Curing my amp's noise and hum

I’m by no means knowledgeable on amps and gear but thought I’d share in case there others out there like me for whom this may be helpful.

Recently I moved my amp which has been largely standing silent for a couple of years to another space in the house and have begun to make more regular use of it.

First challenge was a knob that you use to select the amp voicing. It misbehaved terribly. At the same time the master volume when turned up just a little was crackling and scratchy.

Treatment proved to be simple. Gently work the knobs off. No set screws on this amp’s knobs. I am lucky enough to have my wife’s grinder in the garage which I used to smooth and thin the end of an old bottle opener. That made a perfect tool to get in under the knob to aid as a lever to lift off the knob. Worked it slowly all around the knob to ease it off straight, avoiding risk of bending the pots shaft. Then sprayed and worked in liberal doses of electrical contact cleaner.

That fixed the voice selection knob, removed the master volume scratchiness. But I was left with a nasty hum if turning the master volume more than a quarter turn.

I’d seen YT videos in which the person had taken the back of the amp off to get better access to the pots to apply the cleaner. I’d decided to try that. That didn’t work as there was a PCB covering all the pots and I was not about to try and disassemble that.

But when taking the back off I noticed that there were three wires running from the socket that you plug the power chord into. The power cord plugs into a kettle cord socket, the same as what typically plugs into a PC power supply. The supplied power cord has a two pin plug on the end of it. I assume what is missing is the earth wire and maybe this lack of connecting the amp power supply to the grounding in the wall socket contributed to the hum? Lucky again, I found an old PC kettle chord, plugged that in, and the hum is gone.

If you are experiencing the same and have a power cord with a two pin plug on it, perhaps give this a try.

Makes me wonder why the amp wasn’t supplied with a proper power cord with a three pin plug?

But maybe I’ve done something real dumb here and somebody smarter will point that out and direct me back to my hum-inducing two pin power cord.

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Not had this issue on any of my amps but glad you got it fixed. The explanation sounds logical but even if it didn’t, the problems been solved ! :sunglasses:

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You’ve simply made sure your amp is grounded, which is not a dumb thing (in fact, it’s the opposite :slight_smile: )

As for why they provided a two pin power chord - hard to say if it’s the same where you’re at, but I recently learned that there is much confusion regarding standards on these types of chords. In Denmark we use 3 male pins for grounded power sockets, but in France (for example) they use two male and one female. Yet another standard has the ground connection on the side of the plug.

This is what would fit a Danish grounded wall outlet:

This is what’s typically included with gear:


Note that this type of chord IS actually a grounded 3 wire power chord, despite being a two-pin cable.

I recently went over all of my power connections in my home studio and made sure everything was grounded correctly, and it helped with humm (and safety) a lot.

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Good detective work!

I had to google what type of power connectors you use in SA.

Here, in the UK, all our plugs are 3 pin. That doesn’t, necessarily, mean that the earth wire is used as it’s sometimes made of plastic. But in those cases, the connector into the device is a 2-pin connector. If the connect is a 3-pin “kettle plug” (an IEC C13 connector) then the cable is always earthed.

If the amp is earthed in that way internally, then it really should have an earthed cabled connected.

I don’t know about SA electrical regulations, but here in the UK, devices are either earthed, or “double insulated” which means they have a second layer of electrical insulation between the internal electrics and the outer case. These will, normally, have a symbol like this on them:

Are you sure you are using the cable that was supplied with the amp?

Personally, I couldn’t tell you if the cable that came with my amp is the one I’m using. I have, literally, dozens of those cables all over the place. I have a 19 lt box in my garage which is absolutely full of them!



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Thanks for the replies, guys; much appreciated.

My amp came with a power cord that looks like the second picture that Kasper embedded. I replaced it with one that looks like the first picture.

I can’t shed any light on SA electrical regulations. That’s beyond me.

And as I said, sounds better now.

Good to know I haven’t done anything silly or dangerous.

Well, there you go. It all makes perfect sense then :slight_smile:

Seems like you have the same, or very similar, cables and wall sockets as we do here. In many cases the easiest is perhaps to replace the entire cable - as you did - but if that’s not an option you might be able to buy adapters that converts from “picture 2” to “picture 1” standards. I bought a handful of such adapters…

Is this because they are providing a French power cable?

Yes, but that would only work as a grounded connection in France and other countries that use this wiring system. I don’t think that’s the same issue in SA.

Some research suggests there are multiple types of connector in SA, but the main, official, type is “type N”:

This can work with grounded (3 pin) or ungrounded (2 pin) cables, which are also known as “type C”.

Unless the cable that was shipped was for another, similar, country, then there appears to be no equivalent to the French grounding system. So, in every case where there is a ground, this is a 3rd “male” pin on the plug. There is no case where the ground is a “female” connection on the plug as there is with the French/Danish case.

To me this seems to be the case that the SA regulations must be a bit lax in this area, allowing them to ship a cable which only has 2 wires/connectors. In this case an adaptor wouldn’t help.

In the UK I believe it would be illegal to ship a 3 pin IEC C13 cable which wasn’t grounded.



Actually the correct term for the cable/plug that I mentioned usually comes with gear is a “Schuko plug”. I guess it’s some sort of attempt of an EU standard that can fit multiple types of wall sockets.

AFAIK only France uses that strange male pin in the wall socket, other countries uses those two side connections. The adapter I posted an image of can be bought/used in Denmark, but my guess is that they went for the male pin on that one because it might offer a more secure connection?!? Who knows :wink:

All in all, quite confusing (I think).

Never saw any plugs looking like those you posted images of, perhaps David will recognize them from SA :slight_smile:

Ah, yes, the Shucko plug.

I think the one you have is known as a Hybrid CEE 7/7 plug as it has the hole to accept the ground pin on the French style CEE 7/5 sockets, and the external contacts to accept the grounding terminals on Schuko type sockets.

The Danish standard seems to be a little fragmented in that it will accept various other standards, but in a way that could leave equipment that should be grounded, ungrounded.



Yes, all of that is exactly right.

And tbh I never gave it much thought… until I had a severe case of ground loop noise in my setup that was driving me absolutely crazy. Spent probably a full day researching these standards, the cause of 60hz humm, ground loops, electrical noise (when connecting some equipment to computer) etc etc. Frustrating time to spend, would much rather play, but in the end I managed to get it (pretty much) under control :wink:

Yes, I can understand that.

Electrical sockets and standards can be a minefield, especially when dealing with different countries.

We are lucky in the UK: we have a very robust set of standards which are extremely safe and only one type of socket and plug (for practical purposes) which always has 3 pins, and very strict standards on how cables are wired, which means we would never get into the “wrong cable/connector” situation that either you or David did.

That doesn’t mean we don’t have grounding issues: my Spark 40 amp was supplied with an ungrounded power supply. It was perfectly legally wired (the PSU was double insulated and had the correct 2-pin IEC C7 connector), but it introduced loads of hum to the amp. I replaced it with a grounded PSU (with a 3-pin IEC C5 connector) and it cured the hum.




I had wondered what the hole in the 2 pin plug was for. I’ve never seen an adapter like the picture Kasper shared. That would sort things out

Also never seen anything like the picture Keith shared.

We use either 3 pin plug that looks similar to the one in Kasper’s first picture. Or a 2 pin plug, typically on mobile phone chargers and similar power adapters.

And every now and then the plug that looks like Kasper’s second picture, like my among power cord. But that’s not common. If I have to guess, probably linked to country of manufacture.

Thanks again for setting my mind at ease.

Hi guys, interesting read. I have the same problem but I’ve got a 3 pin plug for my amp. And the hum is not that loud but gets louder when I run the signal through my pedal board. Probably a topic on its own but is there a “rookie mistake” that can be fixed easily with the pedal board? I use good quality connectors and have enough power to supply my pedals. The only cable I am not sure (quality wise) is the main guitar cable going from guitar to pedal board resp. end of pedal board to amp. Could an investment in a more expensive cable be a solution?

In that case, you probably have “Type M”:

These look similar to the ones posted by @Kasper simply because they use round pins and a similar layout, but aren’t the same and aren’t, at all, compatible.



The only thing that seems to universally help is to use a power supply with isolated outputs. If you use a non-isolated supply or, worse still, daisy-chain the power, this can introduce hum.

Almost certainly not.

Cable can be, in many ways, a complex topic, but the basic manufacturing of good cable is well understood. Expensive cable uses the same materials as cheaper cables (at least for the parts that actually matter) and costs about the same to manufacture.

When you pay for expensive cable you are mostly paying for branding and marketing.

Of course, very cheap cable may not be up to spec or may be poorly manufactured so that it breaks easily. But you don’t need to pay more than £15-20 for a 2 metre instrument cable to get a good quality, pretty rugged one.

For patch cables for pedal boards, I wouldn’t pay more than around £5-10 for off-the shelf, made up pedalboard cables.

I would (and have) pay more for a cabling kit, like the Evidence Audio kits, but what you are paying for here is not really the quality, but the convenience, flexibility and ease of use (and, to a degree, the easy maintenance).



Besides what Majik said about using a power supply with isolated outputs (and never “daisy chain” many pedals from the same power supply) it’s also important to understand that not all noise/hum is caused by the same thing.

So far in this thread we’ve discussed electrical noise and ground loops. But another type of noise is what you get from using compressor pedals or distortion/overdrive pedals. Those are effectively raising the “noise floor” of the guitar signal, and grounding won’t fix that. For that kind of noise you need a noise gate pedal (or you can ignore it, some people consider a bit of noise a natural part of a rock guitar tone). Personally I’m in the noise gate camp… especially when playing live gigs or recording.

A good a quite cheap noise gate pedal could be a TC Electronics “Sentry” pedal… and I’m sure there are many more good ones :slight_smile:

@Kasper @Majik thanks for your inputs. I will try some things to see what works and what not.

Looks and sounds right, Keith, based on research doe in years gone by before travelling internationally.