I have unwanted hums/pops/cracks/hiss etc coming from amp. What is causing it?
All amplifiers will have some noise floor. Whether it’s a hiss or low level hum – a perfectly healthy amp is bound to emit some sort of noise when at idle (i.e. when you’re not playing). The amount of noise will vary from model to model and depends on the voicing and design of the amp in question.
High volume settings, high gain settings, and/or bright EQ settings = HISS. No way around it folks; if you opt to play at loud volumes, use gobs of gain, or like to crank the old treble and presence controls til’ your eyes water, your amp will sound like a slowly deflating tractor tire.
If noise goes in, NOISE will come out. If your substandard pedal- board, ancient FX units, or poorly wired/shielded guitar or bass is feeding the amp noise, the same noise will be exponentially amplified by… well…your amplifier. This is also true on the amp’s other end – the AC supply. If the AC supply in your location is poor, or if the outlet you’re connected to is not sufficiently earthed, it can create hum/buzz via the amp’s power supply.
Any amp is susceptible to Radio Frequency Interference. Yep, while we do carefully design our products to minimize the possibility of interference, any amplifier can unfortunately pick up RFI without notice. Needless to say, living/playing in close proximity to radio towers is unfortunately not going to help.
Do you have any general troubleshooting tips to get rid of unwanted noise from my amp?
Regardless of the type of noise you’re encountering, here are a few basic steps that should be addressed:
A defective, cheap, or poorly shielded cable can be susceptible to hum/buzz and interference.
Try another Guitar/Bass.
Earthing – An instrument that is not properly earthed (grounded) will induce hum/buzz and is also susceptible to interference. An instrument that is well earthed, but is still problematic may benefit from having its control cavity lined or painted with shielding. Discuss the possibility and benefits of this with your trusted instrument repair person.
Single Coil Pickups – Single-coils will induce their own 50/60-cycle hum. There’s no way around it. This symptom is characteristic of the single-coil pickup’s design. If your guitar is equipped with three single-coils and a 5-way selector switch, set the switch to position 2 or 4. This creates a hum-canceling effect that eliminates the hum. Not necessarily a problem solver, but another way to qualify whether or not the pickups are the culprit.
Active Pickups – Active pickups require a power source, which in most cases is a 9V battery. When this battery starts to die, it will result in a poor guitar signal and it can even induce distortion.
Disconnect any external FX:
Stompboxes and multi-FX units can be a great addition to any player’s arsenal, but if not functioning properly or inherently noisy, they can be problematic. Also keep in mind that distortion, overdrive, fuzzes, and boosters will tend to exaggerate an amplifier’s noise floor.
Try the amp in another outlet/location altogether:
As mentioned earlier, noise could weasel its way in via the amp’s power supply as well. Try the amp in another AC outlet, another room, or another building to ensure that your AC supply isn’t the culprit.
Turn off any neon/fluorescent lights and dimmer switches:
All three of the aforementioned can induce buzz/hum through the power supply. Eliminate them as variables.
Consider replacing your preamp valves (if applicable):
Microphonic preamp valves can be the cause of all of the initially mentioned symptoms, including popping, crackling, and squealing. If not familiar/comfortable with swapping valves, we suggest having a qualified tech address replacement for you. Should you have replaced the preamp valves with no change, it’s possible that the output valves need replacement (again, if applicable). However as most all-valve Marshall amps require a bias adjustment after output valve replacement, we’d suggest having a tech do this for you as well.
Consider having a technician evaluate your amp:
Should all else fail, the best course would be to have a technician address the problem directly. If the issue is isolated to the amp itself, there could be a number of causes, which would ultimately have to be traced by qualified personnel.