Loud buzzing sound origin

[elgatoguiri]

Hi,


I've got a bass amplifier that has a fairly loud buzzing sound. I currently live in a fairly old house where there weren't earth in every socket so I thought the buzzing came from the lack of grounding. I installed ground wires to all the sockets and the buzzing sort of stopped or at least reduced.


A couple of weeks ago I noticed the buzzing to be louder again and I also noticed that if I put my hand on the amplifier the buzzing ceased or at least reduced. After some fiddling I also noticed that if I bend the ac cord into a loop the buzzing got reduced too. I thought this is because of a bad ac cable so I replaced the ac cable with another one.


The buzzing didn't stop but I noticed that if I maintain a certain size of loop on the ac cable the buzz cease to exist.

So the problem is actually solved but I'd like to know why is this happening and if there is more elegant solution to it then looping the cable?
Thanks!

 

[Pano]

Is it a bass guitar amp? If so, we will move it to the appropriate forum so you can get help.

 

[elgatoguiri]

Yes it is a bass guitar amp.


Thanks for placing it to the right section! I wasn't really sure where to put it.

 

[richie00boy]

Can you try a power cable with ferrite block on (not looped)? I wonder if you have some high frequency rubbish on your mains and its upsetting the transformer in the amp. The loop may be adding a little bit of inductance which is enough to kill the HF.

 

[elgatoguiri]

I put on 6 ferrite beds but nothing changed. The buzzing still continues but I've found out that it doesn't need to be looped. As it is a bass amplifier it has a carrying handle on top. If the cable runs under this handle the buzzing also stops. It's worth to mention that if I simply place my palm on top of the amplifier (where the handle is) the buzzing gets somewhat reduced too.

 

[Sangram]

Moved to Instruments and Amps

 

[JMFahey]

Try to shield amp top.
Remove chassis from cabibnet, glue a sheet of kitchen grade aluminum foil to top, make a small ball of aluminum paper, wrap a couple turns exposed copper wire around it and staple/tack it to foil, the reason being you can´t solder aluminum, solder other end of wire to amp ground.
That top grounded shield will do your hand´s work 100 times better

 

[elgatoguiri]

Ok, thanks I'll try that!

Anyway if someone doesn't mind explaining I would be interested of what exactly is causing the trouble or just giving me some directions so I can look it up.Or if this is because of a failing part I can simply replace it.

 

[diyMartin]

A reason why you may see several suggestions, but no hard "this is the problem" is that unless somebody have encountered the same issue with a similar (if not the same) product, it will be troubleshooting by remote.
There are likely a lot of different root causes for the problem you describe (RF / microwave interference, too-low voltage from the power grid, corroded/broken connections, somebody tinkering with an unclosed computer nearby, power supply components starting fail etc etc).
Based on your description of the problem, the suggestions seems to focus on the idea that you are suffering from some kind of interference - but without being present at your site with the proper measuring equipment the troubleshooting is hard to perform without asking you questions/comming up with suggestions for tests.
So unfortunately there is no direct route


Best regards
Martin

 

[Mark Tillotson]

First start by saying what the amp is, how old it is.