Unbelievable RF interference

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Unbelievable RF interference

Postby playingdead » Wed Jun 18, 2008 6:15 pm

We played outdoors on the Charles River in Boston on Sat. the 7th. I set up my rig, as usual, and it all sounded fine, unless I turned to my left, whereupon I would get the most unbelievably loud HISS through my Tiger's pickups into my rig. I mean, it was LOUD, like a dragon's breath, and I could attenuate it by moving my body toward the water.

Check out this 25 second excerpt from Althea in the first set; I played the first bar of the solo, and turned to my left to adjust the tap tempo on the delay, and it hissed at me. (Made the drummers crack up, too.)

http://www.playingdead.net/hiss.html

I've had a couple of other spotty problems picking up things through the pickups, most notably walkie-talkies from the crew when we played at a ski lodge in Vermont. But never anything like this.

All I can think of is we were right across the water from MIT, so maybe they have some kind of microwave transmissions happening. And the Duck Boats on the river leave from where we were playing, so they may have some sort of shortwave radio thing happening.

Didn't seem to matter which pickup, or single coil or humbucker (I use the bridge humbucker in Althea). The guitar's control cavity is shielded in copper, all the wiring is nice and tight. Is there anything that can be done? I should've tried my Strat backup Jerrycaster, but it was back in the car.

I really have it all sounding good now, but that was hideous!

Vic
Last edited by playingdead on Thu Jun 19, 2008 5:57 am, edited 1 time in total.
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Postby waldo041 » Wed Jun 18, 2008 6:50 pm

vic,

sounds to me like a ground loop. especially if it happens with the pickups in series. don't know if it is the guitar or the new rack. could be the racks grounding also.

check this website out. keyword "harsh buzz"

http://www.guitarnuts.com/technical/ele ... cnoise.php

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Postby playingdead » Thu Jun 19, 2008 3:50 am

Hmmm. Wouldn't it do it at all the venues, though? Unless there was something weird at that particular venue? No one else seemed to be having problems.

All my power goes through a power conditioner, as well, and I had the same 20 amp power feed that the PA and other instruments were using.
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Postby waldo041 » Thu Jun 19, 2008 4:29 am

playingdead wrote:I've had a couple of other spotty problems picking up things through the pickups, most notably walkie-talkies from the crew when we played at a ski lodge in Vermont. But never anything like this.



playingdead wrote:Hmmm. Wouldn't it do it at all the venues, though?



apparently you have run into rf noise before. if there were not some sorta of grounding issue, you'd never be introduced to rf noise. but you are and something in your rig is allowing you to act as an antenna for it.

do you have a string ground on your tiger?

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Postby playingdead » Thu Jun 19, 2008 5:42 am

I don't have a string ground, Waldo ... maybe I need one.

The noise does not stop when I put my hands on the strings, though.

Interesting FAQ here:

http://www.harmony-central.com/Guitar/grounding-faq.txt

I should note that I've had minor RF interference with both my old Twin head and the rack. But this was nuts!
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Postby waldo041 » Thu Jun 19, 2008 6:00 am

playingdead wrote:I don't have a string ground, Waldo ... maybe I need one.


Yes, especially since you play out with big lights and lots of power around you. i found that the string ground also is a shield for the pickups. with out the string ground and in series humbucker with a flourescent lighting you will get horrible noise. with the string ground, problem over. on my axe i drilled under the bridge post and soldered the wire to a spring so that when the post was screwed in, it made contact with the spring and allowed for movement. i would do the string ground.


playingdead wrote:The noise does not stop when I put my hands on the strings, though.


possibly another grounding issue associated with the missing string ground. if it does not go away, your ground and the guitars/gear ground are not one. could be the rack could be the guitar.

peace,
waldo
Last edited by waldo041 on Thu Jun 19, 2008 6:08 am, edited 2 times in total.
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Postby playingdead » Thu Jun 19, 2008 6:00 am

One more thing I just noticed ... the huge hiss is going through the effects loop as well, because when I turn away sharply, you can hear it hiss again on the delay I was using.

That would seem to put it right in the guitar, before the rack, because if it were after the guitar, it wouldn't hiss on the delay, because the delay is in the onboard effects loop.

I think.
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Postby waldo041 » Thu Jun 19, 2008 6:18 am

playingdead wrote:That would seem to put it right in the guitar, before the rack, because if it were after the guitar, it wouldn't hiss on the delay, because the delay is in the onboard effects loop.
I think.


good assumption. again, get a string ground and have the guitar grounding looked over in the axe. jerry's wolf and tiger both had a 10 gauge uninsulated copper wire ran fron the grounded lug of the volume potentiometer to the sleeve of the output jack. EVERYTHING else was grounded to that 10 gauge piece of copper. exactly like a star ground, but instead of lots of ground wire going to one point, grounds could be ran directly to the 10 gauge ground wire. keeping wires shorter. also, the cavities were shielded so the pots were grounded on the bolt side and not soldered to the back of them, causing a ground loop most of the time.

hth~

peace,
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Postby milobender » Thu Jun 19, 2008 7:05 am

Sounds like it's a definate on the guitar being the problem. When you turn it at different angles, you are "adjusting the antena".

I've retrofitted a ground to strings by removing the bridge and the post next to the cavity, drilling a hole thru the mounting lug at an angle down into the cavity, and running a wire from the cavity right into the mounting lug (strip about a quarter inch of the insulation for inside the lug). There is usually alot of play in the mounting post/lug, so if you use smaller gauge, stranded wire, the hight adjusting post will still screw properly and everything is hidden. I hope this isn't too confusing... I do alot better with drawings :D

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Postby ELPManticore » Thu Jun 19, 2008 9:38 am

Hmmm, not nearly as knowledgeable as waldo, but I'm incliced to say its interference, if it were grounding it would be a more constant issue, not when you turn to one direction.

On that note, who knows what it could be with a the shit shooting through the air now; MIT has a HUGE wifi network that you can pick up from central sq down mass ave, so I wouldn't be surpised if it brocasts across the river, staties/locals on the pike or storrow/memorial with a radar trap, boat or air traffic, defective coffe maker, sabotuers... you may never know the source.

When we jam at my buddys place, and my amp is turned up loud enough whith a phaser on, I can get the lights to dim and brighten (in time w/ the phase). Freaky. Don't trust wiring in old barns.
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Postby waldo041 » Thu Jun 19, 2008 9:56 am

ELPManticore wrote:Hmmm, not nearly as knowledgeable as waldo, but I'm incliced to say its interference, if it were grounding it would be a more constant issue, not when you turn to one direction.


it's the lack of proper grouding that is allowing the interference to come thru.

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Postby ELPManticore » Thu Jun 19, 2008 11:19 am

Thanks Waldo...

I always thought that RF interference caused a disburence the EM field arround the pickups, in which case the hum is just as much a part of sound as the string are. (Kind of like playing in front of an old CRT monitor.)


As with alot of things, I don't know too much about electronics, just enough to get me in trouble.

I'm still willing to bet it was the 'man' trying to f with the show via MIT. :D
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Postby waldo041 » Thu Jun 19, 2008 11:53 am

ELPManticore wrote:Thanks Waldo...

I always thought that RF interference caused a disburence the EM field arround the pickups, in which case the hum is just as much a part of sound as the string are. (Kind of like playing in front of an old CRT monitor.)


60 cycle hum and RF interference such as vic is having are 2 different demons. single coil pickups are very susceptible to 60 cycle hum and sound like a hum. in that case, the pickups are actually the antenna picking up the power pulse. proper shielding can help with that. RF interference is caused because something is acting like an antenna, not grounded properly, and picking up radio frequencies from either a lack of string ground, ground loops or rack equipment not grounded properly.

peace,
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Postby Mick » Wed Jun 25, 2008 11:30 am

ELPManticore wrote:Thanks Waldo...

I always thought that RF interference caused a disburence the EM field arround the pickups, in which case the hum is just as much a part of sound as the string are. (Kind of like playing in front of an old CRT monitor.)


If it is RF interference, it can be substantially directional in a particular location like that. As Waldo said, a 60 hz interference would be coming from the AC power in use all around playingdead so it might be somewhat stronger in one direction than another, but I would think it would always be there. My guess is that the shielding is grounded properly, such that when the shielding is picking up the interference, it is grounding it and you don't hear it. When he turns a certain way, and the signal hits ungrounded parts, the interference gets into the signal. Waldo's idea of grounding the strings sounds like a good bet to me, at least it is a good place to start because even if it fails to eliminate the problem, it won't hurt anything.
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Postby ELPManticore » Mon Jun 30, 2008 10:55 am

Waldo -

Thanks for the clarification, totally forogtten that the guitar itself can act as an antenna, but it makes total sense.
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