60 Cycle Hum

Spinner · #1 01-08-2007, 01:52 PM

60 Cycle hum ... is it more a problem with passive instruments picking up noise or can it also be a feature of active basses? Yes, I realise that a decent shielding job can reduce the hum, but just wondering if the onboard pre-amp means its less of a problem in the first place.

Spinner

PilbaraBass · #2 01-08-2007, 05:20 PM

60 cycle hum can enter a signal chain ANYWHERE...

this particular culprit does not really enter through the bass and the lead (that's where EMF comes in), but rather through things like mains-powered preamps and effects, active DI's, and amplifier rigs themselves.

AC - DC power supplies are usually designed to cope with filtering 60 cycles quite well, but when the AC power has high harmonic content (particularly the 180Hz 3rd harmonic), that's when you can get really noisy situations, because the capacitive filters are not designed to cope with it.

To reduce noise from LMI (low frequency Magnetic interference), it is always a good idea to employ good shielding and earthing techniques on your bass' electronics. Hum-bucking pickups are also sometimes necessary. And yes, active systems WILL be a bit less sensitive to LMI (aka RMF) as passive instruments.

Also, when you can, always use balanced signal leads. especially when connecting between two or more mains-powered pieces of gear (like your amp and the front-of-house system)

Spinner · #3 01-09-2007, 12:45 PM

Thanks for the thorough response ..... I understood most of it

Spinner

Blapto · #4 01-09-2007, 01:18 PM

It's also more of a problem in certain situations.
At Bass Central in Florida, it was pretty bad.
Now, back home, same bass (wheee!) it's non existent.
Obviously, different amp, and 50Hz instead of 60Hz.

PilbaraBass · #5 01-09-2007, 03:32 PM

Quote:

Originally Posted by Blapto

It's also more of a problem in certain situations.
At Bass Central in Florida, it was pretty bad.
Now, back home, same bass (wheee!) it's non existent.
Obviously, different amp, and 50Hz instead of 60Hz.

for the record "60-cycle hum" ... is just another name for "mains hum" and whether you're on a 50Hz grid or a 60Hz grid, doesn't matter, same problems exist...just different frequencies ...

Blapto · #6 01-09-2007, 04:04 PM

I do realise that, was just covering all the bases. Basses...

Rattman · #7 01-09-2007, 04:15 PM

Quote:

Originally Posted by PilbaraBass

for the record "60-cycle hum" ... is just another name for "mains hum" and whether you're on a 50Hz grid or a 60Hz grid, doesn't matter, same problems exist...just different frequencies ...

We have this same issue BAD with our house system. Seems that without lifting the grounds on ALL the equipment on-stage, the 60-cycle hum comes thru the mains quite badly. As a direct result of this dangerous "solution", I've been shocked quite painfully twice in the last two weeks, This occurs when patching and unpatching the effects pedal into the monitor 'sub board' which also has a lifted ground. Man that hurts!

We obviously have a major problem with our PA/house power. I believe the sound engineer is calling this a "ground loop" issue. I just know I hate getting shocked. Good thing I don't need a mic, or I'd be getting zapped all the time.

PilbaraBass · #8 01-09-2007, 04:52 PM

Quote:

Originally Posted by Rattman

We have this same issue BAD with our house system. Seems that without lifting the grounds on ALL the equipment on-stage, the 60-cycle hum comes thru the mains quite badly. As a direct result of this dangerous "solution", I've been shocked quite painfully twice in the last two weeks, This occurs when patching and unpatching the effects pedal into the monitor 'sub board' which also has a lifted ground. Man that hurts!

We obviously have a major problem with our PA/house power. I believe the sound engineer is calling this a "ground loop" issue. I just know I hate getting shocked. Good thing I don't need a mic, or I'd be getting zapped all the time.

let's be clear here...getting shocked should NOT happen!!!...
never put yourself in a situation where this can occur...
grounds are there for a reason, that is to prevent stray voltages from building up where your body can come in contact with them...
by compromising a mains grounding system, you can open yourself up to being electrocuted! electrocution = DEATH

ground lifting should ONLY occur on signal levels, NOT on power levels

If you're having that much problem with your house PA and mains, arrange for a competent, and licensed electrician to check the system out.

Please....PLEASE...before someone gets seriously hurt.