Humming noise when guitar is turned up - Music

sounds like bad caps and maybe a failing output transistors. Use Deoxit contact cleaner too.

If it's humming when something is plugged into the input, but not when nothing is plugged in, it's most likely the cable. If it hums when nothing is plugged in, the amp is defective and you need to return/exchange it.

Something is not grounded properly, or it is picking up an unshielded source like a light fixture. Read this

http://www.prosoundweb.com/article/eliminating_troublesom_hum_buzz_created_by_electric_guitars/

try plugging into a different socket if that doesnt solve problem you may need to replace cord. sounds like a loose neutral in socket though.

If the humming ONLY happens when a cable is plugged into the amp, the problem is in the cable or the guitar. Poor quality cables or wrong cables will result in hum. Defective wiring or connectors in the guitar OR having the guitar near a source of magnetic fields will result in hum. We cannot diagnose these possibilities remotely.

Hi,

This would only mean two things:
1. you have a bad capacitor in the circuit or the grounding on the circuit is broken and not filtering the obvious line noise from the circuit.

2. You have what is called, dirty power. That is when you have some kind of electrical device plugged that generates line noise which can be even a florescent light as they generate line noise.

Please take the following steps to narrow down the issue.

Take your setup and plug it in some where you know others can setup their rigs and it is using clean power. If, the humming goes away then it is dirty power where you originally setup.

If, it is still humming then you will need to take your equipment to a qualified marshall dealer have them look at it.

All amplifiers make a little bit of noise (hiss) but it is normally slight and drowned out by playing. However, assuming that this is not normal system hiss, here are a few simple steps to try and locate the source of the problem by process of elimination.

1. SAFETY FIRST - a common cause of a humming or buzzing sound can be a lack of earth (grounding) on the mains supply. With a 240volt AC supply this hum will be at 50hz (in the UK) - frequency may vary in other countries but should be similar. Check the earth first because of risk of electric shock. Until you are satisfied that this is not the cause of the problem DO NOT touch any metal parts of the amp. Remove the mains lead and try a different one. Try plugging the amp into a different mains outlet socket (preferably one on a completely different circuit).
2. Turn off other electrical equipment in the vicinity that may be causing interference. Move the amp a bit, try rotating it by 90 degrees to change relationship to things like mains electric cables in the floor.
3. If you are using the line-out socket to give a feed to a mixer, slave amp or p.a. system unplug this. Sometimes double earthing (through the mains lead of your amp AND the mains lead of the MIXER / PA) will cause an 'earth loop' due to a different resistance at each end. Putting a DI box with an 'earth lift' in between may eliminate this problem. Alternatively there are little gadgets you can buy to do this (I found one intended for car audio systems on Amazon that works very well)
4. Unplug any instrument leads - to eliminate possibilities of interference affecting cables, effects pedals or guitar pick-ups. Also unplug the foot-switch.
5. If that stops it plug a lead in without a guitar on the other end - does the noise return? If yes change the lead. If no plug the guitar in.
6. Try moving the guitar in relation to the amp (turn it around 90 or 180 degrees) - this will be pick-up to amp power supply interference.
7. Does the sound get better or worse if you touch metal parts of the guitar with your hand? This may be a screening issue within the lead or the guitar itself.
8. Try turning all the individual channel tone and gain controls to zero, turn off any effects on the amp panel. If that eliminates it only turn up the controls on channels that you are actually using.

If most of the humming goes away when you unplug the cable from it, the amp is OK and it may be either a poor guitar cable or more likely hum pickup by the pickups on the guitar. If you move the guitar around and near the amp you likely will notice incread hum from the magnetic fields from the amp or other devices as well.

I would also be inclined to check all the larger electrolytic capacitors in the power circuits as well for AC bleed.

You may have a switch with 2 settings somewhere on your amp - one for active and one for passive. try changing that.

If this doesn't work, make sure you got the guitar in the line input, change the lead for another incase it's faulty, turn the volume up on the guitar to activate the pickups, and rock-out when you find the problem and fix it.