Radio interference fixed by 1 cable. Why?

[Rob Strand]

New info 3: The pedal only gets radio (without the jumper from Pot's body to GND) in my parents house (where I built it and suspects it lacks earth connection). In my new place (that has a great electrical network) the pedal is death silent. Near my parents home there is a big antenna (I don't know which type, I guess it's for cellphones

I think that is the key piece of information.   A strong RF source from outside the pedal.  To make devices immune to strong RF you really need to go beyond normal practices.

So what I think is happening is the RF is being picked-up outside the enclosure by the DC power cable then it gets inside of the box via the DC jack.  The simplest solution would be a 10nF to 100nF (experiment) ceramic cap between the DC jack 0V and the chassis (perhaps the unswitched ground of the output jack).  Ideally with short leads on the cap, and more ideally the cap is grounded right at the DC jack, but you can get away with less.

Many different types of RF filtering is possible on the DC.  For example you can put a cap to the enclosure from both the +DC rail and the 0V rail .   You can also have filters with caps and inductors, add a ferrite bead around both DC cables (which forms a common-mode choke).  You can add caps across the DC rails.  The filters are best located at the DC Jack.  Try the simple cap - it works the same as shorting the wires except there's no DC issues.

[PRR]

> gets radio (without the jumper from Pot's body to GND) in my parents house

We have gravel trucks on my road.

If they stay on the road that is OK.

If they are detoured THROUGH the house, that is not OK.

In parents' house you seem to have radio-crap on that long wire between input jack, output jack, and power jack, maybe through the circuit board too (hard to tell). Those gravel trucks taking the tour of the box may be LOUD inside the box.

If you don't have gravel trucks (as in your quieter house), it may not matter.

[Phend]

Another uncommon solution is a ground rod.
Just drill a hole in the floor next to the effect.
Simple wiring.

[Rob Strand]

Another uncommon solution is a ground rod.
Just drill a hole in the floor next to the effect.
Simple wiring.

That type of thing won't help the RF picked-up on the lines too much.   The RF grounding vias cap on the DC lines, or a common mode choke using an overall ferrite tube, is the right thing to do.  You need to shunt the RF currents to the enclosure.

The ground stakes mainly help mains buzz.  It works by diverting capacitively coupled noise from the mains wiring down to earth and away from sensitive audio lines.  (Adding your own ground stake to the mains isn't legal in many countries.)

[Phend]

Interesting...a little off topic, I had a generator installed last week. When I purchased this house 30 years ago I noticed the ground rod was short and loose in the ground. Well it apparently works and has had worked. Getting back to last week, the master electrician doing the wiring had two 3 foot long rods in his truck. In vermont when you hit rocks that's all the further you go. So he gave me the short rods and I put them in and connected them. What happens if you have no ground rod ? I looked it up. Anyway I think I have better grounding now for what ever that is worth ? Not being a master electrician, hard telling not knowing.

[Rob Strand]

Getting back to last week, the master electrician doing the wiring had two 3 foot long rods in his truck. In vermont when you hit rocks that's all the further you go. So he gave me the short rods and I put them in and connected them. What happens if you have no ground rod ? I looked it up. Anyway I think I have better grounding now for what ever that is worth ? Not being a master electrician, hard telling not knowing

Local grounding definitely helps in many cases, especially mains buzz issues.   The specific issue in this thread is the noise source is RF which is better handled by grounding to the enclosure - as local to the *circuit* as possible.

[PRR]

..had two 3 foot long rods in his truck. In vermont when you hit rocks that's all the further you go.

I dunno Vermont. In parts of Maine and in the NEC, if you can't sink an EIGHT foot rod, you try it at an angle. You are not supposed to cut it off. (Or like my house, bend-over the excess.)

So he gave me the short rods and I put them in and connected them. What happens if you have no ground rod ? I looked it up. ....

In most US home power installations you get "A" ground on the Neutral from the street. Problem is that unbalanced ground currents back to the town substation can give Volts of phantom voltage but with possibly substantial available current. Or when a utility ground conductor is stolen or broken, current finds another path. There was a lake once where kids kept drowning, after noting "tingle". The metallic return on the transmission line was down and that power was returning THROUGH the lake water.

It is entirely possible to live without any ground. Your car is full of electrics yet has no dirt rod. In 1908 it was postulated that home electricity would be safer without a ground. One person can touch an ungrounded system and not be shocked. Problem comes when multiple grounds (wet trees, leaky transformers, stray people) exist on both sides of the circuit.

Yes, grounding a local generator to a standard house is tricky.

[Rob Strand]

A very cool video!

Should You Ground a Faraday Cage?

The pedal enclosure acts as a Faraday cage.

The DC cable feeding through the enclosure undermines the shielding.

[Phend]

outside the enclosure by the DC power cable then it gets inside of the box via the DC jack.

If the effect is battery powered only, will it be more immune to RF.?

[amptramp]

outside the enclosure by the DC power cable then it gets inside of the box via the DC jack.

If the effect is battery powered only, will it be more immune to RF.?

I used to test equipment going into ships, spacecraft and aircraft and there are tests for conducted susceptibility and emissions and radiated susceptibility and emissions and operation from a battery eliminates the conducted issues on the power line only.  You are looking at radiated susceptibility from interference on a power line and trying to see if this is the bulk of the interference problem.  It very well might be better on battery power, so try it.  If it is, at least you know something you didn't know before.

[LaloFP]

So what I think is happening is the RF is being picked-up outside the enclosure by the DC power cable then it gets inside of the box via the DC jack.  The simplest solution would be a 10nF to 100nF (experiment) ceramic cap between the DC jack 0V and the chassis (perhaps the unswitched ground of the output jack).  Ideally with short leads on the cap, and more ideally the cap is grounded right at the DC jack, but you can get away with less.

Many different types of RF filtering is possible on the DC.  For example you can put a cap to the enclosure from both the +DC rail and the 0V rail .  You can also have filters with caps and inductors, add a ferrite bead around both DC cables (which forms a common-mode choke).  You can add caps across the DC rails.  The filters are best located at the DC Jack.  Try the simple cap - it works the same as shorting the wires except there's no DC issues.

Awesome! Gonna try it when I can get the pedal again on my parents home, thanks rob!!

If you don't have gravel trucks (as in your quieter house), it may not matter.

The image... hahah

Another uncommon solution is a ground rod.
Just drill a hole in the floor next to the effect.
Simple wiring.

Gonna try it in my parents living room...    

[LaloFP]

Hi guys! Since its really annoying to go to my parents house to test a pedal for radio interferences, I want to force it for testing in my place. (where everything is dead silent...  )

I can modify a wall plug to not having Earth connection in it, for the amp and power supply.

But, for the Radio Intereference source, which would be a great method for testing? I can buy a Walkie Talkie and activate it near the test pedal, but its not that cheap. I suppose I could use my cellphone hardware, but I dont think I have control on the Radio part by software.

Any ideas to build a nice Radio Interference tester?

[FiveseveN]

Federal Communications Commission has entered the chat

[Phend]

Less than $10.00, fun too.

[Rob Strand]

Hi guys! Since its really annoying to go to my parents house to test a pedal for radio interferences, I want to force it for testing in my place. (where everything is dead silent...  )

I can modify a wall plug to not having Earth connection in it, for the amp and power supply.

But, for the Radio Intereference source, which would be a great method for testing? I can buy a Walkie Talkie and activate it near the test pedal, but its not that cheap. I suppose I could use my cellphone hardware, but I dont think I have control on the Radio part by software.

Any ideas to build a nice Radio Interference tester?

Doing it on the cheap.  The best way is to have a noisy environment or a piece of equipment you know generates garbage into other piece of equipment - old CRT monitors were a good source.   It's not really controlled or scientific but it can get you there.   Walkie talkie could be hit and miss depending on the frequencies.   You can easily mod your circuit to remove *that* frequency but do nothing to other frequencies or even make things worse.   It's a tough job doing this stuff properly.

Building proper test system is vary expensive and overwhelming.

At the end of the day I'm against breaking mains earth connections.  It can be a safety hazard. If you are careful you can manage it but the issue is someone else using the equipment. 

You can do things like build a line impedance stabilization network  (LISN) boxes and put inductors on the earth leads.  However you need to make great efforts and spend quite a bit of money on inductors and enclosures for the test equipment.   And ultimately it could perform less well than breaking the earth lead.  From the noises perspective it can still find a path through the other two mains wires and that's where a LISN can help makes things worse.   (You really want a LISN device that just has inductors to disconnect it from the rest of the world, it's not really a LISN.)

[PRR]

nice Radio Interference tester?

Power drill. You need one anyway. Most throw RFI like confetti at New Year's.

[DIY Bass]

Electric beaters always seem to be pretty bad for interference.

[LaloFP]

Oh, that's so sad. I'm gonna test with my power drill and other appliances.

Less than $10.00, fun too.

Nooo, I had one but threw it away cause i didn't use it. Why marie kondo, why?

[GibsonGM]

LaLo, you might try reading up on iductive and capacitive reactance, esp. how they relate to RF...resonance, and coupling.  It does not take much to create a 'phenomenon' like the one you describe. We do it by accident frequently! 

And it is hard to analyze the 'why' you ask, just from the description of a build.  As Rob and others have pointed out, there are very many places something can go wrong (or right, if you are the RF) and turn your circuit in to a radio.
Dirt/corrosion, layout problems and other elements can play roles, sometimes all together (again, very hard to pinpoint if this is the case!). An ungrounded enclosure is sure trouble, but also multiple-grounded ones COULD cause issues (not likely but possible).   

The solutions discussed are things that have been done for ages, which avoid having to dissect each component and its connection, dealing with a transient problem that may or may not be fixed by hunting these things down.

I say "RF is getting in, I have checked my build and it seems fine...how do I eliminate this?" and use those techniques.  There may be a level of RF (the nearby antenna) that is simply too powerful to overcome!!

[LaloFP]

Thank you Mike! Im currently reading this book: Eric Bogatin´s Signal and Power Integrity - Simplified

I didn't read about reactance yet, so I'm going to note it to address it if it's not in the read 

Awesome having you all to chat about this things!!