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Amp humming?

DrGroovenstein

DrGroovenstein

Apr 6, 2000
4,755
705
Livin' in the USA
#1
I picked up a new-to-me-bass, and I noticed some nasty humming going on. I did some experiements, moved to a new outlet, used different basses and I determined a few things.

1.) The bass was humming.

2.) The amp was humming too! The closer I get to the amp, and especially if I face the amp, it starts buzzing and humming, pretty loud too. The further away I get, it goes away or at least it is soft enough where I can't hear it at that distance.

It's an EBS HD-350. This isn't normal right? Time to send the amp for repairs?? Any ideas on what I might be able to check myself?
 
#5
I got the same problem with my warwick tubepath head, It still works fine whilst playing. I play a warwick fna jazzmann which has noisy electronics anyway but i do get it with other basses. I think it could interference with other electrical products in my room as I Don't notice it as much in church or at gigs!
 
#6
It's most likely that your pickups are picking up the hum, and there might not be a lot you can do except keep away from magnetic hum fields, like around your amp. Shielding the bass cavities could help against electrostatic hum fields.
 
#8
+1 to it coming from the bass.

Also, IMHO it's not a safe assumption that, just because it's a top quality bass like an MTD, it's shielding couldn't be improved upon.

My MTD's and Roscoe will hum kinda' bad in some venues. They're shielded well enough for most environments, but not as well as they could be ultimately. My Zons are the best shielded. I can go into rather rude environments and not get much hum... even tho both are single-coil pickup systems, outside a very tolerable level of SC hum (which is I hav a VERY low tolerance for), it's not bad at all.
 
#10
steve4765630 said:
Many times it can be a grounding issue. If the amp has a Ground Lift on it, try it both ways and see if way is better than the other.
Click to expand...

Isn't the ground lift only for the DI?

vic said:
+1 to it coming from the bass.
Click to expand...

Could be. I've noticed noisy instruments at my house a few other times. I'll give it a try at my gig tonight, it's my old amp. I'm praying it does not die!
 
#11
Sean Baumann said:
Isn't the ground lift only for the DI?
Click to expand...
Yes, and that won't do you any good. It's not an earth grounding problem, or it wouldn't be directional related. If you want proof, put a 3-2 adapter on the amp plug and DON'T connect the wire to the screw in the wall plage (thus manually lifting ground). Should be no diff.

Could be. I've noticed noisy instruments at my house a few other times. I'll give it a try at my gig tonight, it's my old amp. I'm praying it does not die!
Click to expand...
Yep, especially when my wife turns on the dining room light upstairs, which is on a dimmer... even when not in a "dimmed" setting. Notice it immediatlely downstairs. Argh! :)

Also, while changing amps SHOULDN'T make it go away, depending on the amp's voicing, it might be a LOT quieter, because it's at a very specific frequency. EBS' tend to accentuate this kind of hum a bit just because they're so bright on the ultra high end, which of course is just part of their classic sound, so not much you can do about it other than fix the "real" problem.

Also, just bring the EBS along. It's light. That way, you have a backup if you need it, and an A/B test if you want it.
 
#12
Reality check:

The pickups on an electric bass pick up changing magnetic fields, that's how they get a signal from the strings.

Lots of things, like amp power transformers, have an external magnetic field that is line frequency, i.e. 50 or 60 Hz, hum frequency. Some types have less than others.

Most shielding won't do anything much about magnetic fields. They are hard to shield against, and if you succeed, you may have a problem picking up the strings...... so transformer hum can get right in, the pickup can pick that up too.

That is what "humbucking" pickups are for..... to cancel out external magnetic fields, while allowing nearby ones to get through. Not the same as shielding, it is a phase cancellation due to clever winding and shaping of the pickup.

Buzzing and humming when you get close to the amp just about HAS to have something to do with the transformer.... its hum field being picked up by the pickups in the bass.

I very much doubt there is any actual defect.

Probably not worth checking with a tech. *Theoretically* a transformer mis-connection *could* cause more than usual hum, but it is very unlikely.

I doubt if its shielding, but naturally it *could* be....... may as well check, which you seem to have done.

I doubt it has to do with grounding either, but you may as well check on that.

Poor shielding usually means it will hum unless you are touching the strings.
 
#13
Jerrold Tiers said:
Reality check:
Click to expand...
Ok, the thing about the sheilding is more about blocking stuff except the part facing the strings, so you get less ambient junk.

Yeah, you can't block the part that needs to be open to the strings, but I found a huge improvement in my J bass... which also has humbuckers... in some really nasty environments where it even got hum (which also happened with my other humbucking basses.) I think the idea is to block all the wiring from being antennae, and it seems to really work for me.

Also, I thought buzzes that go away when you touch the strings are an instrument grounding problem, because your body creates sort of a false ground? In other words, time to rewire to a star config inside the bass?
 
#14
Vic said:
Ok, the thing about the sheilding is more about blocking stuff except the part facing the strings, so you get less ambient junk.

Yeah, you can't block the part that needs to be open to the strings, but I found a huge improvement in my J bass... which also has humbuckers... in some really nasty environments where it even got hum (which also happened with my other humbucking basses.) I think the idea is to block all the wiring from being antennae, and it seems to really work for me.

Also, I thought buzzes that go away when you touch the strings are an instrument grounding problem, because your body creates sort of a false ground? In other words, time to rewire to a star config inside the bass?
Click to expand...

Pickups are magnetic and are sensitive to magnetic fields.

As Jerrold said, humbuckers will be less sensitive to far-field magnetic noise, like hum from transformers, fluorescent balasts, et al, and more sensitive to near-field magnetics, like the field disturbances caused by vibrating strings.

Shielding doesn't help against magnetic fields unless the shield material is magnetically permeable, like steel, mu metal, et al. Cavity shielding is probably most often done with copper, which offers no shielding against magnetic fields but could be highly effective against electrostatic fields. The OP's problem, though, seems to be rooted primarily in magnetic noise from his amp's power transformer and possibly other sources.
 
#15
Vic said:
Also, just bring the EBS along. It's light. That way, you have a backup if you need it, and an A/B test if you want it.
Click to expand...

Yeah, I typo'd. I meant to say the EBS was my only amp not my old amp heh.

I took it along, of course, and I was getting some hiss (normal for my EBS) and yes, during the second song it started humming w/ my Deluxe Jazz. Ugh. Not sure if it is the bass or the amp. Unfortunately I only took one bass, we only played two songs at this benefit thing. I'm trying to think of a better way to tell if it is the amp or the bass(es).
 
#16
Jerrold Tiers said:
Reality check:

I very much doubt there is any actual defect.
Click to expand...

Probably, but it is just very strange. I was getting hum tonight w my Jazz bass that has hum cancelling pickups (97 Jazz Deluxe V) and the pickups were panned dead center. It wasn't your normal 60 cycle hum, it sounded different to my ears. I'll see if I can reproduce and record it with a mic :)
 
#17
maybe try a different cable. I have a cable that has the shield only connected at one end (it's a 3 conductor). It tends to make my sansamp pick up some case noise. Like if I touch the case, it'll buzz. And I don't know why. Anyways, you may try a different cable./
 
#18
Are you standing near a TV or large appliance when you play? Or maybe near the speaker cab? Magnets will cause this hum.. it's especially pronounced on my 5-string active Fender Jazz.. maybe do to the additional pickup size.. When I move about 15 feet from my TV, the sound goes away.
 
#19
Hmm...the ground lift on my SWR SM-500 affects the amp as well as the DI even though it's on the DI. EBS must have a different wiring scheme. It usually solves my hum problems. Some basses are just noisy and there's little you can do about it, others can be cured with copper shielding or using a higher grade cable. Who knows? Just knock out each possibility in a systematic, cost effective way.
 
#20
steve4765630 said:
Hmm...the ground lift on my SWR SM-500 affects the amp as well as the DI even though it's on the DI. EBS must have a different wiring scheme. It usually solves my hum problems. Some basses are just noisy and there's little you can do about it, others can be cured with copper shielding or using a higher grade cable. Who knows? Just knock out each possibility in a systematic, cost effective way.
Click to expand...
Yeah, depends on the amp design. I've seen some amps (such as some peaveys) that have not only ground lift, but also polairy selection on a switch, which IS for the main power supply to the amp.

However, most amps will have a ground lift right by the DI, which is strictly to lift the ground pin at the XLR. Most times, if we get amp hum, it's because there's a ground loop between the mixing board and the stage, so you get hum and the PA gets hum when you're plugged in, but it goes away when you disconnect your DI. That's what that's for.
 

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