Amplifier hum, ground problem possibly?

Hi, I’ve just joined after realising that this forum does have a section about audio hardware and is not just solely computer based. Googling for audio hardware forums brought this up and it was the only place I recognised and so possibly trusted.

Anyway, I’ve had a hifi amp for over ten years being the Sherwood AX4050. It’s developed this hum for a few years that I’ve just lived with. It happens even as a standalone unit with just the speakers attached (it increases slightly if I put it at full volume). I can reduce it by attaching the amp ground to certain RCA plugs on the back (mainly the one I’m using as the sound input source). It also reduces if I attached the amp ground to one of the speakers itself.

I spoke to a friend last night about it who said it could be an internal grounding issue, unsure how to fix it though. Just wondering if I could possibly fix it myself or it’s more of a power issue? Annoyingly I’m looking at at least £40/£50 repair costs (I’m UK based) which I could spend on a second-hand amp. I can take photos of it if need be and appreciate any help with this. Thanks.

Sounds to me like a power issue, possible issue with the transformator (power supply)
Or other bad components in the power cirquit.
My dad had a similar issue with a Harman Kardon amp in the past.
The humming noises in that were caused by a bad trafo.

it could be a ground issue or simply just a noisy power line.

Might try hooking up the amp on the same circuit as something like a microwave and seeing if it gets worse


Not practical for an amp but IF you have a way of running it on battery power, test it that way.

You can also plug it into a power strip and break off the strip’s ground pin as a temp diagnosis tool

If it has developed over time I would say your power supply input caps need replacing, sounds like the mains hum is not being filtered out.

Unplug all inputs and see if it’s still present, if it is then it’s not a grounding issue as there can not be a ground loop if all inputs are disconnected.

The amplifier chassis should also be grounded but while it acts as a Faraday cage for external noise, it almost never has any effect on low frequencies such as the ~50Hz mains hum, these come from either ground loops or insufficient power supply filtering.

It could also just be that you never noticed the mains hum in your amplifier, it is extremely hard to remove this from power amplifiers and even some of the best amp designs around in the consumer space still have some form of mains hum on the outputs when you crank them up with no input to hide it.


NEVER EVER do this! Wow, I am amazed that some people still suggest this.

The earth ground is for safety, if the device develops a fault even if only for that period while your testing and you touch the chassis you will be electrocuted. There are literally thousands of cases where audio equipment has electrocuted and killed people that have done this.

To properly and safely do this you need a mains isolation transformer.


I had a hum problem with the computer attached to the hi fi system via hdmi, i resolved plugging the amplifier into another plug belonging a different electric circuit in the house.
It didn’ t away completely but now it s almost inaudible ( it took me days to find which component was the origin of the hum/noise

Don t mess around the ground line it s dangerous ( even if some components are without ground… but they are made so by design)

Thanks, mains hum sounds like the most probable cause as plugged into a wall socket with just the speakers attached, it hums. I’m also getting a small buzzing and crackling through one speaker when the amp is turned off (a few seconds after). I’ve tried it with other speakers and it’s still the same, so it must be the amp causing it.

One thing though is that the plug is a two-prong that goes into a three-prong converter and the ground pin is plastic (just like in the image).
I sort of doubt this is the issue though as it’s always been like this.

I’m not that skilled in replacing caps, if it is a power caps issue. I’ll check out videos and prices of caps and see.

As in, “Does it work? Ok, now kill it.”

Really only when we’re talking about amps-
Oh wait… yeah, ok. OP is posting about an amp. Yes, you’re right. Not the best idea. Touché.

No… when talking about anything mains powered that has earth ground. If you disconnect earth ground and a short from mains active to chassis occurs no current will flow to ground and your RCD won’t trip, leaving you with an electrocution hazard.

1 Like

Yeah, so your amplifier doesn’t use earth ground, it is double insulated.

True in that sense but as far as repairing electronics that only pull a few watts it isn’t a big deal if you’re just doing it to diagnose a grounding problem.

It isn’t meant to be permanent; just a quick and dirty diagnostic method.

It’s got nothing to do with how much current the device draws in regular operation. A short from mains active to chassis will dump as much current as possible through you before either killing you or vaporizing the short.

If you’re doing it to diagnose a fault you suspect there is a problem with the mains side of things, since you suspect a problem there you are putting your life in your own hands by pulling the ground pin. It is why all electronic repair agents have a mains isolation transformer (also to lift the ground of a test device like an oscilloscope for safe testing)

What if the fault is intermittent and during the process of moving the device (even small vibrations) around to remove the connection the failed part comes into contact with the chassis. Your quick and dirty test method just killed you.

The proper way to test for a ground loop fault is to disconnect any inputs to the device that have a ground signal path (stereo jacks, RCA connectors, etc). If this is not possible, using a mains isolation transformer to lift the ground of the amplifier (if it has a ground). If the amp is double insulated and pulling all external ground signal paths don’t fix the problem, it’s not a ground loop issue.

1 Like

Yes it’s bad general advice

Plug everything in
Hit the power at strip
Does it hum?
Kill the power on strip

Relax it won’t kill you if you don’t touch it

But again everything you are saying is true
It’s kind of like welding
When you’ve done it a bunch you get lazy and close your eyes for a second instead of dropping the mask

So OP, don’t do that. I take it back.

A ground loop is simply a device that has two paths to use for ground, usually one through the mains earth pin, the other through some connected cable to another device that is also connected to the earth pin.

Lets say you do this, and you have an audio input connected, say another device like an iPod. The iPod has it’s chassis connected to audio ground via the stereo cable, which in turn is usually connected to the ground or chassis of the amplifier. If you have a fault and no path to earth ground, your iPod chassis just jumped up to mains potential.

Untrue, If the device you plug in is double insulated (ie, no path to ground) it’s entire chassis will also jump to mains potental, battery power of not. Even the chassis of a speaker (if metal is present) could be connected to audio ground would become live and could kill you.

People have been killed by the XLR connector on balanced cables when some idiot audio engineer decided to disconnect the path to earth. Just picking up the microphone that is 10-20meters from the amp would kill. People forget that anything plugged into the device, even something as benign as headphones can kill.

A mains isolation transformer only costs around $100, is your life really worth the risk?


lol where i live most houses aren’t even grounded. if ppl were dying from it all the time we wouldn’t be a country anymore. also just being grounded won’t save you from all danger, if we are being a safety tinfoil hat here.

It’s not about being grounded, or the house being grounded, it is about providing a safe return path that will trip a breaker.

You have two classes of devices, 1) grounded, 2 ) double insulated.
Grounded devices are what we are discussing here, devices where there is no double insulation and a potential for a human coming into contact with a live chassis.

Double insulated is where the device is insternally insulated, by means of air gaps, insulation, etc… and the chassis is made of a non conductive material, such as plastic, in which case if a wire did come in contact with the chassis it would not pose a risk.

People are dying all the time, which is why these safety measures were introduced, and in most countries are mandatory. I am sorry that you live in a country with low electrical safety standards, it doesn’t mean you should dismiss the dangers.

An RCD is designed to detect this kind of fault and disconnect the power before anyone is injured. If you compromise the earthing of equipment you compromise the safety of the product, as the RCD will not detect any faults as no current will flow until someone touches it.


you can still get shocked and die even being grounded and having a breaker. RCDs won’t protect you from every potentially lethal shock either. 15 deaths a year statistically is absolutely nothing. if you are rich sure your life is precious and you must enslave to death every poor person from the third world that make everything that you use to guarantee every single detail of your own life is covered and yours only.

inb4 Darwin award.

Yes you can… duh! This is not what this discussion is about. An RCD will trip when it detects earth leakage to ground at about 30-40mA, which is still lethal. The difference is though that it will disconnect the power rather then leaving you stuck on the mains voltage limiting the potential hazzard.

An RCD WILL, 100% of the time, trip if you have an active wire shorted to a ground path, such as the chassis of a device. This is the entire point of this device.

Where the hell did you get this from? All life is precious and should be treated as such. It is a tragedy that third world countries do not implement proper safety. It is people like you that dismiss the problem and allow more deaths to occur. An RCD is a cheap device, and I know for a fact that third world countries have access to them, espesially since most of them are manufactured in such places. If you choose not to use one, you’re an idiot, ignorent or both.

Perhaps this will explain it to you in a way that you can understand:

Also for the record… look up what a 3rd world country is. India one of the largest economic countries in the world is by definition a third world country. It has nothing to do with if the country is rich or poor.

1 Like