Reducing RF noise from my PC

[JoshuaHufford]

I play electric guitar and often it is in front of my PC, especially if I'm learning a song etc. Most of my guitars have single coil pickups which pick up just about everything around them and my PC really seems to put out a lot of RF noise. The PC is a custom build that I built myself, I can get the exact specs if needed. Any suggestions on what I could do or a simple way to shield it? Any particular PC cases that are better than others?

Thanks!

 

[bharvey2]

You're in for a tough battle but a few things may help: Get some ferrite beads and place them on all of the cables going in and out of your computer. You'll likely see these built in to older VGA cables. These help attenuate the RF noise emitted from the cables . In that light, keeps cables as short as possible. You might try turning peripherals on and off to see which ones are noisy. This includes your monitor too. As find find noisy ones, you'll need to address them accordingly. Lastly, try rotating the guitar 45 to 90 degrees away from the computer as you play. You may notice that the noise increase or decreases greatly. Are you plugged into the computer in some way as you play? A wireless connection might help. If you're only noticing the noise when you aren't playing, consider a noise gate pedal. You may need to switch to humbuckers

 

[JoshuaHufford]

You're in for a tough battle but a few things may help: Get some ferrite beads and place them on all of the cables going in and out of your computer. You'll likely see these built in to older VGA cables. These help attenuate the RF noise emitted from the cables . In that light, keeps cables as short as possible. You might try turning peripherals on and off to see which ones are noisy. This includes your monitor too. As find find noisy ones, you'll need to address them accordingly. Lastly, try rotating the guitar 45 to 90 degrees away from the computer as you play. You may notice that the noise increase or decreases greatly. Are you plugged into the computer in some way as you play? A wireless connection might help. If you're only noticing the noise when you aren't playing, consider a noise gate pedal. You may need to switch to humbuckers

Thanks for the suggestions.

Not plugged into the PC, although I did try that with an amp simulator but the latency drove me nuts. I have guitars with humbuckers and of course the noise is greatly reduced, but I'm mostly a single coil guy!

 

[prcguy]

What does the noise sound like? If its getting into the pickups of your guitar and its audible its probably not RF but just low frequency electromagnetic fields from a power supply and your pickups are within the lines of force of the transformer or conductors carrying a lot of current. I would do some tests to see if its being picked up on the guitar cable or by the pickups themselves.

Switch pickups on and off to see if it has any effect. Then move the guitar cable around your various computer items to see if you can find a hot spot. That would help identify the source of the interference and also answer if the guitar cable is the major pickup device.

If its the cable then some very high permeability ferrite might help like wrapping many turns of the guitar cable through a #75 mix ferrite core. That will only help if its common mode and riding mostly on the shield. You can also try transformer coupling the guitar to the amp to break any ground connections and float it. A DI box can be good for that if you can make use of the low impedance output.

 

[JoshuaHufford]

I'll see if I can make a recording of it sometime, it is hard to describe.

The noise goes away when I turn down the volume on the guitar, so that would point in the direction of the pickups to me and not the cable.

 

[prcguy]

Possibly, depends on how the volume control is wired up. If it has the outside posts wired to ground and the pickup with the slider feeding the output then that could turn down interference from the cable because the volume control would be shorting out the cable as it turns down. You could put an ohmmeter across the guitar cable and adjust the volume to see if its nearly shorted when turned all the way down and goes higher resistance when its turned up.

I'll see if I can make a recording of it sometime, it is hard to describe.

The noise goes away when I turn down the volume on the guitar, so that would point in the direction of the pickups to me and not the cable.

 

[bharvey2]

Possibly, depends on how the volume control is wired up. If it has the outside posts wired to ground and the pickup with the slider feeding the output then that could turn down interference from the cable because the volume control would be shorting out the cable as it turns down. You could put an ohmmeter across the guitar cable and adjust the volume to see if its nearly shorted when turned all the way down and goes higher resistance when its turned up.

The wiring scheme you describe isn't set in stone for guitars however. It is just as likely that the guitar output is wired across the volume pot (outside legs) and the pickup/pickups connect to the adjustable or slider contact. I know, you'd think that some regulatory body would have risen up by now to govern the proper wiring of electric guitars but oddly, it has escaped bureaucratic scrutiny so far.

Another quick and dirty test would be to have everything up and running and just disconnect the cable from the guitar. (Don't touch the tip of the plug during this test, touch only the barrel of the connector, lest you become an antenna) If the guitar is the issue, and more than likely it is the culprit, noise will be substantially reduced if not eliminated.

 

[prcguy]

I would think the pickups are wired across the outside legs because that would provide a more constant impedance to the pickups. If you wire it with the wiper to the pickups that will vary the resistance across them from zero to full resistance and that will change the tone of the guitar along with volume, which is something to avoid.

The wiring scheme you describe isn't set in stone for guitars however. It is just as likely that the guitar output is wired across the volume pot (outside legs) and the pickup/pickups connect to the adjustable or slider contact. I know, you'd think that some regulatory body would have risen up by now to govern the proper wiring of electric guitars but oddly, it has escaped bureaucratic scrutiny so far.

Another quick and dirty test would be to have everything up and running and just disconnect the cable from the guitar. (Don't touch the tip of the plug during this test, touch only the barrel of the connector, lest you become an antenna) If the guitar is the issue, and more than likely it is the culprit, noise will be substantially reduced if not eliminated.

 

[bharvey2]

I would think the pickups are wired across the outside legs because that would provide a more constant impedance to the pickups. If you wire it with the wiper to the pickups that will vary the resistance across them from zero to full resistance and that will change the tone of the guitar along with volume, which is something to avoid.

Yeah, it makes sense to do it that way for the very reason you mentioned. But, I've seen it done both ways. If you want to see strange and often dangerous execution of electronic tomfoolery. (sounds like a pun but it's closer to reality than you may think) you should get acquainted with the novice DIY electric guitar enthusiasts.

 

[prcguy]

Its both fun and painful to watch people with no training or experience in electronics start experimenting and changing circuits. Sometimes they luck out and get the result they want, most of the time not. But usually the circuit ends up completely backwards and barely able to work, but if it gets the sound they want I guess its good for them.

Yeah, it makes sense to do it that way for the very reason you mentioned. But, I've seen it done both ways. If you want to see strange and often dangerous execution of electronic tomfoolery. (sounds like a pun but it's closer to reality than you may think) you should get acquainted with the novice DIY electric guitar enthusiasts.

 

[bharvey2]

Its both fun and painful to watch people with no training or experience in electronics start experimenting and changing circuits. Sometimes they luck out and get the result they want, most of the time not. But usually the circuit ends up completely backwards and barely able to work, but if it gets the sound they want I guess its good for them.

Ah yes. Case in point: When the band VanHalen started becoming popular, someone I knew got wind of Eddie's use of a variac to produce what is now known as the "brown sound" Being familiar with variacs and tube amps, the concept made sense to me. Lower the supply voltage and desired sound is produced at lower volumes. However, the "someone I knew" somehow got the idea in his head that Eddie used the variac to supply voltage to the input of the amp while he played. I couldn't convince him otherwise at the time. Fortunately, that "someone" couldn't get his hands on a variac.

 

[prcguy]

Yes, a brownout condition will make the amp sound different where its gain and volume will be slightly reduced and it should distort at a lower level. You might also get more of a compression effect at high volume. I kinda met Eddie once with a friend who knew him. They both had the same studio console and I think there were only two or three of that model ever made.

The time I was casually introduced was at a benefit concert and it was the first time the song from Cheech and Chong "Born in East LA" was played publicly. It was Eddie on guitar, my friend on drums, his friend on Bass and Cheech singing. This was around the late 80s.

I had posted a picture of the benefit concert, its post #1,032 here. Maybe you will find a variac on Eddie's amp or maybe not.

https://forums.radioreference.com/threads/what-music-are-you-listening-to.270719/page-52#post-3291540

Ah yes. Case in point: When the band VanHalen started becoming popular, someone I knew got wind of Eddie's use of a variac to produce what is now known as the "brown sound" Being familiar with variacs and tube amps, the concept made sense to me. Lower the supply voltage and desired sound is produced at lower volumes. However, the "someone I knew" somehow got the idea in his head that Eddie used the variac to supply voltage to the input of the amp while he played. I couldn't convince him otherwise at the time. Fortunately, that "someone" couldn't get his hands on a variac.

 

[bharvey2]

Yes, a brownout condition will make the amp sound different where its gain and volume will be slightly reduced and it should distort at a lower level. You might also get more of a compression effect at high volume. I kinda met Eddie once with a friend who knew him. They both had the same studio console and I think there were only two or three of that model ever made.

The time I was casually introduced was at a benefit concert and it was the first time the song from Cheech and Chong "Born in East LA" was played publicly. It was Eddie on guitar, my friend on drums, his friend on Bass and Cheech singing. This was around the late 80s.

I had posted a picture of the benefit concert, its post #1,032 here. Maybe you will find a variac on Eddie's amp or maybe not.

https://forums.radioreference.com/threads/what-music-are-you-listening-to.270719/page-52#post-3291540

Whether or not a variac was in play would probably depend upon when these photos were taken. I know he used one while using Marshall amps but I don't know if the practice continued after moving to Soldano and Peavey. I also noted that in your aforementioned post that the drummer was Dennis Dragon. Any relation to Daryl/Carmen?

 

[prcguy]

The concert and pictures would have been May 12, 1985. Dennis's brothers are/were Darryl and Doug, sisters Carmen and Kathy. Father was Carmen and conductor of the Hollywood Bowl orchestra at one time. Mom was an actress in early films. Dennis was a good friend and I spent some time with much of the family, who sadly are all gone now.

QUOTE="bharvey2, post: 3723749, member: 793891"]
Whether or not a variac was in play would probably depend upon when these photos were taken. I know he used one while using Marshall amps but I don't know if the practice continued after moving to Soldano and Peavey. I also noted that in your aforementioned post that the drummer was Dennis Dragon. Any relation to Daryl/Carmen?
[/QUOTE]

 

[bharvey2]

The concert and pictures would have been May 12, 1985. Dennis's brothers are/were Darryl and Doug, sisters Carmen and Kathy. Father was Carmen and conductor of the Hollywood Bowl orchestra at one time. Mom was an actress in early films. Dennis was a good friend and I spent some time with much of the family, who sadly are all gone now.

[/QUOTE]

Very cool that you got to spend time with the family. Though my knowledge of them is by reputation only, they seemed to be a talented bunch. Too bad they're gone.

 

[prcguy]

They were all musicians, although I forgot what Kathy might have played. Dennis was also a ham operator and had a business band repeater with autopatch that I maintained. It was fun going to the various hill tops it was located at then bringing it down to Moms house on PCH in Malibu right on the beach and working on it. This is the house all the Dragon kids grew up in.

I would have the repeater and my service monitor on one end of a huge long dinner table like you might imagine in a castle with high back chairs that seated at least 12 while Carmen would serenade me on the grand piano playing an intense classical piece. Then Dennis and I would retire to the yard to play some industrial ping pong at the edge of the beach and Carmen might drag out the Harp and play for us. Those were fun times. I also spent a lot of time at a recording studio in the Pt. Dume area of Malibu where Dennis did most of his recording at the time.

Getting back to the guitar noise, it would be nice to hear a recording of the noise to see what might be causing it. If its 60 cycle its more likely to be from a nearby AC power transformer. I have not run into switching power supply magnetic fields in the same way which might get induced into an audio cable and be heard and switchers are more prone to radiated RF which you will not hear directly.

You almost need something to simulate a guitar pickup that can plug into the amp that you can wave around and pinpoint the noise source. Even a small spool of magnet wire like 100-200ft of #24 wire connected to the guitar cable might make a good sniffer pickup.


Very cool that you got to spend time with the family. Though my knowledge of them is by reputation only, they seemed to be a talented bunch. Too bad they're gone.
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