Help with guitar noise please

[sonolink]

This friend of mine recently built a home studio at his place. He's a fine guitar player and tells me that he gets lots of noise at his studio, noise that doesn't happen in other places using the same gear.

View attachment VID-20240206-WA0002.mp4

Any help is appreciated and very welcome
Thanks!
Sono

 

[rogs]

Is there a dimmer switch in use any where near?

 

[sonolink]

No. All lights are off and they're LEDs, no dimmer. Cheers

 

[Newmarket]

Think about what is, or could be, in rooms/buildings either side, below and above. Walls and ceilings are pretty transparent to emi. At a friend's house we spent a good deal of time tracking down the source of a periodic noise through an electric guitar (like once every ten seconds or something) to a DVD player (or it might have been a 'set top box' ) on standby in a downstairs room.

 

[dai h.]

hi, (my novice understanding is that) when you touch the strings (usually connected to the bridge) you are touching circuit ground and your body acts as a electrostatic shield (sort of like putting a ground plane underneath circuitry) through body capacitance (which has more effect since (I presume) you have typical (non-active) passive (high impedance circuitry (high impedance = capacitance has greater effect)) which helps to reduce the higher harmonics of the hum (the "buzz") from noise sources nearby (AC wiring, lights, monitors, whatever).

What I've seen on the better expensive guitars (perhaps not all of them like maybe a jazz guitar where high gain is never used) is well shielded internal cavities using (conductive) paint and foil (copper, aluminum). I think the noise can be worse with (conventional) single-coil pickups, more gain, and the lower you turn down the pot (more impedance in series with the signal). Also how close you are to noise sources and the relative angle of the pickups to whatever noise source(s) nearby. Also maybe pay attention to the input area of the amp (some have extra shielding around the jack which probably helps with more gain and with the pot turned down (lower level signal + more impedance in series with the signal = more susceptibility to noise)).

 

[JohnRoberts]

What is the nature of the noise? (hum?)

Lead guitar pickups are high impedance so can pick up hum from magnetic fields in the room.

With the guitar plugged in using a long cord, does the noise get louder or quieter as he moves around the room? This may suggest where to focus on noise sources.

JR

 

[sonolink]

The guitar is shielded. It happens with both single coils and humbuckers...

What is the nature of the noise? (hum?)

Lead guitar pickups are high impedance so can pick up hum from magnetic fields in the room

With the guitar plugged in using a long cord, does the noise get louder or quieter as he moves around the room? This may suggest where to focus on noise sources.

JR

I believe it is hum. I'll try what you say and report back.

Thanks!
Cheers
Sono

 

[Paul W]

What I've seen on the better expensive guitars (perhaps not all of them like maybe a jazz guitar where high gain is never used) is well shielded internal cavities using (conductive) paint and foil (copper, aluminum). I think the noise can be worse with (conventional) single-coil pickups, more gain, and the lower you turn down the pot (more impedance in series with the signal). Also how close you are to noise sources and the relative angle of the pickups to whatever noise source(s) nearby. Also maybe pay attention to the input area of the amp (some have extra shielding around the jack which probably helps with more gain and with the pot turned down (lower level signal + more impedance in series with the signal = more susceptibility to noise)).

Some guitar repair/mod experts (like Dan Erlewine) say that shielding the pickup cavity can change the shape of the pickups' fields and thus affect the tone of the guitar. Erlewine does not shield his strat pickups for that reason. (The normal Strat pickguard has a little shielding over the pots, but not around the pickups.)

I don't know of any scientific tests of this, unfortunately.

 

[metalockpick]

Once working in a large warehouse, I noticed that the noise was excessive compared to the same gear in my house. We were able to greatly reduce the noise in the warehouse by grounding all of the pallet racks. Likewise, shielding the walls of the studio with metal shielding would certainly improve the performance, and would be very easy to do if the building were constructed with metal studs.

As for guitar noise, using shielded wire for the pickups to the output jack is about 95% of it. Another funny note there is that some late '70s and early '80s Les Paul customs did not have the strings connected to ground, though the circuit was 100% shielded from the pickup to the output jack

 

[JohnRoberts]

This is a pretty well inspected topic, I am not a guitar expert but have paid some attention to the topic over the decades.

I have mixed feelings about hard grounding metal parts of the guitar as that could present a discharge path for shock encounters (like an energized mic).

[TMI warning] last century a Peavey customer was electrocuted by a Peavey guitar that was plugged into a miswired (RPBG) outlet. RPBG connects outlet safety ground to neutral. Generally harmless as long as neutral is indeed the 0V neutral mains power return..... BUT if line (hot) and neutral are inadvertently swapped, RPBG energizes the safety ground. What happened to that unfortunate customer who was playing with a friend using another Peavey guitar amp. Both Peavey amps were UL approved with chassis ground bonded to the line cord safety ground. The deadly event occurred when the two players decided to swap guitars. One was plugged into the deadly RPBG outlet, the other a stove outlet that was actually grounded. This put the full mains voltage potential between the two guitars. The musician who tried to hold both guitars, one in each hand received full mains voltage through his chest, stopping his heart. /TMI]

This is a rather long explanation for why I do not favor solid grounding of metal bits on guitars. The good news is that at the impedances we are dealing with, the metal parts can be capacitor coupled to safety ground (from the guitar amp input jack). This capacitor can be sized appropriately to damp hum pickup while limiting current at 60Hz low enough to not be deadly.

JR

 

[sonolink]

Ok, so the long cable test didn't do nothing. The hum wouldn't change, so I figured the noise comes from the house and there's something wrong with the electrical installation.
Guess what? The ground terminals of the outlets weren't connected to the spike! The spike was there alright but UNCONNECTED!! I guess somebody "forgot" to connect the house to it

Anyway, thanks to all for your input and help
Cheers
Sono

 

[ccaudle]

The spike was there alright but UNCONNECTED!!

By spike you mean the rod pounded into the dirt?
Did correcting the house protective earth connection fix the problem?

 

[Newmarket]

Some guitar repair/mod experts (like Dan Erlewine) say that shielding the pickup cavity can change the shape of the pickups' fields and thus affect the tone of the guitar. Erlewine does not shield his strat pickups for that reason. (The normal Strat pickguard has a little shielding over the pots, but not around the pickups.)

I don't know of any scientific tests of this, unfortunately.

At a technical guess I'd tend to think that copper or aluminium (ie non-ferrous) shielding would have minimal effect.
Steel would affect the field and hence the pickup response. Indeed the sound of a traditional Telecaster pickup is modified by the metal plate it is mounted on.

 

[CJ]

simply put a scope on the power line,

please use an iso xfmr

some amps have very quiet input circuits while others are hideous,

 

[sonolink]

By spike you mean the rod pounded into the dirt?
Did correcting the house protective earth connection fix the problem?

I do
Problem solved once the earth connection was "grounded"

Thanks!
Sono

 

[Audio1Man]

Hi sonolink

If your “GUITAR SYSTEM” is good in other rooms, then the noise in/or around the studio room.
You need to find the noise source. I have found & repaired many noise problems in my career. I have many tools that I use for FINDING/DEBUGGING the problem.

I would suggest that you get a guitar pickup and connect it to a long XLR cable, and hunt all around wall low to high to find the loudest hum/noise.

AC Power panel, house wiring, water pipe, other? that produce MAGNETIC FIELDS.

Good hunting
Duke

 

[dai h.]

Some guitar repair/mod experts (like Dan Erlewine) say that shielding the pickup cavity can change the shape of the pickups' fields and thus affect the tone of the guitar. Erlewine does not shield his strat pickups for that reason. (The normal Strat pickguard has a little shielding over the pots, but not around the pickups.)

I don't know of any scientific tests of this, unfortunately.

At a technical guess I'd tend to think that copper or aluminium (ie non-ferrous) shielding would have minimal effect.
Steel would affect the field and hence the pickup response. Indeed the sound of a traditional Telecaster pickup is modified by the metal plate it is mounted on.

I've seen suggestions to make a break in the (back of the pickguard (usually continuous)) shielding so it doesn't form a loop around the pickup, but looking at say a Suhr (guitar with copper foil back of the pickguard shielding) where there doesn't seem to be one, maybe (as you say, with copper and aluminum) it isn't an issue.

re: Dan Erlewine, no dedicated shield okay, but when you touch circuit ground you are shielding (I would argue) which helps reduce "buzz" (the higher harmonics of hum which are more noticeable and annoying). Strats are an old design, so maybe it made sense to Leo Fender for the body capacitance shielding to be adequate enough since it would cost more and people didn't play with much gain back then (nothing wrong with that but obviously things changed over time). Oh, and if he has some valuable original, then I suppose it would make sense not to mess with things too much.

Also, (if my understanding is correct) if you install an R (and parallel C) network in between circuit ground and bridge as a shock-preventative measure (limits current and doesn't leave the metal bridge, strings floating) you will need to install shielding because the body capacitance "shield" won't function with (something like) 220k between those points (I remember trying this from a Guitar Player mag(?) article and it was too noisy to use). The (often) metal jack plate, cable plugs, amp panels are still accessible though (and metal on the pickup switch). But still a good idea to at least have some awareness of the possibility of getting shocked (and check for voltage differences and take precautions, counter-measures, etc.).

 

[Newmarket]

hi, (my novice understanding is that) when you touch the strings (usually connected to the bridge) you are touching circuit ground and your body acts as a electrostatic shield (sort of like putting a ground plane underneath circuitry) through body capacitance (which has more effect since (I presume) you have typical (non-active) passive (high impedance circuitry (high impedance = capacitance has greater effect)) which helps to reduce the higher harmonics of the hum (the "buzz") from noise sources nearby (AC wiring, lights, monitors, whatever).

I challenge the idea of "body capacitance" here. Where is this capacitance "in the circuit" ? Between "Ground" and ????

The significant effect is that your body is a noise source when it is electrically floating.
When you touch "Ground" (typically by being in contact with the grounded metal parts/strings on a guitar) your body is held at the same potential and ceases to be a source of noise. You could also touch any other grounded metal for a similar effect - equipment rack / metal chassis etc. And it can be useful to arrange such a connection to your body to avoid noise when you might lose connection via the guitar due to playing technique. tapewound or coated strings etc.
I have had people doubt, or full out deny the body as a noise source. I tell them to touch the tip of a 'scope probe and observe the distorted 50Hz waveform on the trace. (60Hz if that is your mains frequency but it doesn't sound as good ).
And if you get a periodic noise at one second intervals - it's your watch (yep - been there )

 

[amplexus]

I challenge the idea of "body capacitance" here. Where is this capacitance "in the circuit" ? Between "Ground" and ????

The significant effect is that your body is a noise source when it is electrically floating.
When you touch "Ground" (typically by being in contact with the grounded metal parts/strings on a guitar) your body is held at the same potential and ceases to be a source of noise. You could also touch any other grounded metal for a similar effect - equipment rack / metal chassis etc. And it can be useful to arrange such a connection to your body to avoid noise when you might lose connection via the guitar due to playing technique.tapewound or coated strings etc.
I have had people doubt, or full out deny the body as a noise source. I tell them to touch the tip of a 'scope probe and observe the distorted 50Hz waveform on the trace. (60Hz if that is your mains frequency but it doesn't sound as good ).
And if you get a periodic noise at one second intervals - it's your watch (yep - been there )

This is all correct and to further this the reason for it as was explained to me is that as big bags of basically salt water we make excellent antennae for EMI which we then re-radiate. The main reason for shield connections to the bridge/strings isn’t because they provide or need shielding particularly but because it provides a ground path for US so that we stop radiating noise into those highly sensitive coils!

 

[dai h.]

I challenge the idea of "body capacitance" here. Where is this capacitance "in the circuit" ? Between "Ground" and ????

The significant effect is that your body is a noise source when it is electrically floating.
When you touch "Ground" (typically by being in contact with the grounded metal parts/strings on a guitar) your body is held at the same potential and ceases to be a source of noise. You could also touch any other grounded metal for a similar effect - equipment rack / metal chassis etc. And it can be useful to arrange such a connection to your body to avoid noise when you might lose connection via the guitar due to playing technique. tapewound or coated strings etc.
I have had people doubt, or full out deny the body as a noise source. I tell them to touch the tip of a 'scope probe and observe the distorted 50Hz waveform on the trace. (60Hz if that is your mains frequency but it doesn't sound as good ).
And if you get a periodic noise at one second intervals - it's your watch (yep - been there )

This is all correct and to further this the reason for it as was explained to me is that as big bags of basically salt water we make excellent antennae for EMI which we then re-radiate. The main reason for shield connections to the bridge/strings isn’t because they provide or need shielding particularly but because it provides a ground path for US so that we stop radiating noise into those highly sensitive coils!

Aah, thanks for the correction guys I guess my understanding was pretty iffy there. I thought touching circuit ground (via strings, bridge) meant that you were at the same potential as circuit ground and acting as a capacitive shield for the electronics. I guess more of a "making sure conductors (in this case the body) aren't left floating" problem?