Better. (<period)|
But in the case of ground lifting on "systems" I don't have a problem with it. As long as there is a reasonable shared safety ground. That is, I've done the ground lift thing on a couple of powered sub woofers and interconnecting cable was monsterous enough that I figure :As long as the system is used like this only: there was no danger. Everything is still grounded, that's why there was a loop in the first place. Obviously we can't control if someone changes something and leaves a ground lifted inappropriately. That's not typically the case. Usually these systems get set up for the "entertainment system" and stay just that way.
|bob p||3/14/2018 2:07 PM|
|the devil standing on my shoulder says, "No". |
The problem is that electrical code requires every ground wire to be of sufficient ampacity to carry the full current rating of the circuit in a fault condition. That means that an 18ga AC supply has to have an 18ga ground wire.
The problem comes along when you cheat by lifting grounds. Then your ground is either via a skinny little interconnect, or you don't have a ground at all.
* In the case where you don't have a ground at all, you've got an electrocution hazard if you get a hot chassis.
* In the case where you're relying upon an interconnect to provide ground, you've got the same electrocution hazard if you're using a directional interconnect that has a ground lift built into it.
* In the case where you're relying upon an interconnect to provide ground, if it's of lesser ampacity than the supply wire coming into the AC powered device, then you've got a fire hazard in the event of an electrical fault condition. Those interconnects are likely to burst into flames and start a house fire if they're ever subjected to enough current to pop a fuse.
It's probably a good idea to review the different types of IEC Protection Classes for the appliance when making these sorts of decisions:
There are a lot of older stereo components that were designed as Class 0 devices. They have 2 prong plugs with no ground wire.
Many recent production amps are Class I devices that have the 3 prong plug and an earthed metal chassis. (The photos of the Cambridge Audio amp in the first post clearly show the Class I safety symbol at the chassis ground point near the toroid.)
Devices like turntables may have a Class 0 power cord but a ground terminal on the chassis for optional grounding. These devices are classified as Class 0I because the ground wire is sufficient for hum reduction but not sufficient for electrical safety.
Then there are the Class II devices, like modern power tools, which are double-insulated.
There are safety ramifications that need to be considered if you decide to convert a Class I device to Class 0.
Be careful out there.
|Chuck H||3/14/2018 5:22 PM|
Understand that I like you, Bob. Just enjoying the banter. And I think it's uber important to have someone around that will site stringencies about solder technique and proper safety grounds.
|bob p||3/15/2018 7:11 AM|
|sometimes i just have too much time on my hands. it shows, eh?|
|analogic||3/15/2018 8:00 AM|
|Hello again guys, |
I did some additional testing today, but the mysery continues. Since some of you suspected that the problem was due to the double amp setup (azur 340 + sub), I disconnected to sub completely, no signal input and no power. Unfortunately this did not effect the humming in any way
I also tried connecting a super short 3.5 mm (20 cm) cable to the amplifier, and although this seemed to reduce the ammount of humming a little bit, it was not at all as low as if I previously had tried without any input at all. HOWEVER I did notice something interesting while doing this. In contrast to what I said the other day that the humming goes away almost entierly when disconnecting the 3.5 mm cable, this was not the case today. I still had very noticable humming without any input to the amplifier and with the amplifier ONLY connected to my speakers. The reason for this strange behavior must be that the humming, as I've stated previously, is highly affected by the way the external cables (speaker cables, 3.5 mm cables) are placed on the ground. If I bundle the cables up, I can make the humming cancel out completely. This must be the reason that The noise disapperared the other day when I disconnected the 3.5 mm cable, the other cables must have been placed in such a way to cancel out the humming.
However I'm still interesting in the custom input shield isolated cable, is this something that could help, given the current status of the problem? Could you explain a bit more in detail what it is, and how hard and expensive it it so make it?
Also, do you guys think it is possible that the "noise cancelling" properties of the amplifier are just bad by design, and my amplifier are picking up more noise in the way I have it placed now as compared to before, making the noise more obvious? It was a very cheap amplifier after all.
edit: I noticed that if I run the 5 meter 3.5 mm cable along one wall, as opposed to the other (my amp is placed in the corner of the room) the humming goes from very noticable, to not noticable at all.
|bob p||3/15/2018 8:05 AM|
The 'special' interconnect that we were talking about is nothing complicated. Just a conventional interconnect that has it's shielded cable disconnected from the plug at one end, the end that gets plugged into the audio source.
if you want to assure that your hum is not being coupled to the inputs, unplug all of the inputs and see if the amp still hums.
edit: if your 5 meter 3.5mm cable is an input cable, and it's running along a wall, chances are that it's picking up AC noise from the house wiring in your wall. replace a low quality cable with one that has high quality shielding, and route the cable away from AC power sources. that might help. high end audio uses balanced lines to avoid these kinds of problems.
|analogic||3/15/2018 8:13 AM|
Alright, I will look into this interconnect, however, given the current circumstances, do you think it will help at all?
Since the humming is not really disturbing while listening to music, it's not that big of a deal really.. It just that I have to turn the amplifier off everytime I'm not listening too it because it gets very disturbing after a while. It would be interesting to know whats causing it though.
|bob p||3/15/2018 8:23 AM|
|IME computer soundcards are notorious sources of AC noise, which makes them poorly suited as a hifi signal source. If the noise goes away when you unplug the wire connecting the PC to the amp's input, that gives you an answer. replacing the AC-powered computer/soundcard with a battery powered device would be a good test to perform.|
|analogic||3/15/2018 8:31 AM|
As I said before, the issue does not seem to lie solely in the 3.5 mm cable, it seems more like the humming gets exacerbated by the way all of the connected cables are placed in relation to each other. Moving the connected cables around (3.5mm/speaker cable) either makes the humming worse, or less
|Helmholtz||3/15/2018 10:54 AM|
A ground loop problem cannot be cured by better grounding or electrical shielding. And it can occur even in battery operated amplifiers. It does not even require a mains ground connection (electrical safety ground) as it develops also in pure signal ground loops.
For instance, the 2 stereo input cables of your amplifier form a perfect ground loop: Their shieldings are low impedance and are connected on both ends (to ground), thus forming a short circuit loop. In this special case the humming will disappear, if you remove the cable of one of the channels as this disrupts the loop.
As a cure you may just disconnect the shielding on one side of one of the cables, if tieing the cables together is not enough.
Ground loops can also involve several connected components and their mains leads. This can make things more complicated. Do not remove/open safety ground connections!
1)Try to identify the receiving loop by moving the cables. Minimize loop area. Keep phono leads as short as possible. If its the two phono cables, try as descibed above.
2)Try to identify the AC field source and increase the distance or turn it off.
|Chuck H||3/15/2018 6:59 PM|
|analogic||3/16/2018 2:33 AM|
You solved it!!
I had a power supply for a tv box similar to this
connected to a power strip (same power strip as the main cord of amp is connected to) which was in very close proximity to one of the speaker cables. I disconnected this and the humming immediately stopped. Thinking back, it's very likely the humming started just when I got this new TV box, I just never connected the dots.
Thank you so much for the detailed answer!
Thanks to everyone else as well, great forum!
|Helmholtz||3/16/2018 7:11 AM|
Great that I could help with just my second post.
The result shows that this was just another EMI issue caused by a switched mode PS. Your cables acted as receiving antennas for the magnetic interference field (via ground loops) as well as for the electric interference field (no loop required), both radiated by the PS and its own cables.
BTW, what do you mean by 3.5mm cables? This term is sometimes used for miniature phone plugs of 3.5mm diameter. But the picture of your amp only shows standard RCA/Cinch connectors.