Electronics/Amp Experts: I could user your help

Melvin7822 · #1 04-06-2011, 03:46 PM

I feel stupid for asking this, but at least I'll learn something. It appears that I'm getting some good 'ole 60 cycle hum from my amp. However, I swear that all the testing I've done proves that it's not.

Allow me to explain. Originally, I swore up and down that my bass was causing it. To verify, I unplugged the cable from the amp with the volume turned up, dead silent. My second test was to plug the cable from my pedal board to the amp, again dead silent. Plug the bass in; hum. I had tried different cables and even a ground lift. My apartment was built in 2009 by the way, so the wiring is pretty much brand new. When testing I was not near any fluorescent lights or my computer.

Well, I sent the bass off for a warranty repair and they said the bass was dead silent. So now, I'm only slightly baffled.

I just received a new bass today that I also heard hum through the amp. So my concern is, is it possible that the amp has a problem? And if so, why is only when a bass is plugged in?

BassmanPaul · #2 04-06-2011, 04:25 PM

Did you use the same signal cable?

RickenBoogie · #3 04-06-2011, 05:30 PM

+1 the cable/ use a good solid instrument cable.

Melvin7822 · #4 04-06-2011, 06:14 PM

That would be a good thought, but I did check with two different cables and even tried a ground lift with the amp.

Sundogue · #5 04-06-2011, 08:04 PM

Have you tried a wireless?

Your bass (or any bass for that matter) through that amp, in THAT location, may be acting as an antenna. You might be picking up something with any bass you plug in.

Have you tried that amp somewhere else (like across town or out in the country, on a gig, at a friends' place, etc.)?

I once had an amp that picked up a French Canadian radio station that depending on how I stood, either sounded like static, or came in clear. But only at my friend's house and nowhere else.

billfitzmaurice · #6 04-06-2011, 08:11 PM

If you only get hum with the bass plugged in the bass is the source. Actives or passives? Does the hum level change when you touch the bridge and/or strings?

Melvin7822 · #7 04-06-2011, 08:54 PM

Quote:

Originally Posted by billfitzmaurice

If you only get hum with the bass plugged in the bass is the source. Actives or passives? Does the hum level change when you touch the bridge and/or strings?

Bill,
That's why I felt dumb asking the question in the first place, because I know better. They're both active Music Man basses. I had sent my Big Al off to SLO to have it looked at confident that I had narrowed it down to the bass, but I received a call today stating that they couldn't find anything wrong. They tried it with several amps and it was dead silent.

Maybe both of my cables are bogus. Who knows? But for all intensive purposes I can rule out the amp since it's dead silent without anything plugged into right?

fdeck · #8 04-06-2011, 09:50 PM

Long shot, but the amp could have an input jack that grounds itself when nothing is plugged in... and a broken ground connection on the sleeve terminal of the jack.

UncleFluffy · #9 04-06-2011, 09:52 PM

Have you tried your bass with someone else's amp and your amp with someone else's bass?

edit: I just read the last paragraph again, so you did. As fdeck said, there might be something to do with the input jack (try cable without bass to test that) or even a noise gate. What model of amp is it?

Melvin7822 · #10 04-06-2011, 11:03 PM

Quote:

Originally Posted by fdeck

Long shot, but the amp could have an input jack that grounds itself when nothing is plugged in... and a broken ground connection on the sleeve terminal of the jack.

Now that's the idea I was looking for. I can at least verify that the jack is good now. Given that it's mounted to a PCB, it still doesn't take the amp out of the running.

As you can see from the above picture, it's not my favorite type of jack but there are two terminals of which I successfully tested continuity for both the tip and the sleeve of the cable I plugged into the jack.

So now the probability is more like 2% amp, 40% cable, and 58% the bass.

lunarpollen · #11 04-06-2011, 11:13 PM

I would get horrible hum no matter what instrument I plugged in to what amp at my previous home. Something in the house wiring was causing it, I think. The hum would go away if I aligned the instrument to the polarity of an electromagnetic field, the angle of which changed depending on where you would stand in the room or the house. Nothing would cure it, it was just a fact of life. Have you tried bringing your bass and amp to other locations, like a studio or a friend's house?

Melvin7822 · #12 04-06-2011, 11:35 PM

Quote:

Originally Posted by lunarpollen

I would get horrible hum no matter what instrument I plugged in to what amp at my previous home. Something in the house wiring was causing it, I think. The hum would go away if I aligned the instrument to the polarity of an electromagnetic field, the angle of which changed depending on where you would stand in the room or the house. Nothing would cure it, it was just a fact of life. Have you tried bringing your bass and amp to other locations, like a studio or a friend's house?

I wish that's what it was. My apartment is actually brand new. The complex was started in 2009, but my apartment was built in 2010. It would hard to believe the wiring is bad, but not impossible.

I've only had the amp in two locations: home and rehearsal. In both places it's the same. I suppose I'll have to wait till I use it somewhere else to confirm.

Downunderwonder · #13 04-06-2011, 11:37 PM

What are the chances any cable acts as an aerial when the circuit is completed with any bass pickup? Pretty damn good.

A big +1 to moving the whole lot to a different location.

Edit, duh, need to get to the real end before replying

JimmyM · #14 04-06-2011, 11:52 PM

Quote:

Originally Posted by Melvin7822

I wish that's what it was. My apartment is actually brand new. The complex was started in 2009, but my apartment was built in 2010. It would hard to believe the wiring is bad, but not impossible.

I've only had the amp in two locations: home and rehearsal. In both places it's the same. I suppose I'll have to wait till I use it somewhere else to confirm.

can you move around and make it go away?

Melvin7822 · #15 04-07-2011, 12:24 AM

Quote:

Originally Posted by JimmyM

can you move around and make it go away?

Yes.

JimmyM · #16 04-07-2011, 03:22 AM

then it's interference from something nearby and not a problem with the bass.

IPYF · #17 04-07-2011, 03:40 AM

I get hum through my fender deville in my house. It's because of the houses electrical wiring and not the amp. Might be a consideration. I take the amp to my rehearsal studio and its silent as the grave.

Maybe you could try a Furman power conditioner or something.

BogeyBass · #18 04-07-2011, 03:56 AM

well if you move around and it goes away...then the bass is just picking up electromagnetic interference from one of many household goodies....like computer monitor, florescent light, light dimmers, fan controller, wireless router...so on and so on....

humbuckers can help but their are not completely noise proof, old school crt monitors are the worst...it drives me crazy when recording at home....huuuuuuuuuuummmmmmmmmmm

GrowlerBox · #19 04-07-2011, 04:13 AM

Quote:

Originally Posted by IPYF

Maybe you could try a Furman power conditioner or something.

Won't do anything. Even if it did, you'd have to run your whole apartment building through it.

Melvin7822 · #20 04-07-2011, 08:38 AM

Quote:

Originally Posted by BogeyBass

well if you move around and it goes away...then the bass is just picking up electromagnetic interference from one of many household goodies....like computer monitor, florescent light, light dimmers, fan controller, wireless router...so on and so on....

humbuckers can help but their are not completely noise proof, old school crt monitors are the worst...it drives me crazy when recording at home....huuuuuuuuuuummmmmmmmmmm

I guess I must've missed something then. Although, I don't know what. The rehearsal space is plagued with fluorescent lighting so I'll just never win there.