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Pickup noise and power supplies - DI box?
MUFF WIGGLER Forum Index -> Guitars, Basses, Amps & FX  
Author Pickup noise and power supplies - DI box?
Hello. I expect this part of the forum might be the best place for my question. If not, please direct me elsewhere.

I've tried to highlight the main questions in bold, in case you don't want to read a wall of text. I need some help choosing the best way to isolate power supplies and reduce noise being picked up by a guitar pickup as much as possible in the following setup:

I've been experimenting with building an instrument where a arduino-controlled DC motor strikes a piece of string or similar with a piece of felt to excite it.

I've bought a cheap single coil guitar pickup to experiment with amplification and I'm now trying to eliminate as much noise as I can. Up until now, I've run the pickup wires over alligator clips to a shielded mono instrument cable to my audio interface, Focusrite Saffire Pro 24. The noise and hum is quite abrasive, and I can get a somewhat decent result by using a software noise gate with noise profiling, but further down the road I know I will need a less computer/software-reliant setup. Both the power supplies for the motor and my laptop add significant noise to the signal, removed both will almost make it tolerable. The pickup is not placed awfully close to the power supplies and moving the pickup away doesn't seem to help a lot. No matter if my laptop's power supply is plugged in or not, the body of the laptop is electrically connected to the signal path, so touching it will cause clicks and fluctuations in noise.

Now, I have no power supply for my audio interface, it draws power from Firewire. Would that make a difference in the signal or would another power supply (hopefully a proper, non-whining model) just add noise?

I've been looking af the possibilities of getting a DI box. I know that it does not magically remove the regular single coil hum, but after reading it seems like it might be a solution when it comes to issues with interfering noise in the power line and ground loops. Correct? My audio interface does have a high-impendence input mode, but that alone doesn't help. Would a DI box with ground lift help? How much reduction in general noise would I be able to achieve just by getting a 'better' pickup?
If a DI box is the way to go, should I keep away from the cheap models? I know the very, very cheap models doesn't even have ground lift, so I would stay away from those.

Thank you.
Single coil pickups are noisy, a humbucker would help. You can try mounting your pickup in an enclosure with copper foil to create a faraday cage, which would reduce EMI. Not having a hi-z input on your interface means you are not impedance matching which adds a significant amount of noise. I would suggest checking out the Eventide - MixingLink which will give you line output with variable gain and several other options.
Only now do I read that humbuckers are named as such because they "buck the hum". I'll check out the Eventide box, thank you.

I do have a hi-z inputs on my audio interface, and it really didn't seem to help a lot, the noise was just as abrasive once the levels were properly set.

I know that I won't achieve a completely noise-free signal before any processing, but I'd like to get as far as I can. Could you imagine that a DI box's ground lift help out with removing the interfering noise from power supplies and grounding in this situation?
Lifting ground will help but the majority of noise is probably from the unshielded pickup.
I tried shielding it with copper tape. First a single wrap around the coil and soldered it to ground, checked for continuity with multimeter and tested. It didn't seem to have any significant effect. Still noise from power supplies and what not. Peeled it off and tried to do with a few more wraps, no significant result. Third time I accidentally pulled off the copper wire soldered to 'hot', peeled off the insulation tape and tried to resolder it but snapped it and I could get a hold of the strand again, so I assume I've fucked it up. Will get a new one.

prscrptn, is there a rule of thumb for how many wraps of copper tape might be sufficient? I've had trouble finding any concrete answers online. Thank you for your help so far.
Maybe too obvious but have you connected pickup ground to the string/bridge? If you havent, that can be a significant cause of noise.... (when you say "piece of string" I presume you mean an *electric* guitar string ie ferrous if you are using a magnetic single coil pickup....). As I say, apologies if this is too obvious and basic....
I've got a lot of half-knowledge, so I'd appreciate most input at this point. I believe I did try that in a earlier iteration of the instrument, but to no avail, but I am probably mistaken. Yes, it's a piece of guitar string or a spring, usually.
I can't check now, since I ruined it. I'll try to salvage what I can from the pickup and try to build a single-magnet coil from the wire if the wax allows the removal of the bare wire.
So for now I can gather that I'll try a combination of either properly shielded single coil pickups through a DI box or a humbucker through DI.
Must be single coils. Not much you can do maybe you could add some shielding around the pickups
“The only way out of the labyrinth of suffering is to forgive.” - Chhaya apk
Another simple point is to check string to pickup distance - the furher away the pickup is, the lower the signal and signal to noise ratio (too close and the magnets will dampen the string). With electric guitars that I own and have built, I line he pickup cavities with copper foil.
forestcaver, sure, that has been taken into consideration. I found the proper sweetspots.

I've decided that I'm going to buy some single-string magnets made by a guy I found online. They appear to be just what I need and can be combined to make humbuckers if need be.
Im not an engineer by any means, but are you not also getting noise from a motor running near the pickup? I would have imagined you'd get all kinds of noise from stray flux, not to mention noise from inductive kickback when youre starting and stopping or changing the speed.
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