Bass amp humming

possible ground loop?

Concerning NOISE, any higher power system is only as good as its weaker links. Single coil pickups in un-shielded or poorly shielded basses, and preamps and/or amps with low signal-to-noise ratios but lots of potential gain are going to be noisy even when any ground loops are ironed out - especially in any environment with dimmers on lights, computer monitors, neon or florescent starters on the same circuit, etc.

A lot of bass gear actually has rather poor s/n specs and any of these issues compound...

greenboy said:

Concerning NOISE, any higher power system is only as good as its weaker links. Single coil pickups in un-shielded or poorly shielded basses, and preamps and/or amps with low signal-to-noise ratios but lots of potential gain are going to be noisy even when any ground loops are ironed out - especially in any environment with dimmers on lights, computer monitors, neon or florescent starters on the same circuit, etc.

A lot of bass gear actually has rather poor s/n specs and any of these issues compound...

Click to expand...

So what singnal-to-noise ratio is good enough then to avoid hum? Of course higher s/n ratio would be always better, but what would you say that would be good enough e.g. for studio?

A lot of bass rig stuff only has around a 80 dB s/n. I get scared when I see anything less than 100 dB for studio, but a good studio often uses gating or downward noise expansion for problematic tracks - or the age-old method of riding the fader when a track is inactive.

Sometimes two pieces of gear can't be stacked directly on top of each other. Not because of ground loops necessarily, but because of inductance. For example, I installed my Mesa M6 in a rack and installed my DBX 160x compressor directly over it. Disaster, as the transformers in each ended up one directly above the other. Had to swap stuff around, putting the DBX a space higher and that cured it.

dmusic148 said:

Sometimes two pieces of gear can't be stacked directly on top of each other. Not because of ground loops necessarily, but because of inductance. For example, I installed my Mesa M6 in a rack and installed my DBX 160x compressor directly over it. Disaster, as the transformers in each ended up one directly above the other. Had to swap stuff around, putting the DBX a space higher and that cured it.

Click to expand...

that's very good info. i seem to remember having the exact same problem in the studio with racking alot of gear.

as a matter of fact, all of the information in the above replies is accurate should be helpful in isolating hum/noise problems.

Yup. That one drove me nuts before I figured it out.

In my practice space I have every possible noise generating opportunity. My bass is a Fender Jazz American Deluxe, with active SCN pickups and the EQ. The space in my house has the main feed of power to my house running under the floor as it was an addition.

I can rotate left and right and NULL the 60cycle hum completely out, but it is rather loud if I have the amps cranked up.

Also when on my big rig and I have multiple SVT-4PRO's playing I feed them with a Radial JD-7, I'm suprised that an amp collection of all 4PRO's would need ground lift, but every amp after the first requires lift to silence their hum from the loops.

Then you move on to my neck pickup is microphonic, I'm not too happy about that. It's like the whole world gangs up on you sometimes. You have to figure out which situation is causing the problem and cure it.

Twisted pair on XLR is the low noise type input with common mode interference being cancelled in the parallel leads. BUT trust me here, that's great for wire routing that stays away from strong electro magnetic fields and mega noise sources. The ELECTRO GODS expect you to use good practices when wiring up your equipment.

Crossing the I's and Dotting the Tee's... There's a lot more concerns than just eliminating a ground loop when it comes to this audio stuff. BOB