Well don't DO that then... (hum rejection)

[caitlin]

I have three active basses (I blame this forum in many ways) two JHS 'Vintage' 4 strings, and a 5 string that I built from a kit, guess which one is being weird.

I have a Zoom B1x 4, which generally I've used on batteries, but it can also eat 5V up its USB socket. The Manual carefully ALWAYS mentions powering it with batteries, either the internal AAs or 'A USB Powerpack' so NOT from a wall wart. So I'm using a wall wart.

With nothing plugged in, it's quiet, but with JUST a cable plugged in there's a hum, no complaints there I just attached an aerial.

Plugging either of the professionally built basses makes the hum go away, totally silent, I assume shunting it to ground but what do I know?

The 5 though quietly sings to itself and the quality of the hum changes with the treble and bass controls. Notably it doesn't matter what ways I wave the bass around the hum doesn't change, it's not coming through the air, it's coming up the wire.

I've shielded the cavity with copper tape which beeps out with a multimeter but it's made no difference to the hum.

If the preamp (ARTEC BE2) is unpowered the hum DOES stop and interestingly if I disconnect the pickups the hum is unchanged (i was going to carry on and shield the pickup cavities, but this suggests I'd get no benefit)

Does this suggest that the preamp is unable to reject the hum from the stomp box or am I likely to be able to wire my way out of this?

Obviously I shouldn't use the zoom guy from a crap power supply, but this has me intrigued.

[bloke_zero]

Might be worth checking your grounding scheme against this article which I found really useful to understand things a little better.  I was under the impression that more grounding was better, but that isn't the case - they reccomend star-grounding:

https://www.fralinpickups.com/2018/11/12/understanding-guitar-grounding/

[Stub Mandrel]

Try different jack leads.

[caitlin]

ah, yes, I should have mentioned that I'd tried two leads. Good shout, that's one way to lose an earth if the shield has failed on the wire.

[Maude]

On 25/11/2020 at 10:24, bloke_zero said:

Might be worth checking your grounding scheme against this article which I found really useful to understand things a little better.  I was under the impression that more grounding was better, but that isn't the case - they reccomend star-grounding:

https://www.fralinpickups.com/2018/11/12/understanding-guitar-grounding/

That's a great link 🙂👍

[rmorris]

So do you get the same problem with the 5 string if you power with batteries.

(If you haven't tried it with batteries - then do it 🙂

[caitlin]

13 minutes ago, rmorris said:

So do you get the same problem with the 5 string if you power with batteries.

(If you haven't tried it with batteries - then do it 🙂

Thanks for reading the topic

[Stub Mandrel]

To be fair, it isn't clear if the hum goes away if you power the Zoom with batteries instead of a wall wart.

[caitlin]

wellll ok then. I take it back. it is of course fine on batteries. it's PURELY because it's being fed noisy power totally against the instructions in the manual. I am categorically doing it wrong. The thing that *interests* me is why two basses can silence it, but this one can't.

[Stub Mandrel]

That is interesting then.

It may be something to do with impedance matching between the bass and the input of the Zoom. Maybe both are floating with no direct path to earth, try a 47K resistor to earth across the bass output jack and see if that makes a difference. Just a hunch...

[caitlin]

Sadly when I measure from the preamp output to the ground it's showing 47K so I think it comes pre-equipped

I'll get the soldering iron hot this afternoon and try and stumble a bit further with this.

I wonder how receptive artec would be to being asked about this directly.

[caitlin]

well, it's NOT silent, but it is very very much quieter. Certainly now when it's plugged in the buzz *reduces* but I've almost no idea what I've changed. the wiring scheme is the same.

I did resolder a couple of things which always carries the *chance* of magically futzing the electrons a bit. I think most of the noise is now down to things being connected with JST connectors rather than being hard soldered. this because I knew stuff would need to go in and come out a few times.

I've learned basically nothing, but have a quieter bass now, which still makes bassy sounds when I wiggle the stringy bits.

I guess i should solder all the wires directly now and commit to it to see if that makes it *really* work right