Why is my amp humming?

[analogic]

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!

Thanks

[The Dude]

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]

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]

Because it doesn't know the words?



Sorry, I couldn't help myself.

[Enzo]

E biddy, everyone!!! He'll be here all week. Try the veal.

[bob p]

I see that you guys from Lansing, Michigan stick together. Hmmm.

[Mick Bailey]

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]

Thanks for all the answers guys!

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.

I did some testing this morning. The humming disappears almost completely if I disconnect the 3.5 mm input connection from the amplifier, I can still hear it if I put my ear right up to the speaker but its very faint. I tried cleaning the input connections, and also using different inputs (aux, CD, etc..) but the humming is still there unfortunately. The humming is not affected by turning the volume knob.

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?

Are you talking about 60 cycle humming or 120 cycle buzzing? Specifying which one is important as it narrows down where to look.

It's 60 hz

Because it doesn't know the words?



Sorry, I couldn't help myself.

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?

From the amp I have two speakers connected, each speaker is connected in parallell to the high level input of a subwoofer(xtz w10.16) which has a 300w amplifier integrated in the subwoofer. The only input to the amplifier is a 5 meter long 3.5 mm cable connected to my computer. My mains lead are in good condition. I'm not sure what you mean by the screw terminal, I will post a picture of what the back of the amp looks like.

[Mick Bailey]

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]

If you have another amplifier setup, try using the Record Out to that amp.
Or the Record Monitor.

Cambridge-Azur-340A-int-sm.pdf

[Chuck H]

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]

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]

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]

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:

http://en.wikipedia.org/wiki/Appliance_classes

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]

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.

And if I were a professional installer that would be paramount. I'm not. And sometimes someone just needs their system to work. See below for other points on this matter.

* In the case where you don't have a ground at all, you've got an electrocution hazard if you get a hot chassis.

Ah! But there is a ground. Otherwise there wouldn't have been a ground loop. Therefor, in my outlined scenario "no ground at all" is impossible

* 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.

Also moot! If you were using a directional interconnect there would be no ground loop to fault with an AC adapter.

* 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.

As I mentioned, this was done where an ample interconnect was used. Though I fully agree that if only a skinny radio shack cable were employed it could be bad in the event of a failure. But I seriously doubt the potential for melted cables prior to a fuse blowing with anything other than the smallest, cheapest interconnection.

It's probably a good idea to review the different types of IEC Protection Classes for the appliance when making these sorts of decisions:

Or, since I'm not legally bound or shy about what I can personally observe as an acceptable condition I can just help my friend to get his entertainment system to stop humming

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.